2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and 3-4-dihydroxyphenylglycol

Cajal-Retzius cells are a class of neurons believed to play critical roles during cortical development. However, their network computational functions remain poorly understood. Although work in the neocortex and hippocampus has shown that Cajal-Retzius cells receive predominantly, if not exclusively, spontaneous GABA(A) receptor-mediated input, the cellular sources originating these events remain unclear. However, a precise definition of the presynaptic GABAergic interneurons contacting Cajal-Retzius cells is important to understand the microcircuits and network patterns controlling their activation. Here, we have taken advantage of electrophysiological and anatomical techniques applied to mouse hippocampal slices in vitro to directly address this question. Our paired recording experiments indicate that Cajal-Retzius cells receive small-amplitude, kinetically slow synaptic input from stratum lacunosum-moleculare interneurons, anatomically identified as neurogliaform cells. In addition, a convergence of optogenetic, electrophysiological, and pharmacological experiments shows that Cajal-Retzius cells receive GABAergic input from oriens lacunosum-moleculare cells and that this input has different physiological properties (i.e., larger amplitude and faster kinetics) from the one provided by neurogliaform cells. Last, we show that GABAergic evoked synaptic input onto Cajal-Retzius cells may either increase their excitability and trigger action potentials or inhibit spontaneous firing by depolarization block. We propose that the specific type of response depends on both the membrane potential of Cajal-Retzius cells and the kinetics of the received GABAergic input. In conclusion, we have unraveled a novel hippocampal microcircuit with complex GABAergic synaptic signaling, which we suggest may play a role in the refinement of the hippocampal network and connections during development.

Topics: Age Factors; Animals; Animals, Newborn; Biophysics; Channelrhodopsins; Electric Stimulation; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; gamma-Aminobutyric Acid; Green Fluorescent Proteins; Hippocampus; In Vitro Techniques; Interneurons; Light; Male; Membrane Potentials; Methoxyhydroxyphenylglycol; Mice; Mice, Transgenic; Mutation; Nerve Net; Neural Inhibition; Optogenetics; Patch-Clamp Techniques; Proteins; Pyridazines; Quinoxalines; Receptors, CXCR4; RNA, Untranslated; Sodium Channel Blockers; Somatostatin; Synaptic Potentials; Tetrodotoxin; Valine

Cognitive flexibility depends on the integrity of the prefrontal cortex (PFC). We showed previously that impaired decision making in pain results from amygdala-driven inhibition of medial PFC neurons, but the underlying mechanisms remain to be determined. Using whole cell patch clamp in rat brain slices and a cognitive behavioral task, we tested the hypothesis that group I metabotropic glutamate receptors (mGluRs) activate feed-forward inhibition to decrease excitability and output function of PFC pyramidal cells, thus impairing decision making. Polysynaptic inhibitory postsynaptic currents (IPSCs) and monosynaptic excitatory postsynaptic currents (EPSCs) were evoked in layer V pyramidal cells by stimulating presumed amygdala afferents. An mGluR1/5 agonist [(S)-3,5-dihydroxyphenylglycine, DHPG] increased synaptic inhibition more strongly than excitatory transmission. The facilitatory effects were blocked by an mGluR1 [(S)-(+)-α-amino-4-carboxy-2-methylbenzeneacetic acid, LY367385], but not mGluR5, antagonist, 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine. IPSCs were blocked by bicuculline and decreased by 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium salt (NBQX). Facilitation of synaptic inhibition by DHPG was glutamate driven because it was blocked by NBQX. DHPG increased frequency but not amplitude of spontaneous IPSCs; consistent with action potential-dependent synaptic inhibition, tetrodotoxin (TTX) prevented the facilitatory effects. DHPG decreased synaptically evoked spikes (E-S coupling) and depolarization-induced spiking [frequency-current (f-I) relationship]. This effect was indirect, resulting from glutamate-driven synaptic inhibition, because it persisted when a G protein blocker was included in the pipette but was blocked by GABA(A) receptor antagonists and NBQX. In contrast, DHPG increased E-S coupling and f-I relationships in mPFC interneurons through a presynaptic action, further supporting the concept of feed-forward inhibition. DHPG also impaired the ability of the animals to switch strategies in a decision-making task; bicuculline restored normal decision making, whereas a GABA(A) receptor agonist (muscimol) mimicked the decision-making deficit. The results show that mGluR1 activates feed-forward inhibition of PFC pyramidal cells to impair cognitive functions.

Topics: Animals; Biofeedback, Psychology; Decision Making; Excitatory Postsynaptic Potentials; Inhibitory Postsynaptic Potentials; Male; Methoxyhydroxyphenylglycol; Neural Inhibition; Organ Culture Techniques; Prefrontal Cortex; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate

Cerebellar Purkinje neurons have intracellular regulatory systems including Ca2+-binding proteins, intracellular Ca2+ stores, Ca2+-ATPase and Na+-Ca2+ exchanger (NCX) that keep intracellular Ca2+ concentration ([Ca2+]i) in physiological range. Among these, NCX interacts with AMPA receptors, activation of which induces cerebellar synaptic plasticity. And the activation of metabotropic glutamate receptor 1 (mGluR1) is also involved in the induction of cerebellar long-term depression. The interaction of NCX with mGluR1 is not known yet. Thus, in this study, the functional relationship between NCX and mGluR1 in modulating the [Ca2+]i in rat Purkinje neurons was investigated. The interaction between NCX and mGluR1 in Purkinje neurons was studied by measuring intracellular Ca2+ transients induced by an agonist of group I mGluRs, 3,5-dihydroxyphenylglycine (DHPG). The DHPG-induced Ca2+ transient was significantly reduced by treatments of NCX inhibitors, bepridil and KB-R7943. When cells were pretreated with antisense oligodeoxynucleotides of NCX, the DHPG-induced Ca2+ transient was also inhibited. These results suggest that NCX modulates the activity of mGluR1 in cerebellar Purkinje neurons. Therefore, NCX appears to play an important role in the physiological function of cerebellar Purkinje neurons such as synaptic plasticity.

Topics: Animals; Animals, Newborn; Bepridil; Calcium; Calcium Channel Blockers; Cells, Cultured; Cerebellum; Drug Interactions; Enzyme Activation; Excitatory Amino Acid Antagonists; Methoxyhydroxyphenylglycol; Oligodeoxyribonucleotides, Antisense; Purkinje Cells; Quinoxalines; Rats; Receptors, Metabotropic Glutamate; Sodium-Calcium Exchanger; Thiourea

Cerebellar Purkinje cells (PCs) receive synaptic input from numerous parallel fibers (PFs) and from a single climbing fiber (CF). At both types of synapses, fast synaptic transmission is mediated by AMPA receptors, while at PF synapses burst activity can additionally recruit metabotropic glutamate receptors (mGluRs) that mediate a slow depolarizing potential. Here, we show that mGluR-activated slow potentials can be evoked throughout the dendrite by CF-evoked complex spike firing in the presence of an mGluR agonist. The CF-triggered mGluR potential was not only blocked by an mGluR antagonist but also when the CF-induced Ca(2+) transient was blocked by an AMPA receptor antagonist, suggesting the possibility that the slow potential can be activated by the simultaneous occurrence of agonist binding at mGluRs and a CF-evoked Ca(2+) transient. In turn, these CF-triggered slow mGluR potentials enhance the complex spike-associated calcium signals throughout the dendrite. Moreover, they provide a mechanism by which CFs can modulate the simple spike frequency of PCs.

Topics: Aniline Compounds; Animals; Aspartic Acid; Calcium; Dendrites; Excitatory Amino Acid Antagonists; Fluoresceins; Membrane Potentials; Methoxyhydroxyphenylglycol; Mice; Patch-Clamp Techniques; Purkinje Cells; Quinoxalines; Receptors, AMPA; Receptors, Metabotropic Glutamate; Synaptic Transmission

The oriens-lacunosum moleculare (O-LM) subtype of interneuron is a key component in the formation of the theta rhythm (8-12 Hz) in the hippocampus. It is known that the CA1 region of the hippocampus can produce theta rhythms in vitro with all ionotropic excitation blocked, but the mechanisms by which this rhythmicity happens were previously unknown. Here we present a model suggesting that individual O-LM cells, by themselves, are capable of producing a single-cell theta-frequency firing, but coupled O-LM cells are not capable of producing a coherent population theta. By including in the model fast-spiking (FS) interneurons, which give rise to IPSPs that decay faster than those of the O-LM cells, coherent theta rhythms are produced. The inhibition to O-LM cells from the FS cells synchronizes the O-LM cells, but only when the FS cells themselves fire at a theta frequency. Reciprocal connections from the O-LM cells to the FS cells serve to parse the FS cell firing into theta bursts, which can then synchronize the O-LM cells. A component of the model O-LM cell critical to the synchronization mechanism is the hyperpolarization-activated h-current. The model can robustly reproduce relative phases of theta frequency activity in O-LM and FS cells.

Topics: Animals; Computer Simulation; Excitatory Amino Acid Antagonists; Hippocampus; In Vitro Techniques; Interneurons; Ion Channels; Membrane Potentials; Methoxyhydroxyphenylglycol; Neural Inhibition; Neural Networks, Computer; Patch-Clamp Techniques; Periodicity; Quinoxalines; Rats; Rats, Wistar; Synaptic Transmission; Theta Rhythm

The synapses formed by the olfactory nerve (ON) convey sensory information to olfactory glomeruli, the first stage of central odor processing. Morphological and behavioral studies suggest that glomerular odor processing is plastic in neonate rodents. However, long-term synaptic plasticity, a cellular correlate of functional and structural plasticity, has not yet been demonstrated in this system. Here, we report that ON-->mitral cell (MC) synapses of 5- to 8-d-old mice express long-term depression (LTD) after brief low-frequency ON stimulation. Pharmacological techniques and imaging of presynaptic calcium signals demonstrate that ON-MC LTD is expressed presynaptically and requires the activation of metabotropic glutamate receptors but does not require fast synaptic transmission. LTD at the ON--> MC synapse is potentially relevant for the establishment, maintenance, and experience-dependent refinement of odor maps in the olfactory bulb.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Animals, Newborn; Calcium; Diagnostic Imaging; Dopamine Antagonists; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Evoked Potentials; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glycine; In Vitro Techniques; Long-Term Synaptic Depression; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred ICR; N-Methylaspartate; Neurons; Olfactory Bulb; Patch-Clamp Techniques; Quinoxalines; Sodium Channel Blockers; Sulpiride; Synapses; Tetrodotoxin; Time Factors; 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

Glutamate transporters are responsible for clearing synaptically released glutamate from the extracellular space. If expressed at high enough densities, transporters can prevent activation of extrasynaptic receptors by rapidly lowering glutamate concentrations to insignificant levels. We find that synaptic activation of metabotropic glutamate receptors expressed by Purkinje cells is prevented in regions of rat cerebellum where the density of the glutamate transporter EAAT4 is high. The consequences of metabotropic receptor stimulation, including activation of a depolarizing conductance, cannabinoid-mediated presynaptic inhibition and long-term depression, are also limited in Purkinje cells expressing high levels of EAAT4. We conclude that neuronal uptake sites must be overwhelmed by glutamate to activate perisynaptic metabotropic glutamate receptors. Regional differences in glutamate transporter expression affect the degree of metabotropic glutamate receptor activation and therefore regulate synaptic plasticity.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Analysis of Variance; Animals; Animals, Newborn; Aspartic Acid; Calcium; Cannabinoids; Cerebellum; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Excitatory Amino Acid Transporter 4; Excitatory Postsynaptic Potentials; Gene Expression Regulation; Glutamic Acid; In Vitro Techniques; Long-Term Synaptic Depression; Membrane Potentials; Methoxyhydroxyphenylglycol; Neuronal Plasticity; Patch-Clamp Techniques; Purkinje Cells; Quinoxalines; Rats; Synapses

We report an activity-induced green fluorescence signal observed when mouse cerebellar slices were illuminated with blue light and parallel fibre-Purkinje cell synapses were activated. The optical signal consisted of an initial increase in fluorescence that peaked within 1-2 s after the onset of stimulation, followed by a long lasting (40 s) transient decrease in fluorescence. Single or tetanic electrical stimuli applied to the molecular layer elicited 'beam-shaped' fluorescence changes along the trajectory of parallel fibres. These signals reported activation of Purkinje cells as they were depressed by antagonists of ionotropic and metabotropic glutamate receptors at Purkinje cells and correlated with Purkinje cell spiking activity. Optical responses induced by direct pharmacological activation of glutamate receptors were reduced by a calcium-free extracellular medium, consistent with the hypothesis that they reflect metabolic activity due to an increased intracellular calcium load associated with neuronal activation. We used these intrinsic fluorescence signals to address the question of whether granule cells excite Purkinje cells only locally via the ascending branches of their axons, or more widespread along the parallel fibre trajectory. White matter stimulation of the mossy fibres also elicited a beam-like fluorescence change along the trajectory of parallel fibres. Simultaneous imaging and extracellular recording demonstrated the association between the beam-like fluorescence signal and Purkinje cell spiking. This non-invasive imaging technique supports the notion that parallel fibre activity, evoked either locally or through the mossy fibre-granule cell pathway, can activate postsynaptic Purkinje cells along more than 3 mm of the parallel fibre trajectory.

Topics: 2-Amino-5-phosphonovalerate; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Calcium; Cerebellum; Chromones; Diagnostic Imaging; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Fluorescence; GABA Antagonists; In Vitro Techniques; Methoxyhydroxyphenylglycol; Mice; Mice, Inbred ICR; Nerve Fibers; Neurons; Picrotoxin; Quinoxalines; Time Factors