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At least 19 recordsLinked to original sources
PubMed1987

The role of spiking local interneurons in shaping the receptive fields of intersegmental interneurons in the locust.

Intracellular recordings were made simultaneously from pairs of spiking local and intersegmental interneurons in the mesothoracic ganglion of the locust Schistocerca gregaria (Forskal). The spiking local interneurons belong to a midline group, and the intersegmental interneurons to a lateral-posterior population that projects ipsilaterally to the metathoracic ganglion. Both respond to mechanosensory inputs from one middle leg. The receptive fields of both types of interneurons were plotted and the contribution of the local interneurons to the shaping of the receptive fields of the intersegmental interneurons was studied. The spiking local interneurons are excited by specific arrays of exteroreceptors and proprioceptors of one leg. They make inhibitory connections with specific intersegmental interneurons which thus have corresponding inhibitory regions to their receptive fields. For example, inhibition from local interneurons with inputs from hairs or campaniform sensilla on the tarsus could sharpen the boundaries of the excitatory receptive field of an intersegmental interneuron by lateral inhibition. Inhibition from local interneurons with inputs from joint proprioceptors suppresses the excitation of an intersegmental interneuron during the antipreferred direction of movement. Rapid alternate movements about one joint can in this way be signaled by an intersegmental interneuron in a phase-locked manner. Certain intersegmental interneurons are excited by exteroreceptive inputs and inhibited by proprioceptive signals, or vice versa. The inhibition could become significant during walking, where the excitatory and inhibitory inputs to an interneuron are likely to be evoked during the different phases of a step cycle. The inhibitory regions of the receptive field of an intersegmental interneuron have never been found to be smaller than the excitatory regions of the receptive field of a presynaptic local interneuron and can result from converging inhibitory inputs from several spiking local interneurons. The inhibitory connections are highly specific: Several local interneurons may be excited by a particular stimulus that also inhibits an intersegmental interneuron, but only a small proportion of the former are the cause of the inhibition in the intersegmental interneuron.

Animals↗
PubMed1990

Parallel motor pathways from thoracic interneurons of the ventral giant interneuron system of the cockroach, Periplaneta americana.

The data described here complete the principal components of the cockroach wind-mediated escape circuit from cercal afferents to leg motor neurons. It was previously known that the cercal afferents excite ventral giant interneurons which then conduct information on wind stimuli to thoracic ganglia. The ventral giant interneurons connect to a large population of interneurons in the thoracic ganglia which, in turn, are capable of exciting motor neurons that control leg movements. Thoracic interneurons that receive constant short latency inputs from ventral giant interneurons have been referred to as type A thoracic interneurons (TIAs). In this paper, we demonstrate that the motor response of TIAs occurs in adjacent ganglia as well as in the ganglion of origin for the TIA. We then describe the pathway from TIAs to motor neurons in both ganglia. Our observations reveal complex interactions between thoracic interneurons and leg motor neurons. Two parallel pathways exist. TIAs excite leg motor neurons directly and via local interneurons. Latency and amplitude of post-synaptic potentials (PSPs) in motor neurons and local interneurons either in the ganglion of origin or in adjacent ganglia are all similar. However, the sign of the responses recorded in local interneurons (LI) and motor neurons varies according to the TIA subpopulation based on the location of their cell bodies. One group, the dorsal posterior group, (DPGs) has dorsal cell bodies, whereas the other group, the ventral median cells, (VMC) has ventral cell bodies. All DPG interneurons either excited postsynaptic cells or failed to show any connection at all. In contrast, all VMC interneurons either inhibited postsynaptic cells or failed to show any connection. It appears that the TIAs utilize directional wind information from the ventral giant interneurons to make a decision on the optimal direction of escape. The output connections, which project not only to cells within the ganglion of origin but also to adjacent ganglia and perhaps beyond, could allow this decision to be made throughout the thoracic ganglia as a single unit. However, nothing in these connections indicates a mechanism for making appropriate coordinated leg movements. Because each pair of legs plays a unique role in the turn, this coordination should be controlled by circuits dedicated to each leg. We suggest that this is accomplished by local interneurons between TIAs and leg motor neurons.

Animals↗
PubMed1989

Intersegmental interneurons can control the gain of reflexes in adjacent segments of the locust by their action on nonspiking local interneurons.

The gain of local reflexes of one leg of a locust can be altered by mechanosensory inputs generated by movements of or tactile inputs to an adjacent leg. Touching the mesothoracic tarsus, for example, increases the number of spikes that are produced by the metathoracic slow extensor tibiae motor neuron and enhances the depolarization of flexor tibiae motor neuron in response to imposed movements of the chordotonal organ in the ipsilateral hind femur. The sensory information from the middle leg is conveyed directly to nonspiking interneurons and motor neurons controlling the movements of the hindleg by a population of mesothoracic intersegmental interneurons (Laurent and Burrows, 1989). The metathoracic nonspiking interneurons receive direct inputs from receptors on a hindleg and are, therefore, a point of convergence for local and intersegmental inputs. We examine here the role of the connections between mesothoracic intersegmental interneurons and metathoracic nonspiking interneurons in controlling metathoracic local reflexes. The amplitude of synaptic potentials evoked in leg motor neurons by the stimulation of local afferents can be modulated by altering the membrane potential of an interposed nonspiking interneuron with current injected through an intracellular electrode. These imposed voltage changes mimic a mesothoracic input and show that the state of a nonspiking local interneuron is a determining factor in the expression of a local reflex. Inputs from mesothoracic intersegmental interneurons may cause large changes in the input conductance of nonspiking interneurons that can shunt a local afferent input. In some nonspiking interneurons, synaptic potentials caused by mesothoracic interneurons can be recorded, but no underlying conductance change can be detected at the recording site. Similarly, a particular nonspiking interneuron may receive synaptic inputs when two distinct regions of a middle leg are touched, but only one of these intersegmental inputs may be effective in reducing the amplitude of a synaptic potential caused by afferents from the hindleg. These results suggest that nonspiking local interneurons may be compartmentalized, with synaptic inputs and their associated conductance changes restricted to particular branches. In this way, an individual nonspiking neuron could contribute simultaneously to several local circuits. The inputs from different intersegmental interneurons could then modulate these pathways independently.

Animals↗
PubMed1993

Excitatory influence of wind-sensitive local interneurons on an ascending interneuron in the cricket cercal sensory system.

This study examined the effects of a set of identified wind-sensitive local interneurons (9DL interneurons) on the wind-evoked spike output and directional sensitivity of an ascending interneuron (10-3) in the cricket (Acheta domesticus) cercal sensory system. Comparison of the directional sensitivities of the 9DL interneurons and 10-3 revealed that 3 of the 9DL interneurons have a large degree of overlap in their excitatory receptive fields with that of 10-3. Photoinactivation of any one of these 3 9DL interneurons resulted in a significant decrease in the spike output of 10-3 at its optimal excitatory wind stimulus positions. However, the overall directional sensitivity of 10-3 remained essentially unchanged. Photoinactivation of the one 9DL interneuron which had no overlap in its excitatory receptive field with 10-3 did not affect 10-3's responsiveness to wind stimuli. Results from simultaneous intracellular recordings of 10-3 and one of the 9DL interneurons which had an excitatory influence on 10-3 showed that depolarization of the local interneuron produced an epsp in 10-3, and could elicit several action potentials. Comparison of the morphologies of the 9DL interneurons and 10-3 revealed that the 3 9DL interneurons which had an excitatory influence on 10-3 all had regions of dendritic overlap with this ascending interneuron.

Action Potentials↗
PubMed1997

Synaptic effects of identified interneurons innervating both interneurons and pyramidal cells in the rat hippocampus.

GABAergic interneurons sculpt the activity of principal cells and are themselves governed by GABAergic inputs. To determine directly some of the sources and mechanisms of this GABAergic innervation, we have used dual intracellular recordings with biocytin-filled microelectrodes and investigated synaptic interactions between pairs of interneurons in area CA1 of the adult rat hippocampus. Of four synaptically-coupled interneuron-to-interneuron cell pairs, three presynaptic cells were identified as basket cells, preferentially innervating somata and proximal dendrites of pyramidal cells, but one differing from the other two in the laminar distribution of its dendritic and axonal fields. The fourth presynaptic interneuron was located at the border between strata lacunosum moleculare and radiatum, with axon ramifying within stratum radiatum. Action potentials evoked in all four presynaptic interneurons were found to elicit fast hyperpolarizing inhibitory postsynaptic potentials (mean amplitude 0.35 +/- 0.10 mV at a membrane potential of -59 +/- 2.8 mV) in other simultaneously recorded interneurons (n=4). In addition, three of the presynaptic interneurons were also shown to produce similar postsynaptic responses in subsequently recorded pyramidal cells (n=4). Electron microscopic evaluation revealed one of the presynaptic basket cells to form 12 synaptic junctions with the perisomatic domain (seven somatic synapses and five synapses onto proximal dendritic shafts) of the postsynaptic interneuron in addition to innervating the same compartments of randomly-selected local pyramidal cells (50% somatic and 50% proximal dendritic synapses, n=12). In addition, light microscopic analysis also indicated autaptic self-innervation in basket (12 of 12) and bistratified cells (six of six). Electron microscopic investigation of one basket cell confirmed six autaptic junctions made by five of its boutons. Together, these data demonstrate that several distinct types of interneuron have divergent output to both principal cells and local interneurons of the same (basket cells) or different type. The fast synaptic effects, probably mediated by GABA in both postsynaptic interneurons and principal cells are similar. These additional sources of GABA identified here in the input to GABAergic cells could contribute to the differential temporal patterning of distinct GABAergic synaptic networks.

Animals↗
PubMed2004

Aging in the rat hippocampus is associated with widespread reductions in the number of glutamate decarboxylase-67 positive interneurons but not interneuron degeneration.

Increased excitability of principal excitatory neurons is one of the hallmarks of aging in the hippocampus, signifying a diminution in the number and/or function of inhibitory interneurons with aging. To elucidate this, we performed comprehensive GABA-ergic interneuron cell counts in all layers of the dentate gyrus and the CA1 and CA3 subfields, using serial sections from adult, middle-aged and aged Fischer 344 rats. Sections were immunostained for glutamate decarboxylase-67 (GAD-67, a synthesizing enzyme of GABA) and GAD-67 immunopositive interneurons were counted using an unbiased cell counting method, the optical fractionator. Substantial declines in the absolute number of GAD-67 immunopositive interneurons were found in all hippocampal layers/subfields of middle-aged and aged animals, in comparison with the adult animals. However, the counts were comparable between the middle-aged and aged groups for all regions. Interestingly, determination of the absolute number of interneurons using neuron-specific nuclear antigen (NeuN) expression in the strata oriens and radiatum of CA1 and CA3 subfields revealed an analogous number of interneurons across the three age groups. Furthermore, the ratio of GAD-67 immunopositive and NeuN positive interneurons decreased from adult age to middle age but remained relatively static between middle age and old age. Collectively, the results underscore that aging in the hippocampus is associated with wide-ranging decreases in the number of GAD-67 immunopositive interneurons and most of the age-related changes in GAD-67 immunopositive interneuron numbers transpire by middle age. Additionally, this study provides novel evidence that age-related reductions in hippocampal GAD-67 immunopositive interneuron numbers are due to loss of GAD-67 expression in interneurons rather than interneuron degeneration.

Age Factors↗
PubMed1986

Identification of thoracic interneurons that mediate giant interneuron-to-motor pathways in the cockroach.

Paired intracellular recordings were made to identify thoracic interneurons that receive stable short latency excitation from giant interneurons (GIs). Eight metathoracic interneurons were identified in which EPSPs were correlated with GI activity which was evoked either by wind or intracellular electrical stimulation or occurred spontaneously. In all cases EPSPs in the thoracic interneurons followed GI action potentials faithfully at short latencies. EPSPs associated with GI action potentials consistently represented the upper range of amplitudes of a large sample of EPSPs recorded in the thoracic interneurons. Seven of the interneurons were correlated with activity in ventral GIs but were not correlated with activity in dorsal GIs. Four of these interneurons were part of a discrete population of interneurons whose somata are located in the dorsal posterior region of the ganglion. The eighth interneuron (designated the T cell) was positively correlated with activity in dorsal GIs. The four dorsal posterior group interneurons and the T cell were depolarized intracellularly to establish their potential for generating motor activity. In all cases evoked activity was stronger in leg motor neurons (primarily Ds and the common inhibitor) located on the side contralateral to the interneuron's soma. The results indicate that significant polysynaptic pathways exist by which GI activity can evoke motor activity. The implications of this conclusion to investigations on the cockroach escape system are discussed.

Animals↗
PubMed2002

Heterosynaptic modulation by the octopaminergic OC interneurons increases the synaptic outputs of protraction phase interneurons (SO, N1L) in the feeding system of Lymnaea stagnalis.

We examined the cholinergic synapses between protraction phase interneurons (SO or N1L) and their targets (N1M interneuron, B1 motoneuron) in the buccal ganglia of the pond snail Lymnaea stagnalis. We have tested the hypothesis that the OC (octopamine-containing) interneuron, an intrinsic modulator of the feeding network, can increase the synaptic efficacy from the SO or N1L to their targets. Prestimulation of the OC interneuron, 4 s before the activation of the SO or N1L increases the strength of their output synapses by 75% (SO)-110% (N1L). The individual excitatory postsynaptic potentials evoked by SO or N1L stimulation increase in size. OC prestimulation also produces an increase in the firing rate of these presynaptic interneurons: SO 40%; N1L 33%. The facilitation lasts up to 6 s after the end of the OC burst. The enhancement of PSPs is seen at all the output synapses (both excitatory and inhibitory) of the SO and N1L interneurons. The output synapses of the non-cholinergic swallowing phase N3p interneuron are not affected, even when the same postsynaptic target is selected. The SO-->N1M, SO-->B1 and N1L-->N1M synapses are also strengthened by bath application of 1-5 microM octopamine (average increase 60%). The major effect is an increased excitability of the SO; the B1 motoneuron response to the main transmitter of the SO, acetylcholine, is unaffected. Increased synaptic outputs of the protraction phase SO and N1L interneurons is functionally significant for generation of feeding pattern in the Lymnaea CNS. Strengthening the connections of SO and N1L to the central pattern generator (N1M) interneurons enhances their ability to drive fictive feeding. Thus heterosynaptic facilitation by the octopaminergic OC interneurons in the central pattern generator network may contribute to the behavioral plasticity of feeding in the intact animal.

Acetylcholine↗
PubMed2002

Calretinin-containing interneurons innervate both principal cells and interneurons in the CA1 region of the human hippocampus.

Hippocampal interneurons consist of functionally diverse cell types, most of them target the dendrites or perisomatic region of pyramidal cells with a few exceptions, like the calretinin-containing cells in the rat: they selectively innervate other interneurons. However, no electron microscopic data are available about the synaptic connections of calretinin-immunoreactive neurons in the human hippocampus. We aimed to provide these data to establish whether interneuron-selective interneurons indeed represent an essential feature of hippocampal circuits across distant species. Two types of calretinin-immunostained terminals were found in the CA1 region: one of them presumably derived from the thalamic reuniens nucleus, and established asymmetric synapses on dendrites and spines. The other type originating from local interneurons formed symmetric synapses on both pyramidal and interneuron dendrites. Distribution of postsynaptic targets showed that 26.8% of the targets were CR-positive interneuron dendrites, and 25.2% proved to be proximal pyramidal dendrites. CR-negative interneuron dendrites were also contacted (12.4%). Small caliber postsynaptic dendrites were not classified (28%). Somata were rarely contacted (7.6%). The present data suggest that calretinin-positive boutons do show a preference for other interneurons, but a considerable proportion of the targets are pyramidal cells. We propose that interneuron-selective inhibitory cells exist in the human Ammon's horn, and boutons innervating pyramidal cells derive from another cell type that might not exist in rodents.

Adult↗
PubMed1990

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase into last order spinal interneurones projecting to acromio- and spinodeltoideus motoneurones in the cat. 1. Location of labelled interneurones and influence of synaptic activity on the transneuronal transport.

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) was used to define the location of last order spinal interneurones projecting to deltoideus motoneurones in C5-C8 of the cat. Labelled interneurones were found bilaterally from rostral C1 to caudal Th5 and from L3 to the L4/5 border. Ipsilaterally they were located in laminae V-IX, while contralaterally they were confined to lamina VIII except for a few cells in laminae VII and IX. To estimate the degree to which interneuronal activity facilitates the transneuronal transport from deltoideus motoneurones, the numbers of labelled interneurones were compared under different experimental conditions after WGA-HRP injection. The number of labelled last order interneurones was larger in one awake and active cat than in one awake but inactive cat and also larger in six anaesthetized animals in which spinal pathways were stimulated to evoke antidromic and synaptic activation of the interneurones, than in two anaesthetized animals without stimulation. It is concluded that the transneuronal transport of WGA-HRP is considerably facilitated by increased activity in the last order interneurones. An overall tendency was observed for a positive correlation between the number of labelled interneurones and the number of primarily stained deltoideus motoneurones. In order to reach a detectable concentration of WGA-HRP in the last order interneurones a certain number of motoneurones has to be labelled to the extent that they appear homogenously black.

Action Potentials↗
PubMed2000

Adenosine action on interneurons and synaptic transmission onto interneurons in rat hippocampus in vitro.

To investigate the action of adenosine on interneurons as well as on excitatory synaptic transmission onto interneurons in the hippocampus, intracellular recordings were made from electrophysiologically identified interneurons in the CA1 region of the hippocampal slice in vitro. The effects of adenosine and the preferential adenosine A1 receptor agonist, chloroadenosine, were examined. Application of 50 microM adenosine and 20 microM chloroadenosine to the bath produced a hyperpolarization of 5.6+/-1.6 (n=5) and 6.1+/-1.4 mV (n=6), respectively, as well as a decrease in membrane input resistance of 18.1+/-3.5% (n=5) and 18.5+/-1.4% (n=6), respectively. Adenosine depressed the postsynaptic potentials (PSPs) elicited in the interneurons by stimulation of Schaffer collateral fibers by 73+/-6.8% (n=5). The amplitude and the duration of the afterhyperpolarization which followed the spike of the action potential were attenuated by 48+/-6.9% and 31+/-8.6%, respectively (n=5). Chloroadenosine depressed the evoked PSPs in these interneurons by 61.2+/-2.7% (n=6) and depressed the duration and the amplitude of the afterhyperpolarization by 85.2+/-4.5% and by 72.6+/-4.8%, respectively (n=6). The data show that adenosine and chloroadenosine directly inhibit hippocampal CA1 interneurons by blocking the synaptic input, by hyperpolarizing the membrane potential and by depressing the afterhyperpolarization following individual action potential spikes. It is proposed that adenosine A1 receptors are present at pre- and/or postsynaptic sites of interneuron synapses in the hippocampal CA1 region. The present findings demonstrate that adenosine A1 receptor activation in CA1 interneurons is able to modulate the excitatory synaptic input to, and excitability of, these neurons. Thus, as adenosine is released during ischemia and epilepsy, adenosine may protect both interneurons and pyramidal cells from glutamate excitotoxicity through activation of adenosine A1 receptors on these neurons in the hippocampus.

2-Chloroadenosine↗
PubMed1976

Convergence on interneurones mediating the reciprocal Ia inhibition of motoneurones. I. Disynaptic Ia inhibition of Ia inhibitory interneurones.

Interneurones identified as mediating the disynaptic reciprocal Ia inhibition of motoneurones (referred to as "Ia inhibitory interneurones") were recorded in the lumbar spinal cord of the cat. It was revealed that the Ia inhibitory interneurones themselves receive disynaptic Ia inhibition. The muscles from which this inhibition is evoked are strictly antagonistic to those supplying their Ia excitation. Similar to the Ia inhibition in motoneurones the Ia inhibition in the Ia inhibitory interneurones is decreased when preceded by an antidromic stimulation of ventral roots. Furthermore, transmission of Ia inhibition to the Ia inhibitory interneurones is facilitated from ipsilateral and contralateral primary afferents as well as several supraspinal pathways analogous to earlier findings for the Ia inhibition of motoneurones. The pattern and control of the Ia inhibition of motoneurones and of Ia inhibitory interneurones display so striking similarities that it is suggested that identical interneurones are responsible. The conclusion thus emerges that "opposite" Ia inhibitory interneurones (i.e. interneurones monosynaptically connected to antagonistic muscles) are mutually inhibiting each other. The functional significance of this organization is discussed.

Afferent Pathways↗
PubMed2005

Relative contribution of Ia inhibitory interneurones to inhibition of feline contralateral motoneurones evoked via commissural interneurones.

The aim of the study was to examine to what extent the crossed inhibition of hindlimb lumbar alpha-motoneurones is evoked via interneurones that mediate reciprocal inhibition between flexors and extensors (Ia inhibitory interneurones), and to what extent via other spinal interneurones. The crossed inhibition was evoked by reticulospinal and vestibulospinal tract fibres, stimulated in the contralateral medullary longitudinal fascicle and the lateral vestibular nucleus, respectively, or by group II muscle afferents in the contralateral quadriceps nerve. The components of the IPSPs recorded in motoneurones that were mediated by Ia inhibitory interneurones were identified by their depression following activation of Renshaw cells. Trisynaptic components of IPSPs of reticulospinal and vestibulospinal origin, and polysynaptic (but not trisynaptic) components of IPSPs from group II afferents were found to be depressed in the majority of the motoneurones, while disynaptic components, those due to direct actions of inhibitory commissural interneurones, were not depressed. These results indicate that the coordination of left and right hindlimb movements based on crossed inhibition from reticulospinal and vestibulospinal neurones, depends on the degree of activation of Ia inhibitory interneurones by muscle spindle afferents and on their inhibition by Renshaw cells. Our results also indicate that Ia inhibitory interneurones do not operate as last-order inhibitory interneurones in crossed trisynaptic pathways from group II afferents, even though they mediate inhibition evoked by interneurones in shared polysynaptic pathways of crossed flexor and extensor reflexes coactivated by group II and other high-threshold muscle, skin and joint afferents.

Animals↗
PubMed1985

Interactions of the slow oscillator interneuron with feeding pattern-generating interneurons in Lymnaea stagnalis.

We have used intracellular recording from groups of interneurons in the feeding system of the pond snail, Lymnaea stagnalis, to examine the connections of a modulatory interneuron, the slow oscillator (SO), with the network of pattern-generating interneurons (N1, N2, and N3). The SO is an interneuron whose axon branches solely within the buccal ganglia. There is only one such cell in each snail. In half the snails the cell body is in the right buccal ganglion and in the other half in the left buccal ganglion. Stimulation of either the SO or one of the N1 pattern-generating interneurons elicits the feeding rhythm, but of all the buccal neurons, only the SO can drive the feeding rhythm at the frequency seen in the intact snail. The SO makes reciprocal excitatory synapses with the N1 interneurons that drive the protraction of the radula. This ensures strong activation of the feeding system. The SO inhibits the N2 interneurons. Postsynaptic potentials evoked by stimulation of the SO facilitate without spike broadening in the SO. The SO is strongly inhibited by N2 and N3 interneurons, which are active during the retraction phase. This gates any excitatory inputs to the SO, probably preventing protraction of the radula while retraction is underway. The results support the idea of a single interneuron capable of driving a hierarchically organized motor system.

Action Potentials↗
PubMed1995

Nonspiking local interneurons in insect leg motor control. II. Role of nonspiking local interneurons in the control of leg swing during walking.

1. Nonspiking local interneurons (NSIs) were recorded intracellularly in the mesothoracic ganglion of semi-intact locusts walking on a treadwheel. Interneurons were characterized by their connectivity to motoneurons. Their activity patterns in the step cycle and the effect current injection had on the leg movement were analyzed. We examined interneurons that provided excitatory or inhibitory synaptic drive to a subset of motoneurons active during the swing movement of walking. 2. Interneuron activity was observed to support or oppose the actual leg movement. Both supporting and opposing interneurons were active simultaneously, lending support to the idea that the actual motor output of walking is generated by the adjustment of parallel antagonistic pathways of signal processing. 3. The examined interneurons showed qualitatively the same patterns of activity during forward and backward walking. This indicates that swing movement in both situations may be generated by similar neuronal networks (although the mechanism of movement reversal remains unclear). 4. At least two functional types of NSIs could be distinguished. First, there were interneurons whose depolarization patterns showed distinct variability, often correlated with duration or amplitude of the swing movement. As a rule, current injection had minor, if any, effects on leg movement. Populations of these interneurons appear to be involved in the control of a coordinated swing movement by driving appropriate sets of muscle groups. The second type of NSIs showed more stereotyped activity patterns that varied relatively little with changes in the swing movement. Current injection had strong effects on the leg movement and could, for example, arrest the leg in the stance phase. These interneurons appear to be primarily involved in the trigger mechanism of leg swing.

Animals↗
PubMed2000

Novel hippocampal interneuronal subtypes identified using transgenic mice that express green fluorescent protein in GABAergic interneurons.

The chief inhibitory neurons of the mammalian brain, GABAergic neurons, are comprised of a myriad of diverse neuronal subtypes. To facilitate the study of these neurons, transgenic mice were generated that express enhanced green fluorescent protein (EGFP) in subpopulations of GABAergic neurons. In one of the resulting transgenic lines, called GIN (GFP-expressing Inhibitory Neurons), EGFP was found to be expressed in a subpopulation of somatostatin-containing GABAergic interneurons in the hippocampus and neocortex. In both live and fixed brain preparations from these mice, detailed microanatomical features of EGFP-expressing interneurons were readily observed. In stratum oriens of the hippocampus, EGFP-expressing interneurons were comprised almost exclusively of oriens/alveus interneurons with lacunosum-moleculare axon arborization (O-LM cells). In the neocortex, the somata of EGFP-expressing interneurons were largely restricted to layers II-IV and upper layer V. In hippocampal area CA1, two previously uncharacterized subtypes of interneurons were identified using the GIN mice: stratum pyramidale interneurons with lacunosum-moleculare axon arborization (P-LM cells) and stratum radiatum interneurons with lacunosum-moleculare axon arborization (R-LM cells). These newly identified interneuronal subtypes appeared to be closely related to O-LM cell, as they selectively innervate stratum lacunosum-moleculare. Whole-cell patch-clamp recordings revealed that these cells were fast-spiking and showed virtually no spike frequency accommodation. The microanatomical features of these cells suggest that they function primarily as "input-biasing" neurons, in that synaptic volleys in stratum radiatum would lead to their activation, which in turn would result in selective suppression of excitatory input from the entorhinal cortex onto CA1 pyramidal cells.

Action Potentials↗
PubMed1988

Activation of DUM cell interneurons by ventral giant interneurons in the cockroach, Periplaneta americana.

Dorsal unpaired median (DUM) cells in orthopteran insects are known to contain the neuromodulatory substance octopamine, and DUM cells with peripheral axons augment synaptic activity at neuromuscular junctions. One of the most studied systems in the cockroach is the giant interneuron (GI) system which controls the initial movements of a wind-mediated escape response. Our data demonstrate that DUM cells that are restricted to the central nervous system (DUM interneurons) receive inputs from ventral giant interneurons (vGIs) but not from dorsal giant interneurons (dGIs). In contrast, DUM cells that have peripheral axons consistently fail to be excited by any giant interneurons. The DUM interneurons are excited by vGIs on both sides of the CNS and, when the vGIs are excited in pairs, summation occurs. Wind fields that have been generated for two of the DUM interneurons are omnidirectional. These data, taken along with the known association of DUM cells with the neuromodulatory substance octopamine, suggest that the DUM interneurons may act to modulate central synapses.

Action Potentials↗
PubMed1990

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase into last order spinal interneurones projecting to acromio- and spinodeltoideus motoneurones in the cat. 2. Differential labelling of interneurones depending on movement type.

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase was used to define the location of last order spinal interneurones projecting to deltoideus motoneurones during voluntary target-reaching and/or in unrestricted walking on the ground. Labelled interneurones were found bilaterally from C2 to Th1 in target-reaching cats and almost exclusively in the C5-Th1 segments in walking cats, although the total number of labelled interneurones in these cats was considerably higher than in the target-reaching cats. These results confirm the previous finding that propriospinal neurones in the C3-C4 segments can mediate the descending command for target-reaching movements with the forelimb. In both groups of cats labelled interneurones were found ipsilaterally in laminae V-IX, while contralaterally they were mainly restricted to lamina VIII. In the forelimb segments there was a larger number of labelled interneurones in the walking cats in the lateral part of laminae V-VII and in laminae VIII and IX. There was a positive, almost linear correlation between the total number of labelled interneurones and motoneurones in all cats. The results suggest that both excitatory and inhibitory last order interneurones can be transneuronally labelled. It is concluded that this method can be used for functional identification of last order interneurones active during the preparation and/or execution of different movements.

Animals↗