Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “interneurons”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed2003

Glutamate receptor subunit 3 (GluR3) immunoreactivity delineates a subpopulation of parvalbumin-containing interneurons in the rat hippocampus.

Rasmussen's encephalitis is a childhood disease resulting in intractable seizures associated with hippocampal and neocortical inflammation. An autoantibody against the GluR3 subunit of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors is implicated in the pathophysiology of Rasmussen's encephalitis. AMPA receptors mediate excitatory neurotransmission in the brain and contain combinations of four subunits (GluR1-4). Although the distributions of GluR1, GluR2, and GluR4 are known in some detail, the cellular distribution of GluR3 in the mammalian brain remains to be described. We developed and characterized a GluR3-specific monoclonal antibody and quantified the cellular distribution of GluR3 in CA1 of the rat hippocampus. GluR3 immunoreactivity was detected in all pyramidal neurons and astrocytes and in most interneurons. We quantified the intensity of GluR3 immunoreactivity in interneuron subtypes defined by their calcium-binding protein content. GluR3 immunofluorescence, but not GluR1 or GluR2 immunofluorescence, was significantly elevated in somata of parvalbumin-containing interneurons compared to pyramidal somata. Strikingly, increased GluR3 immunofluorescence was not observed in calbindin- and calretinin-containing interneurons. Furthermore, 24% of parvalbumin-containing interneurons could be distinguished from surrounding neurons based on their intense GluR3 immunoreactivity. This subpopulation had significantly elevated GluR3 immunoreactivity compared to the rest of parvalbumin-containing interneurons. Electron microscopy revealed enriched GluR3 immunoreactivity in parvalbumin-containing perikarya at cytoplasmic and postsynaptic sites. Parvalbumin-containing interneurons, potent inhibitors of cortical pyramidal neurons, are vulnerable in the brains of epileptic patients. Our findings suggest that the somata of these interneurons are enriched in GluR3, which may render them vulnerable to pathological states such as epilepsy and Rasmussen's encephalitis.

Animals↗
PubMed2004

Parvalbumin-containing interneurons in the basolateral amygdala express high levels of the alpha1 subunit of the GABAA receptor.

The basolateral amygdala (ABL) is essential for the amnestic effects of benzodiazepines in aversive learning tasks. Because the alpha1 subunit of the gamma-aminobutyric acid (GABA)(A) receptor is critical for these amnestic actions, knowledge of the neuronal localization of this subunit in the ABL should contribute to an understanding of the candidate neuronal mechanisms involved. To examine this question, we used dual-labeling immunohistochemical techniques to study the localization of the alpha1 subunit in the ABL. Our results suggest that the alpha1 subunit of the GABA(A) receptor is localized primarily in GABAergic interneurons in the ABL at the somal level, although the intense neuropil staining in the lateral nucleus suggests that distal dendrites of pyramidal projection neurons in this nucleus may also contain high levels of the alpha1 subunit. The great majority of alpha1-immunoreactive interneurons also exhibit immunoreactivity for the beta2/3 subunits of the GABA(A) receptor. Parvalbumin-positive (PV+) interneurons are the main interneuronal subpopulation exhibiting alpha1 immunoreactivity, but some calretinin-positive interneurons also express this subunit. These data suggest that certain subpopulations of GABAergic interneurons in the ABL, especially PV+ cells, receive a robust GABAergic innervation. Because the most likely source of this innervation is intrinsic, these results suggest that PV+ interneurons could constitute an important component of interneuronal networks in the ABL. These networks may be critical for the generation of synchronized rhythmic oscillations involved in consolidation of emotional memories. The activation of alpha1-containing GABA(A) receptors in the ABL by benzodiazepines may disrupt rhythmic oscillations critical for memory consolidation.

Amygdala↗
PubMed2007

Postsynaptic targets of somatostatin-containing interneurons in the rat basolateral amygdala.

The basolateral amygdala contains several subpopulations of inhibitory interneurons that can be distinguished on the basis of their content of calcium-binding proteins or peptides. Although previous studies have shown that interneuronal subpopulations containing parvalbumin (PV) or vasoactive intestinal peptide (VIP) innervate distinct postsynaptic domains of pyramidal cells as well as other interneurons, very little is known about the synaptic outputs of the interneuronal subpopulation that expresses somatostatin (SOM). The present study utilized dual-labeling immunocytochemical techniques at the light and electron microscopic levels to analyze the innervation of pyramidal cells, PV+ interneurons, and VIP+ interneurons in the anterior basolateral amygdalar nucleus (BLa) by SOM+ axon terminals. Pyramidal cell somata and dendrites were selectively labeled with antibodies to calcium/calmodulin-dependent protein kinase II (CaMK); previous studies have shown that the vast majority of dendritic spines, whether CAMK+ or not, arise from pyramidal cells. Almost all SOM+ axon terminals formed symmetrical synapses. The main postsynaptic targets of SOM+ terminals were small-caliber CaMK+ dendrites and dendritic spines, some of which were CaMK+. These SOM+ synapses with dendrites were often in close proximity to asymmetrical (excitatory) synapses to these same structures formed by unlabeled terminals. Few SOM+ terminals formed synapses with CaMK+ pyramidal cell somata or large-caliber (proximal) dendrites. Likewise, only 15% of SOM+ terminals formed synapses with PV+, VIP+, or SOM+ interneurons. These findings suggest that inhibitory inputs from SOM+ interneurons may interact with excitatory inputs to pyramidal cell distal dendrites in the BLa. These interactions might affect synaptic plasticity related to emotional learning.

Amygdala↗
PubMed1982

Locust local nonspiking interneurons which tonically drive antagonistic motor neurons: physiology, morphology, and ultrastructure.

Local nonspiking interneurons have been implicated in the control of behavior. We have characterized the physiology of two local nonspiking interneurons in the locust and subsequently examined the neurons in the light and electron microscopes. Physiologically the two interneurons have opposite effects upon antagonistic motor neurons and are tonically releasing transmitter at their "resting potentials." This combination of tonic release and reciprocal driving of antagonistic motor neurons by single interneurons provides a hitherto undescribed means of controlling posture. One interneuron (DCVII, 4) excites flexor tibiae and inhibits the slow extensor tibiae motor neurons when depolarized. The other interneuron (DCVII, 5) inhibits the flexor tibiae and excites the slow extensor tibiae motor neurons when depolarized. In both cases, when the interneurons are hyperpolarized, they have the opposite effects upon the same motor neurons. Intracellular staining of these neurons confirms that they are local interneurons. Furthermore, an examination of sectioned material shows that the neurons are unique and can be identified as such in a population of locust neurons. Ultrastructurally, we find synapses only on the smaller (less than 2 micrometers) branches. These neurons may form the presynaptic element in either of two configurations, these being the discrete density (one presynaptic) and the dense bar (one presynaptic, two postsynaptic) type of configurations. The functional implications of these findings for neurons controlling posture are discussed.

Animals↗
PubMed1984

The morphological diversity and receptive fields of spiking local interneurons in the locust metathoracic ganglion.

Twenty-one types of spiking local interneurons are described in a segmental ganglion of the locust. All have their cell bodies in a group at the ventral midline of the metathoracic ganglion. The interneurons are characterized by their shape as revealed by intracellular injection of dye, and by their physiology as revealed by intracellular recording. Each interneuron conforms to a basic plan, but the characteristic shape of each is derived from the elaboration of branches in some regions of the neuropil and by their absence in other regions. Some interneurons have ventral branches that extend over most of one-half of the metathoracic neuropil, whilst others have ventral branches restricted to a small region of neuropil. A few interneurons have dorsal branches that enter the first abdominal neuromere . Each type of interneuron is excited by a specific array of mechanoreceptors on the hind leg ipsilateral to its neuropilar branches. Some interneurons have a wide receptive field that encompasses most of the dorsal surfaces of the distal three parts of a leg, whilst others have a field limited to the spurs at the distal end of the tibia. The relationship between the shape of an interneuron and the size or orientation of its receptive field is discussed.

Afferent Pathways↗
PubMed1985

The structure of locust nonspiking interneurones in relation to the anatomy of their segmental ganglion.

The morphology of eight nonspiking local interneurones in the metathoracic ganglion of the locust is described in relation to known tracts, commissures, regions of neuropile, and identified motor neurones. They are compared with the spiking local interneurones in the same ganglion. Each nonspiking local interneurone was injected intracellularly with cobalt, following characterization of its physiological effects on identified leg motor neurones. The shapes of the nonspiking interneurones are diverse, although all have processes restricted to one ganglion and lack an axon. Their cell bodies are distributed in the ventral and dorsal cortex of the ganglion. Interneurones with cell bodies in similar places have similar basic structures, with primary neurites in the same commissure or tract, and major branches in the same tracts. The fine branches of all the interneurones have the same texture throughout, and occur in the same lateral region of neuropile, dorsal to the prominent neurite of the fast extensor tibiae motor neurone. Some interneurones have branches that extend both to the midline and to the dorsal boundary of the neuropile, but none have branches in the ventral, medial neuropile. This distribution of branches corresponds with two known features of the physiology of these interneurones: they make what appear physiologically to be direct connections with motor neurones, and have branches in the same region of the neuropile as the motor neurones. They do not appear to receive direct inputs from hair afferents, and they have no branches in the ventral neuropile to which these afferents project.

Action Potentials↗
PubMed1987

Morphology of local "stridulation" interneurons in the metathoracic ganglion of the acridid grasshopper Omocestus viridulus L.

The morphological characteristics of five types of local spiking interneurons in the metathoracic ganglion of the acridid grasshopper Omocestus viridulus L. have been revealed by intracellular injection of the fluorescent dye Lucifer Yellow. All these neurons are active during induced stridulation and discharge in the stridulation rhythm. They are structurally unlike any of the metathoracic local interneurons previously described in the Acrididae. Type 1: Unilateral interneurons in the metathoracic neuromere; soma in anterior position; arborization dorsal, in anterolateral, posterolateral, and midline regions. Type 2: Unilateral interneurons in the metathoracic neuromere; neurite with characteristic hairpin bend; soma in lateral position; arborization through the lateral neuropil region. Type 3: Unilateral interneurons in the metathoracic and abdominal neuromeres; soma anterior at the base of the connective; arborization dorsal, in anterolateral, posterolateral, and midline regions, with ladderlike branches into the abdominal neuromeres. Type 4: Symmetrically bilateral neurons; soma in ventral median position; arborization dorsal, in anterolateral, posterolateral, and midline regions. Ipsilateral branches mostly smooth, contralateral mostly varicose. Type 5: Asymmetrically bilateral neurons, soma in ventral median position; ipsilateral branches mostly smooth, contralateral mostly varicose. The ipsilateral branches in particular penetrate all layers of the ganglion. The main arborizations of interneurons of types 1 and 4, and to some extent those of types 3 and 5, occupy the same region, which extends very far dorsally into the vicinity of the median and lateral tracts. There are additional antero- and posterolateral branches in the metathoracic neuromere, in positions where in principle they can overlap with the arborizations of the motoneurons. The interneurons of type 2, and to some extent type 5, arborize mainly in a lateral region that also includes deeper layers of the ganglion and hence encompasses the projections of mechanoreceptive proprioceptors. The interneurons of types 1, 3, and 4 have so-called "sister" neurons, identical to the typical neurons in their metathoracic arborizations but with additional collaterals that pass into the mesothoracic ganglion.

Animal Communication↗
PubMed1991

Reidentification of larval interneurons in the pupal stage of the tobacco hornworm, Manduca sexta.

The abdominal prolegs are the primary locomotory appendages of Manduca sexta larvae. After the prolegs are lost at pupation, some of the proleg motoneurons die while the survivors are respecified to carry out different functions in the adult moth. As a first step toward investigating the process of functional respecification at the synaptic level, we searched for larval interneurons that affected the activity of proleg motoneurons, and followed these interneurons into the pupal stage. Interneurons were judged to be individually identifiable based on their effects on proleg motoneuron activity and their anatomical features. Seven larval interneurons were identified and placed in five physiological classes based on their effects on proleg motoneurons: ipsilateral excitors, contralateral excitors, ipsilateral inhibitors, contralateral inhibitors, and bilateral inhibitor-excitors. Four of the larval interneurons produced apparently monosynaptic postsynaptic potentials in proleg motoneuron. Of the five larval interneurons that were reidentified in the early pupal stage, two showed minor but consistent structural modifications from the larval stage. Interneurons that produced unitary postsynaptic potentials in larval motoneurons continued to do so in pupal motoneurons. These studies demonstrate that individually identified interneurons can be followed through the larval-pupal transformation, during the initial stages of motoneuron respecification.

Action Potentials↗
PubMed1993

Intersegmental ascending interneurons controlling uropod movements of the crayfish Procambarus clarkii.

The premotor effects of intersegmental ascending interneurons upon uropod motor neurones in the crayfish Procambarus clarkii (Girard) are examined with intracellular recording and staining techniques. We show that many ascending interneurones can affect the activity of the antagonistic opener and closer motor neurones in the terminal ganglion. Based upon soma position, ascending interneurones are divided into three groups of rostral, medial, and caudal interneurones. Twenty-four ascending interneurones are characterized physiologically according to their inputs from the tailfan and their output effects on the uropod motor neurones of both sides. Each interneurone is identifiable as a unique individual by means of overall shape, soma position, number of main branches, the commissure in which primary neurites cross the midline, axon position in the 5th-6th abdominal connective and physiological responses. They are classified into six classes; coactivating, coinhibiting, reciprocally closing, reciprocally opening, variably effective, and not effective interneurones, according to their premotor effects on the uropod motor neurones. These ascending interneurones seem to act as multifunctional units conveying sensory information from the tailfan to the anterior abdominal ganglia and, at the same time, influencing the uropod motor pattern in the terminal abdominal ganglion.

Animals↗
PubMed2002

Developmental expression of potassium-channel subunit Kv3.2 within subpopulations of mouse hippocampal inhibitory interneurons.

The developmental expression of the voltage-gated potassium channel subunit, Kv3.2, and its localization within specific mouse hippocampal inhibitory interneuron populations were determined using immunoblotting and immunohistochemical techniques. Using immunoblotting techniques, the Kv3.2 protein was weakly detected at postnatal age day 7 (P7), and full expression was attained at P21 in tissue extracts from homogenized hippocampal preparations. A similar developmental profile was observed using immunohistochemical techniques in hippocampal tissue sections. Kv3.2 protein expression was clustered on the somata and proximal dendrites of presumed inhibitory interneurons. Using double immunofluorescence, Kv3.2 subunit expression was detected on subpopulations of GABAergic inhibitory interneurons. Kv3.2 was detected in approximately 100% of parvalbumin-positive interneurons, 86% of interneurons expressing nitric oxide synthase, and approximately 50% of somatostatin-immunoreactive cells. Kv3.2 expression was absent from both calbindin- and calretinin-containing interneurons. Using immunoprecipitation, we further demonstrate that Kv3.2 and its related subunit Kv3.1b are coexpressed within the same protein complexes in the hippocampus. These data demonstrate that potassium channel subunit Kv3.2 expression is developmentally regulated in a specific set of interneurons. The vast majority of these interneuron subpopulations possess a "fast-spiking" phenotype, consistent with a role for currents through Kv3.2 containing channels in determining action potential kinetics in these cells.

Animals↗
PubMed1984

Abdominal positioning interneurons in crayfish: projections to and synaptic activation by higher CNS centers.

Intracellular recording, stimulation, and Lucifer dye injections were used to characterize abdominal positioning interneurons from the neuropile of the second through sixth abdominal ganglia of the crayfish, Procambarus clarkii. Motor outputs of these cells were recorded with extracellular electrodes placed on various flexion and extension roots along the nerve cord. In an effort to assess the functional relationships between the postural interneurons in the abdomen and those known to exist in the circumesophageal connectives ( CECs ), a stimulus pulse train was delivered to each of the CECs while monitoring the intracellular responses of the impaled interneurons. Abdominal positioning interneurons were grouped into four general categories based on their responses to CEC stimulation: 1) those that projected their axons directly through the CECs ; 2) those that were remotely activated to spiking; 3) those locally activated to produce EPSPs or IPSPs; and 4) those that were not affected by CEC stimulation. The majority of abdominal positioning interneurons encountered in this study evoked flexion (N = 82), with relatively fewer evoking extension (N = 29). A major difference appeared between the two classes. Whereas 39% of the flexion interneurons had axons coursing to the brain, only 7% of the axons of extension interneurons coursed rostrally beyond the thoracic level. Finally, the large majority of those flexion and extension interneurons that lacked processes in the CEC received synaptic inputs at various levels along the lower CNS from other CEC neurons. Thus, control of abdominal positioning involves neurons at all levels in the CNS - some sequentially organized, others forming "through" pathways, but all with multiple input sites.

Action Potentials↗
PubMed1992

The paired domain-containing nuclear factor pax[b] is expressed in specific commissural interneurons in zebrafish embryos.

The zebrafish paired box (Pax) genes are expressed in the early neural tube and are thought to be transcription factors that regulate the differentiation of cells in the central nervous system (CNS). The protein product of one of these Pax genes, pax[b], is detectable as a nuclear antigen in all the regions of the embryo that transcribe the gene including the posterior midbrain, the nephritic primordium, the Wolffian duct, the optic stalk, and, in specific neurons, in the hindbrain and spinal cord. The timing and pattern of axonal outgrowth by the early pax[b]-positive neurons suggest that they are the commissural secondary ascending (CoSA) interneurons in the spinal cord; the primary commissural interneurons (MiD2c and MiD3c) in hindbrain rhombomeres mi2 and mi3; and a previously unclassified set of commissural interneurons that we termed the commissural caudalrhombomere ascending (CoCaA) interneurons in the caudal hindbrain. In contrast, the Mauthner interneurons do not express pax[b] early in development. Shortly after the appearance of the first pax[b]-positive interneurons, additional nuclei adjacent to the first pax[b]-positive interneurons become pax[b] positive. This pattern of expression suggests that the pax[b] protein may be involved in determining the identity of specific commissural interneurons.

3,3'-Diaminobenzidine↗
PubMed1988

Ultrastructure of stratum lacunosum-moleculare interneurons of hippocampal CA1 region.

Intracellular recordings were obtained from nonpyramidal neurons (interneurons) in stratum lacunosum-moleculare (L-M) of the CA1 region of guinea pig hippocampal slices. These interneurons had response characteristics that distinguish them from pyramidal cells and other interneuron types: the L-M neurons had relatively broad action potentials with large spike afterhyperpolarizations, high input resistance and little spike-firing adaptation, and low spontaneous activity. Lucifer Yellow (LY) and horseradish peroxidase (HRP) were injected intracellularly into physiologically identified L-M interneurons, and the cells were characterized morphologically using light and electron microscopy. L-M somata were fusiform-shaped (15 x 25 micron), had multiple processes, and were located at the border between stratum (str.) lacunosum-moleculare and str. radiatum. L-M dendrites coursed through str. lacunosum-moleculare and projected into str. radiatum. L-M axons made axodendritic synaptic contacts primarily in str. lacunosum-moleculare and str. radiatum, but also in str. moleculare of the dentate gyrus. These axodendritic synaptic contacts were made onto spiny dendritic processes (presumably pyramidal cell and granule cell dendrites) and onto aspinous dendrites (presumably interneuron dendrites), and appeared to be of the symmetric type (type 2), characteristic of inhibitory synapses. In separate groups of animals, selective lesions were made of afferents to the CA1 and dentate regions of hippocampus, and subsequent degeneration of contacts and L-M interneuron somata and dendrites was examined at the ultrastructural level. Fibers originating from contralateral and ipsilateral CA3 region, and from ipsilateral entorhinal cortex, were found to make synaptic contact onto presumed L-M interneurons. Degenerating terminals appeared to be of the asymmetric type (type 1), characteristic of excitatory synapses. These morphological data are consistent with electrophysiological results showing that L-M interneurons can mediate feedforward inhibition of CA1 pyramidal cells.

Action Potentials↗
PubMed1989

Evidence for respiratory interneurones in the C3-C5 cervical spinal cord in the decorticate rabbit.

In mammals, it has long been considered that the bulbo-spinal inspiratory drive provided a direct (monosynaptic) excitation of phrenic motoneurones (Phr Mns). Although such connections have been demonstrated, recent indirect data strongly suggested that the main inspiratory drive is polysynaptic. We tried to directly demonstrate relay respiratory interneurones at the C3-C6 spinal cord level where the Phr Mn pool is located. The experiments were performed on decorticate, unanaesthetized, bilaterally vagotomized and curarized rabbits and the firing pattern of spinal interneurones was compared to the phrenic bursting. Dorsally and dorso-medially to the Phr Mn pool, different classes of inspiratory (54%) and expiratory (46%) interneurones could be identified in the ventral horn. Three classes of inspiratory interneurones were characterized and classified as "I all" (26%), "I late" (43%) and "I tonic" (29%) according to the terminology used by other authors for the bulbospinal inspiratory neurones which drive the spinal respiratory motoneurones. The expiratory interneurones could also be divided into 3 classes: "E all" (48%), "E late" (10%) and "E tonic" (41%). This first direct evidence of inspiratory interneurones at the C3-C6 spinal cord levels can account for the major polysynaptic excitation of the Phr Mns while the presence of numerous expiratory interneurones at this level suggests a polysynaptic bulbo-spinal inhibitory action onto the Phr Mns. These classes of inspiratory and expiratory interneurones did not always coincide with the bulbo-spinal classes of neurones described elsewhere.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1976

Types of interneurons and their participation in the neuronal network of the medial geniculate body.

Three different types of interneurons can be separated in the Golgi picture, and many of their details can be identified under the electron microscope, in the medial geniculate body (MGB) of the cat: (1) typical short axon Golgi II. cells of the thalamic type, (2) somewhat larger Golgi type II cells with medium range axon, and (3) spidery neurogliform short axon cells. The most distinctive features of the two first types (1) and (2) are their irregular drumstick shape appendages, increasing in number as well as in length and irregularity of their stalks towards the periphery of the dendrites. These appendages form the vast majority of synaptic profiles in the aggregations of synaptic neuropil (glomeruli) of the nuclei, and they are both presynaptic and postsynaptic by the usual standards applied for the evaluation of the polarity of synapses. The characteristic beaded dendrites of the (3) neurogliform cell type can be recognised particulary easily in the electron microscopic picture. They are both presynaptic and postsynaptic in structural polarity. All identified process profiles of interneurons contain flattened (F-type) or pleomorphic synaptic vesicles. Membrane contacts, in which the interneurons appear to be presynaptic are either of the symmetric (Gray type II) or of an intermediate type. The membrane contacts of postsynaptic portions of the interneurons are usually of the asymmetric type (Gray type I) and the presynaptic profiles contain round (R-type) vesicles. The larger one have been shown already earlier to be derived from specific sensory (inferior collicular) afferents, while many of the smaller ones could be identified in the present study as being derived from cortico-geniculate descending pathways, arising from the auditory areas. Some of the synaptic contacts of the interneurons are apparently derived from other interneurons, the presynaptic profiles being often equivocal or more likely of axonal origin (all interneurons have clear axons in the Golgi picture). The occurrence of three distinct types of interneurons--probably all of inhibitory nature--the complexity in synaptic arrangement, and more particularly in the dendritic linkage of numerous synaptic sites does not favour such simple explanations as surround inhibition by forward or by backward inhibition, but suggests more sophisticated modes of impulse processing in the MGB.

Animals↗
PubMed1988

Identification of X versus Y properties for interneurons in the A-laminae of the cat's lateral geniculate nucleus.

Roughly 25% of the neurons in the A-laminae of the cat's lateral geniculate nucleus are local interneurons, while the remaining 75% are relay cells that project to the visual cortex. The interneurons form the focus of our study. The relay cells are either X or Y cells and are thereby integral links in the parallel and independent retino-geniculo-cortical X and Y pathways. Little is known about the response properties of interneurons, largely because it is difficult to identify them clearly during electrophysiological recording. However, they can be identified by morphological criteria. We thus studied their response properties by recording intracellularly from geniculate neurons to characterize them and then injecting them with horseradish peroxidase (HRP); the HRP labeling subsequently allowed us to distinguish relay cells from interneurons. In this manner, we studied 171 relay cells (83 X and 88 Y) and 15 interneurons. The response properties tested for each of the interneurons were indistinguishable from those of the relay X cells. We conclude that these interneurons are directly innervated by retinogeniculate X axons and are firmly embedded in the X pathway. We found no evidence for interneurons in the Y pathway.

Action Potentials↗
PubMed1989

Abdominal positioning interneurons in crayfish: participation in behavioral acts.

Premotor interneurons involved in the abdominal positioning behaviors of the crayfish, Procambarus clarkii, were studied intracellularly, along with motoneuron activity, in semi-intact preparations during episodes of fictive behavior. Each impaled cell was tested by injecting depolarizing current and examining the motor output. If a response was evoked then the cell was classified as a flexion-producing interneuron (FPI), extension-producing interneuron (EPI) or mixed output interneuron (MOI). A platform drop/rise procedure was then used to elicit abdominal extension-like and flexion-like responses. Interneurons that were active during positioning behavior were silenced by hyperpolarization to determine their contribution in generating the underlying motor program. The data were used to assess the degree of participation of these interneurons in abdominal positioning behavior. Fewer than half of the FPIs, EPIs and MOIs became active during the behavioral episodes. Strength of response to depolarizing current was not correlated with the probability that a cell would fire during behavior. Hyperpolarization tests showed that typical FPIs, EPIs and MOIs were only responsible for a small part of the overall motor output. Also, interneurons, regardless of their FPI or EPI classification, were often observed to fire during both flexion-like and extension-like behaviors. Responses of FPIs, EPIs and MOIs to repeated platform movements suggest that these cells may fire according to a probability distribution depending on: (1) strength of the stimulus; (2) location of the stimulus; (3) location of the interneuron. Most identified cells could not readily be assigned to a specific behavior except for the 'T' cell type, which seems intimately involved in most flexion behaviors. The results of this study support the hypothesis that there are few if any 'command neurons', as defined by Kupfermann and Weiss (1978), in the crayfish abdominal positioning system. Abdominal positioning behavior, therefore, is probably under the control of a large network of cells each contributing a small part to the overall motor output.

Abdominal Muscles↗
PubMed1986

A study of the connection between the interneuron initiating pacemaker activity in a bursting neuron and the bursting neuron of the snail Helix pomatia.

The connection between an interneuron initiating pacemaker activity in the bursting RPa1 neuron and the bursting neuron itself (Pin and Gola, 1983) has been analyzed in the snail Helix pomatia. Prolonged depolarization of the interneuronal membrane produced in it a series of action potentials as well as a parallel initiation or enhancement of bursting activity in the RPa1 neuron. If the discharge in the interneuron was evoked by short current pulses of threshold amplitude, no bursting activity was seen in the RPa1 neuron. However, short stimuli delivered on the background of subthreshold depolarization of the interneuronal membrane produced bursting activity in the RPa1 neuron. Under voltage-clamp conditions a slow inward current could be recorded in the RPa1 neuronal membrane after stimulation of the interneuron with a latency of about 2 sec. Short shifts of the holding potential in the hyperpolarizing direction at the maximum of this current produced a transient outward current. Replacement of extracellular Ca2+ by Mg2+ ions, as well as addition of 1 mM CdCl2 to the external solution, prevented the response to the interneuronal stimulation in the RPa1 neuron. Electron microscopic investigation of the interneuron has shown the abundance of Golgi complexes in its cytoplasm with electron-dense granules in their vicinity. It is concluded that the connection between the interneuron and the bursting neuron is of chemical origin, based on secretion by the former of some substances which activate at least two types of ionic channels in the membrane of the RPa1 neuron.

Action Potentials↗