Interneuron

The CINs inhibit MSN output cells in the direct pathway, where D1Rs stimulate, and excite MSNs in the indirect pathway, where D2Rs inhibit (Kaneko et al., 2000).

From: Handbook of Clinical Neurology , 2019

The Brain and Spinal Cord Networks Controlling Locomotion

Larry M. Jordan , Urszula Sławińska , in Neuronal Networks in Brain Part, CNS Disorders, and Therapeutics, 2014

V1 Interneurons

V1 interneurons are all ipsilateral inhibitory interneurons, and they include all RCs and some IaINs. Near V1 interneurons have not been physiologically identified, but this class does non appear to include the inhibitory interneurons responsible for much of the hyperpolarized phase of the motoneuron LDP. Ablation or acute silencing of these neurons reduces locomotor speed, 174 merely it does non reduce the hyperpolarized phase of the LDP. It is clear that some other progenitor domain likely is responsible for other inhibitory interneuron development, because IaINs persist after V1 ablation. 175

In swimming vertebrates such as zebrafish and tadpoles, there is a simpler relationship between embryonic progenitor domains and mature categories of spinal interneurons. For instance, embryonic V1 interneurons generate one type of interneuron in zebrafish and tadpoles 176,177 just several subtypes in mammals, 178,179 including RCs and some Ia inhibitory interneurons (IaINs). Approximately 75% of V1 interneurons are neither RCs nor IaINs, and their physiological identification has not been established.

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Breathe, Walk and Chew: The Neural Challenge: Part I

Dimitri Ryczko , ... Jean-Marie Cabelguen , in Progress in Brain Inquiry, 2010

Lateral interneurons (LINs)

LINs are large cells with lateral dendrites. They are mostly nowadays in the rostral spinal cord (Rovainen, 1974a) and take an ipsilateral axon that can project caudally as far every bit the tail region of the string (Rovainen, 1974a). LINs inhibit ipsilateral CCINs (Buchanan, 1982) but have been shown in rare cases to inhibit MNs (Rovainen, 1982). These cells are directly activated by ipsilateral EINs (Buchanan and Grillner, 1987), only they too receive monosynaptic inputs from contralateral CCINs (Buchanan, 1982) and polysynaptic inputs from DCs (Rovainen, 1974a). The LINs receive excitatory descending inputs from B2–B4 Müller cells (Rovainen, 1974b). The LINs may exist involved in a propriospinal function (Grillner, 2003).

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Tangential Migration in the Telencephalon

Oscar Marín , in The Rat Nervous System (Quaternary Edition), 2015

Striatum

Cortical interneurons are not the only population of cells that migrate tangentially away from the MGE. In addition, this region produces interneurons that migrate tangentially to populate the striatum ( Marín et al., 2000). The MGE produces the three master classes of striatal interneurons: fast-spiking PV+ interneurons, depression-threshold spike SST+ interneurons, and cholinergic interneurons (Marín et al., 2000) (Fig. 5). Genetic fate mapping studies suggests that striatal interneurons ascend primarily from the ventral-most region of the MGE (pMGE5 as divers past Flames et al., 2007) and the dorsal aspect of POA (Flandin et al., 2010), while cortical interneurons derive from the remaining domains of the MGE (pMGE1-pMGE4). The pMGE5 domain include a region that was previously designated as the anterior entopeduncular area, a transition zone between the MGE and the POA.

Effigy v. Tangential migration leads to circuitous nuclear assemblies in the subpallium. The primary structures of the rodent basal ganglia, the caudoputamen nucleus (CPu) and the globus pallidus (GP), incorporate neurons derived from all three main histogenetic domains of subpallium. (A) Schematic representation of a transversal hemi-section through the telencephalon, in which the subpallial migrations of LGE, MGE and POA-derived neurons are illustrated. (B) The CPu consist of GABAergic projection neurons, which migrate radially from the LGE, and GABAergic and cholinergic interneurons, which arise through tangential migration from the MGE and, to a very minor extent, the POA. The GP primarily contains GABAergic projection neurons, most of which migrate radially from the MGE. Some projection neurons in the GP reach this construction through tangential migration from the LGE and the POA. Abbreviations: H, hippocampus; NCx, neocortex; PCX, piriform cortex.

The mechanisms controlling the tangential migration of striatal interneurons have begun to be elucidated. In contrast to cortical interneurons, striatal interneurons exercise not express Neuropilin-ane and Neuropilin-2, receptors for class Iii semaphorins. Consequently, striatal interneurons are not repelled by striatal projection neurons, as happens for cortical interneurons (Marín et al., 2001). In striatal interneurons, the postmitotic expression of Nkx2-1 is required to repress the expression of Neuropilin receptors (Nóbrega-Pereira et al., 2008). Thus, the postmitotic expression of Nkx2-ane distinguishes cortical (Nkx2-1off) from striatal (Nkx2-1on) MGE-derived interneurons.

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Neurobiology of Epilepsy

10. Jiang , ... E. Rossignol , in Progress in Brain Research, 2016

Abstract

GABAergic interneurons of the parvalbumin-positive fast-spiking basket cells subtype (PV INs) are important regulators of cortical network excitability and of gamma oscillations, involved in signal processing and cognition. Impaired development or part of PV INs has been associated with epilepsy in diverse creature models of epilepsy, also as in some genetic forms of epilepsy in humans. In this review, we provide an overview of some of the experimental data linking PV INs dysfunction with epilepsy, focusing on disorders of the specification, migration, maturation, synaptic part, or connectivity of PV INs. Furthermore, we reflect on the potential therapeutic utilize of cell-type specific stimulation of PV INs within agile networks and on the transplantation of PV INs precursors in the treatment of epilepsy and its comorbidities.

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Volume i

Joel C. Bornstein , Jaime P.P. Foong , in Physiology of the Gastrointestinal Tract (6th Edition), 2018

nineteen.3.2.2 Interneurons

Interneurons are integral parts of enteric secretomotor pathways. Several types of myenteric neurons send axons to the submucosal plexus, including ISNs. In guinea-pig ileum, three readily defined classes of myenteric interneurons supply the submucosa, ii comprise Conversation, while the other contains VIP and neuronal nitric oxide synthase (nNOS). One class of ChAT interneurons besides contains somatostatin (SOM) and may take dual functions, as SOM mediates IPSPs in VIP secretomotor neurons. 57 Other Conversation interneurons are immunoreactive for v-HT and provide input to both VIP and cholinergic secretomotor neurons. 57,84,85

At that place is less convincing evidence for submucosal interneurons. Submucosal neurons receive input from other submucosal neurons in guinea-pig ileum, 86–88 but only ISNs accept obvious synaptic connections within the plexus. VIP neurons may have thin connections with other VIP neurons. 87,89 Data from other species are defective.

The picture is even more cloudy in the colon, which contains functionally consummate circuits, 90 but whether these involve interneurons has non been determined. Similarly, whether there are interneurons connecting the layers of the human submucous plexus is unknown.

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INTERNEURONS | Backdrop of Interneurons and their Relation to Epilepsy

C.L. Torborg , C.J. McBain , in Encyclopedia of Basic Epilepsy Research, 2009

Inhibitory interneurons are cardinal regulators of network office. Loss of inhibitory tone, through inhibitory interneuron hypoexcitability or reduced synaptic efficacy, can result in network hyperexcitability, predisposing the brain to epileptiform activity. Voltage-gated potassium channels composed of the Kv3 subfamily are expressed in subsets of inhibitory interneurons and contribute to the excitability of these interneurons by shortening the elapsing of activity potentials, thus increasing firing frequency and decreasing neurotransmitter release probability. Unlike other Kv3-deficient mice, mice lacking Kv3.2 develop spontaneous seizures, suggesting that these channels are necessary for maintaining network stability. Kv3.2-containing channels are distinguished from other Kv3 channels past their sensitivity to protein kinase A (PKA) phosphorylation. Our goal is to sympathise how Kv3 channels govern interneuron excitability, how their channel role is modulated, and how their contribution to interneuron excitability leads to stabilization of network office.

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The Generation of Cortical Interneurons

R. Batista-Brito , G. Fishell , in Patterning and Cell Type Specification in the Developing CNS and PNS, 2013

26.1 Diversity of Mature Cortical Interneurons

Mature interneurons project locally within the cortex, are inhibitory, use gamma-amino-butyric-acrid (GABA) equally their primary neurotransmitter, and class type ii symmetric synapses with their targets. Interneurons provide afferent synapses onto the proximal dendritic branches, initial segment of the axon, and soma of target pyramidal neurons. Unlike excitatory cells, interneurons do not synapse onto dendritic spines of pyramidal cells only rather directly target dendritic shafts. In addition, a subset of cortical interneurons targets other inhibitory cells. Cortical interneurons are largely aspiny, and receive excitatory and inhibitory inputs onto their dendrites. Although far less numerous than the excitatory pyramidal neurons, cortical interneurons are highly diverse. Depending on the scheme of nomenclature, cortical interneurons comprise at least 15 dissimilar subtypes (mayhap as many equally 50) ( Markram et al., 2004; Petilla Interneuron Nomenclature Group et al., 2008). Hippocampal interneurons generally follow the same rules equally cortical interneurons, although the precise categories and number of specific subtypes vary (Klausberger and Somogyi, 2008). Variety of GABAergic cortical interneurons is achieved by the acquisition of a variety of different properties that contribute to their role. Interneurons were first identified and classified on the basis of their morphology. Ramon y Cajal described them as brusque axon cells, whose axons project locally. Axon morphology has been historically considered to exist a critical feature for determining interneuron subtypes. The position of the initial segment, arbor trajectory, branch metrics, and synaptic subcellular selectivity (somata, dendrites, axon, etc.) are used as typical classifiers of interneuron subtype variety (Petilla Interneuron Classification Group et al., 2008). Some other important criterion to consider regarding interneuron diverseness is the precise cortical layers and cell types that particular interneuron subtypes target. Emphasis on this feature seems reasonable, every bit the extent of an axon's ramifications will, to a great extent, determine its output domain. Dendrites (arborization polarity and co-operative metrics) and the morphology of the cell soma (shape and size) are also used for interneuron nomenclature (Petilla Interneuron Nomenclature Grouping et al., 2008). In addition, molecular markers that business relationship for many of the neuron's emergent properties, such as neuropeptides, Ca2+ proteins, ionic channels, receptors, and transporters accept been typically used for interneuron classification (Baraban and Tallent, 2004; Goldberg et al., 2005; Lau et al., 2000; Monyer and Markram, 2004; Rudy and McBain, 2001). Comprehensive subtype analysis based on gene expression has become possible with the appearance of microarray technology (Okaty et al., 2009; Sugino et al., 2006).

The other two criteria widely utilized for interneuron classification are their intrinsic firing properties, and their synaptic interactions, namely, their inputs, the target specificity of their output, and their postsynaptic responses (Somogyi and Klausberger, 2005; Somogyi et al., 1998). The intrinsic and synaptic properties are both clearly adamant by the molecular composition of the prison cell such equally channels and other signaling molecules, also as by the ramification of their processes. Therefore, it is not surprising that there is a stiff correlation between the intrinsic electrophysiology and synaptic responses of an interneuron, and its molecular markers and morphology. However, this correlation is non absolute, and one cannot a priori predict the functional characteristics of an interneuron solely on the basis of its molecular signature. Thus, to both classify and appraise the function of a certain interneuron subtype, it is essential to have a multifaceted approach, including as many features as possible (Petilla Interneuron Nomenclature Grouping et al., 2008).

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Tangential Migration

T.J. Petros , S.A. Anderson , in Cellular Migration and Formation of Neuronal Connections, 2013

twenty.2.1.one Origins and Migratory Routes

GABAergic interneurons are a heterogeneous population of cells that brand up about twenty–30% of cortical neurons and by and large class inhibitory synaptic connections on excitatory projection neurons or other interneurons. Interneurons can be classified on the basis of their morphological, neurochemical, and electrophysiological features ( Petilla Interneuron Classification Group, 2008).

Different the projection neurons that are born inside the cortex, GABAergic interneurons migrate long distances from the subpallium. Initial studies utilized DiI labeling to demonstrate a large population of neurons migrating tangentially into the cortex from the subpallium, more than specifically from evaginations on the ventricular surface known every bit the ganglionic eminences (GEs) (Effigy 20.1; de Carlos et al., 1996; Tamamaki et al., 1997). Analyses of Dlx1 −/−;Dlx2 −/− mice revealed that these migrating cells were probable GABAergic interneurons (Anderson et al., 1997). Technical advances allowed later studies to confirm that most cortical interneurons migrated from the medial GE (MGE), whereas the lateral GE (LGE) gives ascension mainly to olfactory interneurons and striatal projection neurons (Figure 20.ii; Anderson et al., 2001; Lavdas et al., 1999; Wichterle et al., 1999, 2001), both of which are GABAergic. Additionally, the caudal GE (CGE) gives ascension to cortical interneurons that preferentially migrate to more than caudal regions of the telencephalon (Figure 20.ii; Anderson et al., 2001; Nery et al., 2002; Yozu et al., 2005). CGE-derived interneurons requite rise mainly to vertically oriented, calretinin-expressing interneurons (Barrel et al., 2005; Xu et al., 2004), also as VIP-, reelin-, and some NPY-expressing interneuron subgroups (Miyoshi et al., 2010). More than recent findings identified the preoptic area as another source of tangentially migrating cortical interneurons (Gelman et al., 2009; Figure 20.ane; encounter Batista-Brito and Fishell 2009 and Welagen and Anderson 2010, for a review of cortical interneuron origins).

Figure xx.ii. Schematic depicting tangential migration routes of olfactory interneurons from the LGE (red) through the rostral migratory stream (RMS) into the olfactory bulb (OB), and cortical interneurons from the MGE (light-green) and CGE (blue) that populate the entire cognitive cortex.

Interneuron progenitors follow two principal routes from the MGE into the cortex: before built-in cells (E12–E14) primarily migrate through the marginal zone (MZ) of the cortex, but a more prominent band of migrating interneurons is observed in the intermediate zone (IZ)/SVZ after in the development (E14–E16) (Figure twenty.iii; reviewed in Marín and Rubenstein, 2003; Métin et al., 2006). From these 2 streams, interneurons so enter the cortical plate, likely using the radial glia fibers every bit scaffolding. Although migrating interneurons are somewhat dispersed within the streams, they may contact each other to influence migration patterns, as interneurons increment branching dynamics upon contacting each other in culture (Sang and Tan, 2003). Interestingly, the medial portion of the cortex is inhibitory to migrating neurons in vitro at E12.v, and merely becomes permissive to invading interneurons at after ages (Britto et al., 2006). Whether this mechanism is utilized in vivo to command the accelerate of migrating interneurons is unclear.

Figure 20.iii. Schematic of a coronal section through the forebrain depicting the two primary pathways of tangentially migrating interneurons (blue dotted line) through the marginal zone (MZ) and intermediate zone/subventricular zone (IZ/SVZ). Interneurons exit the streams and enter the cortical plate (CP), with many interneurons diving toward VZ before ascending into the CP. Also shown are the gauge location of guidance cues and growth factors that guide migrating interneurons along their routes. The membrane-bound neuregulin-i (+) is restricted to the LGE and striatum, whereas the diffusible form of neuregulin-i is expressed along the SVZ/IZ route.

 Reproduced from Flames N, Long JE, Garratt AN, et al. (2004) Short- and long-range attraction of cortical GABAergic interneurons by neuregulin-1. Neuron 44: 251–261.

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Neuroanatomy of the Spinal Cord

Susan A. Darby , Robert J. Frysztak , in Clinical Anatomy of the Spine, Spinal Cord, and Ans (Third Edition), 2014

Dorsal horn interneurons

Interneurons in the dorsal horn play a primal office in modifying sensory information and ongoing movements, as well as controlling all reflexive movements. They form the neuronal circuitry that links sensory fibers with the tract neurons that provide the major output of the dorsal horn. Numerous studies take described the interneurons located in the superficial dorsal horn ( Todd, 2010). In that location are ii classes of interneurons: excitatory, which employ the neurotransmitter glutamine; and inhibitory, which utilize gamma-aminobutyric acid (GABA) and/or glycine equally their neurotransmitter. Since most main afferent terminals exhibit axoaxonic synapses, it has been suggested that ane part of GABAergic interneurons is to provide presynaptic inhibitory input to afferent fibers. Interneurons in lamina 2 take been classified as either islet, central, vertical, or radial on the footing of their dendritic morphology. Studies using immunocytochemistry methods indicate that the islet cells are GABAergic, radial cells are glutaminergic, vertical cells are mostly GABAergic merely can be glutaminergic and key cells which tin can be either type. An additional 30% take still to exist classified. Lamina I interneurons have been described as pyramidal, fusiform, or multipolar. Nevertheless, projection neurons are nowadays in this lamina and may have been inadvertently classified as office of the population because they have not been distinguished from the interneurons. The extensive branching of the afferent inputs to the spinal string results in simultaneous activation of many types of interneurons. The activity of these interneurons and their subsequent synapses on cells in the ventral horn (motor systems), ascending tracts (sensory perception of stimuli), descending tracts (sensitivity of motor and sensory pools), and other interneurons in the spinal cord controls the overall sensitivity and general responsiveness of all neurons in the spinal cord. The balance betwixt the firing of excitatory and inhibitory interneurons is critical in the maintenance of normal sensory office. Disruptions in the transmission from interneuronal circuits can result in allodynia (see Appendix 2) or the development and maintenance of inflammation and neuropathic pain (Todd, 2010). In addition to the input from afferent fibers, the spinal interneurons receive input from other sources including descending fibers from college centers. The superficial dorsal horn receives input from serotonergic fibers, noradrenergic fibers, and GABAergic fibers, all of which originate in different brain stalk nuclei (Todd, 2010). Additional sources that influence spinal interneurons include ventral horn alpha motor neurons, local (at the level) interneurons, brusk propriospinal neurons (from i or ii levels to a higher place or beneath), and long propriospinal neurons (ascending and descending betwixt all levels of the string). This vast array of interconnections among and between the various interneurons besides contributes to the general responsiveness of the spinal string to both afferent (sensory or reflexive) and efferent (motor or voluntary) stimuli. The interconnections between the interneurons are mutually inhibitory, meaning that only i set of pathways tin exist active at any time. When ane detail response pathway and its respective interneurons are activated, all other interneuronal pathways typically are inhibited. This allows the spinal cord to respond selectively to whatsoever input, either afferent or efferent, without inappropriately activating other antagonistic pathways that might hinder the appropriate response. In addition, interneurons tin modulate or alter the normal output of college-social club neurons. 1 case of this is related to the gate control theory of pain (see Fig. 11-6), in which nonnociceptive afferents reduce the output of second-guild pain fibers via inhibitory interneurons in the dorsal horn. Therefore interneurons are the cardinal building blocks of all spinal reflexes, and can command or attune most afferent and efferent data at the level of the spinal cord (run across the Spinal Motor Neurons and Motor Coordination department subsequently in this chapter).

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Mechanisms of Memory

Rebecca A. Piskorowski , Vivien Chevaleyre , in Learning and Retentivity: A Comprehensive Reference (2nd Edition), 2017

four.07.2.3.2 Dendritic Interneurons

Interneurons that target the dendrites of excitatory cells, or dendritic interneurons, are a very large and diverse class of cells. As Fig. 2 illustrates, these cells can either limited PV or CCK, as well as other markers to help differentiate the dissimilar classes. These other markers include somatostatin, calbindin, calretinin, and vasoactive intestinal polypeptide (VIP) (McBain and Fisahn, 2001). In all hippocampal regions, unlike dendritic regions receive input from dissimilar sources, and thus, each dendritic compartment, with its unique functional dynamics, contributes in a different mode to the computational task of the neuron. Thus, this extremely rich group of interneurons farther contributes to this task. 1 interesting function of the dendritic targeting interneurons is how these cells contribute to limiting the synaptic plasticity at excitatory synapses between areas CA3 and CA1 in stratum radiatum (Chevaleyre and Piskorowski, 2014).

Figure 2. Illustration of the diversity of PV- and CCK-expressing interneurons. (A) The majority of PV-expressing   interneurons have their soma located in the stratum pyramidale (SP) or in stratum oriens (SO). However, their axonal projections vary between the dissimilar subclasses of interneurons. Basket cells and axo-axonic cells target the soma and axon initial segment of the pyramidal neuron (PN). In contrast, bistratified cells connect the proximal office of the apical dendrite in stratum radiatum (SR) and the basal dendrites in SO. Some PV-expressing   cells have their soma in So simply but target the nearly distal part of the apical dendrite in stratum lacunosum moleculare (SLM). They are called oriens-lacunosum moleculare (O-LM) cells. (B) A like variety is observed for CCK-expressing   interneurons. Their soma is in the pyramidal layer or at the border between SR and SLM. They can target the soma (basket cells) the proximal upmost and basal dendrite of the PN (Schaffer collateral–associated interneurons) or the apical dendrite only (lacunosum moleculare-radiatum perforant path–associated interneurons). It should be noted that there is a preferential targeting of deep PNs (with their soma close to SO) by PV-expressing   handbasket cells. In contrast, CCK-expressing   handbasket cells connect both deep PNs and superficial PNs (soma close to SR) to a similar extent.

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