fg-9041 and bicuculline-methiodide

Interictal spikes in models of focal seizures and epilepsies are sustained by the synchronous activation of glutamatergic and GABAergic networks. The nature of population spikes associated with seizure initiation (pre-ictal spikes; PSs) is still undetermined. We analyzed the networks involved in the generation of both interictal and PSs in acute models of limbic cortex ictogenesis induced by pharmacological manipulations. Simultaneous extracellular and intracellular recordings from both principal cells and interneurons were performed in the medial entorhinal cortex of the in vitro isolated guinea pig brain during focal interictal and ictal discharges induced in the limbic network by intracortical and brief arterial infusions of either bicuculline methiodide (BMI) or 4-aminopyridine (4AP). Local application of BMI in the entorhinal cortex did not induce seizure-like events (SLEs), but did generate periodic interictal spikes sensitive to the glutamatergic non-NMDA receptor antagonist DNQX. Unlike local applications, arterial perfusion of either BMI or 4AP induced focal limbic SLEs. PSs just ahead of SLE were associated with hyperpolarizing potentials coupled with a complete blockade of firing in principal cells and burst discharges in putative interneurons. Interictal population spikes recorded from principal neurons between two SLEs correlated with a depolarizing potential. We demonstrate in two models of acute limbic SLE that PS events are different from interictal spikes and are sustained by synchronous activation of inhibitory networks. Our findings support a prominent role of synchronous network inhibition in the initiation of a focal seizure.

Topics: 4-Aminopyridine; Action Potentials; Animals; Bicuculline; Computer Simulation; Convulsants; Disease Models, Animal; Electric Stimulation; Entorhinal Cortex; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Female; Guinea Pigs; In Vitro Techniques; Models, Biological; Neural Inhibition; Potassium Channel Blockers; Quinoxalines; Seizures

Axon conduction fidelity is important for signal transmission and has been studied in various axons, including the Schaffer collateral axons of the hippocampus. Previously, we reported that high-frequency stimulation (HFS) depresses Schaffer collateral excitability when assessed by whole-cell recordings from CA3 pyramidal cells but induces biphasic excitability changes (increase followed by decrease) in extracellular recordings of CA1 fiber volleys. Here, we examined responses from proximal (whole-cell or field-potential recordings from CA3 pyramidal cell somata) and distal (field-potential recordings from CA1 stratum radiatum) portions of the Schaffer collaterals during HFS and burst stimulation in hippocampal slices. Whole-cell and dual-field-potential recordings using 10-100-Hz HFS revealed frequency-dependent changes like those previously described, with higher frequencies producing more drastic changes. Dual-field-potential recordings revealed substantial differences in the response to HFS between proximal and distal regions of the Schaffer collaterals, with proximal axons depressing more strongly and only distal axons showing an initial excitability increase. Because CA3 pyramidal neurons normally fire in short bursts rather than long high-frequency trains, we repeated the dual recordings using 100-1,000-ms interval burst stimulation. Burst stimulation produced changes similar to those during HFS, with shorter intervals causing more drastic changes and substantial differences observed between proximal and distal axons. We suggest that functional differences between proximal and distal Schaffer collaterals may allow selective filtering of nonphysiological activity while maximizing successful conduction of physiological activity throughout an extensive axonal arbor.

Topics: Action Potentials; Animals; Bicuculline; Biophysical Phenomena; Dizocilpine Maleate; Electric Stimulation; Excitatory Amino Acid Antagonists; Female; GABA-A Receptor Antagonists; Hippocampus; In Vitro Techniques; Nerve Fibers; Nerve Net; Neurons; Patch-Clamp Techniques; Phosphinic Acids; Propanolamines; Quinoxalines; Rats; Rats, Sprague-Dawley; Reaction Time

Although the contribution of postsynaptic mechanisms to long-term synaptic plasticity has been studied extensively, understanding the contribution of presynaptic modifications to this process lags behind, primarily because of a lack of techniques with which to directly and quantifiably measure neurotransmitter release from synaptic terminals. Here, we developed a method to measure presynaptic activity through the biotinylation of vesicular transporters in vesicles fused with presynaptic membranes during neurotransmitter release. This method allowed us for the first time to selectively quantify the spontaneous or evoked release of glutamate or GABA at their respective synapses. Using this method to investigate presynaptic changes during the expression of group I metabotropic glutamate receptor (mGluR1/5)-mediated long-term depression (LTD) in cultured rat hippocampal neurons, we discovered that this form of LTD was associated with increased presynaptic release of glutamate, despite reduced miniature EPSCs measured with whole-cell recording. Moreover, we found that specific blockade of AMPA receptor (AMPAR) endocytosis with a membrane-permeable GluR2-derived peptide not only prevented the expression of LTD but also eliminated LTD-associated increase in presynaptic release. Thus, our work not only demonstrates that mGluR1/5-mediated LTD is associated with increased endocytosis of postsynaptic AMPARs but also reveals an unexpected homeostatic/compensatory increase in presynaptic release. In addition, this study indicates that biotinylation of vesicular transporters in live cultured neurons is a valuable tool for studying presynaptic function.

Topics: Analysis of Variance; Animals; Bicuculline; Biophysics; Biotin; Biotinylation; Electric Stimulation; Endocytosis; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Hippocampus; Long-Term Synaptic Depression; Methoxyhydroxyphenylglycol; Microtubule-Associated Proteins; Neurons; Neurotransmitter Agents; Organ Culture Techniques; Patch-Clamp Techniques; Peptides; Potassium; Presynaptic Terminals; Protein Transport; Quinoxalines; Rats; Receptors, AMPA; Receptors, Metabotropic Glutamate; Receptors, Transferrin; Sodium Channel Blockers; Succinimides; Synaptotagmin I; Tetradecanoylphorbol Acetate; Tetrodotoxin; Vesicular Glutamate Transport Protein 1; Vesicular Inhibitory Amino Acid Transport Proteins

Cortical pyramidal neurons alter their responses to input signals depending on behavioral state. We investigated whether changes in somatic inhibition contribute to these alterations. In layer 5 pyramidal neurons of rat visual cortex, repetitive firing from a depolarized membrane potential, which typically occurs during arousal, produced long-lasting depression of somatic inhibition. In contrast, slow membrane oscillations with firing in the depolarized phase, which typically occurs during slow-wave sleep, produced long-lasting potentiation. The depression is mediated by L-type Ca2+ channels and GABA(A) receptor endocytosis, whereas potentiation is mediated by R-type Ca2+ channels and receptor exocytosis. It is likely that the direction of modification is mainly dependent on the ratio of R- and L-type Ca2+ channel activation. Furthermore, somatic inhibition was stronger in slices prepared from rats during slow-wave sleep than arousal. This bidirectional modification of somatic inhibition may alter pyramidal neuron responsiveness in accordance with behavioral state.

Topics: 2-Amino-5-phosphonovalerate; Action Potentials; Animals; Animals, Newborn; Bicuculline; Dendrites; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Electric Stimulation; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; Inhibitory Postsynaptic Potentials; Neural Inhibition; Patch-Clamp Techniques; Pyramidal Cells; Quinoxalines; Rats; Rats, Sprague-Dawley; Spider Venoms; Visual Cortex

In layer 4 of the somatosensory cortex, the glutamatergic synapses that interconnect spiny stellate (SpS) neurons, which are the major targets of thalamocortical input, differ from most other neocortical excitatory synapses in that they have an extremely large NMDA receptor (NMDAR)-mediated component that is relatively insensitive to voltage-dependent Mg2+ blockade. We now report that this unique feature of the NMDA response reflects the distinctive subunit composition of the underlying receptors. We studied NMDAR-mediated miniature EPSCs (mEPSCs) and NMDA channel currents in tangential brain slices of mouse barrel cortex, which exclusively contain layer 4. NMDAR-mediated mEPSCs in SpS neurons were prominent at negative membrane potentials, and NMDA channels in outside-out patches excised from the somata of the same neurons had relatively low conductance and reduced susceptibility to Mg2+ block. These are characteristic features of heteromeric NMDAR assemblies that contain the NR2C subunit. Some patches also contained NMDA channels with higher conductance and a greater sensitivity to Mg2+. In the neocortex of transgenic mice in which a beta-galactosidase (lacZ) indicator gene was controlled by the NR2C promoter, the lacZ indicator was densely expressed in layer 4. In current-clamp recordings, blockade of NMDARs caused hyperpolarization and an increase in apparent input resistance. Our data demonstrate that the SpS neurons of layer 4 functionally express NR2C subunits; this is the likely explanation for their ability to generate large NMDAR-mediated EPSPs that are effective at resting potential, without previous depolarization.

Topics: 2-Amino-5-phosphonovalerate; Animals; Bicuculline; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Genes, Reporter; Glutamic Acid; Lac Operon; Lidocaine; Magnesium; Membrane Potentials; Mice; Mice, Transgenic; Nerve Tissue Proteins; Neurons; Patch-Clamp Techniques; Promoter Regions, Genetic; Protein Subunits; Quinoxalines; Receptors, N-Methyl-D-Aspartate; Sodium Channel Blockers; Somatosensory Cortex; Synapses; Synaptic Transmission; Tetrodotoxin

Rhubarb extracts provide neuroprotection after brain injury, but the mechanism of this protective effect is not known. The present study tests the hypothesis that rhubarb extracts interfere with the release of glutamate by brain neurons and, therefore, reduce glutamate excitotoxicity. To this end, the effects of emodin, an anthraquinone derivative extracted from Rheum tanguticum Maxim. Ex. Balf, on the synaptic transmission of CA1 pyramidal neurons in rat hippocampus were studied in vitro. The excitatory postsynaptic potential (EPSP) was depressed by bath-application of emodin (0.3-30 microM). Paired-pulse facilitation (PPF) of the EPSP was significantly increased by emodin. The monosynaptic inhibitory postsynaptic potential (IPSP) recorded in the presence of glutamate receptor antagonists (DNQX and AP5) was not altered by emodin. Emodin decreased the frequency, but not the amplitude, of the miniature EPSP (mEPSP). The inhibition of the EPSP induced by emodin was blocked by either 8-CPT, an adenosine A1 receptor antagonist, or by adenosine deaminase. These results suggest that emodin inhibits the EPSP by decreasing the release of glutamate from Schaffer collateral/commissural terminals via the activation of adenosine A1 receptors in rat hippocampal CA1 area and that the neuroprotective effects of rhubarb extracts may result from decreased glutamate excitotoxicity.

Topics: Adenosine; Adenosine Deaminase; Animals; Bicuculline; Dose-Response Relationship, Drug; Drug Interactions; Electrophysiology; Emodin; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Hippocampus; In Vitro Techniques; Male; Neural Inhibition; Purinergic P1 Receptor Antagonists; Pyramidal Cells; Quinoxalines; Rats; Rats, Wistar; Synaptic Transmission; Theophylline; Valine

Benzodiazepines are among the most widely prescribed therapeutic agents, having anxiolytic, anticonvulsant, sedative/hypnotic, and amnestic properties (Mehta and Ticku, Brain Res. Rev. 29 (1999) 196). Recent research indicates that these disparate actions are dissociable (Nature 401 (1999) 796; Science 290 (2000) 131; Kralic et al., Neuropharmacology 43 (2002) 685). Behavioral studies indicate that the amygdala plays a critical role in the anxiolytic effect of benzodiazepines (Nagy et al., Neuropharmacology 18 (1979) 573; The amygdala: anxiety and benzodiazepines. The Amygdala: a Functional Analysis. p. 195). However, the neuronal substrates of this anxiolytic effect remain unclear. Our study characterizes the physiological response to acute application of the benzodiazepine diazepam and the non-benzodiazepine sedative zolpidem using whole cell patch recording in two discrete amygdala subnuclei. We found that acute application of diazepam enhances GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) with equal potency in the basolateral (BL) and central (Ce) amygdala subnuclei. However, zolpidem enhanced IPSCs with similar potency only in the BL, and was effective in the Ce only at high concentrations. This finding is in agreement with histochemical data regarding the localization of GABA(A) receptor isoforms in the amygdala (J. Comp. Neurol. 359 (1995) 154; Brain Res. 964 (2003) 91) and suggests that anxiolytic effects of allosteric modulators of the GABA(A) receptor may be further dissociated from their hypnotic/sedative effects.

Topics: Amygdala; Animals; Animals, Newborn; Bicuculline; Diazepam; Dose-Response Relationship, Drug; Drug Interactions; Electric Stimulation; Evoked Potentials; Excitatory Amino Acid Antagonists; GABA Agonists; GABA Antagonists; GABA Modulators; In Vitro Techniques; Male; Neural Inhibition; Patch-Clamp Techniques; Pyridines; Quinoxalines; Rats; Rats, Sprague-Dawley; Valine; Zolpidem

Dark rearing prolongs the critical period for experience-dependent modification of visual cortical functions. To test whether long-term potentiation (LTP) could potentially underlie this modification, we studied the age and experience dependence of LTP, induced in layer 2/3 cells by layer 4 stimulation continued for 15 min at 2 Hz, in rat visual cortical slices. This LTP was independent of N-methyl-D-aspartate receptor (NMDAR) activation, but it likely required Ni(2+)-sensitive Ca(2+) channel activation for induction. LTP occurred frequently during development, but rarely in adulthood. Dark rearing prevented this developmental decline. These age- and experience-dependent changes were demonstrated in both excitatory postsynaptic potentials recorded from pyramidal cells under a local blockade of inhibition and extracellular field potentials. These results suggest the possible involvement of NMDAR-independent LTP in the experience-dependent development of visual cortex.

Topics: 2-Amino-5-phosphonovalerate; Aging; Animals; Animals, Newborn; Bicuculline; Darkness; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA-A Receptor Antagonists; In Vitro Techniques; Long-Term Potentiation; Nickel; Pyramidal Cells; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Visual Cortex

The electrophysiological properties of mossy cells were examined in developing mouse hippocampal slices using whole-cell patch-clamp techniques, with particular reference to the dorsoventral difference. Dorsal mossy cells exhibited a higher spontaneous excitatory postsynaptic potential (EPSP) frequency and larger maximal EPSP amplitude than ventral mossy cells. On the other hand, the blockade of synaptic inputs with glutamatergic and GABAergic antagonists disclosed a remarkable dorsoventral difference in the intrinsic activity: none (0/27) of the dorsal mossy cells showed intrinsic bursting, whereas the majority (35/47) of the ventral mossy cells exhibited intrinsic rhythmic bursting. To characterize the ionic currents underlying the rhythmic bursting of mossy cells, we used somatic voltage-clamp recordings in the subthreshold voltage range. Ventral bursting cells possessed both hyperpolarization-activated current (Ih) and persistent sodium current (INaP), whereas dorsal and ventral nonbursting cells possessed Ih but no INaP. Blockade of Ih with cesium did not affect the intrinsic bursting of ventral mossy cells. In contrast, the blockade of INaP with tetrodotoxin or phenytoin established a stable subthreshold membrane potential in ventral bursting cells. The current-voltage curve of ventral bursting cells showed a region of tetrodotoxin-sensitive negative slope conductance between -55 mV and a spike threshold ( approximately -45 mV). On the other hand, no subthreshold calcium conductances played a significant role in the intrinsic bursting of ventral mossy cells. These observations demonstrate the heterogeneous electrophysiological properties of hilar mossy cells, and suggest that the subthreshold INaP plays a major role in the intrinsic rhythmic bursting of ventral mossy cells.

Topics: 2-Amino-5-phosphonovalerate; Anesthetics, Local; Animals; Anticonvulsants; Bicuculline; Cadmium; Calbindin 2; Cesium; Dentate Gyrus; Drug Combinations; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; Glutamate Decarboxylase; Immunohistochemistry; In Vitro Techniques; Ion Channels; Isoenzymes; Membrane Potentials; Mice; Mice, Inbred C57BL; Microscopy, Confocal; Neurons; Nickel; Patch-Clamp Techniques; Phenytoin; Quinoxalines; S100 Calcium Binding Protein G; Tetrodotoxin

Striatal inhibition plays an important role in models of cortex-basal ganglia function and is altered in many basal ganglia diseases. The gamma-aminobutyric acid ergic spiny projection neuron comprises >95% of striatal neurons, but despite strong anatomical evidence, the electrophysiological properties and functions of their local axon collaterals are unknown. We simultaneously recorded from adjacent spiny projection neurons (<5-10 microm) in whole-cell patch mode and demonstrated a fast synaptic connection between 2669 pairs in cortex-striatum-substantia nigra organotypic cultures and 538 pairs in acute striatal slices. The synapse, which was blocked by gamma-aminobutyric acid type A antagonists, displayed a wide range of failure rates, was depolarizing at rest, and reversed above -60 mV. Presynaptic bursts of action potentials were highly correlated with total postsynaptic depolarization at rest. Synaptic transmission was optimized for burst discharge >14 Hz and showed considerable short-term plasticity, including paired-pulse depression at intervals <25 ms, intraburst facilitation, and interburst augmentation. This activity-dependent collateral interaction provides the basis for a new class of basal ganglia models in which striatal neurons cooperate as well as compete during processing of cortical inputs.

Topics: Action Potentials; Animals; Bicuculline; Cerebral Cortex; Corpus Striatum; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; Memory, Short-Term; Neurons; Organ Culture Techniques; Patch-Clamp Techniques; Picrotoxin; Quinoxalines; Rats; Substantia Nigra; Synapses; Synaptic Transmission

Ethanol (EtOH) is a potent inhibitor of N-methyl-D-aspartate (NMDA) receptor-mediated activity in a number of brain areas, and recent studies have indicated that this inhibitory effect of ethanol is more powerful in the juvenile brain compared with the adult brain. However, previous direct developmental comparisons have been limited to studies of extracellular responses in the hippocampus. To begin an assessment of the mechanisms underlying this developmental sensitivity, we assessed the inhibitory effect of EtOH on NMDA receptor-mediated synaptic transmission in neocortical slices from adult (95-135 days old) and juvenile (28-32 days old) rats using the whole cell patch-clamp recording technique. In the presence of 6,7-dinitroquinoxaline-2,3-dione (20 microM) and bicuculline methiodine (20 microM), NMDA receptor-mediated excitatory postsynaptic currents were isolated from pyramidal cells of the posterior cingulate cortex (PCC). In slices from juvenile rats 5, 10, 30, and 60 mM EtOH reduced the mean amplitude of NMDA receptor-mediated EPSCs by 11, 22, 35, and 46%, respectively. However, the same concentrations of EtOH inhibited the mean amplitude of EPSCs by only 4, 8, 15, and 31% in slices from adult rats. This developmental difference in the potency of EtOH against NMDA receptor-mediated EPSCs was also observed when the holding potential of the neurons was increased to +30 mV, although the inhibitory effect of ethanol on adult neurons was diminished at that voltage. These results provide a cellular analysis of the enhanced potency of ethanol against NMDA receptor-mediated EPSCs in neocortical cells from juvenile animals compared with adults.

Topics: 2-Amino-5-phosphonovalerate; Age Factors; Animals; Bicuculline; Central Nervous System Depressants; Ethanol; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Gyrus Cinguli; Male; Patch-Clamp Techniques; Pyramidal Cells; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

During postnatal development, the retinocollicular pathway undergoes activity-dependent refinement, resulting in the precise retinotopic map seen in adults. Previous studies established that retinal efferents reach the mouse superior colliculus (SC) by embryonic day 16. Morphologically, synapses were found in the rat SC before birth. As part of an extended project aimed at understanding the development of synaptic transmission in the visual layers of the SC, we report here the presence of functionally active synapses immediately after birth. Circuit activity in mouse SC neurons was detected in horizontal slices of the visual layers using cell-attached voltage clamp. The spontaneous discharge of action potentials was abolished by glutamatergic blockers and facilitated by bicuculline, showing that circuit activity is based on synaptic transmission and that the action of gamma-aminobutyric acid is inhibitory. Using whole-cell voltage clamp, spontaneous glutamatergic postsynaptic currents as well as miniature GABAergic postsynaptic currents were recorded on postnatal day 1. Excitatory and inhibitory postsynaptic currents could also be evoked by electrical stimulation. Glutamatergic postsynaptic currents comprised both (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate receptor-mediated components. The early function of glutamatergic and GABAergic synaptic transmission in the visual layers of SC suggests that SC neurons are able to process information originating from retinal axons immediately after birth.

Topics: 2-Amino-5-phosphonovalerate; Animals; Animals, Newborn; Bicuculline; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Mice; Mice, Inbred C57BL; Nicotinic Antagonists; Organ Culture Techniques; Quinoxalines; Rats; Rats, Wistar; Species Specificity; Superior Colliculi; Synaptic Transmission; Tubocurarine

Afferent stimulation of pyramidal cells in the basolateral amygdala produced mixed excitatory postsynaptic potentials (EPSPs) mediated by N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors during whole cell current-clamp recordings. In the presence of GABA(A) receptor blockade, the mixed EPSPs recruited a large "all-or-none" depolarizing event. This recruited event was voltage dependent and had a distinct activation threshold. An analogous phenomenon elicited by exogenous glutamate in the presence of tetrodotoxin (TTX) was blocked by Cd(2+), suggesting that the event was a Ca(2+) spike. Selective glutamatergic blockade revealed that these Ca(2+) spikes were recruited readily by single afferent stimulus pulses that elicited NMDA EPSPs. In contrast, non-NMDA EPSPs induced by single stimuli failed to elicit the Ca(2+) spike even at maximal stimulus intensities although these non-NMDA EPSPs depolarized the soma more effectively than mixed EPSPs. Elongation of non-NMDA EPSPs by cyclothiazide or brief trains of stimulation were also unable to elicit the Ca(2+) spike. Blockade of K(+) channels with intracellular Cs(+) enabled single non-NMDA EPSPs to activate the Ca(2+) spike. The finding that voltage-dependent calcium channels are activated preferentially by NMDA-receptor-mediated EPSPs provides a mechanism for NMDA-receptor-dependent plasticity independent of Ca(2+) influx through the NMDA receptor.

Topics: 2-Amino-5-phosphonovalerate; Action Potentials; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Amygdala; Animals; Bicuculline; Calcium; Calcium Channels; Cesium; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glutamic Acid; Male; N-Methylaspartate; Patch-Clamp Techniques; Potassium Channel Blockers; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Synapses; Tetrodotoxin

Whole-cell recordings were used to investigate long-term potentiation of inhibitory synaptic currents (IPSCs) in neurons of deep cerebellar nuclei (DCN) in slices. IPSCs were evoked by electrical stimulation of the white matter surrounding the DCN in the presence of non-N-methyl-D-aspartate (non-NMDA) glutamate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (20 microM). High-frequency stimulation induced a long-term potentation (LTP) of the IPSC amplitude without changing its reversal potential, rise time, and decay-time constant. This LTP did not require the activation of postsynaptic gamma-aminobutyric acid-A (GABA(A)) receptors but depended on the activation of NMDA receptors. LTP of IPSCs in DCN neurons could also be induced by voltage-depolarizing pulses in postsynaptic neurons and appeared to depend on an increase in intracellular calcium as the LTP was blocked when the cells were loaded with a calcium chelator, 1,2-bis-(2-amino-phenoxy)-N,N,N', N'-tetraacetic acid (BAPTA, 10 mM). LTP of IPSCs was accompanied by an increase in the frequency of spontaneous IPSCs and miniature IPSCs (recorded in the presence of tetrodotoxin 1 microM), but there was no significant change in their amplitude. In addition, during the LTP, the amplitude of response to exogenously applied GABA(A) receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol hydrochloride was increased. Intracellular application of tetanus toxin, a powerful blocker of exocytosis, in DCN neuron prevented the induction of LTP of IPSCs. Our results suggest that the induction of LTP of IPSCs in the DCN neurons likely involves a postsynaptic locus. Plasticity of inhibitory synaptic transmission in DCN neurons may play a crucial role in cerebellar control of motor coordination and learning.

Topics: 2-Amino-5-phosphonovalerate; Action Potentials; Animals; Bicuculline; Calcium; Cerebellar Nuclei; Chelating Agents; Electric Stimulation; Excitatory Amino Acid Antagonists; GABA Agonists; GABA Antagonists; GABA-A Receptor Agonists; GABA-A Receptor Antagonists; In Vitro Techniques; Intracellular Fluid; Long-Term Potentiation; Neural Inhibition; Patch-Clamp Techniques; Quinoxalines; Rats; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission; Tetanus Toxin

In humans with temporal lobe epilepsy and kainate-treated rats, the mossy fibers of the dentate granule cells send collateral axons into the inner molecular layer. Prior investigations on kainate-treated rats demonstrated that abnormal hilar-evoked events can occasionally be observed in slices with mossy fiber sprouting when gamma-aminobutyric acid-A (GABAA)-mediated inhibition is blocked with bicuculline. However, these abnormalities were observed infrequently, and it was unknown whether these rats were epileptic. Wuarin and Dudek reported that in slices from kainate-induced epileptic rats (3-13 mo after treatment), hilar stimulation evoked abnormal events in most slices with mossy fiber sprouting exposed simultaneously to bicuculline and elevated extracellular potassium concentration [K+]o. Using the same rats, extracellular recordings were obtained from granule cells in hippocampal slices to determine whether 1) hilar stimulation could evoke abnormal events in slices with sprouting in normal artificial cerebrospinal fluid (ACSF), 2) adding only bicuculline could unmask hilar-evoked abnormalities and glutamate-receptor antagonists could block these events, and 3) increasing only [K+]o could unmask these abnormalities. In normal ACSF, hilar stimulation evoked abnormal field potentials in 27% of slices with sprouting versus controls without sprouting (i.e., saline-treated or only 2-4 days after kainate treatment). In bicuculline (10 microM) alone, hilar stimulation triggered prolonged field potentials in 84% of slices with sprouting, but not in slices from the two control groups. Addition of the N-methyl-D-aspartate (NMDA) receptor antagonist, DL-2-amino-5-phosphonopentanoic acid (AP5), either blocked the bursts or reduced their probability of occurrence. The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainate receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX), always eliminated the epileptiform bursts. In kainate-treated rats with sprouting, but not in saline-treated controls, abnormal hilar-evoked responses were also revealed in 6-9 mM [K+]o. Additionally, 63% of slices with sprouting generated spontaneous bursts lasting 1-40 s in ACSF containing 9 mm [K+]o; similar bursts were not observed in controls. These results indicate that 1) mossy fiber sprouting is associated with new glutamatergic pathways, and although NMDA receptors are important for propagation through these circuits, AMPA receptor activation is crucial, 2) modes

Topics: 2-Amino-5-phosphonovalerate; Animals; Bicuculline; Dentate Gyrus; Electric Stimulation; Electrophysiology; Epilepsy; Epilepsy, Temporal Lobe; Evoked Potentials; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Humans; In Vitro Techniques; Kainic Acid; Male; Motor Activity; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Reference Values

Prenatal cocaine exposure results in several documented changes in neurotransmitter receptor number and structure. Increases have been reported for cortical catecholamine and indoleamine receptor number and binding affinity, in the subunit expression of glutamatergic NMDA and AMPA receptors in the striatum, and in GABA immunoreactivity in the anterior cingulate cortex. We sought information on the functional consequences of cocaine-induced alterations in receptor structure/number. Since hippocampal amino acid neurotransmitters are of critical importance and have been shown to be affected by cocaine, we studied field potentials produced by synaptic activation of isolated glutamatergic NMDA and AMPA receptors and GABAa and GABAb responsive receptors in area CA1 of rabbit hippocampal slices. We found the GABAa receptor population produced significantly larger field potentials in cocaine-exposed offspring compared to controls, while other receptors produced responses similar to controls.

Topics: Animals; Bicuculline; Cocaine; Female; Hippocampus; In Vitro Techniques; Membrane Potentials; Pregnancy; Prenatal Exposure Delayed Effects; Quinoxalines; Rabbits; Receptors, AMPA; Receptors, GABA-A; Receptors, GABA-B; Receptors, N-Methyl-D-Aspartate; Synapses

Repetitive stimuli reliably induce long-term potentiation (LTP) of synapses in the upper layers of the granular somatosensory cortex but not the agranular motor cortex of rats. Herein we examine, in these same cortical areas, short-term changes in synaptic strength that occur during the LTP induction period. theta-Burst stimulation produced a strong short-term enhancement of synapses in the granular area but only weak enhancement in the agranular area. The magnitude of enhancement during stimulation was strongly correlated with the magnitude of LTP subsequently expressed. Short-term enhancement was abolished by an antagonist of N-methyl-D-aspartate (NMDA) receptors but remained in the presence of a non-NMDA receptor antagonist. Inhibitory postsynaptic potentials of the granular and agranular areas displayed similar frequency sensitivity, but the frequency sensitivity of NMDA receptor-dependent excitatory postsynaptic potentials differed significantly between areas. We propose that pathway-specific differences in short-term enhancement are due to variations in the frequency dependence of NMDA currents; different capacities for short-term enhancement may explain why repetitive stimulation more readily induces LTP in the somatosensory cortex than in the motor cortex.

Topics: 2-Amino-5-phosphonovalerate; Animals; Bicuculline; gamma-Aminobutyric Acid; In Vitro Techniques; Long-Term Potentiation; Motor Cortex; Neurons; Nifedipine; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Somatosensory Cortex; Synapses; Synaptic Transmission

Adenosine is a CNS depressant with both pre- and postsynaptic actions. Presynaptically, adenosine decreases neurotransmitter release in the hippocampus but only at excitatory terminals. In the thalamus, however, we show that, in addition to its actions at excitatory synapses, adenosine strongly suppresses monosynaptic inhibitory currents both in relay cells of the thalamic ventrobasal complex (VB) and in inhibitory neurons of the nucleus reticularis thalami (nRt). A concomitant increase in transmission failures and results coefficient of variation analysis are both consistent with a presynaptic mechanism. Pharmacological manipulations support an A1 receptor-mediated process. Slow thalamic oscillations induced in vitro by extracellular stimulation and recorded with extracellular multiunit electrodes in VB and nRt are dampened by adenosine without affecting their periodicity. We conclude that adenosine can presynaptically down-regulate inhibitory postsynaptic responses in thalamus and exert robust antioscillatory effects, likely by synergistic depression of both excitatory and inhibitory neurotransmitter release.

Topics: Adenosine; Animals; Bicuculline; Electric Conductivity; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Male; Quinoxalines; Rats; Receptors, Purinergic P1; Synapses; Thalamus; Theophylline

Anatomic and physiologic studies in the rat have shown projections from the hippocampal formation (HF) and mediodorsal (MD) thalamic nucleus to the medial prefrontal cortex (mPFC). The authors used multi-barrel iontophoresis to: confirm the neurotransmitter used in the projection from HF to mPFC; investigate the role of GABAergic inhibition in the regulation of this projection; and examine the functional convergence of projections from HF and MD onto single mPFC neurons. During HF stimulation, nine cells (6%) showed excitation followed by prolonged inhibition, 39 cells (26%) showed prolonged inhibition alone and 100 cells (68%) showed no clear response. In a further 12 cells that showed no predrug excitation to HF stimulation (representing 16% of the cells in this category), iontophoresis of the GABAA antagonist bicuculline methiodide (BMI) revealed excitatory responses. A total of six mPFC cells (38% of the cells showing excitatory responses to HF stimulation) showed convergent excitation to HF and MD thalamic (or adjacent paratenial nucleus) stimulation. Five out of eight (63%) of the predrug or BMI-revealed excitatory responses of mPFC neurons to HF stimulation were selectively decreased after AMPA antagonist iontophoresis (either CNQX or DNQX). These data confirm that the HF projection to prefrontal cortex is, at least in part, glutamatergic; suggest that the responses of mPFC neurons to activity in this HF pathway are regulated by GABAergic inhibition; and indicate that projections from HF and MD converge onto single mPFC neurons.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Baclofen; Bicuculline; Brain Mapping; Electric Stimulation; Electrophysiology; GABA-A Receptor Antagonists; GABA-B Receptor Antagonists; gamma-Aminobutyric Acid; Glutamic Acid; Limbic System; Male; Neurons; Organophosphorus Compounds; Piperazines; Prefrontal Cortex; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Thalamus

The aim of this study was to elucidate the involvement of kainate (KA) type glutaminergic, GABAergic and adrenergic receptors in the ventromedial nucleus of the hypothalamus (VMH) in inducing running activity and metabolic adaptations. Injection of either KA or bicuculline methiodide (BM), a GABAA receptor antagonist, into the VMH of conscious rats resulted in an increase in plasma glucose, norepinephrine, epinephrine and corticosterone, as well as running activity. KA or BM increased plasma glucose and catecholamine even under urethane anesthesia. Co-injection of either alpha- or beta-adrenergic receptor antagonist, i.e. phentolamine or timolol, respectively, with KA into the VMH of conscious rats elicited only a slight increase in plasma glucose and catecholamines, though it successfully induced hyper-running. However, plasma corticosterone was higher in the animals injected with adrenergic blockers, suggesting that an insufficient supply of energy substrates would enhance the activity of the hypothalamo-pituitary-adrenal system. We conclude that: (1) KA type glutaminergic and GABAergic receptors in the VMH are involved in regulating running activity and the sympathetic nervous system; (2) the brain noradrenergic system may mediate the KA action on the sympathetic nervous system.

Topics: Animals; Bicuculline; Energy Metabolism; Hypothalamus, Middle; Male; Quinoxalines; Rats; Rats, Wistar; Receptors, Adrenergic; Receptors, GABA; Receptors, Glutamate; Receptors, Kainic Acid; Running

The long-term modification of inhibitory postsynaptic potentials (IPSPs) was studied in visual cortex slices taken from developing rats. IPSPs evoked by layer IV stimulation were intracellularly recorded from layer V cells while excitatory synaptic transmission was blocked by NMDA and non-NMDA receptor antagonists. High-frequency conditioning stimulation of layer IV induced long-term potentiation of IPSPs. By contrast, long-term depression (LTD) of IPSPs was induced by the same conditioning stimulation applied while NMDA receptor-mediated synaptic transmission was unmasked by removing the NMDA antagonist from and adding a GABAA receptor antagonist to the medium. The LTD of IPSPs was also induced by NMDA application to the cells. The plasticity of IPSPs might explain the postnatal development of selective responsiveness of visual cortical cells.

Topics: 2-Amino-5-phosphonovalerate; Animals; Animals, Newborn; Bicuculline; Conditioning, Psychological; Electric Stimulation; Evoked Potentials; GABA-A Receptor Antagonists; In Vitro Techniques; Membrane Potentials; Neuronal Plasticity; Neurons, Afferent; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate; Synapses; Synaptic Transmission; Visual Cortex

We have previously shown that blockade of neurotransmission mediated by gamma-aminobutyric acid (GABA) in the ventromedial nucleus of the hypothalamus (VMH) by the microinjection of a GABAA receptor antagonist, bicuculline methiodide (BM), exclusively induced running activity in the rat. The purpose of the present study was to examine the role of receptors for excitatory amino acids (EAAs) in the VMH in inducing hyper-running and to clarify the interaction between GABA and EAAs in the VMH in controlling running activity. Although the injection of neither N-methyl-D-aspartate (NMDA) nor quisqualate into the VMH induced hyper-running, kainate (KA) produced running activity in a dose-dependent manner with similar features to that induced by BM. This effect of KA was blocked by a non-NMDA receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX). GABA injected simultaneously with KA into the VMH failed to affect hyper-running induced by KA. On the other hand, DNQX significantly suppressed the BM-induced running activity. These results suggest that endogenous EAAs acting on the KA-type receptor in the VMH facilitates running activity and that the release of such EAAs from the nerve terminal is presynaptically inhibited by GABA.

Topics: Animals; Bicuculline; Female; GABA-A Receptor Antagonists; gamma-Aminobutyric Acid; Kainic Acid; Microinjections; Motor Activity; Quinoxalines; Rats; Rats, Wistar; Receptors, GABA-A; Ventromedial Hypothalamic Nucleus

Modulation of gamma-aminobutyric acid (GABA)-mediated inhibition, and glutamate-mediated excitation by highly selective mu and delta opioid agonists was studied using intracellular recordings of CA1 pyramidal neuron synaptic responses in superfused hippocampal slices. Equimolar concentrations of the selective mu agonist, [Tyr-(D-Ala)-Gly-(N-Me-Phe)-Gly-ol]-enkephalin (DAGO), or the delta selective agonist, [D-Pen2,D-Pen5]-enkephalin (DPDPE), reversibly increased the amplitudes of excitatory post-synaptic potentials (EPSPs), evoked by Schaffer collateral/commissural stimulation, without altering the input resistance or resting membrane potential of these CA1 pyramidal neurons. The increased EPSP amplitudes resulting from superfusion with the enkephalin analogs were qualitatively similar to those caused by the GABAA receptor antagonist, bicuculline methiodide (BMI). Specific stimulation/recording protocols and micro-lesions of the slices were used to evoke relatively pure forms of recurrent and feed-forward GABA-mediated inhibitory post-synaptic potentials (IPSPs). The mu opioid agonist DAGO reduced both recurrent and feed-forward IPSPs, while the delta agonist DPDPE had no effect upon these responses. To test the hypothesis that the enhancement of pyramidal neuron EPSPs by delta (and mu) opioids was due to the reduction of an inhibitory potential that was coincident with the EPSP, DPDPE or the mu agonist, DAGO, were applied while recording monosynaptic IPSPs following the elimination of EPSPs by the glutamate receptor antagonists, D,L-2-amino-5-phosphonovalerate (APV) and 6,7-dinitroquinoxaline-2,3-dione (DNQX). The mu agonist, DAGO, reversibly reduced these pharmacologically isolated IPSPs, while the delta agonist, DPDPE, had no effect upon these responses. Despite the fact that the delta agonist, DPDPE, had no effect on recurrent, feed-forward or monosynaptic evoked IPSPs, this enkephalin did reversibly reduce the frequency of spontaneously occurring IPSPs, measured using whole-cell recordings with pipettes containing 65 mM KCl. The mu agonist, DAGO, and the GABAA antagonist, BMI, similarly reduced spontaneous IPSP rates. We conclude from these data that mu and delta opioid receptor activation increases EPSPs via the reduction of a form of GABAergic inhibition that is difficult to characterize, and which may be distinct from conventional feed-forward and recurrent inhibition. Furthermore, delta opioids seem to reduce this form of GABAergic inhibition sel

Topics: 2-Amino-5-phosphonovalerate; Analgesics; Animals; Axons; Baclofen; Bicuculline; Electric Stimulation; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Evoked Potentials; gamma-Aminobutyric Acid; Glutamates; Glutamic Acid; Hippocampus; In Vitro Techniques; Male; Neurons; Pyramidal Tracts; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta; Receptors, Opioid, mu; Synapses

1. gamma-Aminobutyric acidA (GABAA) receptor-mediated inhibition of pyramidal neuron dendrites was studied in area CA1 of the rat hippocampal slice preparation with the use of intracellular and extracellular recording and one-dimensional current source-density (CSD) analysis. 2. Electrical stimulation of Schaffer collateral/commissural fibers evoked monosynaptic excitatory postsynaptic potentials (EPSPs) and population EPSPs, which were followed by biphasic inhibitory postsynaptic potentials (IPSPs). In the presence of the excitatory amino acid receptor antagonists 6,7-dinitroquinoxaline-2,3-dione (DNQX) and D,L-2-amino-5-phosphonovalerate (APV), stimulation in stratum radiatum evoked monosynaptic fast, GABAA and late, GABAB receptor-mediated IPSPs and fast and late positive field potentials recorded in s. radiatum. 3. Fast monosynaptic IPSPs and fast positive field potentials evoked in the presence of DNQX and APV were reversibly abolished by the GABAA receptor antagonist bicuculline methiodide (BMI; 30 microM) and were not changed by the GABAB receptor antagonist P-[3-aminopropyl]-P-diethoxymethylphosphinic acid (CGP 35,348; 0.1-1.0 mM). CGP 35,348 (0.1 mM) reversibly blocked late monosynaptic IPSPs and late positive field potentials. These results suggest that fast field potentials are GABAA receptor-mediated population IPSPs (GABAA, fast pIPSPs) and that late field potentials are GABAB receptor-mediated population IPSPs (GABAB, late pIPSPs). 4. Fast pIPSPs were reversibly abolished when the extracellular Cl- concentration [( Cl-]o) was reduced from 132 to 26 mM in parallel with a depolarizing shift in the reversal potential of fast IPSPs. Paired or repetitive stimulation in s. radiatum reversibly depressed fast pIPSPs and fast IPSPs. Paired-pulse depression of fast pIPSPs was reversibly antagonized by CGP 35,348 (0.4-0.8 mM). 5. Laminar analysis of s. radiatum-evoked fast pIPSPs and one-dimensional CSD analysis revealed active current sources in s. radiatum and passive current sinks in s. oriens and s. lacunosum moleculare. S. radiatum sources were abolished by pressure application of BMI in s. radiatum but not in s. oriens. Stimulation in s. oriens, s. pyramidale, or s. lacunosum moleculare evoked GABAA current sources horizontal to the stimulation site. Changes in the dendritic location of inhibitory current with changes in stimulus location paralleled changes in the distribution of excitatory current. 6. In the presence of 4-aminopyridine (50-100 m

Topics: 2-Amino-5-phosphonovalerate; Animals; Bicuculline; Chlorides; Dendrites; Evoked Potentials; GABA-A Receptor Antagonists; Hippocampus; In Vitro Techniques; Kinetics; Mathematics; Membrane Potentials; Models, Neurological; Neurons; Organophosphorus Compounds; Pyramidal Tracts; Quinoxalines; Rats; Receptors, GABA-A; Synapses