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PubMed2001

Medium afterhyperpolarization and firing pattern modulation in interneurons of stratum radiatum in the CA3 hippocampal region.

Stratum (st.) radiatum interneurons represent a heterogeneous class of hippocampal cells with as yet poorly characterized physiological properties. Intracellular staining with biocytin, in situ hybridization, and patch-clamp recording have been combined to investigate the morphological and electrophysiological properties of these cells in the CA3 hippocampal region in young rats [postnatal days 10 to 21 (P10-21)]. Labeled cells presented a heterogeneous morphology with various soma shapes, often found multipolar, and dendritic arborizations confined to st. radiatum. The passive membrane properties of these st. radiatum interneurons showed instead no significant differences between P10 and P21. Low resting potential, high-input resistance, and short time constants characterized CA3 st. radiatum interneurons, which were silent at rest. Action potentials, elicited by brief current pulses, were lower and shorter than in pyramidal cells and followed by a Ca(2+)-dependent medium-duration afterhyperpolarizing potential (mAHP). Prolonged depolarizing current injection generated trains of action potentials that fired at constant frequency after a slight accommodation. The maximum steady-state firing rate was 31 +/- 4 (SD) Hz. Hyperpolarizing current pulses revealed a prominent inward rectification characterized by a "sag," followed by a depolarizing rebound that triggered action potentials. Sag and anodal brake excitation were blocked by Cs(+), suggesting that they were mediated by a hyperpolarization-activated cation conductance (I(h)). In the presence of tetrodotoxin and tetraethylammonium, biphasic tail currents were elicited in voltage clamp after a depolarizing step inducing Ca(2+) influx. Tail currents presented a fast Ca(2+)-activated and apamin-sensitive component (I(AHP)) and were further reduced by carbachol. The presence of I(AHP) was consistent with the high expression level of the apamin-sensitive SK2 subunit transcript in CA3 st. radiatum interneurons as detected by in situ hybridization. Different pharmacological agents were shown to affect the afterhyperpolarizing potential as well as the firing properties of st. radiatum interneurons. Exposure to Ca(2+)-free solutions mainly affected the late phase of repolarization and strongly reduced the mAHP. The mAHP was also attenuated by carbachol and by apamin, suggesting it to be partly mediated by I(AHP). Reduction of the mAHP increased the interneuron firing frequency. In conclusion, st. radiatum interneurons of CA3 hippocampal region represent a class of nonpyramidal cells with action potentials followed by an AHP of relatively short duration, partially generated by apamin and carbachol-sensitive conductances involved in the regulation of the cell firing rate.

Action Potentials↗
PubMed2001

Contribution of the hyperpolarization-activated current (I(h)) to membrane potential and GABA release in hippocampal interneurons.

Intrinsic GABAergic interneurons provide inhibitory input to the principal neurons of the hippocampus. The majority of interneurons located in stratum oriens (s.o.) of the CA1 region express the hyperpolarization-activated cation current known as I(h). In an effort to elucidate the role of this current in regulating the baseline excitability of these neurons and its participation in the regulation of the release of GABA onto CA1 pyramidal neurons, we utilized whole cell electrophysiological recordings from both populations of cells. In voltage-clamp experiments, hyperpolarization of the interneuron membrane initiated a large inward current with an estimated activation threshold of 51.6 +/- 7.6 mV and a half-maximal voltage of -73.0 +/- 7.0 mV. This current was blocked by bath application of the I(h) inhibitors ZD 7288 (50 microM) or cesium (2 mM). Current-clamp experiments at the interneuron resting membrane potential (-61.3 +/- 1.2 mV) revealed a significant hyperpolarization, a decrease in the rate of spontaneous action potential discharge, an increase in the cellular input resistance, and the elimination of rebound afterdepolarizations during blockade of I(h) with ZD 7288 (50 microM). The hyperpolarizing effect of ZD 7288 was also substantially larger in interneurons clamped near -80 mV using current injection through the pipette. In addition to neurons exhibiting I(h), recordings were obtained from a small population of s.o. interneurons that did not exhibit this current. These cells demonstrated resting membrane potentials that were significantly more negative (-73.6 +/- 5.5 mV) than those observed in neurons expressing I(h), suggesting that this current contributes to more depolarized membrane potentials in these cells. Recordings from postsynaptic pyramidal neurons demonstrated that blockade of I(h) with ZD 7288 caused a substantial reduction (approximately 43%) in the frequency of spontaneous action potential-dependent inhibitory postsynaptic currents (IPSCs), without altering their average amplitude. However, miniature action-potential-independent IPSC frequency, amplitude, and decay kinetics were unaltered by ZD 7288. These data suggest that I(h) is active at the resting membrane potential in s.o. interneurons and as a result contributes to the spontaneous activity of these cells and to the tonic inhibition of CA1 pyramidal neurons in the hippocampus.

Animals↗
PubMed2000

The interneurons of the abdominal positioning system of the crayfish. How these neurons were established and their use as identified cells and command elements.

Arthropods with segmented abdomens show similar abdominal positioning behaviors. It has been possible to gain some understanding of the neural basis of these behaviors in lobsters and crayfish using standard intracellular and dye-filling techniques. Typically crayfish and lobsters have six abdominal segments each controlled by a set of flexor and extensor tonic muscles. Each segment has a dozen tonic motor neurons controlled in turn by a large number of interneurons. A similar set of phasic muscles, motor neurons and interneurons control a fast system. The fast components underlie such behaviors as escape and swimming. Lucifier-filled microelectrodes were used to stimulate, record and dye-fill the motor neurons and interneurons of the tonic systems. It was soon apparent that all of these neurons are identifiable. These data allowed us to determine how many interneurons served in a circuit generating a behavior, while the use of pairs of electrodes permitted the study of synaptic interactions between interneurons. Interneurons involved in abdominal positioning produced either flexion (flexion producing interneurons or FPI), extension (EPI) or inhibition (I). Significantly, FPIs tended to synaptically excite other FPIs and inhibit EPIs. In turn EPIs excited other EPIs and inhibited FPIs. As a result, impaling and stimulating an FPI, for example, tended to recruit others and their combined activity evoked a natural-looking behavior. The inhibition between FPI and EPI and vice versa tended to account for the reciprocity seen between the two behaviors in all experiments. Finally the synaptic connections between EPI-EPI on FPI-FPI were found to be essentially invariable. Thus repeated stimulation of an FPI or the stimulation of this same FPI in another preparation, at another time, gave essentially the same overall behavior such that the stimulation of one FPI or EPI could evoke a wide spread output resembling a normal behavior.

Animals↗
PubMed2006

Multidirectional and multizonal tangential migration of GABAergic interneurons in the developing cerebral cortex.

Most GABAergic interneurons originate from the basal forebrain and migrate tangentially into the cortex. The migratory pathways and mode of interneuron migration within the developing cerebral cortex, however, previously was largely unknown. Time-lapse imaging and in vivo labelling with glutamate decarboxylase (GAD)67-green fluorescence protein (GFP) knock-in embryonic mice with expression of GFP in gamma-aminobutyric acid (GABA)ergic neurons indicated that multidirectional tangential (MDT) migration of interneurons takes place in both the marginal zone (MZ) and the ventricular zone (VZ) of the cortex. Quantitative analysis of migrating interneurons showed that rostrocaudally migrating neurons outnumber those migrating mediolaterally in both of these zones. In vivo labelling with a lipophilic dye showed that the MDT migration in the MZ occurs throughout the cortex over distances of up to 3 mm during a period of a few days. These results indicate that MZ cortical interneurons undergo a second phase of tangential migration in all directions and over long distances, after reaching the cortex by dorsomedial tangential migration. The MDT migration in the MZ may disperse and intermix interneurons within the cortex, resulting in a balanced distribution of interneuron subtypes.

Animals↗
PubMed1999

Engrailed-1 and netrin-1 regulate axon pathfinding by association interneurons that project to motor neurons.

During early development, multiple classes of interneurons are generated in the spinal cord including association interneurons that synapse with motor neurons and regulate their activity. Very little is known about the molecular mechanisms that generate these interneuron cell types, nor is it known how axons from association interneurons are guided toward somatic motor neurons. By targeting the axonal reporter gene &tgr;-lacZ to the En1 locus, we show the cell-type-specific transcription factor Engrailed-1 (EN1) defines a population of association neurons that project locally to somatic motor neurons. These EN1 interneurons are born early and their axons pioneer an ipsilateral longitudinal projection in the ventral spinal cord. The EN1 interneurons extend axons in a stereotypic manner, first ventrally, then rostrally for one to two segments where their axons terminate close to motor neurons. We show that the growth of EN1 axons along a ventrolateral pathway toward motor neurons is dependent on netrin-1 signaling. In addition, we demonstrate that En1 regulates pathfinding and fasciculation during the second phase of EN1 axon growth in the ventrolateral funiculus (VLF); however, En1 is not required for the early specification of ventral interneuron cell types in the embryonic spinal cord.

Animals↗
PubMed2001

Physiological characterisation of antennal mechanosensory descending interneurons in an insect (Gryllus bimaculatus, Gryllus campestris) brain.

We investigated five different descending brain interneurons with dendritic arborizations in the deutocerebrum in the crickets Gryllus bimaculatus and G. campestris. These interneurones convey specific antennal mechanosensory information to the ventral nerve cord and all responded to forced antennal movements. These interneurones coded for velocity and showed preferences for distinct sectors of the total range of antennal movements. Their axons descended into the posterior connective either ipsilateral or contralateral to the cell body. Electrical stimulation of sensory nerves indicated that the interneurons received input from different afferents of the two antennal base segments. One interneuron had a particularly large axon with a conduction velocity of 4.4 ms(-1). This was the only one of the five interneurons that also received visual input. Its activity was reduced during voluntary antennal movements. The reduction in activity occurred even after de-efferentation of the antenna, indicating that it had a central origin. Although we do not have experimental evidence for behavioural roles for the descending antennal mechanosensory interneurons, the properties described here suggest an involvement in the perception of objects in the path of the cricket.

Animals↗
PubMed2002

GABA-like immunoreactivity in nonspiking interneurons of the locust metathoracic ganglion.

Nonspiking interneurons are important components of the premotor circuitry in the thoracic ganglia of insects. Their action on postsynaptic neurons appears to be predominantly inhibitory, but it is not known which transmitter(s) they use. Here, we demonstrate that many but not all nonspiking local interneurons in the locust metathoracic ganglion are immunopositive for GABA (gamma-aminobutyric acid). Interneurons were impaled with intracellular microelectrodes and were shown physiologically to be nonspiking. They were further characterized by defining their effects on known leg motor neurons when their membrane potential was manipulated by current injection. Lucifer Yellow was then injected into these interneurons to reveal their cell bodies and the morphology of their branches. Some could be recognised as individuals by comparison with previous detailed descriptions. Ganglia were then processed for GABA immunohistochemistry. Fifteen of the 17 nonspiking interneurons studied were immunopositive for GABA, but two were not. The results suggest that the majority of these interneurons might exert their well-characterized effects on other neurons through the release of GABA but that some appear to use a transmitter other than GABA. These nonspiking interneurons are therefore not an homogeneous population with regard to their putative transmitter.

Animals↗
PubMed2006

Layer acquisition by cortical GABAergic interneurons is independent of Reelin signaling.

Functioning of the cerebral cortex requires the coordinated assembly of circuits involving glutamatergic projection neurons and GABAergic interneurons. Despite their segregated origin in different regions of the telencephalon, projection neurons and interneurons born synchronically end up adopting the same cortical layer, suggesting that layer acquisition is highly coordinated for both neuronal types. The radial migration and laminar arrangement of projection neurons depends on Reelin, a secreted glycoprotein expressed near the pial surface during embryogenesis. In contrast, the mechanisms controlling layer acquisition by cortical interneurons remain essentially unknown. Here, we have used an ultrasound-guided transplantation approach to analyze the mechanisms underlying the acquisition of laminar locations by cortical interneurons. We found that layer acquisition by cortical GABAergic interneurons does not directly depend on Reelin signaling. Moreover, interneurons invade their target layers well after synchronically generated projection neurons reach their final destination. These results suggest a model in which cues provided by projection neurons guide cortical interneurons to their appropriate layer, and reveal that, at least for some neuronal types, long-range radial migration does not directly require Reelin.

Animals↗
PubMed2006

Phase precession in hippocampal interneurons showing strong functional coupling to individual pyramidal cells.

Although hippocampal interneurons typically do not show discrete regions of elevated firing in an environment, such as seen in pyramidal cell place fields, they do exhibit significant spatial modulation (McNaughton et al., 1983a). Strong monosynaptic coupling between pyramidal neurons and nearby interneurons in the CA1 stratum pyramidale has been strongly implicated on the basis of significant, short-latency peaks in cross-correlogram plots (Csicsvari et al., 1998). Furthermore, interneurons receiving a putative monosynaptic connection from a simultaneously recorded pyramidal cell appear to inherit the spatial modulation of the latter (Marshall et al., 2002). Buzsaki and colleagues hypothesize that interneurons may also adopt the firing phase dynamics of their afferent place cells, which show a phase shift relative to the hippocampal theta rhythm as a rat passes through the place field ("phase precession"). This study confirms and extends the previous reports by showing that interneurons in the dorsal and middle hippocampus with putative monosynaptic connections with place cells recorded on the same tetrode share other properties with their pyramidal cell afferents, including the spatial scale of the place field of pyramidal cell, a characteristic of the septotemporal level of the hippocampus from which the cells are recorded, and the rate of phase precession, which is slower in middle regions. Furthermore, variations in pyramidal cell place field scale within each septotemporal level attributable to task variations are similarly associated with variations in interneuron place field scale. The available data strongly suggest that spatial selectivity of CA1 stratum pyramidale interneurons is inherited from a small cluster of local pyramidal cells and is not a consequence of spatially selective synaptic input from CA3 or other sources.

Action Potentials↗
PubMed2004

Cortical GABA interneurons in neurovascular coupling: relays for subcortical vasoactive pathways.

The role of interneurons in neurovascular coupling was investigated by patch-clamp recordings in acute rat cortical slices, followed by single-cell reverse transcriptase-multiplex PCR (RT-mPCR) and confocal observation of biocytin-filled neurons, laminin-stained microvessels, and immunodetection of their afferents by vasoactive subcortical cholinergic (ACh) and serotonergic (5-HT) pathways. The evoked firing of single interneurons in whole-cell recordings was sufficient to either dilate or constrict neighboring microvessels. Identification of vasomotor interneurons by single-cell RT-mPCR revealed expression of vasoactive intestinal peptide (VIP) or nitric oxide synthase (NOS) in interneurons inducing dilatation and somatostatin (SOM) in those eliciting contraction. Constrictions appeared spatially restricted, maximal at the level of neurite apposition, and were associated with contraction of surrounding smooth muscle cells, providing the first evidence for neural regulation of vascular sphincters. Direct perfusion of VIP and NO donor onto the slices dilated microvessels, whereas neuropeptide Y (NPY) and SOM induced vasoconstriction. RT-PCR analyses revealed expression of specific subtypes of neuropeptide receptors in smooth muscle cells from intracortical microvessels, compatible with the vasomotor responses they elicited. By triple and quadruple immunofluorescence, the identified vasomotor interneurons established contacts with local microvessels and received, albeit to a different extent depending on interneuron subtypes, somatic and dendritic afferents from ACh and 5-HT pathways. Our results demonstrate the ability of specific subsets of cortical GABA interneurons to transmute neuronal signals into vascular responses and further suggest that they could act as local integrators of neurovascular coupling for subcortical vasoactive pathways.

Animals↗
PubMed2005

Neurotensin activates GABAergic interneurons in the prefrontal cortex.

Converging data suggest a dysfunction of prefrontal cortical GABAergic interneurons in schizophrenia. Morphological and physiological studies indicate that cortical GABA cells are modulated by a variety of afferents. The peptide transmitter neurotensin may be one such modulator of interneurons. In the rat prefrontal cortex (PFC), neurotensin is exclusively localized to dopamine axons and has been suggested to be decreased in schizophrenia. However, the effects of neurotensin on cortical interneurons are poorly understood. We used in vivo microdialysis in freely moving rats to assess whether neurotensin regulates PFC GABAergic interneurons. Intra-PFC administration of neurotensin concentration-dependently increased extracellular GABA levels; this effect was impulse dependent, being blocked by treatment with tetrodotoxin. The ability of neurotensin to increase GABA levels in the PFC was also blocked by pretreatment with 2-[1-(7-chloro-4-quinolinyl)-5-(2,6-dimethoxyphenyl)pyrazole-3-yl)carbonylamino]tricyclo(3.3.1.1 [EC] .3.7)decan-2-carboxylic acid (SR48692), a high-affinity neurotensin receptor 1 (NTR1) antagonist. This finding is consistent with our observation that NTR1 was localized to GABAergic interneurons in the PFC, particularly parvalbumin-containing interneurons. Because neurotensin is exclusively localized to dopamine axons in the PFC, we also determined whether neurotensin plays a role in the ability of dopamine agonists to increase extracellular GABA levels. We found that D2 agonist-elicited increases in PFC GABA levels were blocked by pretreatment with SR48692, consistent with data indicating that D2 autoreceptor agonists increase neurotensin release from dopamine-neurotensin axons in the PFC. These findings suggest that neurotensin plays an important role in regulating prefrontal cortical interneurons and that it may be useful to consider neurotensin agonists as an adjunct in the treatment of schizophrenia.

Animals↗
PubMed2004

Distance-dependent scaling of calcium transients evoked by backpropagating spikes and synaptic activity in dendrites of hippocampal interneurons.

Although interactions between backpropagating action potentials and synaptic stimulations have been extensively studied in pyramidal neurons, dendritic propagation and the summation of these signals in interneurons are not nearly as well known. In this study, two-photon imaging was used to explore the basic properties of dendritic calcium signaling in CA1 stratum radiatum interneurons. In contrast to hippocampal pyramidal neurons, the backpropagating action potential-evoked calcium transients in dendrites of interneurons underwent a distance-dependent increment. Although, in proximal dendrites, an increment could be attributed to a smaller dendrite diameter, distal dendrites did not show such dependence. Calcium responses in interneurons had a smaller amplitude, slower rise time, and decay than in pyramidal neurons. To explore the factors underlying the difference, we compared the calcium-binding capacity in interneurons and in pyramidal neurons. Our finding that endogenous calcium buffers had a higher level in interneurons may primarily explain the different kinetics and amplitudes of calcium transients. Synaptic stimulation-evoked calcium transients were also larger at distant dendritic locations. The spread of these signals was restricted to 12-13 microm long dendritic compartments. Supporting the reported lack of long-term potentiation in these interneurons, we found only sublinear or linear summations of calcium responses to coincident synaptic inputs and backpropagating spikes.

Action Potentials↗
PubMed2006

A specific role for NR2A-containing NMDA receptors in the maintenance of parvalbumin and GAD67 immunoreactivity in cultured interneurons.

Several lines of evidence suggest that a hypoglutamatergic condition may induce a phenotypic loss of cortical parvalbumin (PV)-positive GABAergic interneurons, such as that observed in brain tissue of schizophrenic subjects. However, it is not known whether the loss of PV interneurons is a consequence of the hypoglutamatergic condition or a secondary aspect of the disease. We characterized the signaling and subunit expression of NMDA receptors in cultured cortical PV interneurons and determined whether a hypoglutamatergic condition, created by direct application of sublethal concentrations of ketamine or subunit-selective NMDA receptor antagonists, can affect the expression of the GABAergic markers as observed in vivo. Real-time PCR performed on mRNA isolated from single neurons showed that PV interneurons present a fivefold higher NR2A/NR2B ratio than pyramidal neurons. Brief, nontoxic, exposure to NMDA led to an increase in ERK1/2 (extracellular signal-regulated kinase 1/2) and cAMP response element-binding protein phosphorylation in PV interneurons, and this increase was blocked by the NR2A-selective antagonist NVP-AAM077. Application of the nonselective NMDA receptor antagonist ketamine, at sublethal concentrations, induced a time and dose-dependent decrease in parvalbumin and GAD67 immunoreactivity specifically in PV interneurons. These effects were reversible and were also observed with the NR2A-selective antagonist, whereas the NR2B-selective antagonist Ro-25-6981 only partially reduced GAD67 immunoreactivity. Coexposure to the calcium channel opener BayK, or the group I metabotropic glutamate receptor agonist DHPG [(RS)-3,5-dihydroxyphenylglycine] attenuated the decrease in GAD67 and parvalbumin induced by the NMDA receptor antagonists. These results suggest that the activity of NR2A-containing NMDA receptors play a pivotal role in the maintenance of the GABAergic function of PV interneurons.

Animals↗
PubMed1999

Selective excitation of subtypes of neocortical interneurons by nicotinic receptors.

The cellular mechanisms by which neuronal nicotinic cholinergic receptors influence many aspects of physiology and pathology in the neocortex remain primarily unknown. Whole-cell recordings and single-cell reverse transcription (RT)-PCR were combined to analyze the effect of nicotinic receptor agonists on different types of neurons in acute slices of rat neocortex. Nicotinic receptor agonists had no effect on pyramidal neurons and on most types of interneurons, including parvalbumin-expressing fast spiking interneurons and somatostatin-expressing interneurons, but selectively excited a subpopulation of interneurons coexpressing the neuropeptides vasoactive intestinal peptide (VIP) and cholecystokinin. This excitation persisted in the presence of glutamate, GABA, and muscarinic receptor antagonists and in the presence of tetrodotoxin and low extracellular calcium, suggesting that the depolarization was mediated through the direct activation of postsynaptic nicotinic receptors. The responses were blocked by the nicotinic receptor antagonists dihydro-beta-erythroidine and mecamylamine and persisted in the presence of the alpha7 selective nicotinic receptor antagonist methyllycaconitine, suggesting that the involved nicotinic receptors lacked the alpha7 subunit. Single-cell RT-PCR analysis indicated that the majority of the interneurons that responded to nicotinic stimulation coexpressed the alpha4, alpha5, and beta2 nicotinic receptor subunits. Therefore, these results provide a role for non-alpha7 nicotinic receptors in the selective excitation of a subpopulation of neocortical interneurons. Because the neocortical interneurons expressing VIP have been proposed previously to regulate regional cortical blood flow and metabolism, these results also provide a cellular basis for the neuronal regulation of cortical blood flow mediated by acetylcholine.

Acetylcholine↗
PubMed1999

Muscarinic receptor activity induces an afterdepolarization in a subpopulation of hippocampal CA1 interneurons.

Cholinergic input to the hippocampus may be involved in important behavioral functions and the pathophysiology of neurodegenerative diseases. Muscarinic receptor activity in interneurons of the hippocampus may play a role in these actions. In this study, we investigated the effects of muscarinic receptor activity on the excitability of different subtypes of interneurons in rat hippocampal CA1. Most interneurons displayed an afterhyperpolarizing potential (AHP) after depolarization by injected current or synaptic stimulation. In the presence of a muscarinic agonist, the AHP of a subset of these interneurons was replaced by an afterdepolarization (ADP), often of sufficient magnitude to evoke action potentials in the absence of further stimulation. The ADP was insensitive to cadmium and low extracellular calcium. It was blocked by low extracellular sodium but not by tetrodotoxin or low concentrations of amiloride. Muscarinic ADPs were sometimes observed in isolation but were often accompanied by depolarizing, hyperpolarizing, or biphasic changes in the membrane potential. Interneurons with muscarinic ADPs were found in all strata of CA1 and did not fall into a single morphological classification. The potential functions of the prolonged action potential output of interneurons produced by the ADP could include changes in hippocampal circuit properties and facilitation of the release of peptide cotransmitters in these interneurons.

Acetylcholine↗
PubMed2000

Membrane and synaptic actions of halothane on rat hippocampal pyramidal neurons and inhibitory interneurons.

A relatively small number of inhibitory interneurons can control the excitability and synchronization of large numbers of pyramidal neurons in hippocampus and other cortical regions. Thus, anesthetic modulation of interneurons could play an important role during anesthesia. The aim of this study was to investigate effects of a general anesthetic, halothane, on membrane and synaptic properties of rat hippocampal interneurons. GABA receptor-mediated IPSCs were recorded with whole-cell patch-clamp techniques in visually identified CA1 pyramidal cells and interneurons located at the border of stratum lacunosum-moleculare and stratum radiatum. Halothane (0.35 mm congruent with 1.2 vol%) depressed evoked IPSC amplitudes recorded from both pyramidal cells and inhibitory interneurons. Also, halothane considerably prolonged the decay time constant of evoked IPSCs in pyramidal cells and interneurons. The frequencies of miniature IPSCs were increased by halothane (two- to threefold) in both types of neuron. On the other hand, halothane effects on resting membrane potentials were variable but minimal in both types of neurons. In current-clamp recordings, halothane depressed EPSP amplitudes and increased IPSP amplitudes recorded from both types of neurons. In addition, halothane increased the failure rate of synaptically evoked action potentials. Taken together, these data provide evidence that halothane increases GABA(A) receptor-mediated synaptic inhibition between synaptically connected interneurons and depresses excitatory transmission, similar to effects observed in pyramidal neurons.

Action Potentials↗
PubMed2002

Drosophila HB9 is expressed in a subset of motoneurons and interneurons, where it regulates gene expression and axon pathfinding.

Motoneurons are an essential component of all metazoan nervous systems, but it is unknown whether there is an evolutionarily conserved mechanism for generating motoneurons during neurogenesis. In the vertebrate CNS, HB9/MNR2 transcription factors are specifically expressed in all somatic motoneurons and are necessary to distinguish motoneurons from interneurons, in part by repressing interneuron-specific gene expression. Here, we identify and characterize the single Drosophila ortholog of the HB9/MNR2 gene family. Drosophila HB9 is detected in a subset of motoneurons with ventral muscle targets and in a small group of interneurons, including the well characterized serotonergic interneurons. RNA interference knockdown of HB9 levels leads to defects in motoneuron ventral muscle target recognition, ectopic expression of a marker for dorsally projecting motoneurons (Even-skipped), and defects in serotonergic interneuronal projections. Conversely, ectopic HB9 expression causes an expansion of ventral motoneuron projections and repression of Even-skipped. Thus, Drosophila HB9 is required in a subset of motoneurons and interneurons for establishing proper axon projections but does not have a general role in distinguishing motoneuron and interneuron cell types.

Animals↗
PubMed1987

Immunocytochemical and pharmacological evidence for GABAergic spiking local interneurons in the locust.

In the locust thoracic nervous system, spiking local interneurons within a ventral midline population are stained by a polyclonal antibody raised against GABA. Their cell bodies, their primary neurites in ventral commissure II, and their prominent neurites in the perpendicular tract linking ventral and dorsal fields of fine branches are all stained. Individual interneurons in this population were labeled with Lucifer yellow after their receptive fields had been determined physiologically. Alternate sections were stained with the antibody. Some, but not all, of the spiking local interneurons labeled with Lucifer yellow are also stained with the antibody. Apart from having somata that lie more posteriorly within the midline population, the antibody-stained interneurons cannot be distinguished on morphological or physiological grounds from those that are unstained. The way in which this cytochemical heterogeneity within an otherwise homogenous population might arise during development is discussed. A second group of spiking local interneurons with similar sensory input to that of the ventral midline population, but with cell bodies in the anterior lateral region of the ganglion and primary neurites in ventral commissure I, are not stained. Interneurons in the midline group receive direct inputs from sensory neurons and some directly inhibit particular leg motor neurons that mediate interjoint and tactile reflexes. Picrotoxin reversibly blocks the inhibition of the motor neurons and therefore abolishes these reflexes. Immunocytochemical and pharmacological experiments thus suggest that inhibition by some spiking local interneurons may be mediated by GABA.

Action Potentials↗