The Group III metabotropic glutamate receptors (mGluR) are located presynaptically on axon terminals and act as autoreceptors and heteroreceptors by inhibiting neurotransmitter release. Much has been learned about these receptors through exogenous application of L-serine-O-phosphate (L-SOP), an endogenous amino acid derivative and known activator of the Group III mGluRs. We hypothesized that L-SOP is the endogenous co-agonist at the high affinity Group III mGluR, mGluR4. We found the EC50 of L-SOP at mGluR4 was 0.5 μM, and determined that the concentration of L-SOP in whole brain was approximately 5 μM. An immunocytochemical survey revealed that cells containing the enzymatic machinery necessary for L-SOP synthesis and metabolism were observed in two brain regions known to express mGluR4, namely, cerebellum and hippocampus. In the cerebellum, the L-SOP synthetic and metabolic enzymes were found in Bergmann glia and Purkinje cells, two cells which form a tripartite synapse with parallel fiber axon terminals where the mGluR4 subtype is exclusively expressed at high levels. In the hippocampus, the L-SOP metabolic enzyme was detected in young neurons emanating from the neurogenic subventricular zone. Attempts to raise endogenous levels of L-SOP by crippling the L-SOP metabolizing enzyme (phosphoserine phosphatase), over-expressing the L-SOP synthesizing enzyme (phosphoserine aminotransferase), or through dietary protein restriction, to study the effects on neurotransmission and neurodevelopment in the central nervous system (CNS) were unsuccessful, suggesting that the production of L-SOP remains stable despite manipulation of the synthetic and metabolic enzymes. Finally, the ability of L-SOP to modulate glutamate release from presynaptic terminals was examined in cerebellar synaptosomes. Co-incident activation of presynaptic mGluR4 and presynaptic GABAA receptors facilitated glutamate release, suggesting that simultaneous activation of parallel fibers and Bergmann glia may serve to enhance synaptic transmission. This observation expands the traditional view of Group III mGluRs acting solely as inhibitory autoreceptors. Taken together, these results provide compelling evidence to support the hypothesis that L-SOP is the endogenous agonist at mGluR4, and possibly other Group III mGluRs.

The induction of synaptic plasticity at CA1 synapses requires NMDAR activation. Modulation of NMDAR function by various GPCRs can shift the thresholds for LTP and LTD induction and contribute to metaplasticity. Here we showed that the activity of GluN2A- and GluN2B-containing NMDARs is differentially regulated by Gαi/o-coupled, Gαq- and Gαs-coupled receptors. Furthermore, enhancing the relative function of GluN2A-to-GluNB NMDAR activity by GPCRs can alter the balance of LTP and LTD induction and contribute to metaplasticity. In CA1 neurons, activation of the Gαs-coupled D1/D5R selectively recruited Fyn kinase and enhanced GluN2B-mediated NMDAR currents. Biochemical experiments confirmed that D1/D5R stimulation activates Fyn kinase and enhances the tyrosine phosphorylation of GluN2B subunits. In contrast, activation of the Gαq-coupled PAC1R selectively recruited Src kinase to enhance the function of GluN2A-containing NMDARs. Enhancing the functional ratio of GluN2A-to-GluN2B subunits by PAC1R activation lowered the threshold for LTP induction whereas enhancing the functional ratio of GluN2B-to-GluN2A subunits by D1/D5R activation increased the threshold for LTP induction. Unexpectedly, activation of the Gαi/o-coupled mGluR2/3 enhanced NMDAR-mediated function via a previously unidentified mechanism. Inhibition of the cAMP-PKA pathway via mGluR2/3 activation resulted in activation of Src via decreased phosphorylation of its C-terminal Tyr527 by Csk. Stimulation of mGluR2/3 selectively potentiated the function of GluN2A-containing NMDARs but whether it shifted the modification threshold θm to the left requires further investigation.

GABA is the major inhibitory neurotransmitter in the central nervous system. It binds to two types of receptors –ionotropic GABAA and metabotropic GABAB. The GABAA receptor directly gates a Clionophore that causes hyperpolarization in mature excitatory neurons while GABAB receptor mediates a slower hyperpolarizing response via G-protein coupled receptor (GPCR) activated potassium channels. This signaling mechanism gets further complicated by the heterogeneous GABA receptor subunit composition that influences the response kinetics in the postsynaptic membrane. In this thesis, the focus has been to decipher the role of GABAA receptors in relation to cellular excitability in the subiculum under physiological and pathophysiological conditions. The subiculum, considered as the output structure of hippocampus, modulates information flow from hippocampus to various cortical and sub-cortical areas and has been implicated in learning and memory, rhythm generation and various neurological disorders. It gates hippocampal activity with its well orchestrated and fine tuned intrinsic and local network properties. Over the years many studies have shown the involvement of subiculum in temporal lobe epilepsy where it forms the focal point of epileptiform activities with altered cellular and network properties. The subiculum is characterized by the presence of a significant population of burst firing neurons that lead local epileptiform activity. By virtue of its bursting nature and recurrent connections, it is a potential site for seizure generation and maintenance. Epileptiform activities are dynamic in nature and change temporally and spatially according to the alterations in electrophysiological properties of neurons. Transitions to different electrical activities in neurons following a prolonged challenge with epileptogenic stimulus have been shown in other brain structures, but not in the subiculum. Considering the importance of the subicular burst firing neurons in the propagation of epileptiform activity to the entorhinal cortex, we have explored the phenomenon of electrophysiological phase transitions in the burst firing neurons of the subiculum in an in vitro brain slice model of epileptogenesis. Whole-cell patch clamp and extracellular field recordings revealed a distinct phenomenon in the subiculum wherein an early hyperexcitable phase was followed by a late suppressed phase upon continuous perfusion with epileptogenic 4-amino pyridine and magnesium-free medium. The late suppressed phase was characterized by inhibitory post-synaptic potentials (IPSPs) in pyramidal excitatory neurons and bursting activity in local fast spiking interneurons at a frequency of 0.1-0.8 Hz. The IPSPs were mediated by GABAA receptors that coincided with excitatory synaptic inputs to attenuate action potential discharge. These IPSPs ceased following a cut between the CA1 and subiculum. Our results suggest the importance of feedforward inhibition in the suppression of epileptiform activity in subiculum to mediate a homeostatic response towards the induced hyper-excitability. GABA release from presynaptic nerve endings activates postsynaptic GABAA receptors, which evoke faster phasic inhibitory postsynaptic currents (IPSCs) and non-inactivating inhibitory tonic current, mediated through extrasynaptic GABAA receptors. These receptors are heteropentameric GABA-gated channels assembled from 19 possible subunits (α1-6, β1-3, γ1-3, δ, π, ρ1-3, θ, and ε). The 2 major subunits involved in tonic GABAA currents in the hippocampus are α5 and δ subunits. Tonic GABAA receptor mediated inhibitory current plays an important role in neuronal physiology as well as pathophysiology such as mood disorders, insomnia, epilepsy, autism spectrum disorders and schizophrenia. While the alterations of various electrical properties due to tonic inhibition have been studied in neurons from different regions, its influence on intrinsic subthreshold resonance in pyramidal excitatory neurons having hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is not known. In the present study, we show the involvement of α5βγ GABAA receptors in mediating picrotoxin sensitive tonic current in subicular pyramidal neurons using known pharmacological agents that target specific GABAA receptor subunits. We further investigated the contribution of tonic conductance in regulating subthreshold electrophysiological properties using current clamp and dynamic clamp experiments. Our experiments suggest that tonic GABAergic inhibition can actively modulate subthreshold properties of subicular pyramidal neurons including resonance due to HCNchannels that may potentially alter the response dynamics in an oscillating neuronal network.

Chez les mammifères, le glutamate est un neuromédiateur bien connu au niveau du système nerveux central et plus récemment un rôle immunomodulateur lui a été reconnu. Le glutamate est le ligand de récepteurs ionotopiques (iGluRs) qui sont des récepteurs-canaux perméables à divers cations dont le calcium (non-selective cation channels, NSCC). Chez Arabidopsis thaliana, une famille de 20 gènes de iGluRs homologues des iGluRs de mammifères a été identifiée et leur implication dans divers processus biologiques est suggérée. Dans ce travail où nous utilisons des suspensions de cellules de tabac (Nicotiana tabacum var Xanthi), divers arguments suggèrent que ces iGluR sont fonctionnels dans le tabac : influx de calcium et élévation rapide et transitoire de la concentration en calcium cytosolic libre en réponse à l’addition de glutamate, inhibition de ces effets par 4 antagonistes de iGluRs animaux (compétitifs ou non compétitifs), désensibilisation, et pH dépendance des effets. Pour la première fois chez les plantes nous montrons que le glutamate induit la production de NO très vraisemblablement via l’activation de iGluRs. De plus, nous démontrons que ce(s) iGluRs sont impliqués dans le mode d’action, via les flux de calcium, de la cryptogéine une protéine de 10 kDa de Phytophthora cryptogea, éliciteur des réactions de défense chez le tabac. Néanmoins, à ce niveau, les iGluRs ne sont pas impliqués dans la plupart des événements calcium-dépendants induits par la cryptogéine dont l’activation des MAPKs et de canaux anioniques, la production de H2O2 (activation de la NADPH-oxydase) et la réponse hypersensible. En revanche, ils sont tout ou partiellement responsables de la production de NO décrite pour la première fois par le passé en réponse à la cryptogéine. Ces résultats suggèrent que différents types de canaux calciques activés par divers médiateurs, génèrent, via le calcium, des messages spécifiques décodés par des protéines associées à chacun de ces types de canaux et impliquées dans des réponses biologiques différentes. Dans le mode d’action de la cryptogéine, nous démontrons que l’activation des iGluRs est possible grâce à l’exocytose de glutamate dans l’apoplaste, induite par la cryptogéine. Ainsi, ce travail est la première démonstration du rôle de iGluRs potentiels dans la défense chez les plantes et de leur implication dans la production de NO. Nos résultats sont un argument supplémentaire à la conservation des mécanismes de la défense dans le monde vivant et posent le problème du rôle du glutamate dans la signalisation chez les plantes. / Glutamate is recognized as the primary excitatory neurotransmitter in the mammalian central nervous system (CNS) but recent studies have shown that glutamate has an important additional immunomodulator role. Glutamate is the ligand of ionotropic glutamate receptors (iGluRs), which are non-selective cation channels (NSCC), permeable to calcium. In plants, animal iGluR homologs were found that were involved in many developmental processes. Here we demonstrate the involvement of putative iGluRs in calcium signalling in response to cryptogein which is a 10 kDa protein secreted by the oomycete Phytophthora cryptogea and is an elicitor of defence in tobacco. Using transformed tobacco cell suspensions expressing aequorin in the cytosol or in the nucleus, our results have shown that glutamate induces a strong and transient [Ca2+]cyt elevation without [Ca2+]nuc changes. Glutamate-induced [Ca2+]cyt elevation was a result of calcium influx from the extracellular medium and was inhibited by different GluR inhibitors. This data suggest the presence of functional calcium channels of GluRs-type in tobacco. Nevertheless, glutamate does not induce some of the calcium-dependent characteristic events of the defence pathways, which are H2O2 production, MAPK activation and hypersensitive response, but promoted NO production. Further, Ca2+ influx,[Ca2+]cyt elevation and NO production induced by cryptogein were shown to be partially inhibited by the glutamate receptor inhibitors, suggesting that cryptogein treatment could activate a calcium channel of the GluR-type leading to plant defense signalling through NO production. We have also demonstrated that cryptogein induces an efflux of glutamate in the apoplast by the process of exocytosis thus activating the GluRs in tobacco. This is the first demonstration for a potential GluR(s) involvement in plant defense signalling, furthermore by mechanisms that showed homology with glutamate effect on neuronal cells.

La synapse glutamatergique est formée par une présynapse axonale et une postsynapse dont le support est l'épine dendritique. L'épine présente des récepteurs membranaires du glutamate liés à des protéines d'échafaudage sous-membranaires. Ces protéines de la densité postsynaptique (PSD) permettent de relier les récepteurs à leurs voies de signalisation. Les récepteurs NMDA sont reliés aux récepteurs métabotropiques du glutamate (mGluR1/5) via le complexe PSD95/GKAP/Shank/Homer. Au cours de ma thèse, j'ai caractérisé la dynamique d'interactions protéiques au sein de ce complexe et étudié les conséquences fonctionnelles sur l'activité des récepteurs.Homer est une protéine multimérique reliant mGluR5 au complexe PSD95/GKAP/Shank. La forme monomérique Homer1a est incapable de relier mGluR5 à Shank. Nous avons montré que la rupture du complexe par l'expression de Homer1a permet une interaction directe entre les récepteurs NMDA et mGluR5 et une inhibition des courants NMDA. Nous avons validé que ce processus intervient lors de la potentialisation synaptique. J'ai également étudié le rôle de l'interaction entre GKAP et DLC2, une chaîne légère de transporteurs moléculaires. Après avoir caractérisé l'occurrence et la dynamique de l'interaction GKAP-DLC2, j'ai montré que l'activité neuronale entraîne une augmentation de cette interaction et une accumulation synaptique de GKAP. De plus, cette interaction permet d'acheminer PSD95 dans les épines et d'augmenter les courants NMDA. L'ensemble de ces résultats montre que les protéines d'échafaudage participent à la signalisation des récepteurs, modulent la transmission synaptique et sous-tendent les mécanismes de plasticité à long terme. / The glutamatergic synapse is composed by an axonal presynapse and a postsynapse which is supported by a dendritic spine. The spine contains membrane glutamatergic receptors connected to sub-membrane scaffolding proteins. These postsynaptic density (PSD) proteins allow to link receptors to their signaling pathways. NMDA receptors are associated to metabotropic glutamate receptors (mGluR1/5) through the PSD95/GKAP/Shank/Homer protein complex. During my PhD, I have characterized protein-protein interactions dynamic in this complex and studied functional consequences on receptor activity.Homer is a multimeric protein linking mGluR5 to the PSD95/GKAP/Shank complex. The monomeric form Homer1a is unable to connect mGluR5 to Shank. We have shown that complex disruption by Homer1a expression induces a direct interaction between NMDA and mGluR5 and subsequent inhibition of NMDA currents. We have shown that this process occurs during synaptic potentiation.I have also studied the interaction between GKAP and DLC2, a light chain shared by molecular transporters. I have characterized the occurrence and dynamic of GKAP-DLC2 interaction and shown that neuronal activity increases this interaction leading to synaptic accumulation of GKAP. Moreover, this interaction allows PSD95 targeting into dendritic spines and NMDA currents increase. Together, these results show that scaffolding proteins participate to receptor signaling, modulate synaptic transmission and underlie long-term synaptic plasticity mechanisms.

Glutamate is the main excitatory neurotransmitter in the mammalian brain and its transmission is responsible for higher brain functions, such as learning, memory and cognition. Glutamate action is mediated by a variety of glutamate receptors, though their properties were until now studied predominantly in neurons. Glutamate receptors are expressed also in NG2-glia, however their role under physiological conditions as well as in pathological states of the central nervous system is not fully understood. The aim of this work is to elucidate the presence, composition and function of these receptors in NG2-glia under physiological conditions and following focal cerebral ischemia. For this purpose we used transgenic mice, in which NG2-glia are labeled by a fluorescent protein for their precise identification. To analyze the expression pattern of glutamate receptors in NG2-glia we employed single-cell RT-qPCR. Furthermore, we used calcium imaging to characterize their functional properties.

Die exzitatorische Neurotransmission im gesamten Zentralnervensystem (ZNS) der Wirbeltiere wird weitgehend durch die α-Amino-3-hydroxy-5-methyl-4-isoxazolpropionsäure-Rezeptoren (AMPARs) vermittelt. AMPARs sind Glutamat-gesteuerte Ionenkanäle, die sich an der postsynaptischen Membran befinden, wo sie den Kern makromolekularer Komplexe mit einer Reihe von Hilfsproteinen bilden, die die Rezeptorfunktion konzertiert regulieren. Die bekanntesten dieser Proteine sind die transmembranen AMPA-Rezeptor-Regulierungsproteine (TARPs). TARPs zeigen eine verwirrende Reihe von Effekten auf den Handel, die synaptische Verankerung, die Gate-Kinetik und die Pharmakologie von AMPARs. Über die strukturellen Merkmale des AMPAR-TARP-Komplexes wurde zunehmendes Wissen gesammelt. Die molekularen Mechanismen, die der TARP-Modulation der AMPARs zugrunde liegen, sind jedoch noch nicht vollständig aufgeklärt. In der vorliegenden Studie wurden die AMPAR-TARP-Interaktionen mit Hilfe der Elektrophysiologie in 293 Zellen der menschlichen embryonalen Niere (HEK) untersucht. Die Rolle der extrazellulären TARP-Schleifen, Loop1 (L1) und Loop2 (L2), bei der Modulation der AMPAR-Ansteuerung wurde analysiert. Es wurde ein Modell für die TARP-Modulation vorgeschlagen, das auf vorhergesagten zustandsabhängigen Wechselwirkungen von TARP L1 und L2 mit dem AMPAR basiert. Da die nativen AMPARs im Gehirn hauptsächlich aus heterotetrameren Zusammensetzungen von vier verschiedenen Untereinheiten (GluA1-4) bestehen, wurden außerdem verschiedene Zusammensetzungen von AMPAR-Untereinheiten getestet. Es wurden sowohl gemeinsame als auch von den Untereinheiten abhängige Mechanismen der AMPAR-Modulation durch TARPs beobachtet. Zusammenfassend liefern diese Experimente den Nachweis, dass TARP L1 und L2 nicht an der Assoziation von AMPAR-TARP-Komplexen beteiligt sind und die Modulation der AMPAR-Ansteuerung durch TARPs vollständig erklären können. / Excitatory neurotransmission throughout the vertebrate central nervous system (CNS) is largely mediated by the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). AMPARs are glutamate-gated ion channels located at the postsynaptic membrane, where they compose the hub of macromolecular complexes with a number of auxiliary proteins that concertedly regulate the receptor function. Among these proteins the most known ones are the transmembrane AMPA receptor regulatory proteins (TARPs). TARPs show a bewildering array of effects on the trafficking, synaptic anchoring, gating kinetics and pharmacology of AMPARs. Growing knowledge has been gathered about the structural features of the AMPAR-TARP complex. However, the molecular mechanisms underlying TARP modulation of AMPARs have not been fully revealed yet. Given that higher brain functions rely upon AMPAR activity and dysregulation of AMPARs has been associated to life-threatening CNS disorders, big efforts are being made to unravel the molecular machinery behind AMPAR regulation and to identify AMPAR auxiliary proteins as potential pharmacological targets. In the present study, AMPAR-TARP interactions were investigated using electrophysiology in human embryonic kidney (HEK) 293 cells. The role of TARP extracellular loops, Loop1 (L1) and Loop2 (L2), in the modulation of AMPAR gating was analysed. A model for TARP modulation has been proposed, based on predicted state-dependent interactions of TARP L1 and L2 with the AMPAR. Moreover, considering that native AMPARs in the brain mainly consist of heterotetrameric assemblies of four distinct subunits (GluA1-4), different AMPAR subunit compositions were tested. Common as well as subunit-dependent mechanisms of AMPAR modulation by TARPs have been observed. In summary, these experiments provided evidence that TARP L1 and L2 are not involved in association of AMPAR-TARP complexes and can entirely account for the modulation of AMPAR gating by TARPs.

Ionotropic glutamate AMPA-type receptors mediate fast excitatory neurotransmission in the central nervous system and are essential for synaptic plasticity. Expression of the receptor subunits varies with cell type, stage of development and brain region. Subunit composition determines functional properties of the receptor, including gating kinetics and synaptic trafficking. The research aimed to selectively disrupt the GluA1 subunit abundantly expressed in the hippocampus of the wild-type mouse, so as to examine its role in learning and memory. Site-directed monoclonal antibodies were engineered to target the extracellular amino-terminal domain of GluA1 for subunit-selective manipulation. The antibody-binding region was selected for heterogeneity and accessibility based on the amino acid sequences and crystal structures solved for the AMPA receptor subunits. Immunisations of peptide antigen in mice generated serum antibodies that recognise the equivalent epitope on the fully folded GluA1 subunit. The antigen-binding Fab fragment of the monoclonal anti-GluA1 antibody was cloned from hydridoma mRNA and purified from large-scale transient expression in mammalian cells. Biophysical characterisations of anti-GluA1 Fab immunoglobulin showed high specificity and affinity for the target subunit. Acute bilateral intrahippocampal administration of anti-GluA1 Fab protein into awake, behaving wild-type mice produced dissociations in spatial memory performance that resembled GluA1-/- knockout mice. Impaired short-term spatial working memory but intact long-term spatial reference memory observed with anti-GluA1 Fab infusions suggested that the immunoglobulin reagent exerted an acute, reversible, localised, GluA1-specific antagonism in the brain. The findings argue for a critical involvement of the hippocampal GluA1 subunit in certain short-term memory processes, but not in other distinct long-term memory processes. Temporal resolution of the antibody-mediated disruption revealed novel fractionations of short-term memory performance never before observed in the GluA1-/- knockout mice, demonstrating the strength of the monoclonal anti-GluA1 antibodies as an investigative tool.

L’objectif premier de notre projet était d’établir un modèle animal de douleur chronique orofaciale, lequel pourrait imiter la sensibilité retrouvée chez les patients souffrant de douleur orofaciale myalgique. Nous avons procédé à des injections intramusculaires de saline acide (2 injections à 2 jours d’intervalle pH 4.0) pour induire une sensibilisation mécanique des mucles massétérins. La réponse nocifensive a été mesurée à l’aide de filaments de von Frey avant et après ces injections dans des rats Sprague-Dawley. Par la suite, le potentiel analgésique de différents antagonistes des récepteurs glutamatergiques fût évalué par l’injection intramusculaire de ces antagonistes à différents moments. Nos résultats suggèrent que deux injections de saline acide, produisent une hypersensibilité mécanique signalée par l’augmentation du nombre de réponses à l’application de filaments de von Frey. Cet effet dure plusieurs semaines et est bilatéral, même lorsque les injections sont unilatérales, indiquant qu’une composante centrale est forcément impliquée. Toutefois, une composante périphérique impliquant les récepteurs glutamatergiques semble présider le tout puisque les antagonistes glutamatergiques, appliqués de façon préventive empêchent le développement de l’hypersensibilité. Cependant, le maintien de cette hypersensibilité doit dépendre de mécanismes centraux puisque l’application d’antagonistes une fois la sensibilisation induite, ne diminue en rien le nombre de réponses obtenues. Ce modèle semble approprié pour reproduire une hypersensibilité musculaire durable de bas niveau. Nos données indiquent que les récepteurs glutamatergiques périphériques participent à l’induction de cette hypersensibilité de longue durée. Nous croyons que ce modèle pourra éventuellement contribuer à une meilleure compréhension des mécanismes à l’origine des myalgies faciales persistantes. / The first objective of this project was to establish an animal model of chronic orofacial pain, which could mimic symptoms of patients suffering from orofacial myalgia. We used acidic saline injections (2 injections, 2 days apart at pH 4.0) in masseteric muscles to induce mechanical hypersensitivity. Nocifensive behavior was measured before and after the injections using von Frey filaments in male Sprague Dawley rats. Later, the potential analgesic effect of glutamate receptors antagonists was measured by intramuscular administration of these antagonists at different times. Our results suggest that two injections of acidic saline produce a mechanical hypersensitivity as reflected by the increased number of responses to applications of von Frey filaments. This effect lasts several weeks and is bilateral, even when the injections are unilateral, indicating that a central component must be involved. However, the initial stage of induction of this hypersensitivity involves peripheral glutamate receptors since injection of their antagonists before the second acidic saline injection prevents development of the nocifensive response, whereas their injection at later times is ineffective in blocking development of the response. This model based on a double injection of acidic saline seems appropriate to reproduce low intensity, long-lasting muscle pain. Our data suggests that peripheral glutamate receptors are involved in the induction of this long-term hypersensitivity. We believe that this model may contribute to a better understanding of the mechanisms behind persistent orofacial muscle pain.

Cortical malformations as a result of altered development are a common cause of human epilepsy. The cellular mechanisms that render neurons of malformed cortex epileptogenic remain unclear. Using a rat model of the malformation of microgyria, a previous study showed an alteration in the number of immunocytochemically-identified parvalbumin cells, a GABAergic inhibitory interneurons subtype (Rosen et al., 1998). A second study showed no change in the total number of GABAergic neurons (Schwarz et al., 2000). Consequently, we hypothesize that interneuron subtypes are differentially affected by maldevelopment. The present study investigated (1) whether interneuron subtype identity is retained in malformed cortex, based on chemical content, and (2) whether the proportion of three chemical subtypes is altered in malformed cortex. Here we demonstrate that three non-overlapping subtype markers remain non-overlapping in malformed cortex, but show altered distributions. These findings suggest that an increase in one subpopulation of interneurons may compensate for a corresponding decrease in a second subset.