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 163 records · Page 9Linked to original sources
PubMed2004

Calbindin-containing interneurons are a target for VIP-immunoreactive synapses in rat primary somatosensory cortex.

Inhibitory interneurons in cerebral cortex are morphologically and physiologically extremely heterogeneous. This greatly interferes with an understanding of their functions. Progress has been made by classifying these neurons with the aid of molecular markers, e.g., neuropeptides or calcium-binding proteins, which are reliably expressed by certain subpopulations. We have used this approach to demonstrate an output of a subpopulation of cortical interneurons which express vasoactive intestinal polypeptide (VIP). By double immunostaining and correlated light and electron microscopy, we show that calbindin (CB)-containing interneurons located in layers II-VI of rat barrel cortex are targets of symmetric VIP-immunoreactive synapses. All CB-immunoreactive interneurons showed numerous contacts of VIP boutons on proximal and distal dendritic segments. A great majority of CB-immunoreactive interneurons (214/222) displayed such close appositions with VIP boutons on their soma as well. Quantification revealed that the number of VIP-immunoreactive boutons on CB-immunoreactive somata and dendrites of specified order is comparable for the different cortical layers. In conclusion, all calbindin-containing cortical interneurons seem to be under direct influence of other GABAergic interneurons expressing the peptide VIP. An indirect functional consequence of this may be disinhibition of pyramidal cells, which are considered the major target of calbindin interneurons. However, since the examined types of interneurons are intricately embedded in networks of yet different interneurons, the outcome of these multiple inhibitory interactions is likely to be less simplistic. It may be related to the timing of pyramidal cell discharge within and across layers of cortical columns.

Animals↗
PubMed2001

Quantitative analyses of anatomical and electrotonic structures of local spiking interneurons by three-dimensional morphometry in crayfish.

We quantitatively investigated the three-dimensional structure of the dendrites of local spiking interneurons using a confocal laser scanning microscope in the terminal abdominal ganglion of crayfish. We also studied their passive membrane properties electrophysiologically using the single-electrode current clamp techniques to analyze their electrotonic structure. All of the local spiking interneurons examined in this study lacked distinctive axonal structure and had a monopolar cell body that was connected with a fine primary process to a thick main segment. Numerous fine secondary processes projected from the main segment in the ganglionic neuropile. The average anatomical length of a secondary process from the main segment to its terminal was 261.9 +/- 15.2 microm. The average input resistance and membrane time constant of local spiking interneurons, obtained from their voltage responses to intracellular injection of step current pulses in the main segment, were 15.2 +/- 1.6 MOmega and 13.9 +/- 1.9 msec, respectively. Calculation of the electrotonic length of dendritic processes based on morphological and physiological data obtained in this study revealed that the average electrotonic length of secondary processes in local spiking interneurons was significantly longer than in local nonspiking interneurons, although both types of local interneurons showed apparently similar anaxonic structure. The steady-state voltage attenuation factors for the secondary processes of local spiking interneurons were significantly greater than those of local nonspiking interneurons in both centrifugal and centripetal directions. The larger electrotonic structure of local spiking interneurons compared to that of nonspiking interneurons appears to be compensated for by their excitable dendritic membrane.

Action Potentials↗
PubMed2006

Novel interneuronal network in the mouse posterior piriform cortex.

The neural circuits of the piriform cortex mediate field potential oscillations and complex functions related to integrating odor cues with behavior, affective states, and multisensory processing. Previous anatomical studies have established major neural pathways linking the piriform cortex to other cortical and subcortical regions and major glutamatergic and GABAergic neuronal subtypes within the piriform circuits. However, the quantitative properties of diverse piriform interneurons are unknown. Using quantitative neural anatomical analysis and electrophysiological recording applied to a GAD65-EGFP transgenic mouse expressing GFP (green fluorescent protein) under the control of the GAD65 promoter, here we report a novel inhibitory network that is composed of neurons positive for GAD65-EGFP in the posterior piriform cortex (PPC). These interneurons had stereotyped dendritic and axonal properties that were distinct from basket cells or interneurons expressing various calcium-binding proteins (parvalbumin, calbindin, and calretinin) within the PPC. The GAD65-GFP neurons are GABAergic and outnumbered any other interneurons (expressing parvalbumin, calbindin, and calretinin) we studied. The firing pattern of these interneurons was highly homogenous and is similar to the regular-spiking nonpyramidal (RSNP) interneurons reported in primary sensory and other neocortical regions. Robust dye coupling among these interneurons and expression of connexin 36 suggested that they form electrically coupled networks. The predominant targets of descending axons of these interneurons were the dendrites of Layer III principal cells. Additionally, synapses were found on dendrites and somata of deep Layer II principal neurons and Layer III basket cells. A similar interneuronal subtype was also found in GAD65-EGFP-negative mouse. The extensive dendritic bifurcation at superficial lamina IA among horizontal afferent fibers and unique axonal targeting pattern suggests that these interneurons may play a role in direct feedforward inhibitory and disinhibitory olfactory processing. We conclude that the GAD65-GFP neurons may play distinct roles in regulating information flow and olfactory-related oscillation within the PPC in vivo.

Animals↗
PubMed1988

Responses of spiking local interneurones in the locust to proprioceptive signals from the femoral chordotonal organ.

The responses of spiking local interneurones of a ventral midline population in the metathoracic ganglion of the locust, Schistocerca gregaria, to controlled movements of a proprioceptor, the femoral chordotonal organ (FCO) in a hindleg, were revealed by intracellular recording. Afferents from the FCO which signal specific features of the movement or angle of the femoro-tibial joint, can make direct excitatory synapses with particular interneurones in this population (Burrows 1987a). Some interneurones in this population are excited only by flexion, some only by extension, but others by both flexion and extension movements of the femoro-tibial joint. Interneurones excited by one direction of movement may be either unaffected, or inhibited by the opposite movement. The balance between excitation and inhibition is determined by the range over which the movement occurs, and can increase the accuracy of a representation of a movement. The response of some interneurones has tonic components, so that the angle of the joint over a certain range is represented in the frequency of their spikes. Different interneurones respond within different ranges of femoro-tibial angles so that information about the position of the joint is fractionated amongst several members of the population. These interneurones respond to repetitive movements, similar to those used by the locust during walking, with bursts of spikes whose number and frequency are determined by the repetition rate and amplitude of the movement. A brief movement of the FCO may induce effects which persist for many seconds and outlast the changed pattern of afferent spikes. The sign of such an effect depends upon the preceding history of stimulation. Other interneurones respond only to movement so that their response is more phasic. The velocities to which they respond fall within the range of those generated by twitches of the flexor and extensor tibiae muscles and the movements of the tibia during locomotion. Some interneurones respond only to a specific range of velocities because they are inhibited by all other movements. Some interneurones respond to repetitive movements with reliable bursts of spikes, whilst in others the frequency of spikes may be raised but may contain no cyclical information.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Morphological and physiological characterization of individual olfactory interneurons connecting the brain and eyestalk ganglia of the crayfish.

1. In order to understand the functional organization of the crustacean olfactory system, we are using intracellular recording and staining techniques to correlate the structure and function of single, odorant-sensitive interneurons in the brain of the crayfish Procambarus clarkii. We describe here the anatomy and physiology of interneurons that connect the brain with the medullae terminales or other eyestalk ganglia. 2. All of the interneurons in our study are at least third-order olfactory neurons (second-order olfactory interneurons) because they respond to chemostimulation of the olfactory organ (the antennules) but do not branch in the olfactory lobe (the neuropil to which primary olfactory receptor cells of the antennules project). 3. Much of the central nervous system, including the three main divisions of the brain (protocerebrum, deuterocerebrum, tritocerebrum) and the medullae terminales, are involved in integrating olfactory or multimodal (including olfactory) information, since these areas contain neurites of olfactory interneurons. Previous studies have indicated that regions involved in such processing include the olfactory lobes and accessory lobes of the deuterocerebrum, and regions I, II, IV, and VII (in some species) of the medullae terminales. Our results show that also prominent among regions involved in olfactory or multimodal (including olfactory) integration are the anterior and posterior optic neuropils of the protocerebrum, the lateral and medial antennular neuropils of the deuterocerebrum, the tegumentary neuropils and the antennal neuropils of the tritocerebrum, and neuropils III, VI, XII of the medullae terminales. 4. These olfactory interneurons were sensitive to chemostimulation (unimodal), chemo- and mechanostimulation (bimodal), or chemo-, mechano-, and photostimulation (trimodal). Responses could be excitatory or inhibitory, even for a given neuron. Morphologically complex interneurons (those having bilateral branching) were more likely to have complex response characteristics (trimodal sensitivity) than were morphologically simpler interneurons (those having unilateral branching). Olfactory interneurons with a soma in the medulla terminalis showed the most complex response profiles: they were trimodal, and were exicted by odorants but were inhibited by touch and/or light. This finding suggests that these are complex, high order interneurons. 5. Our studies reveal that olfactory and other sensory information is transmitted between the brain and the medullae terminales (and possibly other eyestalk ganglia) by a coactivated, parallel array of structurally and functionally diverse neurons.

Action Potentials↗
PubMed1986

Frequency coding of waterborne vibrations by abdominal mechanosensory interneurons in the crayfish, Procambarus clarkii.

Nine identified interneurons that originate in the 6th abdominal ganglion were studied with intracellular techniques while activating the receptors presynaptic to them with coherent water vibrations of precisely controlled amplitude and frequency. Each of the interneurons showed a characteristic response to different stimulus frequencies that was consistent from animal to animal. As a first approximation, the cells were categorized as low pass, broad band, and high pass interneurons. Two interneurons classified as low pass interneurons (LPIs) have low thresholds to waterborne vibrations below 100 Hz, are inhibited by stimuli above 100 Hz, and respond maximally to 30 Hz stimuli. Three interneurons classified as broad band interneurons (BBIs) respond maximally to stimuli from 30-60 Hz, but also respond well to oscillations as low as 1 Hz and as high as 80 Hz. This class is heterogeneous, spanning the range between low pass and high pass interneurons. Two interneurons classified as high pass interneurons (HPIs) have very high thresholds to water oscillations below 6 Hz. They respond best to 60 Hz oscillations, above which their responsiveness sharply declines, although they continue to respond weakly up to 400 Hz. Two other neurons, also classified as HPIs, responded with relatively few spikes to the stimuli we used. As a result, they do not show a clear peak responsiveness to a particular stimulus frequency.

Animals↗
PubMed1986

Postural interneurons in the abdominal nervous system of lobster. II. Evidence for neurons having both command and driver roles.

The nature of the synaptic relationship between 7 identified postural interneurons and 5 pairs of superficial motoneurons was examined by obtaining dual intracellular recordings from interneuron-motoneuron pairs in the lobster 2nd abdominal ganglion. For six different interneuron-motoneuron pairs EPSPs recorded from motoneurons occurred with a short (1 to 3 ms) fixed latency following each presynaptic spike recorded from the interneuron. This suggests that there is a monosynaptic relationship between these interneurons and motoneurons. Monosynaptic pathways accounted for 27% of all excitatory connections. Preliminary evidence indicates that the monosynaptic potentials are mediated by an excitatory chemical synapse since: all IPSPs occurred with latencies greater than 5 ms, there was no evidence for electrical coupling, and one of the interneurons produced facilitating PSPs. A majority of all monosynaptic connections were made by two of the flexion producing interneurons (FPIs), 201 and 301. The synaptic outputs of these FPIs were similar in that both made monosynaptic connections with a different bilaterally homologous pair of motoneurons. Both also produced larger EPSPs and more vigorous spiking in contralateral members of the bilateral motoneuron pairs. A previous study demonstrated that interneurons 201 and 301 are the only postural interneurons yet identified that express motor programs indistinguishable from command neurons. Taken together, these results suggest that certain intersegmental interneurons share properties with command neurons and driver neurons, and that there may not be a sharp morphological or functional distinction between these two cell types.

Abdomen↗
PubMed1986

Postural interneurons in the abdominal nervous system of lobster. III. Pathways mediating intersegmental spread of excitation.

The multisegmented abdomen of crayfish and lobster assumes a variety of postures as components of different behavioral acts. Experimentally these postures can be maintained by activating any of a number of premotor positioning interneurons. The pathways by which the motor output in two or more segments is coordinated were here investigated for a small group of identified postural interneurons whose somata lie in the 2nd abdominal ganglion (A2). Stimulation of all postural interneurons examined evokes a motor output in other abdominal ganglia through which the axon of the neuron passes as well as in the ganglion of origin (ganglion containing the neuron's cell body). The spread of motor excitation away from the originating ganglion occurs via two general pathways. In the first pathway connections to postural motoneurons are made directly by processes of the postural interneuron which pass into ganglia distal to the originating ganglion. Examples of this are shown for two flexion producing interneurons (FPIs) 201 and 301. Each of these FPIs makes monosynaptic connections with motoneurons in A2 and with a homologous set of motoneurons in A3. All postural interneurons fired a set of corollary discharge interneurons (CDIs) whose activities were recorded from the abdominal connectives. Two FPIs, 202 and 301, and a third interneuron, 503, produced motor outputs in ganglia to which they did not project. The motor specificity established in A2 by stimulation of FPIs 202 and 301 (whose axons pass caudally) was preserved in more rostral ganglia, such as A1. Therefore, different sets of CDIs can be specifically recruited to spread the same motor program that is initiated in the originating ganglion to ganglia that do not receive projections from the stimulated postural interneuron. CDIs, in addition, have the capacity to elicit motor programs in distal ganglia that are markedly different from that expressed in the ganglion of origin. For example, although 503 produced an inhibitory output in the abdominal ganglia that it innervated (A1 and A2), a flexion response was generated by it in more caudal ganglia. The caudal flexion response was mediated in part through a monosynaptic activation of FPI 201 and through other unidentified CDIs. Thus, the interneuronal circuitry for postural control is composed of numerous components, some of which have regional control over different portions of the abdominal nerve cord. Depending upon the required movement, select components are coactivated, either serially or in parallel, to effect a variety of spatially distinct positions.

Abdomen↗
PubMed2004

Synaptic interactions between nonspiking local interneurones in the terminal abdominal ganglion of the crayfish.

Nonspiking local interneurones are the important premotor elements in arthropod motor control systems. We have analyzed the synaptic interactions between nonspiking interneurones in the crayfish terminal (6th) abdominal ganglion using simultaneous intracellular recordings. Only 15% of nonspiking interneurones formed bi-directional excitatory connections. In 77% of connections, however, the nonspiking interneurones showed a one-way inhibitory interaction. In these cases, the presynaptic nonspiking interneurones received excitatory synaptic inputs from the sensory afferents innervating hairs on the surface of the uropods and the postsynaptic nonspiking interneurones received inhibitory synaptic inputs that were partly mediated by the inputs to the presynaptic nonspiking interneurones. The membrane hyperpolarization of the postsynaptic nonspiking interneurones mediated by the presynaptic nonspiking interneurones was reduced in amplitude when the hyperpolarizing current was injected into the postsynaptic interneurones, or when the external bathing solution was replaced with one containing low calcium and high magnesium concentrations. The role of these interactions in the circuits controlling the movements of the terminal appendages is discussed.

Abdomen↗
PubMed1998

Consistency of interneuronal group formation in response to stimulation of identified cells.

In crayfish stimulation of abdominal positioning interneurons (APIs) recruits other interneurons producing various abdominal movements. We investigated whether: (1) the same API from different preparations activated a similar number or group of interneurons, (2) different APIs activated different groups, and (3) repeated stimulation of an API consistently affected a similar set of interneurons. To quantify the similarities and differences of the recruited interneuronal groups we compared the number of interneurons affected, their firing frequencies, and motor outputs. Three types of APIs (Curly Q, L and T) were identified and each type was stimulated in three preparations. Our results showed that for the Curly Q and L cells, each cell type activated interneuronal groups that were statistically similar in number and firing frequency. The T cell activated interneuronal groups that were more variable. Some APIs generally provided a repeatable motor output; all did not. The interneuronal groups activated by the Curly Q, L and T cells were very different from each other. Repeated stimulation of one Curly Q cell affected similar although not identical sets of interneurons. These data suggest that repeated motor outputs could be produced by a similar but not identical group of cells.

Action Potentials↗
PubMed2001

Distribution of NADPH-diaphorase-positive ascending interneurones in the crayfish terminal abdominal ganglion.

Previous neuropharmacological studies have described the presence of a nitric oxide-cGMP signalling pathway in the crayfish abdominal nervous system. In this study we have analysed the distribution of putative nitric oxide synthase (NOS)-containing ascending interneurones in the crayfish terminal abdominal ganglion using NADPH-diaphorase (NADPHd) histochemistry. Ascending intersegmental interneurones were stained intracellularly using the fluorescent dye Lucifer yellow and the ganglia containing the stained interneurones subsequently processed for NADPHd activity. Fluorescence persisted throughout histochemical processing. These double-labelling experiments showed that 12 of 18 identified ascending interneurones were NADPHd positive. Thus many ascending interneurones that process mechanosensory signals in the terminal ganglion may contain NOS, and are themselves likely sources of NO which is known to modulate their synaptic inputs. Three clear relationships emerged from our analysis between the effects of NO on the synaptic inputs of interneurones, their output properties and their staining for NADPH-diaphorase. First were class 1 interneurones with no local outputs in the terminal ganglion, the NE type interneurones, which had sensory inputs that were enhanced by NO and were NADPHd positive. Second were class 1 interneurones with local and intersegmental output effects that had sensory inputs that were also enhanced by NO but were NADPHd negative. Third were class 2 interneurones with local and intersegmental outputs that had synaptic inputs that were depressed by the action of NO but were NADPHd positive. These results suggest that NO could selectively enhance specific synaptic connections and sensory processing pathways in local circuits.

Abdomen↗
PubMed2006

The contribution of the pleural type 12 interneuron to swim acceleration in Clione limacina.

The pteropod mollusc, Clione limacina, swims by alternate dorsal-ventral flapping movements of its wing-like parapodia. The basic swim rhythm is produced by a network of pedal swim interneurons that comprise a swim central pattern generator (CPG). Serotonergic modulation of both intrinsic cellular properties of the swim interneurons and network properties contribute to swim acceleration, the latter including recruitment of type 12 interneurons into the CPG. Here we address the role of the type 12 interneurons in swim acceleration. A single type 12 interneuron is found in each of the pleural ganglia, which contributes to fast swimming by exciting the dorsal swim interneurons while simultaneously inhibiting the ventral swim interneurons. Each type 12 interneuron sends a single process through the pleural-pedal connective that branches in both ipsilateral and contralateral pedal ganglia. This anatomical arrangement allowed us to manipulate the influence of the type 12 interneurons on the swim circuitry by cutting the pleural-pedal connective followed by a "culture" period of 48 h. The mean swim frequency of cut preparations was reduced by 19% when compared to the swim frequency of uncut preparations when stimulated with 10(-6) M serotonin; however, this decrease was not statistically significant. Additional evidence suggests that the type 12 interneurons may produce a short-term, immediate effect on swim acceleration while slower, modulatory inputs are taking shape.

Animals↗
PubMed2004

Postnatal shifts of interneuron position in the neocortex of normal and reeler mice: evidence for inward radial migration.

During development, interneurons migrate to precise positions in the cortex by tangential and radial migration. The objectives of this study were to characterize the net radial migrations of interneurons during the first postnatal week, and to investigate the role of reelin signaling in regulating those migrations. To observe radial migrations, we compared the laminar positions of interneurons (immunoreactive for GABA or Dlx) in mouse neocortex on postnatal days (P) 0.5 and P7.5. In addition, we used bromodeoxyuridine birthdating to reveal the migrations of different interneuron cohorts. To study the effects of reelin deficiency, experiments were performed in reeler mutant mice. In normal P0.5 cortex, interneurons were most abundant in the marginal zone and layer 5. By P7.5, interneurons were least abundant in the marginal zone, and were distributed more evenly in the cortical plate. This change was attributed mainly to inward migration of middle- to late-born interneurons (produced on embryonic days (E) 13.5 to E16.5) from the marginal zone to layers 2-5. During the same interval, late-born projection neurons (non-immunoreactive for GABA or Dlx) migrated mainly outward, from the intermediate zone to upper cortical layers. In reeler cortex, middle- and late-born interneurons migrated from the superplate on P0.5, to the deep cortical plate on P7.5. Late-born projection neurons in reeler migrated in the opposite direction, from the intermediate zone to the deep cortical plate. We conclude that many middle- and late-born interneurons migrate radially inward, from the marginal zone (or superplate) to the cortical plate, during the first postnatal week in normal and reeler mice. We propose that within the cortical plate, interneuron laminar positions may be determined in part by interactions with projection neurons born on the same day in neurogenesis.

Animals↗
PubMed2005

Properties of external plexiform layer interneurons in mouse olfactory bulb slices.

In the external plexiform layer (EPL) of the main olfactory bulb, apical dendrites of inhibitory granule cells form large numbers of synapses with mitral and tufted (M/T) cells, which regulate the spread of activity along the M/T cell dendrites. The EPL also contains intrinsic interneurons, the functions of which are unknown. In the present study, recordings were obtained from cell bodies in the EPL of mouse olfactory bulb slices. Biocytin-filling confirmed that the recorded cells included interneurons, tufted cells, and astrocytes. The interneurons had fine, varicose dendrites, and those located superficially bridged the EPL space below several adjacent glomeruli. Interneuron activity was characterized by high frequency spontaneous excitatory postsynaptic potential/currents that were blocked by the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione and largely eliminated by the voltage-sensitive Na+ channel blocker, tetrodotoxin. Interneuron activity differed markedly from that of tufted cells, which usually exhibited spontaneous action potential bursts. The interneurons produced few action potentials spontaneously, but often produced them in response to depolarization and/or olfactory nerve (ON) stimulation. The responses to depolarization resembled responses of late- and fast-spiking interneurons found in other cortical regions. The latency and variability of the ON-evoked responses were indicative of polysynaptic input. Interneurons expressing green fluorescent protein under control of the mouse glutamic acid decarboxylase 65 promoter exhibited identical properties, providing evidence that the EPL interneurons are GABAergic. Together, these results suggest that EPL interneurons are excited by M/T cells via AMPA/kainate receptors and may in turn inhibit M/T cells within spatial domains that are topographically related to several adjacent glomeruli.

Action Potentials↗
PubMed2005

A role for L-type calcium channels in the maturation of parvalbumin-containing hippocampal interneurons.

While inhibitory interneurons are well recognized to play critical roles in the brain, relatively little is know about the molecular events that regulate their growth and differentiation. Calcium ions are thought to be important in neuronal development and L-type voltage gated Ca(+2) channels have been implicated in activity-dependent mechanisms of early-life. However, few studies have examined the role of these channels in the maturation of interneurons. The studies reported here were conducted in hippocampal slice cultures and indicate that the L-type Ca(+2) channel agonists and antagonists accelerate and suppress respectively the growth of parvalbumin-containing interneurons. The effects of channel blockade were reversible suggesting they are not the result of interneuronal cell death. Results from immunoblotting showed that these drugs have similar effects on the expression of the GABA synthetic enzymes, glutamic acid decarboxylase65, glutamic acid decarboxylase67 and the vesicular GABA transporter. This suggests that L-type Ca(+2) channels regulate not only parvalbumin expression but also interneuron development. These effects are likely mediated by actions on the interneurons themselves since the alpha subunits of L-type channels, voltage-gated calcium channel subunit 1.2 and voltage-gated calcium channel subunit 1.3 were found to be highly expressed in neonatal mouse hippocampus and co-localized with parvalbumin in interneurons. Results also showed that while these interneurons can contain either subunit, voltage-gated calcium channel subunit 1.3 was more widely expressed. Taken together results suggest that an important subset of developing interneurons expresses L-type Ca(+2) channels alpha subunits, voltage-gated calcium channel subunit 1.2 and especially voltage-gated calcium channel subunit 1.3 and that these channels likely regulate the development of these interneurons in an activity-dependent manner.

Animals↗
PubMed2004

Plasticity of interneuronal species diversity and parameter variance in neurological diseases.

Interneuronal diversity reflects the division of labor between numerous highly specialized interneuronal species, each performing a set of specific functions in neuronal networks. The rich diversity of interneurons found in the normal healthy brain is often significantly altered in neurological and psychiatric diseases. In genetic and developmental disorders, the diversity of interneuronal networks is compromised because of disturbances in the generation, specification or migration of specific interneuronal subtypes. Following insults related to trauma and seizures, the relative abundance of interneuronal subtypes might change, and entire interneuronal species can be lost from the network. In addition to the complete or partial loss of interneuronal subgroups, heterogeneity can also be altered in more subtle ways, as a result of changes in cell-to-cell variance of a particular parameter within specific interneuronal populations. Computational and experimental studies show that alterations in cellular and synaptic GABAergic heterogeneity can significantly modulate both firing rates and network coherence, indicating that plasticity of interneuronal diversity is likely to be an important mechanistic component of malfunctioning cortical networks in many pathological states.

Animals↗
PubMed2003

Subtypes of substance P receptor immunoreactive interneurons in the rat basolateral amygdala.

Local injections of the neurotoxin SP-saporin into the basolateral amygdala (BLA) are reported to specifically lesion substance P receptor immunoreactive (SPR-IR) interneurons, and to reduce anxiety related behavior. Hence, this technique might provide a means to study how defined interneuron populations regulate neuronal activity in the BLA. However, what interneuron subgroups in the BLA might be targeted by SP-saporin lesions has not been established. This study has used dual-labeling immunofluorescence in the rat BLA to examine SPR-IR neurons for their colocalization with the calcium-binding proteins; calbindin-D28k (CB), parvalbumin (PV), and calretinin (CR); and the neuropeptides somatostatin (SOM) and neuropeptide Y (NPY). We found that all NPY-IR neurons and 45% of SOM-IR interneurons expressed SPR-IR, and that 50% and 51% of the SPR-IR interneuron population expressed NPY- and SOM-IR, respectively. Previous studies have reported that approximately a third of SOM-IR interneurons also express NPY, which suggests a large degree of overlap between the NPY, SOM and SPR expressing neurons in the BLA. We also found that the majority of SPR-IR cells were CB-IR (62%), but that these interneurons represented only 2.8% of the total CB-IR population. Moreover, SPR-IR interneurons did not express either PV-or CR- IR. Hence, SP-saporin lesions would ablate all interneurons in the BLA that contain NPY, but leave the majority of the CB-IR cells intact, and have no effect on the CR- and PV-IR populations. Consequently, these results support the use of SP-saporin lesions as a useful technique to study the role of NPY-IR interneurons in the BLA.

Amygdala↗
PubMed2003

Functional relation between interneuron input and population activity in the rat hippocampal cornu ammonis 1 area.

Inhibitory interneurons are important components of the cornu ammonis 1 (CA1) network, as they are strategically positioned to control network information transfer. We investigated in detail synaptic input to individual CA1 interneurons (mainly basket and bistratified cells) after the local circuit was activated through the Schaffer-Commissural pathway and related this input to the population activity of the pyramidal cells. Synaptic responses were measured under whole-cell voltage clamp and population activity was determined from local field potentials. The synaptic input that was evoked in CA1 interneurons fell into two distinct groups. Disynaptic input with a long latency always started after the population spike with a mean latency of 3.0+/-0.3 ms (n=22) in respect to the peak of the population spike. This type of synaptic input to the interneurons was causally linked to the occurrence and amplitude of the population spike and most likely driven by CA1 pyramidal cells. Short-latency monosynaptic input occurred 0.8+/-0.2 ms (n=18) before the peak of the population spike. Its timing was strictly linked to the stimulus and showed significantly less jitter than long-latency input. In the absence of a population spike only short-latency input could be observed. Whether an interneuron receives direct monosynaptic Schaffer input or disynaptic input from the pyramidal cell population determines when that interneuron will be recruited in the network after Schaffer collateral stimulation. In addition, we found that the relation between the strength of the synaptic input and the population activity was different for the two types of input. Short-latency monosynaptic input showed large sensitivity to input changes at stimulus intensities that evoked little activity in the pyramidal cell population. In contrast, the amplitude of the long-latency disynaptic input to the interneurons closely reflected the population activity and increased gradually with stimulus intensity. Interneurons receiving the first type of input may expand the input sensitivity of the network, while interneurons receiving the second type could be involved in overall normalization of the output of the CA1 network. Our results underscore the importance of knowledge of the input to an interneuron for the understanding of its inhibitory role in the network.

Animals↗