piperidines and 2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline

Numerous studies suggest that the a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type (AMPA) receptor appears to play a central role in mediating brain functions, such as learning and memory. Trafficking of this receptor is related to different long-term memory processes. This study explores the role of two AMPA receptor (AMPAR) modulators in object recognition memory (ORM) reconsolidation.. First, the effects of immediate administration of each drug after memory reactivation were investigated and compared. Then, this drug's efficient time window and its effects without memory reactivation were investigated.. Immediate CX546 administration after reactivation did not affect ORM reconsolidation. In contrast, administration of 10-mg/kg NBQX significantly impaired ORM reconsolidation within a 6-h time window. Importantly, the observed effects were not attributed to the exploratory behavior or locomotor activity of mice.. These findings provide new evidence that the AMPA receptor plays an important role in the reconsolidation phase of ORM.

Topics: Animals; Dioxoles; Learning; Memory Consolidation; Memory, Long-Term; Mice; Piperidines; Quinoxalines; Receptors, AMPA; Recognition, Psychology

The impairment of social behaviors induced by social defeat stress exposure as juveniles is resistant to some antidepressants and an antipsychotic, although the underlying mechanisms and/or therapeutic target are not yet clear. In this study, we investigated the involvement of the glutamatergic neuronal system in the impairment of social behaviors in this model, as this system is known to be involved in many central pathologies. Acute administration of ketamine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist and subsequent stimulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, attenuated the expression of impairment of social behaviors. Lack of the NMDA receptor GluN2A subunit or acute administration of ifenprodil, an NMDA receptor GluN2B subunit antagonist, did not cause an effect. There were no significant changes in NMDA function, as determined by the ratios of phosphorylated NMDA receptor subunits in the prefrontal cortex and hippocampus. 2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione, a selective AMPA receptor antagonist, prevented the effect of ketamine on the expression of impairment of social behaviors. On the contrary, the ratio of phosphorylated AMPA receptor GluA1 subunit in the hippocampus was significantly increased in the non-tested, defeated group. Ketamine increased the level of total protein, but not the ratio of phosphorylated GluA1 in the hippocampus of the non-tested, defeated group. In conclusion, exposure to social defeat stress as juveniles may induce the expression of impairment of social behaviors in adolescents via functional changes in GluA1. Activators of AMPA receptor signaling, such as ketamine, may constitute a novel treatment strategy for stress-related psychiatric disorders in adolescents with adverse juvenile experiences.

Topics: Age Factors; Animals; Hippocampus; Ketamine; Male; Mice; Piperidines; Prefrontal Cortex; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Social Behavior; Stress, Psychological

Higher-order thalamic nuclei, such as the posterior medial nucleus (POm) in the somatosensory system or the pulvinar in the visual system, densely innervate the cortex and can influence perception and plasticity. To systematically evaluate how higher-order thalamic nuclei can drive cortical circuits, we investigated cell-type selective responses to POm stimulation in mouse primary somatosensory (barrel) cortex, using genetically targeted whole-cell recordings in acute brain slices. We find that ChR2-evoked thalamic input selectively targets specific cell types in the neocortex, revealing layer-specific modules for the summation and processing of POm input. Evoked activity in pyramidal neurons from deep layers is fast and synchronized by rapid feedforward inhibition from GABAergic parvalbumin-expressing neurons, and activity in superficial layers is weaker and prolonged, facilitated by slow inhibition from GABAergic neurons expressing the 5HT3a receptor. Somatostatin-expressing GABAergic neurons do not receive direct input in either layer and their spontaneous activity is suppressed during POm stimulation. This novel pattern of weak, delayed, thalamus-evoked inhibition in layer 2 suggests a longer integration window for incoming sensory information and may facilitate stimulus detection and plasticity in superficial pyramidal neurons.

Topics: Animals; Channelrhodopsins; Excitatory Amino Acid Antagonists; Inhibitory Postsynaptic Potentials; Mice; Mice, Inbred C57BL; Nerve Net; Neural Pathways; Parvalbumins; Piperidines; Potassium Channel Blockers; Pyramidal Cells; Quinoxalines; Receptors, Serotonin, 5-HT3; Sodium Channel Blockers; Somatosensory Cortex; Somatostatin; Tetrodotoxin; Thalamic Nuclei; Vasoactive Intestinal Peptide

Epilepsy may arise following acute brain insults, but no treatments exist that prevent epilepsy in patients at risk. Here we examined whether a combination of two glutamate receptor antagonists, NBQX and ifenprodil, acting at different receptor subtypes, exerts antiepileptogenic effects in the intrahippocampal kainate mouse model of epilepsy. These drugs were administered over 5 days following kainate. Spontaneous seizures were recorded by video/EEG at different intervals up to 3 months. Initial trials showed that drug treatment during the latent period led to higher mortality than treatment after onset of epilepsy, and further, that combined therapy with both drugs caused higher mortality at doses that appear safe when used singly. We therefore refined the combined-drug protocol, using lower doses. Two weeks after kainate, significantly less mice of the NBQX/ifenprodil group exhibited electroclinical seizures compared to vehicle controls, but this effect was lost at subsequent weeks. The disease modifying effect of the treatment was associated with a transient prevention of granule cell dispersion and less neuronal degeneration in the dentate hilus. These data substantiate the involvement of altered glutamatergic transmission in the early phase of epileptogenesis. Longer treatment with NBQX and ifenprodil may shed further light on the apparent temporal relationship between dentate gyrus reorganization and development of spontaneous seizures.

Topics: Animals; Anticonvulsants; Dentate Gyrus; Disease Models, Animal; Drug Administration Schedule; Drug Therapy, Combination; Electroencephalography; Epilepsy; Humans; Kainic Acid; Male; Mice; Neurons; Piperidines; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Time Factors; Treatment Outcome

Chronic social isolation (SI)-reared mice exhibit aggressive and depressive-like behaviors. However, the pathophysiological changes caused by chronic SI remain unclear. The hypothalamus and amygdala have been suggested to be associated with the stress of SI. In addition to serotonin 3 (5-HT3) receptors, AMPA receptors have also been suggested to be involved in aggressive behavior and depressive-like symptoms in animals. Therefore, we examined whether chronic SI affects AMPA and 5-HT3 receptor expression levels in these regions. A Western blot analysis revealed that after four weeks of SI, mice exhibited up-regulated AMPA receptor subunit (GluR1, GluR2) protein levels in the amygdala and down-regulated hypothalamic 5-HT3 receptor protein levels. The AMPA/kainate receptor antagonist NBQX (10 mg/kg; i.p.) attenuated SI-induced depressive-like symptoms but not aggressive behavior. Intra-amygdalar infusions of the selective AMPA receptor agonist (S)-AMPA (10 μM) induced despair-like behavior, but not sucrose preference or aggressive behavior, in mice not reared in SI (naïve mice). Alternatively, treatment with the 5-HT3 receptor agonist SR57227A (3.0 mg/kg; i.p.) decreased aggression levels. In addition, intra-hypothalamic infusions of the 5-HT3 receptor antagonist ondansetron (3 μM) did not trigger aggressive behavior in naïve mice; however, the administration of ondansetron (0.3 mg/kg; i.p.) increased aggression levels in two-week SI mice, which rarely exhibited the aggressive behavior. Moreover, ondansetron did not affect the depressive-like symptoms of the SI mice. These results suggest that SI-induced up-regulation of GluR1 and GluR2 subunits protein levels in the amygdalar region and down-regulation of 5-HT3 receptor proteins level in the hypothalamic region are associated with the effect of AMPA receptor agonist and 5-HT3 receptor antagonist -induced aggressive behavior and depressive-like symptoms.

Topics: Aggression; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Amygdala; Animals; Depression; Food Preferences; Glutamate Decarboxylase; Hypothalamus; Injections, Intraperitoneal; Male; Mice; Microinjections; Motor Activity; Neurons; Ondansetron; Piperidines; Quinoxalines; Receptors, AMPA; Receptors, Serotonin, 5-HT3; Social Isolation

Ketamine exerts fast acting, robust, and lasting antidepressant effects in a sub-anesthetic dose, however, the underlying mechanisms are still not fully elucidated. Recent studies have suggested that ketamine's antidepressant effects are probably attributed to the activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. The present study aimed to observe the effects of AMPA receptor modulators on mammalian target of rapamycin (mTOR) and brain-derived neurotrophic factor (BDNF) expression during the procedure of ketamine exerting antidepressant effects. Therefore, we pretreated rats with NBQX, an AMPA receptor antagonist, or CX546, an AMPA receptor agonist, and subsequently observed the immobility time during the forced swimming test (FST) and the hippocampal and prefrontal cortical levels of mTOR and BDNF. The results showed ketamine decreased the immobility time of rats during the FST and increased the hippocampal and prefrontal cortical mTOR and BDNF. NBQX pretreatment significantly increased the immobility time and decreased the levels of mTOR and BDNF when compared with vehicle 1 (DMSO) pretreatment. CX546 pretreatment significantly decreased the immobility time and increased the levels of mTOR and BDNF when compared with vehicle 2 (DMSO+ethanol) pretreatment. Our results suggest ketamine-induced antidepressant effects are associated with AMPA receptors-mediated upregulation of mTOR and BDNF in rat hippocampus and prefrontal cortex.

Topics: Animals; Antidepressive Agents; Brain-Derived Neurotrophic Factor; Dioxoles; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Hippocampus; Ketamine; Piperidines; Prefrontal Cortex; Quinoxalines; Rats; Receptors, AMPA; TOR Serine-Threonine Kinases; Up-Regulation

α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor stimulation has been proposed to be a common neural mechanism of metabotropic glutamate 2/3 (mGlu2/3) receptor antagonists and an N-methyl-D-aspartate receptor antagonist, ketamine, exerting antidepressant effects in animal models. AMPA receptor stimulation has also been shown to mediate an increase in the extracellular level of serotonin (5-HT) in the medial prefrontal cortex by an mGlu2/3 receptor antagonist in rats. However, involvement of the serotonergic system in the actions of mGlu2/3 receptor antagonists and ketamine is not well understood.. We investigated involvement of the serotonergic system in the effects of an mGlu2/3 receptor antagonist, 2S-2-amino-2-(1S,2S-2-carboxycycloprop-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495), and ketamine in a novelty-suppressed feeding (NSF) test in mice.. The intraperitoneal administration of LY341495 or ketamine at 30 min prior to the test significantly shortened latency to feed, which was attenuated by an AMPA receptor antagonist, 2,3-dioxo-6-nitro-1,2,3,4-tetrahydr-obenzo[f]quinoxaline-7-sulfonamide (NBQX). The effects of LY341495 and ketamine were no longer observed in mice pretreated with a tryptophan hydroxylase inhibitor, para-chlorophenylalanine (PCPA). Moreover, the effects of LY341495 and ketamine were blocked by a 5-HT1A receptor antagonist, N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridynyl) cyclohexane-carboxamide (WAY100635), but not by a 5-HT2A/2C receptor antagonist, ritanserin. Likewise, an AMPA receptor potentiator, 2,3-dihydro-1,4-benzodioxin-7-yl-(1-piperidyl)methanone (CX546), shortened latency to feed in the NSF test, which was prevented by depletion of 5-HT and blockade of 5-HT1A receptor.. These results suggest that AMPA receptor-dependent 5-HT release and subsequent 5-HT1A receptor stimulation may be involved in the actions of an mGlu2/3 receptor antagonist and ketamine in the NSF test.

Topics: Amino Acids; Animals; Antidepressive Agents; Dioxoles; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Feeding Behavior; Fenclonine; Ketamine; Male; Mice, Inbred C57BL; Neuropsychological Tests; Piperazines; Piperidines; Pyridines; Quinoxalines; Receptors, AMPA; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Ritanserin; Serotonin 5-HT1 Receptor Antagonists; Serotonin 5-HT2 Receptor Antagonists; Tryptophan Hydroxylase; Xanthenes

The neurosteroid 17β-estradiol (E2) is synthesized by aromatase in both male and female hippocampi and is known to modulate hippocampal synaptic functions. However, as some contradictory findings regarding the modulatory effects of E2 have been reported in the literature, its physiological role and mechanism of action in the hippocampus remain controversial. Our recent study showed that a low E2 dose (1 nM) increased the amplitude of NMDA receptor-mediated EPSCs (NMDAR-EPSCs) and lowered the threshold for the induction of NMDA receptor-dependent long-term potentiation (NMDAR-LTP), while a high E2 dose (7 nM) exerted opposite effects in the dentate gyrus of juvenile male rat hippocampal slices. The present study is a follow-up that explores the underlying mechanism of this bidirectional effect of E2. We found that the ERα agonist PPT reproduced the actions of the low E2 dose on NMDAR-EPSCs and NMDAR-LTP, while the ERβ agonist DPN reproduced the actions of the high E2 dose. Moreover, PPT, but not DPN, restored the decrease in NMDAR-EPSCs induced by the aromatase inhibitor letrozole, suggesting that E2 synthesized constitutively in the hippocampus enhances NMDA receptor function via ERα. The PPT-induced enhancement in NMDAR-EPSCs was mediated by Src family kinase, but was not caused by NR2B modulation. These findings demonstrate that E2 exerts condition-dependent bidirectional effects on NMDA receptor-mediated transmission and, thus, synaptic plasticity via ERα and ERβ in the dentate gyrus of juvenile male rats.

Topics: Animals; Dentate Gyrus; Dose-Response Relationship, Drug; Estradiol; Estrogen Receptor alpha; Estrogen Receptor beta; Estrogens; Excitatory Postsynaptic Potentials; Female; Ginsenosides; In Vitro Techniques; Male; NAD; Phenols; Piperazines; Piperidines; Quinoxalines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Sapogenins

Long-term levodopa replacement therapy in Parkinson's disease is confounded by abnormal involuntary movements, known as levodopa induced dyskinesia (LID). Dysfunctional glutamatergic neurotransmission has been implicated in the pathogenesis of LID making metabotropic and ionotropic glutamate receptors attractive novel therapeutic targets. The objective of the present study was to investigate the antidyskinetic site of action of different glutamate receptor antagonists in the brain. For that purpose, metabotropic glutamate subtype 5 (3-((2-Methyl-1,3-thiazol-4-yl)ethynyl)pyridine hydrochloride, MTEP), NMDA NR2B selective ((aR,bS)-a-(4-Hydroxyphenyl)-b-methyl-4-(phenylmethyl)-1-piperidinepropanol maleate, Ro 25-6981) and AMPA (2,3-Dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium salt, NBQX) receptor antagonists or saline were administered by intracerebral infusion in the caudate-putamen (CPu), the substantia nigra zona reticulata (SNr) or the subthalamic nucleus (STN) of 6-hydroxydopamine-lesioned rats exhibiting LID. Dyskinesia was assessed with the modified version of the rat Abnormal Involuntary Movements scale (AIMS). Ro 25-6981 and to a lesser extent NBQX improved dyskinesia (82% and 19% reduction in AIM score respectively) after infusion in the caudate-putamen. None of the three drugs managed to noticeably reduce AIM score after infusion in the SNr. MTEP was the only drug that produced a reduction in AIM score (48%) when infused in STN. In conclusion, while the striatum proved important in the antidyskinetic action of NMDA and AMPA receptor antagonists, the results of this study highlight also the importance of the metabotropic glutamate receptors that reside in the STN as therapeutic targets in the treatment of LID.

Topics: Animals; Anti-Dyskinesia Agents; Disease Models, Animal; Dyskinesia, Drug-Induced; Excitatory Amino Acid Antagonists; Infusions, Intraventricular; Levodopa; Male; Oxidopamine; Phenols; Piperidines; Putamen; Quinoxalines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, AMPA; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Substantia Nigra; Subthalamic Nucleus; Thiazoles

R-type calcium channels in postsynaptic spines signal through functional calcium microdomains to regulate a calcium/calmodulin-sensitive potassium channel that in turn regulates postsynaptic hippocampal long-term potentiation (LTP). Here, we ask whether R-type calcium channels in presynaptic terminals also signal through calcium microdomains to control presynaptic LTP. We focus on presynaptic LTP at parallel fiber to Purkinje cell synapses in the cerebellum (PF-LTP), which is mediated by calcium/calmodulin-stimulated adenylyl cyclases. Although most presynaptic calcium influx is through N-type and P/Q-type calcium channels, blocking these channels does not disrupt PF-LTP, but blocking R-type calcium channels does. Moreover, global calcium signaling cannot account for the calcium dependence of PF-LTP because R-type channels contribute modestly to overall calcium entry. These findings indicate that, within presynaptic terminals, R-type calcium channels produce calcium microdomains that evoke presynaptic LTP at moderate frequencies that do not greatly increase global calcium levels.

Topics: Adenosine A1 Receptor Antagonists; Analysis of Variance; Animals; Animals, Newborn; Calcium; Calcium Channel Blockers; Calcium Channels, R-Type; Calcium Signaling; Cerebellum; Dose-Response Relationship, Drug; Electric Stimulation; Excitatory Amino Acid Antagonists; GABA Antagonists; In Vitro Techniques; Long-Term Potentiation; Membrane Microdomains; Neural Pathways; Nickel; omega-Agatoxin IVA; omega-Conotoxin GVIA; Patch-Clamp Techniques; Phosphinic Acids; Piperidines; Presynaptic Terminals; Propanolamines; Purkinje Cells; Pyrazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Sodium Channel Blockers; Spider Venoms; Tetrodotoxin; Xanthines

In cerebral cortex there is a developmental switch from NR2B- to NR2A-containing NMDA receptors (NMDARs) driven by activity and sensory experience. This subunit switch alters NMDAR function, influences synaptic plasticity, and its dysregulation is associated with neurological disorders. However, the mechanisms driving the subunit switch are not known. Here, we show in hippocampal CA1 pyramidal neurons that the NR2B to NR2A switch driven acutely by activity requires activation of NMDARs and mGluR5, involves PLC, Ca(2+) release from IP(3)R-dependent stores, and PKC activity. In mGluR5 knockout mice the developmental NR2B-NR2A switch in CA1 is deficient. Moreover, in visual cortex of mGluR5 knockout mice, the NR2B-NR2A switch evoked in vivo by visual experience is absent. Thus, we establish that mGluR5 and NMDARs are required for the activity-dependent NR2B-NR2A switch and play a critical role in experience-dependent regulation of NMDAR subunit composition in vivo.

Topics: Adaptation, Physiological; Animals; Animals, Newborn; Electric Stimulation; Enzyme Inhibitors; Estrenes; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Female; Hippocampus; In Vitro Techniques; Male; Mice; Mice, Knockout; Models, Biological; N-Methylaspartate; Piperidines; Pyramidal Cells; Pyridines; Pyrrolidinones; Quinoxalines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate; Synapses; Thiazoles; Time Factors; Visual Cortex

During development there is an activity-dependent switch in synaptic N-Methyl-D-aspartate (NMDA) receptor subunit composition from predominantly GluN2B to GluN2A, though the precise role of this switch remains unknown. By deleting GluN2 subunits in single neurons during synaptogenesis, we find that both GluN2B and GluN2A suppress AMPA receptor expression, albeit by distinct means. Similar to GluN1, GluN2B deletion increases the number of functional synapses, while GluN2A deletion increases the strength of unitary connections without affecting the number of functional synapses. We propose a model of excitatory synapse maturation in which baseline activation of GluN2B-containing receptors prevents premature synapse maturation until correlated activity allows induction of functional synapses. This activity also triggers the switch to GluN2A, which dampens further potentiation. Furthermore, we analyze the subunit composition of synaptic NMDA receptors in CA1 pyramidal cells, provide electrophysiological evidence for a large population of synaptic triheteromeric receptors, and estimate the subunit-dependent open probability.

Topics: Animals; Dendrites; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Hippocampus; Mice; Patch-Clamp Techniques; Piperidines; Protein Subunits; Pyramidal Cells; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synapses

The endocannabinoid (eCB) system and the cannabinoid CB1 receptor (CB1R) play key roles in the modulation of brain functions. Although actions of eCBs and CB1Rs are well described at the synaptic level, little is known of their modulation of neural activity at the network level. Using microelectrode arrays, we have examined the role of CB1R activation in the modulation of the electrical activity of rat and mice cortical neural networks in vitro. We find that exogenous activation of CB1Rs expressed on glutamatergic neurons decreases the spontaneous activity of cortical neural networks. Moreover, we observe that the net effect of the CB1R antagonist AM251 inversely correlates with the initial level of activity in the network: blocking CB1Rs increases network activity when basal network activity is low, whereas it depresses spontaneous activity when its initial level is high. Our results reveal a complex role of CB1Rs in shaping spontaneous network activity, and suggest that the outcome of endogenous neuromodulation on network function might be state dependent.

Topics: 4-Aminopyridine; Action Potentials; Animals; Animals, Newborn; Benzothiadiazines; Brain; Cannabinoid Receptor Modulators; Cells, Cultured; Electric Stimulation; Endocannabinoids; Excitatory Amino Acid Antagonists; GABA Antagonists; In Vitro Techniques; Mice; Mice, Transgenic; Nerve Net; Neural Inhibition; Neurons; Organophosphorus Compounds; Picrotoxin; Piperidines; Potassium Channel Blockers; Pyrazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptor, Cannabinoid, CB1; Sodium Channel Blockers; Tetrodotoxin; Valine

The role of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor activation in the regulation of dopamine release by the metabotropic glutamate (mGlu) 2/3 receptors in the nucleus accumbens (NAc) shell was investigated using an in vivo microdialysis evaluation. The local application of 10 microM of LY341495, an mGlu 2/3 receptor antagonist, significantly increased extracellular dopamine levels in the NAc shell in freely moving rats. Pretreatment with an AMPA receptor antagonist, NBQX (0.3 mg/kg, i.p.) significantly attenuated the increase in dopamine release induced by LY341495 application to the basal level, while the systemic administration of NBQX alone had no effect on dopamine release in this region of the brain. Moreover, the local application of an AMPA receptor potentiator, CX546, at 100 or 300 microM also enhanced dopamine release in the NAc shell in a concentration-dependent manner. These findings suggest that the activation of the postsynaptic AMPA receptor plays a role in mediating the regulation of dopamine release by the mGlu 2/3 receptor in the NAc shell.

Topics: Amino Acids; Animals; Dioxoles; Dopamine; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Male; Microdialysis; Nucleus Accumbens; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Metabotropic Glutamate; Xanthenes

Diffuse brain injury is a leading cause of mortality in infants and children under 4 years of age and results in cognitive deficits in survivors. The anatomic basis for these behavioral deficits may be traumatic axonal injury (TAI), which manifests as impaired axonal transport (IAT) and neurofilament compaction (NFC), and may occur as a result of glutamate receptor activation. The extent of IAT and NFC was evaluated at 6, 24 and 72 h following non-contusive brain trauma in the 17 day-old rat to examine the causal relationship between these two pathologic entities; in addition, the effect of antagonists to the ionotropic glutamate receptors on TAI was evaluated. At 6 h post-injury, NFC was observed primarily in the cingulum, and appeared as swollen axons and terminal bulbs. By 24 h, swollen axons were additionally present in the corpus callosum and lateral white matter tracts, and appeared to increase in diameter. At 72 h, the extent of axonal swellings exhibiting compacted neurofilaments appeared to decrease, and was accompanied by punctate immunoreactivity within axon tracts suggestive of axonal degeneration. Although NFC was present in the same anatomical locations where axonal accumulation of amyloid precursor protein (APP) has been observed, double-label immunohistochemistry revealed no evidence of colocalization of compacted neurofilament and APP. Pre-injury treatment with either the NMDA receptor antagonist, ifenprodil, or the AMPA receptor antagonist, NBQX, had no significant effect on the extent of TAI, suggesting that excitotoxicity may not be a primary mechanism underlying TAI. Importantly, these data are indicative of the heterogeneity of mechanisms underlying TAI in the traumatically-injured immature brain.

Topics: Amyloid beta-Protein Precursor; Animals; Axonal Transport; Axons; Brain; Brain Injuries; Excitatory Amino Acid Antagonists; Female; Immunohistochemistry; Intermediate Filaments; Male; Neurons; Photomicrography; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Time Factors

Somatic spiking is known to regulate dendritic signaling and associative synaptic plasticity in many types of large neurons, but it is unclear whether somatic action potentials play similar roles in small neurons. Here we ask whether somatic action potentials can also influence dendritic signaling in an electrically compact neuron, the cerebellar stellate cell (SC). Experiments were conducted in rat brain slices using a combination of imaging and electrophysiology. We find that somatic action potentials elevate dendritic calcium levels in SCs. There was little attenuation of calcium signals with distance from the soma in SCs from postnatal day 17 (P17)-P19 rats, which had dendrites that averaged 60 microm in length, and in short SC dendrites from P30-P33 rats. Somatic action potentials evoke dendritic calcium increases that are not affected by blocking dendritic sodium channels. This indicates that dendritic signals in SCs do not rely on dendritic sodium channels, which differs from many types of large neurons, in which dendritic sodium channels and backpropagating action potentials allow somatic spikes to control dendritic calcium signaling. Despite the lack of active backpropagating action potentials, we find that trains of somatic action potentials elevate dendritic calcium sufficiently to release endocannabinoids and retrogradely suppress parallel fiber to SC synapses in P17-P19 rats. Prolonged SC firing at physiologically realistic frequencies produces retrograde suppression when combined with low-level group I metabotropic glutamate receptor activation. Somatic spiking also interacts with synaptic stimulation to promote associative plasticity. These findings indicate that in small neurons the passive spread of potential within dendrites can allow somatic spiking to regulate dendritic calcium signaling and synaptic plasticity.

Topics: Action Potentials; Age Factors; Analysis of Variance; Animals; Benzofurans; Biophysical Phenomena; Calcium; Cerebellum; Dendrites; Electric Stimulation; Ethers, Cyclic; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; In Vitro Techniques; Nerve Net; Neurons; Patch-Clamp Techniques; Piperidines; Pyrazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptor, Cannabinoid, CB1; Receptors, Glutamate; Signal Transduction; Sodium; Sodium Channel Blockers; Synapses; Tetrodotoxin

The cerebellum controls complex, coordinated, and rapid movements, a function requiring precise timing abilities. However, the network mechanisms that underlie the temporal organization of activity in the cerebellum are largely unexplored, because in vivo recordings have usually targeted single units. Here, we use tetrode and multisite recordings to demonstrate that Purkinje cell activity is synchronized by a high-frequency (approximately 200 Hz) population oscillation. We combine pharmacological experiments and modeling to show how the recurrent inhibitory connections between Purkinje cells are sufficient to generate these oscillations. A key feature of these oscillations is a fixed population frequency that is independent of the firing rates of the individual cells. Convergence in the deep cerebellar nuclei of Purkinje cell activity, synchronized by these oscillations, likely organizes temporally the cerebellar output.

Topics: Action Potentials; Anesthesia; Animals; Benzodiazepines; Benzoxazines; Biological Clocks; Cannabinoids; Cerebellum; Dose-Response Relationship, Radiation; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; Inhibitory Postsynaptic Potentials; Male; Models, Neurological; Morpholines; Naphthalenes; Picrotoxin; Piperidines; Purkinje Cells; Pyrazoles; Quinoxalines; Rats; Rats, Wistar; Reaction Time

Odor coding in mammals is widely believed to involve synchronized gamma frequency (30-70 Hz) oscillations in the first processing structure, the olfactory bulb. How such inputs are read in downstream cortical structures however is not known. Here we used patch-clamp recordings in rat piriform cortex slices to examine cellular mechanisms that shape how the cortex integrates inputs from bulb mitral cells. Electrical stimulation of mitral cell axons in the lateral olfactory tract (LOT) resulted in excitation of pyramidal cells (PCs), which was followed approximately 10 ms later by inhibition that was highly reproducible between trials in its onset time. This inhibition was somatic in origin and appeared to be driven through a feedforward mechanism, wherein GABAergic interneurons were directly excited by mitral cell axons. The precise inhibition affected action potential firing in PCs in two distinct ways. First, by abruptly terminating PC excitation, it limited the PC response to each EPSP to exactly one, precisely timed action potential. In addition, inhibition limited the summation of EPSPs across time, such that PCs fired action potentials in strong preference for synchronized inputs arriving in a time window of <5 ms. Both mechanisms would help ensure that PCs respond faithfully and selectively to mitral cell inputs arriving as a synchronized gamma frequency pattern.

Topics: Action Potentials; Animals; Animals, Newborn; Bicuculline; Cerebral Cortex; Dose-Response Relationship, Radiation; Electric Stimulation; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; In Vitro Techniques; Lysine; Models, Neurological; Nerve Net; Neurons; Olfactory Pathways; Patch-Clamp Techniques; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Triazines

The release of inhibitory transmitters from CNS neurons can be modulated by ionotropic glutamate receptors that are present in the presynaptic terminals. In the cerebellum, glutamate released from climbing fibers (but not from parallel fibers) activates presynaptic AMPA receptors and suppresses the release of the inhibitory transmitter GABA from basket cells onto postsynaptic Purkinje cells. This input-specific modulation has been attributed to the close proximity of the climbing fibers to the axons of the basket cells. Our recent work indicates that glutamate released from parallel fibers can "spill over" and reach the axons of stellate cells. Here I test the possibility that this spillover glutamate can activate presynaptic AMPA receptors in stellate cells and in this way modulate their release of GABA. I find that stimulation of parallel fibers activates AMPA receptors and transiently suppresses autoreceptor and autaptic GABAergic currents in stellate cells. Activation of AMPA receptors reduces the release of GABA and the suppression occurs more frequently in immature cells that have a high release probability. By contrast the release of GABA from mature stellate cells that have a low release probability is potentiated by the activation of NMDA-type glutamate receptors on presynaptic terminals. Thus during development, the glutamatergic modulation of GABA release switches from an AMPA-receptor-mediated transient suppression to a NMDA-receptor-induced lasting potentiation.

Topics: Age Factors; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Animals, Newborn; Cerebellum; Dose-Response Relationship, Radiation; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Interneurons; Mice; Morpholines; Neural Inhibition; Patch-Clamp Techniques; Piperidines; Pyrazoles; Quinoxalines; Receptors, AMPA

The present study examined the role of mGlu(2/3) receptors in short-term social memory using the social recognition paradigm in rats in which an adult rat is exposed to the same juvenile rat in two successive interactions. Intraperitoneal administration of the mGlu(2/3) receptor antagonist MGS0039 (0.3-3 mg/kg) or the ampakine CX546 (0.3-3 mg/kg) significantly and dose-dependently reduced the adult rat's social investigation of the same juvenile rat during the second encounter which occurred 120 min after the first encounter, indicating that both MGS0039 and CX546 enhanced social recognition. Pretreatment with the AMPA receptor antagonist NBQX (0.1-1 mg/kg, s.c.) significantly attenuated the effects of MGS0039 (3 mg/kg, i.p.) in the social recognition test. These results suggest that the mGlu(2/3) receptor blockade increases social recognition memory, presumably through stimulation of the AMPA receptor.

Topics: Animals; Bridged Bicyclo Compounds; Dicarboxylic Acids; Dioxoles; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Injections, Intraperitoneal; Male; Memory, Short-Term; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Metabotropic Glutamate

Synaptic NMDA-type glutamate receptors (NMDARs) play important roles in synaptic plasticity, brain development, and pathology. In the last few years, the view of NMDARs as relatively fixed components of the postsynaptic density has changed. A number of studies have now shown that both the number of receptors and their subunit compositions can be altered. During development, the synaptic NMDARs subunit composition changes, switching from predominance of NR2B-containing to NR2A-containing receptors, but little is known about the mechanisms involved in this developmental process. Here, we report that, depending on the pattern of NMDAR activation, the subunit composition of synaptic NMDARs is under extremely rapid, bidirectional control at neonatal synapses. This switching, which is at least as rapid as that seen with AMPARs, will have immediate and dramatic consequences on the integrative capacity of the synapse.

Topics: Aging; Animals; Brain; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glutamic Acid; Long-Term Potentiation; Male; Organ Culture Techniques; Piperidines; Protein Subunits; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Synapses; Synaptic Transmission; Time Factors

Endocannabinoids can act as retrograde messengers that allow postsynaptic cells to regulate the strength of their synaptic inputs. In the cerebellum, Purkinje cells (PCs) release endocannabinoids through two mechanisms. Synaptic activation evokes local endocannabinoid release that relies on a pathway that involves the metabotropic glutamate receptor mGluR1 and phospholipase-C (PLC). In contrast, depolarization evokes endocannabinoid release from the entire dendritic arbor. This leads to depolarization-induced suppression of inhibitory (DSI) and excitatory (DSE) synapses by a mechanism that does not involve mGluR1 or PLC. This latter mechanism of endocannabinoid release has only been observed under artificial conditions that transiently elevate postsynaptic calcium to >5 microm. Here, we tested the possibility that this mechanism could lead to retrograde inhibition in response to more realistic calcium signals. At both climbing fiber and inhibitory synapses onto PCs, we found that prolonging the elevation of calcium significantly lowered the peak calcium required to evoke PLC-independent endocannabinoid release. This suggests that the mechanism of endocannabinoid release involved in DSI and DSE is likely to evoke endocannabinoid release in response to physiologically relevant levels of calcium. When dendritic calcium was elevated to 0.4-1 microm for 15 s or more, endocannabinoid release from PCs selectively suppressed inhibitory synapses. This suggests that inhibitory synapses are more sensitive to prolonged calcium increases. Thus, in contrast to localized retrograde inhibition evoked by synaptic activation, modest but sustained calcium elevation could globally suppress inhibitory synapses onto PCs.

Topics: Animals; Calcium; Cannabinoid Receptor Modulators; Cerebellum; Dendrites; Dose-Response Relationship, Radiation; Electric Stimulation; Endocannabinoids; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; In Vitro Techniques; Membrane Potentials; Neural Inhibition; Patch-Clamp Techniques; Piperidines; Purkinje Cells; Pyrazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Synapses; Time Factors

Allodynia or hyperalgesia induced by peripheral nerve injury may be involved in changes in the sensitivity of neurotransmitters at the spinal cord level. In order to clarify the functional role of neurotransmitters in peripheral nerve injury, we used rats with nerve injury induced by chronic constriction of the sciatic nerve (CCI rat model) and estimated the effects of the intrathecal injection of drugs known to affect glutamate and tachykinin receptors. In sham-operated rats, the NMDA receptor agonist NMDA and AMPA-kinate receptor agonist RS-(5)-bromowillardin reduced withdrawal latency. The non-competitive NMDA receptor antagonist MK-801, competitive NMDA receptor antagonist AP-5 and AMPA-kinate receptor antagonist NBQX increased withdrawal latency. Substance P (SP) increased the withdrawal latency but only transitorily. The NK1 receptor antagonist RP67580 increased withdrawal latency, but the NK2 receptor antagonist SR48968 did not show an effect. In CCI rats, RS-(5)-bromowillardin reduced withdrawal latency, but NMDA did not show an effect. NBQX increased withdrawal latency, while MK-801 and AP-5 showed little or no effect. SP reduced withdrawal latency, and both RP67580 and SR48968 increased it. These results indicate that the alteration in sensitivity of ionotropic glutamate receptors and tachykinin receptors in the spinal cord contribute to development and maintenance of nerve injury-evoked neuropathic pain.

Topics: Alanine; Analgesics; Animals; Behavior, Animal; Benzamides; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Indoles; Isoindoles; Male; N-Methylaspartate; Pain; Pain Measurement; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Kainic Acid; Receptors, Tachykinin; Sciatic Nerve; Spinal Cord; Substance P; Valine

Theta rhythms are behaviorally relevant electrical oscillations in the mammalian brain, particularly the hippocampus. In many cases, theta oscillations are shaped by inhibitory postsynaptic potentials (IPSPs) that are driven by glutamatergic and/or cholinergic inputs. Here we show that hippocampal theta rhythm IPSPs induced in the CA1 region by muscarinic acetylcholine receptors independent of all glutamate receptors can be briefly interrupted by action potential-induced, retrograde endocannabinoid release. Theta IPSPs can be recorded in CA1 pyramidal cell somata surgically isolated from CA3, subiculum, and even from their own apical dendrites. These results suggest that perisomatic-targeting interneurons whose output is subject to inhibition by endocannabinoids are the likely source of theta IPSPs. Interneurons having these properties include the cholecystokinin-containing cells. Simultaneous recordings from pyramidal cell pairs reveal synchronous theta-frequency IPSPs in neighboring pyramidal cells, suggesting that these IPSPs may help entrain or modulate small groups of pyramidal cells.

Topics: Action Potentials; Amino Acids; Animals; Cannabinoid Receptor Modulators; Carbachol; Cholinergic Agonists; Endocannabinoids; Excitatory Amino Acid Antagonists; Hippocampus; In Vitro Techniques; Male; Methoxyhydroxyphenylglycol; Neural Inhibition; Piperidines; Pyrazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Muscarinic; Spectrum Analysis; Synapses; Theta Rhythm; Time Factors; Xanthenes

We investigated the mechanisms by which activation of group I metabotropic glutamate receptors (mGluRs) and CB1 cannabinoid receptors (CB1Rs) leads to inhibition of synaptic currents at the calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB) of the rat auditory brainstem. In approximately 50% of the MNTB neurons tested, activation of group I mGluRs by the specific agonist (s)-3,5-dihydroxyphenylglycine (DHPG) reversibly inhibited AMPA receptor- and NMDA receptor-mediated EPSCs to a similar extent and reduced paired-pulse depression, suggestive of an inhibition of glutamate release. Presynaptic voltage-clamp experiments revealed a reversible reduction of Ca2+ currents by DHPG, with no significant modification of the presynaptic action potential waveform. Likewise, in approximately 50% of the tested cells, the CB1 receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN) reversibly inhibited EPSCs, presynaptic Ca2+ currents, and exocytosis. For a given cell, the amount of inhibition by DHPG correlated with that by WIN. Moreover, the inhibitory action of DHPG was blocked by the CB1R antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) and occluded by WIN, indicating that DHPG and WIN operate via a common pathway. The inhibition of EPSCs by DHPG, but not by WIN, was abolished after dialyzing 40 mm BAPTA into the postsynaptic cell, suggesting that DHPG activated postsynaptic mGluRs. Light and electron microscopy immunolabeling indicated a presynaptic expression of CB1Rs and postsynaptic localization of mGluR1a. Our data suggest that activation of postsynaptic mGluRs triggers the Ca2+-dependent release of endocannabinoids that activate CB1 receptors on the calyx terminal, which leads to a reduction of presynaptic Ca2+ current and glutamate release.

Topics: 2-Amino-5-phosphonovalerate; Action Potentials; Amino Acids; Animals; Benzoxazines; Brain Stem; Calcium Signaling; Cannabinoid Receptor Modulators; Endocannabinoids; Evoked Potentials, Auditory, Brain Stem; Glycine; Ion Transport; Morpholines; Naphthalenes; Nerve Endings; Patch-Clamp Techniques; Picrotoxin; Piperidines; Pyrazoles; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptor, Cannabinoid, CB1; Receptors, Metabotropic Glutamate; Receptors, Presynaptic; Resorcinols; Scopolamine; Synaptic Transmission; Xanthenes

It is widely believed that long-term depression (LTD) and its counterpart, long-term potentiation (LTP), involve mechanisms that are crucial for learning and memory. However, LTD is difficult to induce in adult cortex for reasons that are not known. Here we show that LTD can be readily induced in adult cortex by the activation of NMDA receptors (NMDARs), after inhibition of glutamate uptake. Interestingly there is no need to activate synaptic NMDARs to induce this LTD, suggesting that LTD is triggered primarily by extrasynaptic NMDA receptors. We also find that de novo LTD requires the activation of NR2B-containing NMDAR, whereas LTP requires activation of NR2A-containing NMDARs. Surprisingly another form of LTD, depotentiation, requires activation of NR2A-containing NMDARs. Therefore, NMDARs with different synaptic locations and subunit compositions are involved in various forms of synaptic plasticity in adult cortex.

Topics: 2-Amino-5-phosphonovalerate; Animals; Aspartic Acid; Cerebral Cortex; Dicarboxylic Acids; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glutamic Acid; Long-Term Potentiation; Long-Term Synaptic Depression; N-Methylaspartate; Neurons; Neurotransmitter Uptake Inhibitors; Phenols; Picrotoxin; Piperidines; Protein Subunits; Pyrrolidines; Quinoxalines; Rats; Receptors, Metabotropic Glutamate; Receptors, N-Methyl-D-Aspartate

In the rat, postsynaptic 5-hydroxytryptamine2A receptors medial prefrontal cortex control the activity of the serotonergic system through changes in the activity of pyramidal neurons projecting to the dorsal raphe nucleus. Here we extend these observations to mouse brain. The prefrontal cortex expresses abundant 5- hydroxytryptamine2A receptors, as assessed by immunohistochemistry, Western blots and in situ hybridization procedures. The application of the 5-hydroxytryptamine2A/2C agonist DOI (100 microm) by reverse dialysis in the medial prefrontal cortex doubled the local release of 5-hydroxytryptamine. This effect was reversed by coperfusion of tetrodotoxin, and by the selective 5-hydroxytryptamine2A receptor antagonist M100907, but not by the 5-hydroxytryptamine2C antagonist SB-242084. The effect of DOI was also reversed by prazosin (alpha1-adrenoceptor antagonist), BAY x 3702 (5-hydroxytryptamine1A receptor agonist), NBQX (alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate/kainic acid antagonist) and 1S,3S-ACPD (mGluR II/III agonist), but not by dizocilpine (N-methyl-d-aspartate antagonist). alpha-Amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate mimicked the 5-hydroxytryptamine elevation produced by DOI, an effect also reversed by BAY x 3702. Likewise, the coperfusion of classical (chlorpromazine, haloperidol) and atypical antipsychotic drugs (clozapine, olanzapine) fully reversed the 5-hydroxytryptamine elevation induced by DOI. These observations suggest that DOI increases 5-hydroxytryptamine release in the mouse medial prefrontal cortex through the activation of local 5-hydroxytryptamine2A receptors by an impulse-dependent mechanism that involves/requires the activation of local alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate receptors. This effect is reversed by ligands of receptors present in the medial prefrontal cortex, possibly in pyramidal neurons, which are involved in the action of antipsychotic drugs. In particular, the reversal by classical antipsychotics may involve blockade of alpha1-adrenoceptors, whereas that of atypical antipsychotics may involve 5-hydroxytryptamine2A receptors and alpha1-adrenoceptors.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Aminopyridines; Anesthetics, Local; Animals; Antipsychotic Agents; Benzopyrans; Blotting, Western; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Fluorobenzenes; Immunohistochemistry; In Situ Hybridization; Indoles; Indophenol; Male; Mice; Mice, Inbred C57BL; Microdialysis; Piperidines; Prazosin; Prefrontal Cortex; Quinoxalines; Receptor, Serotonin, 5-HT2A; Receptors, Serotonin; RNA, Messenger; Serotonin; Serotonin Antagonists; Serotonin Receptor Agonists; Tetrodotoxin; Thiazoles; Time Factors

The regulation of NMDA receptor (NMDAR) subunit composition and expression during development is thought to control the process of thalamocortical afferent innervation, segregation, and plasticity. Thalamocortical synaptic plasticity in the mouse is dependent on NMDARs containing the NR2B subunit, which are the dominant form during the "critical period" window for plasticity. Near the end of the critical period there is a gradual increase in the contribution of NR2A subunits that happens in parallel to changes in NMDAR-mediated current kinetics. However, no extension of the critical period occurs in NR2A knockout mice, despite the fact that NMDA subunit composition and current kinetics remain immature past the end of the critical period. These data suggest that regulation of NMDAR subunit composition is not essential for closing the critical period plasticity window in mouse somatosensory barrel cortex.

Topics: Animals; Brain Mapping; Critical Period, Psychological; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Gene Expression Regulation, Developmental; Long-Term Potentiation; Mice; Mice, Inbred C57BL; Mice, Knockout; Neuronal Plasticity; Piperidines; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Somatosensory Cortex; Synapses; Thalamus

Tachykinins have been suggested to play a significant role in the mammalian striatum, at least in part by the control of acetylcholine release from cholinergic interneurons. In the present study, we have examined the ability of known tachykinin agonists and antagonists to modulate the activity of these interneurons in mouse striatal slices. Using whole-cell patch-clamp recordings, the selective neurokinin-1, neurokinin-2 and neurokinin-3 receptor agonists [sar9,Met(O2)11]substance P, [beta-ala8]neurokinin A(4-10) and senktide each produced a dose-dependent depolarization of visually identified cholinergic interneurons that was retained under conditions designed to interrupt synaptic transmission. The nature of these neurons and the expression of multiple tachykinin receptors was confirmed using single-cell reverse transcriptase-polymerase chain reaction analysis. Using in vitro superfusion techniques, the selective neurokinin-1, neurokinin-2 and neurokinin-3 receptor agonists [sar9,Met(O2)11]substance P, [beta-ala8]neurokinin A(4-10) and senktide, respectively, each produced a dose-dependent increase in acetylcholine release, the selectivity of which was confirmed using the neurokinin-1, neurokinin-2 and neurokinin-3 receptor antagonists SR140333, GR94800 and SR142801 (100 nM). U73122 (10 microM), a phospholipase C inhibitor, blocked [sar9,Met(O2)11]substance P- and senktide-induced acetylcholine release, but had no effect on [beta-ala8]neurokinin A(4-10)-induced release. The protein kinase C inhibitors chelerythrine and Ro-31-8220 (both 1 microM) significantly inhibited responses induced by all three agonists. These findings indicate that tachykinins modulate the activity of mouse striatal cholinergic interneurons. Furthermore, neurokinin-2 receptors are shown to perform a role in mouse that has not been identified previously in other species.

Topics: 2-Amino-5-phosphonovalerate; Acetylcholine; Alkaloids; Animals; Benzophenanthridines; Choline O-Acetyltransferase; Corpus Striatum; Electrophysiology; Enzyme Inhibitors; Estrenes; Excitatory Amino Acid Antagonists; In Situ Hybridization; Indoles; Interneurons; Membrane Potentials; Mice; Mice, Inbred C57BL; Neurokinin A; Oligopeptides; omega-N-Methylarginine; Peptide Fragments; Phenanthridines; Phosphodiesterase Inhibitors; Piperidines; Pyrrolidinones; Quinoxalines; Quinuclidines; Receptors, Neurokinin-1; Receptors, Neurokinin-2; Receptors, Neurokinin-3; Receptors, Tachykinin; RNA, Messenger; Signal Transduction; Substance P; Tachykinins; Tetrodotoxin; Tritium

N-methyl-D-aspartate (NMDA) and non-NMDA receptors were found to be involved in development of functional disorders caused by hexachlorophene. In order to specify the role of glutamate receptors we studied the protective effects of the selective antagonist of the kainate/(+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor/channel 1,2,3,4-tetrahydro-6-nitro-2, 3-dioxo-benzo[f]quinoxaline-7-sulphonamide disodium (NBQX) and of the non-competitive NMDA receptor antagonist ifenprodil tartrate on coordinative motor behaviour of adult male Wistar rats as assessed in a simple 'ladder-test'. Neurotoxic injury of the cerebrum after hexachlorophene administration and putative amelioration after treatment with test substances was demonstrated histologically. Hexachlorophene-induced motor disturbance remitted spontaneously when stopping the noxis, but remittance occurred significantly earlier when NBQX [0.45 and 0.6 mg/kg intraperitoneal (i.p.)] was applied as well. Ifenprodil (0.15 to 1.2 mg/kg) did not improve the motor function. Vacuolation of white matter of the whole cerebrum was observed after 3 weeks of treatment with hexachlorophene. These morphological alterations caused by hexachlorophene treatment [central nervous system (CNS) vacuolation] spontaneously revert only after 5-6 weeks. The 5-day duration with test substances was too short for remission of vacuolation which thus may not apply to the situation after treatment with glutamate antagonists, despite improvement of motor function. The results suggest that kainate/AMPA receptor channels are at least partially involved in the mechanism of brain damage induced by hexachlorophene, however, the polyamine binding site of the NMDA receptor evidently is not involved.

Topics: Animals; Behavior, Animal; Brain; Brain Edema; Excitatory Amino Acid Antagonists; Hexachlorophene; Male; Motor Activity; Motor Skills Disorders; Piperidines; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate

Previous work showed that the dorsal periaqueductal gray is involved in the inhibition of fear-potentiated startle. The present study investigated the effects of blockade and stimulation of Kainate/AMPA and GABA(A) receptors within the dorsal periaqueductal gray on expression and conditioned inhibition of fear-potentiated startle. Blockade of the Kainate/AMPA receptors enhanced whereas stimulation of the Kainate/AMPA receptors decreased expression of fear-potentiated startle. These effects do not reflect conditioned inhibition since this modulation was not changed by injections of Kainate/AMPA receptor agonists or antagonists into the dorsal periaqueductal gray. Stimulation and blockade of GABA(A) receptors within the dorsal periaqueductal gray neither affected expression of fear-potentiated startle nor its conditioned inhibition. The present results together with findings from the literature indicate that glutamate in the dorsal periaqueductal gray is a critical substrate for the expression and modulation of fear-related behaviours.

Topics: Acoustic Stimulation; Animals; Conditioning, Classical; Electroshock; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Fear; Kainic Acid; Light; Male; Microinjections; Periaqueductal Gray; Picrotoxin; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, GABA-A; Receptors, Kainic Acid; Reflex, Startle

Aniracetam, 1-(1,3-benzodioxol-5-yl-carbonyl)piperidine (1-BCP) and cyclothiazide, three compounds considered to enhance cognition through modulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors, were evaluated in the 'kynurenate test', a biochemical assay in which some nootropics have been shown to prevent the antagonism by kynurenic acid of the N-methyl-D-aspartate (NMDA)-evoked [3H]noradrenaline ([3H]NA) release from rat hippocampal slices. Aniracetam attenuated the kynurenate (100 microM) antagonism of the [3H]NA release elicited by 100 microM NMDA with high potency (EC50< or =0.1 microM). Cyclothiazide and 1-BCP were about 10 and 100 times less potent than aniracetam, respectively. The effect of aniracetam persisted in the presence of the AMPA receptor antagonist 6-nitro-7-sulphamoyl-benzo[f]quinoxaline-2,3-dione (NBQX) added at 5 microM, a concentration that did not affect NMDA receptors; in contrast, NBQX reduced the effect of 1-BCP and abolished that of cyclothiazide. The AMPA-evoked release of [3H]NA from hippocampal slices or synaptosomes was enhanced by cyclothiazide, less potently by 1-BCP and weakly by aniracetam. High concentrations of kynurenate (1 mM) antagonized the AMPA-evoked [3H]NA release in slices; this antagonism was attenuated by 1 microM cyclothiazide and reversed to an enhancement of AMPA-evoked [3H]NA release by 10 microM of the drug, but was insensitive to 1-BCP or aniracetam. It is concluded that aniracetam exerts a dual effect on glutamatergic transmission: modulation of NMDA receptor function at nanomolar concentrations, and modulation of AMPA receptors at high micromolar concentrations. As to cyclothiazide and 1-BCP, our data concur with the idea that both compounds largely act through AMPA receptors, although an NMDA component may be involved in the effect of 1-BCP.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Antihypertensive Agents; Benzothiadiazines; Dioxoles; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Heterocyclic Compounds; Hippocampus; In Vitro Techniques; Kynurenic Acid; Male; N-Methylaspartate; Nootropic Agents; Norepinephrine; Piperidines; Pyrrolidinones; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Tritium

Glutamate-induced changes in intracellular free Ca++ concentration ([Ca++]i) were recorded in resting and electrically-stimulated primary cultures of rat cerebral cortical cells, employing the Ca++ indicator Fura 2. A brief (10 min) exposure to glutamate led to a concentration-dependent basal [Ca++]i increase, measured 30 min after glutamate removal. In order to unmask more subtle modifications in [Ca++]i movements associated with neurosecretion, the glutamate effect was also studied in electrically-stimulated cells. The application of trains (10 s) of electrical pulses (intensity 30 mA, duration 1 ms) induced frequency-related Na+- and Ca++-dependent [Ca++]i transients. A 5 min treatment with 50 microM glutamate reduced to 48% the electrically-evoked [Ca++]i transients, evaluated 30 min after glutamate challenge. The neuroprotective effect of sodium 4,6-dichloro-3-[(E)-3-(N-phenyl)propenamide]indole-2-carboxylate (GV150526A), a new indole derivative with high affinity and selectivity for the glycine site of the NMDA receptor-channel complex, was compared with that of DL-2-amino-5-phosphonopentanoic acid (AP5), ifenprodil, 7-chlorokynurenic acid and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)-quinoxaline (NBQX) on glutamate-induced [Ca++]i changes in resting and electrically-stimulated cells. In both experimental conditions, GV150526A showed to be the most potent compound. Moreover, GV150526A and 7-chlorokynurenic acid were 2-3 times more active in stimulated neurons than in resting neurons, indicating a major involvement of the glycine site in the protection of the cells kept in an active state.

Topics: Animals; Calcium; Cells, Cultured; Cerebral Cortex; Drug Interactions; Electric Stimulation; Excitatory Amino Acid Antagonists; Glutamic Acid; Indoles; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

The benzoylpiperidine 1-(1,3-benzodioxol-5-ylcarbonyl)-piperidine (1-BCP), and related compounds, potentiate alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acidergic (AMPAergic) synaptic currents in central neurons, and improve performance of rodents and humans on learning and memory tasks. Their physiological actions are similar but not identical to thiazides, which also enhance AMPAergic synaptic responses and improve performance of rats in water-maze and passive-avoidance tests. Thiazides also dramatically increase AMPA receptor-mediated neuronal death in vitro and in vivo. Here it was evaluated whether 1-BCP potentiated AMPA receptor-mediated excitotoxicity in hippocampal neuron cultures. Glutamate + MK 801 (to block NMDA receptors) + 1 mM 1-BCP produced neuronal death that was reversed by 10 microM 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX), a selective AMPA receptor antagonist. 1-BCP and drugs with similar activities can facilitate AMPA receptor-mediated excitotoxicity.

Topics: Animals; Benzothiadiazines; Cell Survival; Cells, Cultured; Dioxoles; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glutamic Acid; Hippocampus; Neurons; Neurotoxins; Piperidines; Quinoxalines; Rats; Receptors, AMPA

The mechanism by which substance P depolarizes cholinergic interneurons in the rat striatum was studied using whole-cell recording techniques. In all cases the effects of substance P were mimicked by the neurokinin1 receptor agonist [Sar9, Met(O2)11] substance P and were antagonized by the neurokinin1 receptor antagonist SR140333. [Sar9, Met(O2)11] substance P was found to depolarize cholinergic interneurons by the induction of a calcium-activated inward current at -60 mV. This inward current was irreversibly potentiated by photolysis of caged GTPgammaS within neurons implicating the involvement of a G-protein. The [Sar9, Met(O2)11] substance P-induced inward current was inhibited by the phospholipase C inhibitor U-73122, and by the inclusion of the inositol-1,4,5-triphosphate receptor antagonist heparin in the electrode solution. These findings suggest that neurokinin1 receptors depolarize cholinergic interneurons in the rat striatum primarily through a phosphoinositide signalling pathway.

Topics: 2-Amino-5-phosphonovalerate; Acetylcholine; Animals; Chelating Agents; Corpus Striatum; Diazonium Compounds; Electric Stimulation; Estrenes; Excitatory Amino Acid Antagonists; Guanosine 5'-O-(3-Thiotriphosphate); Interneurons; Male; Membrane Potentials; Patch-Clamp Techniques; Phenoxyacetates; Phosphodiesterase Inhibitors; Photochemistry; Piperidines; Pyrrolidinones; Quinoxalines; Quinuclidines; Rats; Rats, Sprague-Dawley; Receptors, Neurokinin-1; Substance P; Synaptic Transmission; Tachykinins; Tetrodotoxin

We have studied in a well-characterized in vitro neuronal system, cultures of cerebellar granule cells, the toxicity of polyamines endogenously present in the brain: spermine, spermidine, and putrescine. Twenty-four-hour exposure of mature (8 days in vitro) cultures to 1-500 microM spermine resulted in a dose-dependent death of granule cells, with the half-maximal effect being reached below 50 microM concentration. Putrescine was moderately toxic but only at 500 microM concentration. Spermidine was tested at 50 and 100 microM concentration and its toxicity was evaluated to be about 50% that of spermine. Neuronal death caused by spermine occurred, at least in part, by apoptosis. Spermine toxicity was completely prevented by competitive (CGP 39551) and noncompetitive (MK-801) antagonists of the NMDA receptor, but was unaffected by a non-NMDA antagonist (NBQX) or by antagonists of the polyamine site present on the NMDA receptor complex, such as ifenprodil. A partial protection from spermine toxicity was obtained through the simultaneous presence of free radical scavengers or through inhibition of the free radical-generating enzyme nitric oxide synthase, known to be partially effective against direct glutamate toxicity. The link between spermine toxicity and glutamate was further strengthened by the fact that, under culture conditions in which glutamate toxicity was ineffective or much reduced, spermine toxicity was absent or very much decreased. Exposure to spermine was accompanied by a progressive accumulation of glutamate in the medium of granule cell cultures. This was attributed to glutamate leaking out from dying or dead cells and was substantially prevented by the simultaneous presence of MK-801 or CGP 39551. The present results demonstrate that polyamines are toxic to granule cells in culture and that this toxicity is mediated through the NMDA receptor by interaction of exogenously added polyamines with endogenous glutamate released by neurons in the medium. The involvement of brain polyamines, in particular spermine and spermidine, in excitotoxic neuronal death is strongly supported by our present results.

Topics: 2-Amino-5-phosphonovalerate; Animals; Apoptosis; Aspartic Acid; Butylated Hydroxytoluene; Cells, Cultured; Cerebellar Cortex; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Female; Free Radical Scavengers; Glutamic Acid; L-Lactate Dehydrogenase; Male; Nerve Tissue Proteins; Neurons; Neuroprotective Agents; Nitric Oxide Synthase; Nitroarginine; Piperidines; Putrescine; Quinoxalines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Spermidine; Spermine; Vitamin E

To evaluate the role played by nitric oxide in global cerebral ischaemia we examined the effects of 7-nitroindazole and a sodium salt of 7-nitroindazole (inhibitors of neuronal nitric oxide (NO) synthase) and NG-nitro-L-arginine methyl ester (a more general inhibitor of NO synthase) in the gerbil model of cerebral ischaemia. Four experiments were carried out. In the first experiment, animals were either sham-operated, subjected to 5 min bilateral carotid occlusion (BCAO) or administered 7-nitroindazole or NG-nitro-L-arginine methyl ester immediately after occlusion followed by three further doses at 3, 6 and 24 h post-occlusion. In the second experiment, we examined the effects of a sodium salt of 7-nitroindazole, which is more soluble than 7-nitroindazole, using the same protocol. In the third experiment, the effects of the sodium salt of 7-nitroindazole administered at 10 mg/kg at 0, 3, 6, 24, 27, 30, 33, 52, 55, 72, 75 and 78 h post-occlusion or at 0.05 mg/h for 72 h via mini-pumps were evaluated. In separate experiments, we examined the effects of three reference compounds dizocilpine (MK-801), 2, 3-dihydroxy-6-nitro-7-sulphamoyl-benz(F)-quinoxaline (NBQX) and eliprodil using the same model. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5 min bilateral carotid occluded animals 5 days after surgery. Both 7-nitroindazole and NG-nitro-L-arginine methyl ester provided significant neuroprotection (P < 0.01) against this neuronal death. The sodium salt of 7-nitroindazole showed no protection when administered up to 12 times post-occlusion, but did provide significant (P < 0.01) neuroprotection when administered via mini-pump. The neuroprotection was similar to that provided by MK-801 and eliprodil, but not as good as that observed with NBQX. These results indicate that nitric oxide plays a role in ischaemic cell death and that selective neuronal nitric oxide synthase inhibitors can protect against ischaemic brain damage.

Topics: Animals; Brain Ischemia; Disease Models, Animal; Dizocilpine Maleate; Enzyme Inhibitors; Gerbillinae; Indazoles; Male; Neuroprotective Agents; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Piperidines; Quinoxalines

Anoxic depolarization (AD) and failure of ion homeostasis play an important role in ischemia-induced neuronal injury. In the present study, different drugs with known ion-channel-modulating properties were examined for their ability to interfere with cardiac-arrest-elicited AD and with the changes in the extracellular ion activity in rat brain. Our results indicate that only drugs primarily blocking membrane Na+ permeability (NBQX, R56865, and flunarizine) delayed the occurrence of AD, while compounds affecting cellular Ca2+ load (MK-801 and nimodipine) did not influence the latency time. The ischemia-induced [Na+]e reduction was attenuated by R56865. Blockade of the ATP-sensitive K+ channels with glibenclamide reduced the [K+]e increase upon ischemia, indicating an involvement of the KATP channels in ischemia-induced K+ efflux. The KATP channel opener cromakalim did not affect the AD or the [K+]e concentration. The ischemia-induced rapid decline of extracellular calcium was attenuated by receptor-operated Ca2+ channel blockers MK-801 and NBQX, but not by the voltage-operated Ca2+ channel blocker nimodipine, R56865, and flunarizine.

Topics: Adenosine Triphosphate; Animals; Benzothiazoles; Calcium; Dizocilpine Maleate; Flunarizine; Glyburide; Heart Arrest; Hypoxia; Ion Channels; Male; Nimodipine; Piperidines; Potassium; Potassium Channels; Quinoxalines; Rats; Rats, Wistar; Sodium; Thiazoles

The behavioural and convulsant effects of imipenem (Imi), a carbapenem derivative, were studied after intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures. The anticonvulsant effects of some excitatory amino acid antagonists and muscimol (Msc), a GABAA agonist, against seizures induced by i.p. or i.c.v. administration of Imi were also evaluated. The present study demonstrated that the order of anticonvulsant activity in our epileptic model, after i.p. administration, was (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten-5,10-imine maleate (MK-801) > (+/-)(E)-2-amino-4-methyl-5-phosphono-3-pentenoate ethyl ester (CGP 39551) > 3-((+/-)-2-carboxypiperazin-4-yl)propenyl-1-phosphonic acid (CPPene) > 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CCP) > 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)-quinoxaline (NBQX). Ifenprodil, a compound acting on the polyamine site of NMDA receptor complex was unable to protect against seizures induced by Imi, suggesting that the poliamine site did not exert a principal role in the genesis of seizures induced by Imi. In addition, the order of anticonvulsant potency in our epileptic model, after i.c.v. administration, was CPPene > MK-801 > Msc > (-)-2-amino-7-phosphonic acid (AP7) > gamma-D-glutamylaminomethylsulphonate (gamma-D-GAMS) > NBQX > kynurenic acid (KYNA) > 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX). The relationship between the different site of action and the anticonvulsant activity of these derivatives was discussed. Although the main mechanism of Imi induced seizures cannot be easily determined, potential interactions with the receptors of the excitatory amino acid neurotransmitters exists. In fact, antagonists of excitatory amino acids are able to increase the threshold for the seizures or to prevent the seizures induced by Imi. In addition, Imi acts on the central nervous system by inhibition of GABA neurotransmission and Msc, a selective GABAA agonist, was able to protect against seizures induced by Imi.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Anticonvulsants; Dizocilpine Maleate; Excitatory Amino Acids; Glutamine; Imipenem; Kynurenic Acid; Mice; Mice, Inbred DBA; Muscimol; Piperazines; Piperidines; Quinoxalines; Seizures

The selective alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX) and the selective N-methyl-D-aspartate (NMDA) receptor antagonists MK 801 and ifenprodil were administered to Mongolian gerbils following a 5 min period of bilateral carotid artery occlusion. NBQX when given 4, 6 or 24 h after ischaemia gave a reduced loss of hippocampal CA1 neurones compared to control animals receiving vehicle only. Dizocilipine (MK 801) (1-10 mg/kg i.p.) and ifenprodil (a total of 45 mg/kg i.p.) gave no protection. The peak levels of NBQX obtained in the cerebrospinal fluid of gerbils receiving the neuroprotective dose (3 x 30 mg/kg i.p.) was 1 microM. In gerbil cortex slices, this concentration had no effect on NMDA-evoked depolarization, but had a moderate effect on kainate and gave a total blockade of AMPA depolarizations. It is concluded that antagonists of non-NMDA glutamate receptor subtypes, possibly AMPA, may be a useful therapeutic approach for cerebral ischaemia-related brain damage following global ischaemia.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Cerebral Cortex; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; Gerbillinae; Hippocampus; Ibotenic Acid; Ischemic Attack, Transient; Kinetics; Male; Neurons; Piperidines; Quinoxalines; Receptors, AMPA; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate

The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)-quinoxaline (NBQX) did not impair working memory measured as alternation behavior in the Y-maze in mice. No depressant effect on alternation was detected even when NBQX impaired locomotion measured as the total number of arm entries. Similar profile of action in the Y-shaped maze was observed after administration of an anti-ischemic drug ifenprodil. In contrast, the N-methyl-D-aspartate (NMDA) antagonist (D-(E)-4-(3-phosphonoprop-2-enyl)piperazine-2-carboxylate (D-CPPene) impaired spontaneous alternation. In the step-through passive avoidance task, mice were trained to avoid dark compartment entry. NBQX and ifenprodil did not impair learning in this task when administered before or immediately after training. In contrast, D-CPPene disturbed acquisition when administered before but not immediately after training or before retention test. These observations suggest that AMPA receptors are not critically involved in the formation of spatial working memory and acquisition (storage) in the passive avoidance, and have no effect on recall (retrieval) from long-term memory.

Topics: Animals; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Male; Maze Learning; Memory; Mice; Neuropsychological Tests; Piperazines; Piperidines; Quinoxalines; Reaction Time