Greater than 50% of all spinal cord injuries (SCIs) in humans occur at the cervical level and the biggest desire of quadriplegic patients is recovery of hand and digit function. Several weeks after spinal cord injury, re-organization and re-modeling of spared endogenous pathways occurs and plasticity of both supraspinal and interneuronal networks are believed to mediate functional recovery. Propriospinal interneurons (PNs) are neurons found entirely in the spinal cord with axons projecting to different spinal segments. PNs function by modulating locomotion, integrating supraspinal motor pathways and peripheral sensory afferents. Recent studies have postulated that if PNs are spared following SCI, these neurons can contribute to functional recovery by establishing synaptic connections onto motor neurons. However, to what extent cervical PNs are involved in recovery of reaching behavior is not known. In our first study, we generated a lentiviral vector that permits highly efficient retrograde transport (HiRet) upon uptake at synaptic terminals in order to map supraspinal and interneuronal populations terminating near forelimb motoneurons (MNs) innervating the limb. With this vector, we found neurons labeled within the C3-C4 spinal cord and in the red nucleus, two major populations which are known to modulate forelimb reaching behavior. We also proceeded to use a novel two-viral vector method to specifically label ipsilateral C3-C4 PNs with tetracycline-inducible GFP. Histological analysis showed detailed labeling of somas, dendrites along with axon terminals. Based on this data, we proceeded to determine the contribution of C3-C4 PNs and rubrospinal neurons on forelimb reaching and grasping before and after cervical SCI. In our second study, we have examined a double-infection technique for shutdown of PNs and rubrospinal neurons (RSNs) in adult rats. Adult rats were microinjected with a lentiviral vector expressing tetracycline-inducible inhibitory DREADDs into C6-T1 spinal levels. Adeno-associated viral vectors (AAV2) expressing TetON mixed with GIRK2 were injected into the red nucleus and C3-C4 spinal levels respectively. Rats were tested for deficits in reaching behaviors upon application of doxycycline and clozapine-n-oxide (CNO) administration. No behavioral deficits were observed pre-injury. Rats then received a C5 spinal cord lesion to sever cortical input to forelimb motoneurons and were allowed four weeks to spontaneously recover. Upon re-administration of CNO to activate inhibitory DREADDs, deficits were observed in forelimb reaching. Histological analysis of the C3-C4 spinal cord and red nucleus showed DREADD+ neurons co-expressing GIRK2 in somas and dendrites of PNs and RSNs. PN terminals expressing DREADD were observed near C6-T1 motoneurons and in the brainstem. Control animals did not show substantial deficits with CNO administration. These results indicate both rubro- and propriospinal pathways are necessary for recovery of forelimb reaching. In a separate study, we sought to determine if promoting severed CST sprouting rostral to a C5 lesion near C3-C4 PNs could improve behavioral recovery post SCI. Past studies have examined sprouting and regeneration of corticospinal tract (CST) fibers post-cervical SCI through viral upregulation of key components of the PI3K/Akt/mTOR cascade. We examined the regenerative growth potential of CST fibers that are transduced with AAV2 expressing constituively active Akt3 or STAT3 both separately and in combination (Akt3 + STAT3). We have observed significant increases in CST axonal sprouting and regeneration in Akt3 and Akt3 + STAT3 transduced samples. However, no recovery was observed as animals transduced with viral constitutively active Akt3 displayed an epileptic phenotype. Further, epileptic animals with constitutively active Akt3 were found to have significant cortical neuron cell hypertrophy, activatived astrogliosis, increased dendritic arbors and hemimegencephalitis (HME). These results indicate a new model for examining mechanisms of HME and mTOR hyperactivity-induced epilepsy in adult rodents. / Biomedical Sciences

Der Hippokampus spielt eine wichtige Rolle bei der Erfassung, Festigung und dem Wiederabrufen von Gedächtnisinhalten. Diese Prozesse werden von Oszillationen begleitet, die synchronisierte neuronale Aktivität wiederspiegeln. Der erste Teil dieser Arbeit konzentriert sich auf ‘ripples’, eine schnell schwingende Netzwerkaktivität, die an der Festigung von Gedächtnisinhalten beteiligt ist. Das Subikulum ist eine der Hauptausgangsstationen des Hippokampus und überträgt Informationen zu Zielregionen außerhalb dieser Region. Um dies besser zu verstehen, habe ich hier die Eigenschaften von subikulären Pyramidenzellen und deren Regulierung während ripples untersucht. Es zeigte sich, dass eine Untergruppe von Zellen, burst (in Salven) feuernde Zellen, ihre Aktivität erhöht, während eine zweite Untergruppe, regulär feuerende Zellen, ihre Aktivitaet während ripples vermindert. Ferner ist bei regulär feuernden Zellen das Verhältnis zwischen Inhibition und Exzitation höher als bei burst feuernden Zellen. Zusammen mit Erkenntnissen aus früheren Studien lassen diese Ergebnisse vermuten, dass Information während ripples hauptsächlich zu Zielregionen der burst feuernden Zellen geleitet wird. Neben Pyramidenzellen beherbergt der Hippokampus auch eine Vielzahl verschiedener Interneurone. Im zweiten Teil dieser Arbeit habe ich O-LM Interneurone der hippokampalen Region CA1 untersucht. Diese spielen eine wichtige Rolle bei der Kontrolle von Eingängen aus dem entorhinalen Kortex. Wir konnten zeigen, dass die exzitatorische Übertragung auf O-LM Interneurone durch Serotonin, einem von den Raphe-Kernen ausgeschütteten Neuromodulator, vermindert wird. Dies geschieht durch einen präsynaptischen Mechanismus, der wahrscheinlich eine Verminderung des Kalziumeinstroms in präsynaptische Endigungen umfasst. Eine Verminderung der Aktivität von O-LM Interneuronen durch Serotonin könnte die synaptische Übertragung von Signalen aus dem entorhinalen Kortex auf CA1 Pyramidenzelldendriten erleichtern. / The hippocampus plays an important role in the acquisition, consolidation and retrieval of memory. These processes are accompanied by hippocampal oscillations, which reflect synchronized neuronal activity. The first part of this thesis focuses on ripples, a fast oscillatory activity which is involved in memory consolidation. The subiculum as one of the main output areas of the hippocampus is ideally suited to mediate information transfer to extrahippocampal targets. Here I investigated the properties of subicular pyramidal cells and their modulation during ripples. I found that a subset of subicular pyramidal cells increases its firing rate during ripples whereas another subset decreases its firing rate. Furthermore I was able to identify a correlate between modulation and cell subtype: burst firing cells increased their firing rate, and regular firing cells decreased their firing rate. We could further show that regular firing cells receive a higher ratio of inhibition to excitation as compared to burst firing cells. Together with earlier work, these results suggest that information transferred during ripples is likely to be routed preferentially to target regions of the burst firing subtype. Besides pyramidal cells, the hippocampus hosts a variety of interneuron types. The second part of this thesis focuses on GABAergic O-LM interneurons of hippocampal area CA1, which play an important role in controlling input from the entorhinal cortex. We could show that excitatory transmission from local pyramidal cells onto O-LM interneurons is decreased by serotonin, a neuromodulator released from the midbrain raphe nuclei. This modulation is mediated by a presynaptic mechanism and is likely to involve a decrease in calcium influx into presynaptic terminals. We conclude that serotonin, by decreasing O-LM output, might release fibers from entorhinal cortex impinging onto CA1 pyramidal cell dendrites from inhibition.

Der Morbus Parkinson ist die häufigste Erkrankung der Basalganglien und wird durch einen Abbau der dopaminergen Neurone in der Substantia nigra des Mittelhirns verursacht. Um Wege zu finden, die Nebenwirkungen bisheriger Therapien dieser Erkrankung zu vermeiden, sollten neue Angriffspunkte für pharmakologische Interventionen gesucht werden. Prinzipiell ist dabei jeder Schritt einer Signaltransduktions-Kaskade zu prüfen. Dazu gehören präsynaptische Transmitterfreisetzung, G-Protein-gesteuerte Effektormechanismen oder Veränderungen prä- und postsynaptischer Potentiale, wie sie durch ein bestimmtes lokales Ionenkanalmuster festgelegt werden. Aufgrund ihrer enormen molekularen Vielfalt bei gleichzeitig weiter, aber spezifischer Verbreitung, stellen Kaliumkanäle interessante Angriffspunkte für neue therapeutische Strategien dar. Die vorliegende Arbeit untersucht die zelluläre und subzelluläre Verteilung aller Mitglieder der Kir2-Familie, einer Gruppe von Proteinen, die einwärts-gleichrichtende Kaliumkanäle bildet. Zu diesem Zweck wurden polyklonale, monospezifische, affinitätsgereinigte Antikörper gegen den wenig konservierten carboxyterminalen Anteil der Kir2.1-, Kir2.2-, Kir2.3- und Kir2.4-Proteine hergestellt. Alle Untereinheiten der Kir2-Familie wurden an den Somata und Dendriten der meisten striatalen Neurone nachgewiesen. Zwei dieser Kanäle zeigten jedoch ein inhomogenes Verteilungsmuster: Das "patch"-Kompartiment des Striatums wurde von der Expression des Kir2.3-Kanals ausgespart, und das Kir2.4-Protein wurde am stärksten auf den tonisch aktiven, cholinergen striatalen Interneuronen exprimiert. Diese beiden Strukturen stellen die Schlüsselstellen für die Kontrolle und Regulation der dopaminergen und cholinergen Transmission im Striatum dar, weswegen ihnen eine zentrale Rolle für die efferenten Projektionen der Basalganglien zukommt. Die nachgewiesene heterogene Lokalisation der Kir2.3- und Kir2.4-Untereinheit an diesen strategisch relevanten Strukturen macht diese Kanäle zu viel versprechenden Angriffspunkten für zukünftige Pharmakotherapien. / Parkinson’s disease is the most frequent movement disorder caused by loss of dopaminergic neurons in the midbrain. Intentions to avoid side effects of conventional therapy should aim to identify additional targets for potential pharmacological intervention. In principle, every step of a signal transduction cascade, such as presynaptic transmitter release, type and occupation of postsynaptic receptors, G protein-mediated effector mechanisms, and the alterations of pre- or postsynaptic potentials as determined by the local ion channel composition, have to be considered. Due to their diversity and their widespread but distinct localizations, potassium channels represent interesting candidates for new therapeutic strategies. As a first step, the present report aimed to study the cellular and subcellular distribution of the individual members of the Kir2 family in the striatum, a group of proteins forming inwardly rectifying potassium channels. For this purpose polyclonal, monospecific, affinity purified antibodies against the less conserved carboxyterminal sequences from the Kir2.1, Kir2.2, Kir2.3, and Kir2.4 proteins were prepared. All subunits of the Kir2 family were detected on somata and dendrites of most striatal neurons. However, the distribution of two of them was not homogeneous. Striatal patch areas were largely devoid of the Kir2.3 protein, and the Kir2.4 subunit was most prominently expressed on the tonically active, giant cholinergic interneurons of the striatum. These two structures are among the key players in regulating dopaminergic and cholinergic neurotransmission within the striatum, and therefore are of major importance for the output of the basal ganglia. The heterogeneous localization of the Kir2.3 and the Kir2.4 subunits with respect to these strategic structures pinpoints these channel proteins as promising targets for future pharmacological efforts.

No description available.

This thesis describes the developmental expression and anatomical distribution of Copine-6, a neuron specific member of the Copine family of calcium-dependent phospholipid-binding proteins, in rodent brain. A polyclonal antibody targeting the full Copine-6 sequence has been characterised prior to its employment for the immunohistochemical analysis of rodent embryonic and adult brain tissue. Several different Copine-6 labelled neuron populations in the neocortex, hippocampus and olfactory bulbs were discovered, and one of these with an unusual ‘spiny’ morphology in the adult rodent corpus callosum, bordering the neurogenic subventricular zone and rostral migratory stream, was studied in detail. A full molecular characterisation of these Copine-6 ‘spiny’ neurons showed that these cells are mature, GABAergic, axonless interneurons with putative synaptic communication, unusual for their location in the white matter close to the region of adult neurogenesis. A full bromodeoxyuridine (BrdU) birth-dating analysis was performed, which indicated an early embryonic birthdate for the Copine-6 spiny cells. This timeframe is typical of cortical GABAergic interneurons suggesting that their unusual positioning is programmed from embryogenesis. Furthermore, electron microscopic analysis of these Copine-6 interneurons in Chapter 5 confirms that indeed these cells contain vesicles and are synaptically integrated as postsynaptic recipients. The presence of vesicles in the architecturally dendritic processes is suggestive of dendro-dendritic signalling by these cells. Observations from electron microscopic nanoparticle labelling also showed that the Copine-6 protein is restricted to the plasma membrane, smooth endoplasmic reticulum, and multi-vesicular bodies. These embryonically generated Copine-6 labelled axonless interneurons are a novel neuron population in the corpus callosum, and the presence of vesicles in the dendritic processes of these cells suggests that they might have a novel communication mechanism.

The activity of networks subserving memory and learning in the hippocampus is under the control of GABAergic interneurons. In order to test the contribution of distinct cell types, I have recorded extracellularly, labelled, and identified different types of interneuron in area CA3 of the hippocampus, a region implicated in the generation of gamma and theta oscillations, and the initiation of sharp-waves. I present here a detailed analysis of the spike timing of parvalbumin-positive (PV) basket and physiologically identified pyramidal cells in area CA3, relative to various network states recorded in area CA3 and CA1 simultaneously. Additionally, I have shown by detailed analysis that five classes of previously recorded and identified CA1 interneuron fired with cell type specific firing patterns relative to local gamma oscillations. In CA3, PV basket cells fired phase locked to theta and gamma oscillations recorded in CA1 as well as in CA3, and increased their firing rates during CA1 sharp-waves. Pyramidal cells in CA3 were also phase-locked, but fired at phases different from basket cells. During theta oscillations, CA3 pyramidal and PV basket cells were phase locked to both CA1 and CA3 theta equally, suggesting a wide coherence of these oscillations; in contrast, cells fired more strongly phase-locked to gamma oscillations in CA3 than in CA1, suggesting a specific role for CA3 in the generation of this rhythm. In contrast to theta and gamma oscillations, CA3 basket cells were phase-locked to ripples in area CA3 but not in CA1. Overall, my results show that the spike timing of several types of interneuron in CA1, and PV basket cells in CA3, is correlated in a cell- and area-specific manner with the generation of particular states of synchronous activity.

Les interneurones GABAergiques constituent une population mineure de cellules par rapport aux neurones glutamatergiques dans le néocortex. Cependant ils contrôlent fortement l'excitabilité neuronale, la dynamique des réseaux neuronaux et la plasticité synaptique. L'importance des circuits GABAergiques dans le processus fonctionnel et la plasticité des réseaux corticaux est soulignée par des résultats récents qui montrent que des modifications très précises et fiables des circuits GABAergiques sont associées à divers troubles du développement neurologique et à des défauts dans les fonctions cérébrales. De ce fait, la compréhension des mécanismes cellulaires et moléculaires impliquant le développement des circuits GABAergiques est la première étape vers une meilleure compréhension de la façon dont les anomalies de ces processus peuvent se produire. La molécule d’adhésion cellulaire neurale (NCAM) appartient à la super-famille des immunoglobulines de reconnaissance cellulaire et est impliquée dans des interactions homophiliques et hétérophiliques avec d’autres molécules. Même si plusieurs rôles de NCAM ont été démontrés dans la croissance neuronale, la fasciculation axonale, la formation et la maturation de synapses, de même que dans la plasticité cellulaire de plusieurs systèmes, le rôle de NCAM dans la formation des synapses GABAergiques reste inconnu. Ce projet visait donc à déterminer le rôle précis de NCAM dans le processus de maturation des synapses GABAergiques dans le néocortex, en modulant son expression à différentes étapes du développement. L’approche choisie a été de supprimer NCAM dans des cellules GABAergiques à paniers avant la maturation des synapses (EP12-18), pendant la maturation (EP16-24), ou durant le maintien de celles-ci (EP24-32). Les méthodes utilisées ont été le clonage moléculaire, l’imagerie confocale, la culture de coupes organotypiques et des techniques morphométriques de quantification de l’innervation GABAergique. Nos résultats montrent que l’inactivation de NCAM durant la phase de maturation des synapses périsomatiques (EP16-24) cause une réduction du nombre de synapses GABAergiques périsomatiques et du branchement de ces axones. En revanche, durant la phase de maintien (EP26-32), l’inactivation de NCAM n’a pas affecté ces paramètres des synapses GABAergiques. Or, il existe trois isoformes de NCAM (NCAM120, 140 et 180) qui pourraient jouer des rôles différents dans les divers types cellulaires ou à des stades développementaux différents. Nos données montrent que NCAM120 et 140 sont nécessaires à la maturation des synapses périsomatiques GABAergiques. Cependant, NCAM180, qui est l’isoforme la plus étudiée et caractérisée, ne semble pas être impliquée dans ce processus. De plus, l’inactivation de NCAM n’a pas affecté la densité des épines dendritiques ou leur longueur. Elle est donc spécifique aux synapses périsomatiques GABAeriques. Finalement, nos résultats suggèrent que le domaine conservé C-terminal KENESKA est essentiel à la maturation des synapses périsomatiques GABAergiques. Des expériences futures nous aiderons à mieux comprendre la mécanistique et les différentes voies de signalisation impliquées. / GABAergic interneurons, though a minor population in the neocortex, play an important role in cortical function and plasticity. Alterations in GABAergic circuits are implicated in various neurodevelopmental disorders. The GABAergic network comprises diverse interneuron subtypes that have different morphological and physiological characteristics, and localize their synapses onto distinct subcellular locations on the postsynaptic targets. Precisely how activity and molecularly driven mechanisms conspire to achieve the remarkable specificity of GABAergic synapse localization and formation is unknown. Therefore, unravelling the cellular and molecular mechanisms involved in this process is crucial for a better understanding of both cortical function and the basis of various neurological disorders. Here we focus our study on a subtype of GABAergic neurons - the basket interneurons which localize synapses, called perisomatic synapses, onto the soma and proximal dendrites of the postsynaptic targets, and tightly regulate their firing patterns. Although recent studies have shown the activity dependence of basket synapse formation, the molecular mechanisms implicated in the perisomatic synapse formation process are poorly understood. NCAM, the neural cell adhesion molecule, is a prime molecular player implicated both in early synaptogenesis events, and during maturation of glutamatergic synapses in the hippocampus. Recent studies have implicated the polysialylated form of NCAM (PSA-NCAM) in basket synapse formation. However, whether and how NCAM per se plays a role in the formation of GABAergic synapses is unknown. Using single cell genetics to knock down NCAM in individual basket interneurons at specific developmental time periods, we characterized the role of NCAM during perisomatic synapse formation and maintenance. Here we show that loss of NCAM during perisomatic synapse formation from equivalent postnatal day (EP) 16 to EP24, in organotypic slices from mouse visual cortex, significantly retards the process of basket cell axonal branching and bouton formation. However, loss of NCAM at a later stage (EP26 to EP32), when the synapses are already formed, did not affect the number or intricacy of perisomatic synapses. NCAM is therefore implicated in perisomatic synapse formation but not in its maintenance. Further studies also show that isoforms of NCAM, such as NCAM140 and NCAM120 are involved in perisomatic GABAergic synapse maturation. However, NCAM180 is not implicated in this process. Also, NCAM does not affect dendritic spine density and length during maturation and maintenance phases, therefore its action is specific only to GABAergic perisomatic synapses. Finally, the highly conserved C-terminal domain KENESKA is essential for GABAergic perisomatic synapse maturation. Future experiments will help us clarify this mechanism and the involved signalling pathways related to NCAM.

HIV is capable of causing a set of neurological diseases collectively termed the HIV Associated Neurocognitive Disorders (HAND). Worsening pathology is observed in HIV+ individuals who use opioid drugs. Memory problems are often observed in HAND, implicating HIV pathology in the hippocampus, and are also known to be exacerbated by morphine use. HIV-1 Tat was demonstrated to reduce spatial memory performance in multiple tasks, and individual subsets of CA1 interneurons were found to be selectively vulnerable to the effects of Tat, notably nNOS+/NPY- interneurons of the pyramidal layer and stratum radiatum, PV+ neurons of the pyramidal layer, and SST+ neurons of stratum oriens. Each of these interneuron subsets are hypothesized to form part of a microcircuit involved in memory formation. Electrophysiological assessment of hippocampal pyramidal neurons with Tat and morphine together revealed that Tat caused a reduction in firing frequency, however, chronic morphine exposure did not have any effect. When morphine was removed after chronic exposure, non-interacting effects of Tat and morphine withholding on firing frequency were observed, suggesting that a homeostatic rebalancing of CA1 excitation/inhibition balance takes place in response to chronic morphine exposure independently of any Tat effects. Additionally, differential morphological effects of Tat and morphine were observed in each of the three major dendritic compartments, with SR being less affected, suggesting complex circuit responses to these insults reflecting local change and potentially changes in inputs from other brain regions. Behaviorally, Tat and morphine interactions occur in spatial memory, with morphine potentially obviating Tat effects.

Hokkaido University (北海道大学) / 博士 / 医学

Les interneurones GABAergiques constituent une population mineure de cellules par rapport aux neurones glutamatergiques dans le néocortex. Cependant ils contrôlent fortement l'excitabilité neuronale, la dynamique des réseaux neuronaux et la plasticité synaptique. L'importance des circuits GABAergiques dans le processus fonctionnel et la plasticité des réseaux corticaux est soulignée par des résultats récents qui montrent que des modifications très précises et fiables des circuits GABAergiques sont associées à divers troubles du développement neurologique et à des défauts dans les fonctions cérébrales. De ce fait, la compréhension des mécanismes cellulaires et moléculaires impliquant le développement des circuits GABAergiques est la première étape vers une meilleure compréhension de la façon dont les anomalies de ces processus peuvent se produire. La molécule d’adhésion cellulaire neurale (NCAM) appartient à la super-famille des immunoglobulines de reconnaissance cellulaire et est impliquée dans des interactions homophiliques et hétérophiliques avec d’autres molécules. Même si plusieurs rôles de NCAM ont été démontrés dans la croissance neuronale, la fasciculation axonale, la formation et la maturation de synapses, de même que dans la plasticité cellulaire de plusieurs systèmes, le rôle de NCAM dans la formation des synapses GABAergiques reste inconnu. Ce projet visait donc à déterminer le rôle précis de NCAM dans le processus de maturation des synapses GABAergiques dans le néocortex, en modulant son expression à différentes étapes du développement. L’approche choisie a été de supprimer NCAM dans des cellules GABAergiques à paniers avant la maturation des synapses (EP12-18), pendant la maturation (EP16-24), ou durant le maintien de celles-ci (EP24-32). Les méthodes utilisées ont été le clonage moléculaire, l’imagerie confocale, la culture de coupes organotypiques et des techniques morphométriques de quantification de l’innervation GABAergique. Nos résultats montrent que l’inactivation de NCAM durant la phase de maturation des synapses périsomatiques (EP16-24) cause une réduction du nombre de synapses GABAergiques périsomatiques et du branchement de ces axones. En revanche, durant la phase de maintien (EP26-32), l’inactivation de NCAM n’a pas affecté ces paramètres des synapses GABAergiques. Or, il existe trois isoformes de NCAM (NCAM120, 140 et 180) qui pourraient jouer des rôles différents dans les divers types cellulaires ou à des stades développementaux différents. Nos données montrent que NCAM120 et 140 sont nécessaires à la maturation des synapses périsomatiques GABAergiques. Cependant, NCAM180, qui est l’isoforme la plus étudiée et caractérisée, ne semble pas être impliquée dans ce processus. De plus, l’inactivation de NCAM n’a pas affecté la densité des épines dendritiques ou leur longueur. Elle est donc spécifique aux synapses périsomatiques GABAeriques. Finalement, nos résultats suggèrent que le domaine conservé C-terminal KENESKA est essentiel à la maturation des synapses périsomatiques GABAergiques. Des expériences futures nous aiderons à mieux comprendre la mécanistique et les différentes voies de signalisation impliquées. / GABAergic interneurons, though a minor population in the neocortex, play an important role in cortical function and plasticity. Alterations in GABAergic circuits are implicated in various neurodevelopmental disorders. The GABAergic network comprises diverse interneuron subtypes that have different morphological and physiological characteristics, and localize their synapses onto distinct subcellular locations on the postsynaptic targets. Precisely how activity and molecularly driven mechanisms conspire to achieve the remarkable specificity of GABAergic synapse localization and formation is unknown. Therefore, unravelling the cellular and molecular mechanisms involved in this process is crucial for a better understanding of both cortical function and the basis of various neurological disorders. Here we focus our study on a subtype of GABAergic neurons - the basket interneurons which localize synapses, called perisomatic synapses, onto the soma and proximal dendrites of the postsynaptic targets, and tightly regulate their firing patterns. Although recent studies have shown the activity dependence of basket synapse formation, the molecular mechanisms implicated in the perisomatic synapse formation process are poorly understood. NCAM, the neural cell adhesion molecule, is a prime molecular player implicated both in early synaptogenesis events, and during maturation of glutamatergic synapses in the hippocampus. Recent studies have implicated the polysialylated form of NCAM (PSA-NCAM) in basket synapse formation. However, whether and how NCAM per se plays a role in the formation of GABAergic synapses is unknown. Using single cell genetics to knock down NCAM in individual basket interneurons at specific developmental time periods, we characterized the role of NCAM during perisomatic synapse formation and maintenance. Here we show that loss of NCAM during perisomatic synapse formation from equivalent postnatal day (EP) 16 to EP24, in organotypic slices from mouse visual cortex, significantly retards the process of basket cell axonal branching and bouton formation. However, loss of NCAM at a later stage (EP26 to EP32), when the synapses are already formed, did not affect the number or intricacy of perisomatic synapses. NCAM is therefore implicated in perisomatic synapse formation but not in its maintenance. Further studies also show that isoforms of NCAM, such as NCAM140 and NCAM120 are involved in perisomatic GABAergic synapse maturation. However, NCAM180 is not implicated in this process. Also, NCAM does not affect dendritic spine density and length during maturation and maintenance phases, therefore its action is specific only to GABAergic perisomatic synapses. Finally, the highly conserved C-terminal domain KENESKA is essential for GABAergic perisomatic synapse maturation. Future experiments will help us clarify this mechanism and the involved signalling pathways related to NCAM.