Enigmatic GABAergic networks in adult neurogenic zones

Neural Progenitor Cells and the Hypothalamus

Neural progenitor cells (NPCs) are multipotent neural stem cells (NSCs) capable of self-renewing and differentiating into neurons, astrocytes and oligodendrocytes. In the postnatal/adult brain, NPCs are primarily located in the subventricular zone (SVZ) of the lateral ventricles (LVs) and subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). There is evidence that NPCs are also present in the postnatal/adult hypothalamus, a highly conserved brain region involved in the regulation of core homeostatic processes, such as feeding, metabolism, reproduction, neuroendocrine integration and autonomic output. In the rodent postnatal/adult hypothalamus, NPCs mainly comprise different subtypes of tanycytes lining the wall of the 3^rd ventricle. In the postnatal/adult human hypothalamus, the neurogenic niche is constituted by tanycytes at the floor of the 3^rd ventricle, ependymal cells and ribbon cells (showing a gap-and-ribbon organization similar to that in the SVZ), as well as suprachiasmatic cells. We speculate that in the postnatal/adult human hypothalamus, neurogenesis occurs in a highly complex, exquisitely sophisticated neurogenic niche consisting of at least four subniches; this structure has a key role in the regulation of extrahypothalamic neurogenesis, and hypothalamic and extrahypothalamic neural circuits, partly through the release of neurotransmitters, neuropeptides, extracellular vesicles (EVs) and non-coding RNAs (ncRNAs).

A New Hypothesis for Alzheimer's Disease: The Lipid Invasion Model

This paper proposes a new hypothesis for Alzheimer's disease (AD)-the lipid invasion model. It argues that AD results from external influx of free fatty acids (FFAs) and lipid-rich lipoproteins into the brain, following disruption of the blood-brain barrier (BBB). The lipid invasion model explains how the influx of albumin-bound FFAs via a disrupted BBB induces bioenergetic changes and oxidative stress, stimulates microglia-driven neuroinflammation, and causes anterograde amnesia. It also explains how the influx of external lipoproteins, which are much larger and more lipid-rich, especially more cholesterol-rich, than those normally present in the brain, causes endosomal-lysosomal abnormalities and overproduction of the peptide amyloid-β (Aβ). This leads to the formation of amyloid plaques and neurofibrillary tangles, the most well-known hallmarks of AD. The lipid invasion model argues that a key role of the BBB is protecting the brain from external lipid access. It shows how the BBB can be damaged by excess Aβ, as well as by most other known risk factors for AD, including aging, apolipoprotein E4 (APOE4), and lifestyle factors such as hypertension, smoking, obesity, diabetes, chronic sleep deprivation, stress, and head injury. The lipid invasion model gives a new rationale for what we already know about AD, explaining its many associated risk factors and neuropathologies, including some that are less well-accounted for in other explanations of AD. It offers new insights and suggests new ways to prevent, detect, and treat this destructive disease and potentially other neurodegenerative diseases.

The Structural E/I Balance Constrains the Early Development of Cortical Network Activity

Neocortical networks have a characteristic constant ratio in the number of glutamatergic projection neurons (PN) and GABAergic interneurons (IN), and deviations in this ratio are often associated with developmental neuropathologies. Cultured networks with defined cellular content allowed us to ask if initial PN/IN ratios change the developmental population dynamics, and how different ratios impact the physiological excitatory/inhibitory (E/I) balance and the network activity development. During the first week in vitro, the IN content modulated PN numbers, increasing their proliferation in networks with higher IN proportions. The proportion of INs in each network set remained similar to the initial plating ratio during the 4 weeks cultivation period. Results from additional networks generated with more diverse cellular composition, including early-born GABA neurons, suggest that a GABA-dependent mechanism may decrease the survival of additional INs. A large variation of the PN/IN ratio did not change the balance between isolated spontaneous glutamatergic and GABAergic postsynaptic currents charge transfer (E/I balance) measured in PNs or INs. In contrast, the E/I balance of multisynaptic bursts reflected differences in IN content. Additionally, the spontaneous activity recorded by calcium imaging showed that higher IN ratios were associated with increased frequency of network bursts combined with a decrease of participating neurons per event. In the 4th week in vitro, bursting activity was stereotypically synchronized in networks with very few INs but was more desynchronized in networks with higher IN proportions. These results suggest that the E/I balance of isolated postsynaptic currents in single cells may be regulated independently of PN/IN proportions, but the network bursts E/I balance and the maturation of spontaneous network activity critically depends upon the structural PN/IN ratio.

Extracellular Vesicles, Influential Players of Intercellular Communication within Adult Neurogenic Niches

Adult neurogenesis, involving the generation of functional neurons from adult neural stem cells (NSCs), occurs constitutively in discrete brain regions such as hippocampus, sub-ventricular zone (SVZ) and hypothalamus. The intrinsic structural plasticity of the neurogenic process allows the adult brain to face the continuously changing external and internal environment and requires coordinated interplay between all cell types within the specialized microenvironment of the neurogenic niche. NSC-, neuronal- and glia-derived factors, originating locally, regulate the balance between quiescence and self-renewal of NSC, their differentiation programs and the survival and integration of newborn cells. Extracellular Vesicles (EVs) are emerging as important mediators of cell-to-cell communication, representing an efficient way to transfer the biologically active cargos (nucleic acids, proteins, lipids) by which they modulate the function of the recipient cells. Current knowledge of the physiological role of EVs within adult neurogenic niches is rather limited. In this review, we will summarize and discuss EV-based cross-talk within adult neurogenic niches and postulate how EVs might play a critical role in the regulation of the neurogenic process.

Spinal Cord Stem Cells In Their Microenvironment: The Ependyma as a Stem Cell Niche

The ependyma of the spinal cord is currently proposed as a latent neural stem cell niche. This chapter discusses recent knowledge on the developmental origin and nature of the heterogeneous population of cells that compose this stem cell microenviroment, their diverse physiological properties and regulation. The chapter also reviews relevant data on the ependymal cells as a source of plasticity for spinal cord repair.

Neurotransmitter-Regulated Regeneration in the Zebrafish Retina

Current efforts to repair damaged or diseased mammalian retinas are inefficient and largely incapable of fully restoring vision. Conversely, the zebrafish retina is capable of spontaneous regeneration upon damage using Müller glia (MG)-derived progenitors. Understanding how zebrafish MG initiate regeneration may help develop new treatments that prompt mammalian retinas to regenerate. We show that inhibition of γ-aminobutyric acid (GABA) signaling facilitates initiation of MG proliferation. GABA levels decrease following damage, and MG are positioned to detect decreased ambient levels and undergo dedifferentiation. Using pharmacological and genetic approaches, we demonstrate that GABA_A receptor inhibition stimulates regeneration in undamaged retinas while activation inhibits regeneration in damaged retinas.

Neuronal Circuitry Mechanisms Regulating Adult Mammalian Neurogenesis

The adult mammalian brain is a dynamic structure, capable of remodeling in response to various physiological and pathological stimuli. One dramatic example of brain plasticity is the birth and subsequent integration of newborn neurons into the existing circuitry. This process, termed adult neurogenesis, recapitulates neural developmental events in two specialized adult brain regions: the lateral ventricles of the forebrain. Recent studies have begun to delineate how the existing neuronal circuits influence the dynamic process of adult neurogenesis, from activation of quiescent neural stem cells (NSCs) to the integration and survival of newborn neurons. Here, we review recent progress toward understanding the circuit-based regulation of adult neurogenesis in the hippocampus and olfactory bulb.

Regulation of adult neurogenesis by GABAergic transmission: signaling beyond GABAA-receptors

In the adult mammalian brain, neurogenesis occurs in the olfactory bulb (OB) and in the dentate gyrus (DG) of the hippocampus. Several studies have shown that multiple stages of neurogenesis are regulated by GABAergic transmission with precise spatio-temporal selectivity, and involving mechanisms common to both systems or specific only to one. In the subgranular zone (SGZ) of the DG, GABA neurotransmitter, released by a specific population of interneurons, regulates stem cell quiescence and neuronal cell fate decisions. Similarly, in the subventricular zone (SVZ), OB neuroblast production is modulated by ambient GABA. Ambient GABA, acting on extrasynaptic GABAA receptors (GABAAR), is also crucial for proper adult-born granule cell (GC) maturation and synaptic integration in the OB as well as in the DG. Throughout adult-born neuron development, various GABA receptors and receptor subunits play specific roles. Previous work has demonstrated that adult-born GCs in both the OB and the DG show a time window of increased plasticity in which adult-born cells are more prone to modification by external stimuli. One mechanism that controls this "critical period" is GABAergic modulation. Indeed, depleting the main phasic GABAergic inputs in adult-born neurons results in dramatic effects, such as reduction of spine density and dendritic branching in adult-born OB GCs. In this review, we systematically compare the role of GABAergic transmission in the regulation of adult neurogenesis between the OB and the hippocampus, focusing on the role of GABA in modulating plasticity and critical periods of adult-born neuron development. Finally, we discuss signaling pathways that might mediate some of the deficits observed upon targeted deletion of postsynaptic GABAARs in adult-born neurons.

GABAergic striatal neurons project dendrites and axons into the postnatal subventricular zone leading to calcium activity

GABA regulates the behavior of neuroblasts and neural progenitor cells in the postnatal neurogenic subventricular zone (SVZ) through GABAA receptor (GABAAR)-mediated calcium increases. However, the source of GABA necessary for sufficient GABAAR-mediated depolarization and calcium increase has remained speculative. Here, we explored whether GABAergic striatal neurons functionally connect with SVZ cells. Using patch clamp recordings or single cell electroporation, striatal neurons along the SVZ were filled with a fluorescent dye revealing that they send both dendrites and axons into the SVZ. About 93% of the recorded neurons were medium spiny or aspiny GABAergic neurons and each neuron sent 3-4 processes into the SVZ covering ~56 μm. Using calcium imaging, we found that depolarization of striatal neurons led to increased calcium activity in SVZ cells that were mediated by GABAAR activation. Collectively, these findings undercover a novel mode of signaling in the SVZ providing a mechanism of brain activity-mediated regulation of postnatal neurogenesis through GABAergic striatal activity.

Endocannabinoid signalling in neuronal migration

The endocannabinoid (eCB) system consists of several endogenous lipids, their target CB1 and CB2 receptors and enzymes responsible for their synthesis and degradation. The most abundant eCB in the central nervous system (CNS), 2-arachidonoyl glycerol (2-AG), triggers a broad range of signalling events by acting on CB1, the most abundant G protein-coupled receptor in the CNS. The eCB system regulates many physiological processes including neurogenesis, axon guidance and synaptic plasticity. Recent studies have highlighted an additional important role for eCB signalling in neuronal migration, which is crucial to achieve the complex architecture and efficient wiring of the CNS. Indeed, eCB signalling controls migration both pre- and post-natally, regulating interneuron positioning in the developing cortex and hippocampus and the polarised motility of stem cell-derived neuroblasts. While these effects may contribute to cognitive deficits associated with cannabis consumption, they also provide potential opportunities for endogenous stem cell-based neuroregenerative strategies.

GABA(A) receptor agonist and antagonist alter vestibular compensation and different steps of reactive neurogenesis in deafferented vestibular nuclei of adult cats

Strong reactive cell proliferation occurs in the vestibular nuclei after unilateral vestibular neurectomy (UVN). Most of the newborn cells survive, differentiate into glial cells and neurons with GABAergic phenotype, and have been reported to contribute to recovery of the posturo-locomotor functions in adult cats. Because the GABAergic system modulates vestibular function recovery and the different steps of neurogenesis in mammals, we aimed to examine in our UVN animal model the effect of chronic infusion of GABA(A) receptor (R) agonist and antagonist in the vestibular nuclei. After UVN and one-month intracerebroventricular infusions of saline, GABA(A)R agonist (muscimol) or antagonist (gabazine), cell proliferation and differentiation into astrocytes, microglial cells, and neurons were revealed using immunohistochemical methods. We also determined the effects of these drug infusions on the recovery of posturo-locomotor and oculomotor functions through behavioral tests. Our results showed that surprisingly, one month after UVN, newborn cells did not survive in the UVN-muscimol group whereas the number of GABAergic pre-existent neurons increased, and the long-term behavioral recovery of the animals was drastically impaired. Conversely, a significant number of newborn cells survived up to 1 month in the UVN-gabazine group whereas the astroglial population increased, and these animals showed the fastest recovery in behavioral functions. This study reports for the first time that GABA plays multiple roles, ranging from beneficial to detrimental on the different steps of a functional postlesion neurogenesis and further, strongly influences the time course of vestibular function recovery.

Stromal derived growth factor-1 (CXCL12) modulates synaptic transmission to immature neurons during post-ischemic cerebral repair

In response to ischemic injury, the brain mounts a repair process involving the development of new neurons, oligodendrocytes, and astrocytes. However, the manner in which new neurons integrate into existing brain circuitry is not well understood. Here we observed that during the four weeks after transient middle cerebral artery occlusion (MCAO), doublecortin (DCX)-expressing neural progenitors originating in the subventricular zone (SVZ) were present in the ischemic lesion borderzone, where they received γ-aminobutyric acid (GABA) inputs, a feature that is common to newly developing neurons. The chemokine stromal derived factor-1 (SDF-1 or CXCL12) was enriched in lesional endothelial and microglial cells for up to four weeks after transient MCAO, and application of SDF-1 to acute brain slices enhanced GABAergic inputs to the new neurons. These observations suggest that SDF-1 is in a position to coordinate neovascularization and neurogenesis during the repair process after cerebral ischemia-reperfusion.

Impact of omega-6 polyunsaturated fatty acid supplementation and γ-aminobutyric acid on astrogliogenesis through the endocannabinoid system

Neural stem cells express cannabinoid CB1 and CB2 receptors and the enzymes for the biosynthesis and metabolism of endocannabinoids (eCBs). Here we have studied the role of neural stem cell-derived eCBs as autonomous regulatory factors during differentiation. First, we examined the effect of an indirect eCB precursor linoleic acid (LA), a major dietary omega-6 fatty acid, on the eCB system in neural stem/progenitor cells (NSPCs) cultured in DMEM/F12 supplemented with N2 (N2/DF) as monolayer cells. LA upregulated eCB system-related genes and 2-arachidonoylglycerol (2-AG), but not anandamide (AEA), levels. Glial fibrillary acidic protein (GFAP) was significantly higher under LA-enriched conditions, and this effect was inhibited by the cannabinoid receptor type-1 (CB1) antagonist AM251. Second, the levels of AEA and 2-AG, as well as of the mRNA of eCB system-related genes, were measured in NSPCs after γ-aminobutyric acid (GABA) treatment. GABA upregulated AEA levels significantly in LA-enriched cultures and increased the mRNA expression of the 2-AG-degrading enzyme monoacylglycerol lipase. These effects of GABA were reproduced under culture conditions using neurobasal media supplemented with B27, which is commonly used for neurosphere culture. GABA stimulated astroglial differentiation in this medium as indicated by increased GFAP levels. This effect was abolished by AM251, suggesting the involvement of AEA and CB1 in GABA-induced astrogliogenesis. This study highlights the importance of eCB biosynthesis and CB1 signalling in the autonomous regulation of NSPCs and the influence of the eCB system on astrogliogenesis induced by nutritional factors or neurotransmitters, such as LA and GABA.

Differentiation of human neural progenitor cells in functionalized hydrogel matrices

Hydrogel-based three-dimensional (3D) scaffolds are widely used in the field of regenerative medicine, translational medicine, and tissue engineering. Recently, we reported the effect of scaffold formation on the differentiation and survival of human neural progenitor cells (hNPCs) using PuraMatrix™ (RADA-16) scaffolds. Here, we were interested in the impact of PuraMatrix modified by the addition of short peptide sequences, based on a bone marrow homing factor and laminin. The culture and differentiation of the hNPCs in the modified matrices resulted in an approximately fivefold increase in neuronal cells. The examination of apoptotic and necrotic cells, as well as the level of the anti-apoptotic protein Bcl-2, indicates benefits for cells hosted in the modified formulations. In addition, we found a trend to lower proportions of apoptotic or necrotic neuronal cells in the modified matrices. Interestingly, the neural progenitor cell pool was increased in all the tested matrices in comparison to the standard 2D culture system, while no difference was found between the modified matrices. We conclude that a combination of elevated neuronal differentiation and a protective effect of the modified matrices underlies the increased proportion of neuronal cells.

NKCC1 knockdown decreases neuron production through GABA(A)-regulated neural progenitor proliferation and delays dendrite development

Signaling through GABA(A) receptors controls neural progenitor cell (NPC) development in vitro and is altered in schizophrenic and autistic individuals. However, the in vivo function of GABA(A) signaling on neural stem cell proliferation, and ultimately neurogenesis, remains unknown. To examine GABA(A) function in vivo, we electroporated plasmids encoding short-hairpin (sh) RNA against the Na-K-2Cl cotransporter NKCC1 (shNKCC1) in NPCs of the neonatal subventricular zone in mice to reduce GABA(A)-induced depolarization. Reduced GABA(A) depolarization identified by a loss of GABA(A)-induced calcium responses in most electroporated NPCs led to a 70% decrease in the number of proliferative Ki67(+) NPCs and a 60% reduction in newborn neuron density. Premature loss of GABA(A) depolarization in newborn neurons resulted in truncated dendritic arborization at the time of synaptic integration. However, by 6 weeks the dendritic tree had partially recovered and displayed a small, albeit significant, decrease in dendritic complexity but not total dendritic length. To further examine GABA(A) function on NPCs, we treated animals with a GABA(A) allosteric agonist, pentobarbital. Enhancement of GABA(A) activity in NPCs increased the number of proliferative NPCs by 60%. Combining shNKCC1 and pentobarbital prevented the shNKCC1 and the pentobarbital effects on NPC proliferation, suggesting that these manipulations affected NPCs through GABA(A) receptors. Thus, dysregulation in GABA(A) depolarizing activity delayed dendritic development and reduced NPC proliferation resulting in decreased neuronal density.

GABAA receptor signaling induces osmotic swelling and cell cycle activation of neonatal prominin+ precursors

Signal-regulated changes in cell size affect cell division and survival and therefore are central to tissue morphogenesis and homeostasis. In this respect, GABA receptors (GABA(A)Rs) are of particular interest because allowing anions flow across the cell membrane modulates the osmolyte flux and the cell volume. Therefore, we have here investigated the hypothesis that GABA may regulate neural stem cell proliferation by inducing cell size changes. We found that, besides neuroblasts, also neural precursors in the neonatal murine subependymal zone sense GABA via GABA(A) Rs. However, unlike in neuroblasts, where it induced depolarization-mediated [Ca(2+)](i) increase, GABA(A) Rs activation in precursors caused hyperpolarization. This resulted in osmotic swelling and increased surface expression of epidermal growth factor receptors (EGFRs). Furthermore, activation of GABA(A) Rs signaling in vitro in the presence of EGF modified the expression of the cell cycle regulators, phosphatase and tensin homolog and cyclin D1, increasing the pool of cycling precursors without modifying cell cycle length. A similar effect was observed on treatment with diazepam. We also demonstrate that GABA and diazepam responsive precursors represent prominin(+) stem cells. Finally, we show that as in in vitro also in in vivo a short administration of diazepam promotes EGFR expression in prominin(+) stem cells causing activation and cell cycle entry. Thus, our data indicate that endogenous GABA is a part of a regulatory mechanism of size and cell cycle entry of neonatal stem cells. Our results also have potential implications for the therapeutic practices that involve exposure to GABA(A) Rs modulators during neurodevelopment.

GABAergic signalling in a neurogenic niche of the turtle spinal cord

The region that surrounds the central canal (CC) in the turtle spinal cord is a neurogenic niche immersed within already functional circuits, where radial glia expressing brain lipid binding protein (BLBP) behave as progenitors. The behaviour of both progenitors and neuroblasts within adult neurogenic niches must be regulated to maintain the functional stability of the host circuit. In the brain, GABA plays a major role in this kind of regulation but little is known about GABAergic signalling in neurogenic niches of the postnatal spinal cord. Here we explored the action of GABA around the CC of the turtle spinal cord by combining patch-clamp recordings of CC-contacting cells, immunohistochemistry for key components of GABAergic signalling and Ca(2+) imaging. Two potential sources of GABA appeared around the CC: GABAergic terminals and CC-contacting neurones. GABA depolarized BLBP(+) progenitors via GABA transporter-3 (GAT3) and/or GABA(A) receptors. In CC-contacting neurones, GABA(A) receptor activation generated responses ranging from excitation to inhibition. This functional heterogeneity appeared to originate from different ratios of activity of the Na(+)-K(+)-2Cl(-) co-transporter (NKCC1) and the K(+)-Cl(-) co-transporter (KCC2). In both progenitors and immature neurones, GABA induced an increase in intracellular Ca(2+) that required extracellular Ca(2+) and was blocked by the selective GABA(A) receptor antagonist gabazine. Our study shows that GABAergic signalling around the CC shares fundamental properties with those in the embryo and adult neurogenic niches, suggesting that GABA may be part of the mechanisms regulating the production and integration of neurones within operational spinal circuits in the turtle.

Neurotransmitters couple brain activity to subventricular zone neurogenesis

Adult neurogenesis occurs in two privileged microenvironments, the hippocampal subgranular zone of the dentate gyrus and the subventricular zone (SVZ) along the lateral ventricle. This review focuses on accumulating evidence suggesting that the activity of specific brain regions or bodily states influences SVZ cell proliferation and neurogenesis. Neuromodulators such as dopamine and serotonin have been shown to have long-range effects through neuronal projections into the SVZ. Local γ-aminobutyric acid and glutamate signaling have demonstrated effects on SVZ proliferation and neurogenesis, but an extra-niche source of these neurotransmitters remains to be explored and options will be discussed. There is also accumulating evidence that diseases and bodily states such as Alzheimer's disease, seizures, sleep and pregnancy influence SVZ cell proliferation. With such complex behavior and environmentally-driven factors that control subregion-specific activity, it will become necessary to account for overlapping roles of multiple neurotransmitter systems on neurogenesis when developing cell therapies or drug treatments.

GABA(A) receptor and glycine receptor activation by paracrine/autocrine release of endogenous agonists: more than a simple communication pathway

It is a common and widely accepted assumption that glycine and GABA are the main inhibitory transmitters in the central nervous system (CNS). But, in the past 20 years, several studies have clearly demonstrated that these amino acids can also be excitatory in the immature central nervous system. In addition, it is now established that both GABA receptors (GABARs) and glycine receptors (GlyRs) can be located extrasynaptically and can be activated by paracrine release of endogenous agonists, such as GABA, glycine, and taurine. Recently, non-synaptic release of GABA, glycine, and taurine gained further attention with increasing evidence suggesting a developmental role of these neurotransmitters in neuronal network formation before and during synaptogenesis. This review summarizes recent knowledge about the non-synaptic activation of GABA(A)Rs and GlyRs, both in developing and adult CNS. We first present studies that reveal the functional specialization of both non-synaptic GABA(A)Rs and GlyRs and we discuss the neuronal versus non-neuronal origin of the paracrine release of GABA(A)R and GlyR agonists. We then discuss the proposed non-synaptic release mechanisms and/or pathways for GABA, glycine, and taurine. Finally, we summarize recent data about the various roles of non-synaptic GABAergic and glycinergic systems during the development of neuronal networks and in the adult.

NKCC1 controls GABAergic signaling and neuroblast migration in the postnatal forebrain

From an early postnatal period and throughout life there is a continuous production of olfactory bulb (OB) interneurons originating from neuronal precursors in the subventricular zone. To reach the OB circuits, immature neuroblasts migrate along the rostral migratory stream (RMS). In the present study, we employed cultured postnatal mouse forebrain slices and used lentiviral vectors to label neuronal precursors with GFP and to manipulate the expression levels of the Na-K-2Cl cotransporter NKCC1. We investigated the role of this Cl- transporter in different stages of postnatal neurogenesis, including neuroblast migration and integration in the OB networks once they have reached the granule cell layer (GCL). We report that NKCC1 activity is necessary for maintaining normal migratory speed. Both pharmacological and genetic manipulations revealed that NKCC1 maintains high [Cl-]i and regulates the resting membrane potential of migratory neuroblasts whilst its functional expression is strongly reduced at the time cells reach the GCL. As in other developing systems, NKCC1 shapes GABAA-dependent signaling in the RMS neuroblasts. Also, we show that NKCC1 controls the migration of neuroblasts in the RMS. The present study indeed indicates that the latter effect results from a novel action of NKCC1 on the resting membrane potential, which is independent of GABAA-dependent signaling. All in all, our findings show that early stages of the postnatal recruitment of OB interneurons rely on precise, orchestrated mechanisms that depend on multiple actions of NKCC1.

Physiological roles of ion channels in adult neural stem cells and their progeny

Elucidation of the machinery of adult neurogenesis is indispensable for the treatment of neurodegenerative diseases by therapeutic drugs and/or by neural stem cell (NSC) transplantation. It is well known that membrane ion channels play a critical role in cell function, including proliferation, apoptosis and migration in a wide range of cells. In NSC research, interdisciplinary collaboration between cell biologists and membrane physiologists has been pursued principally to monitor ion channel and synaptic currents as a hallmark of neuronal differentiation and maturation of NSC progeny. Nevertheless, less attention had been paid to a functional role of ion channels in NSCs or their immature progeny. Recently, however, evidence regarding their functional relevance has started to accumulate. In focusing on the early stages of the neurogenic process during which NSCs give rise to neuroblasts, this review highlights the latent ability of ion channels to act as functional regulators of adult neurogenesis.

GABAergic control of neurite outgrowth and remodeling during development and adult neurogenesis: general rules and differences in diverse systems

During development, Gamma-aminobutyric acidergic (GABAergic) neurons mature at early stages, long before excitatory neurons. Conversely, GABA reuptake transporters become operative later than glutamate transporters. GABA is therefore not removed efficiently from the extracellular domain and it can exert significant paracrine effects. Hence, GABA-mediated activity is a prominent source of overall neural activity in developing CNS networks, while neurons extend dendrites and axons, and establish synaptic connections. One of the unique features of GABAergic functional plasticity is that in early development, activation of GABA_A receptors results in depolarizing (mainly excitatory) responses and Ca²⁺ influx. Although there is strong evidence from several areas of the CNS that GABA plays a significant role in neurite growth not only during development but also during adult neurogenesis, surprisingly little effort has been made into putting all these observations into a common framework in an attempt to understand the general rules that regulate these basic and evolutionary well-conserved processes. In this review, we discuss the current knowledge in this important field. In order to decipher common, universal features and highlight differences between systems throughout development, we compare findings about dendritic proliferation and remodeling in different areas of the nervous system and species, and we also review recent evidence for a role in axonal elongation. In addition to early developmental aspects, we also consider the GABAergic role in dendritic growth during adult neurogenesis, extending our discussion to the roles played by GABA during dendritic proliferation in early developing networks versus adult, well established networks.

NMDA receptors activated by subventricular zone astrocytic glutamate are critical for neuroblast survival prior to entering a synaptic network

Even before integrating into existing circuitry, adult-born neurons express receptors for neurotransmitters, but the intercellular mechanisms and their impact on neurogenesis remain largely unexplored. Here, we show that neuroblasts born in the postnatal subventricular zone (SVZ) acquire NMDA receptors (NMDARs) during their migration to the olfactory bulb. Along their route, neuroblasts are ensheathed by astrocyte-like cells expressing vesicular glutamate release machinery. Increasing calcium in these specialized astrocytes induced NMDAR activity in neuroblasts, and blocking astrocytic vesicular release eliminated spontaneous NMDAR activity. Single-cell knockout of NMDARs using neonatal electroporation resulted in neuroblast apoptosis at the time of NMDAR acquisition. This cumulated in a 40% loss of neuroblasts along their migratory route, demonstrating that NMDAR acquisition is critical for neuroblast survival prior to entering a synaptic network. In addition, our findings suggest an unexpected mechanism wherein SVZ astrocytes use glutamate signaling through NMDARs to control the number of adult-born neurons reaching their final destination.

GABA(A) Increases Calcium in Subventricular Zone Astrocyte-Like Cells Through L- and T-Type Voltage-Gated Calcium Channels

In the adult neurogenic subventricular zone (SVZ), the behavior of astrocyte-like cells and some of their functions depend on changes in intracellular Ca²⁺ levels and tonic GABA_A receptor activation. However, it is unknown whether, and if so how, GABA_A receptor activity regulates intracellular Ca²⁺ dynamics in SVZ astrocytes. To monitor Ca²⁺ activity selectively in astrocyte-like cells, we used two lines of transgenic mice expressing either GFP fused to a Gq-coupled receptor or DsRed under the human glial fibrillary acidic protein (hGFAP) promoter. GABA_A receptor activation induced Ca²⁺ increases in 40–50% of SVZ astrocytes. GABA_A-induced Ca²⁺ increases were prevented with nifedipine and mibefradil, blockers of L- and T-type voltage-gated calcium channels (VGCC). The L-type Ca²⁺ channel activator BayK 8644 increased the percentage of GABA_A-responding astrocyte-like cells to 75%, suggesting that the majority of SVZ astrocytes express functional VGCCs. SVZ astrocytes also displayed spontaneous Ca²⁺ activity, the frequency of which was regulated by tonic GABA_A receptor activation. These data support a role for ambient GABA in tonically regulating intracellular Ca²⁺ dynamics through GABA_A receptors and VGCC in a subpopulation of astrocyte-like cells in the postnatal SVZ.

Neurotransmitter signaling in postnatal neurogenesis: The first leg

Like the liver or other peripheral organs, two regions of the adult brain possess the ability of self-renewal through a process called neurogenesis. This raises tremendous hope for repairing the damaged brain, and it has stimulated research on identifying signals controlling neurogenesis. Neurogenesis involves several stages from fate determination to synaptic integration via proliferation, migration, and maturation. While fate determination primarily depends on a genetic signature, other stages are controlled by the interplay between genes and microenvironmental signals. Here, we propose that neurotransmitters are master regulators of the different stages of neurogenesis. In favor of this idea, a description of selective neurotransmitter signaling and their functions in the largest neurogenic zone, the subventricular zone (SVZ), is provided. In particular, we emphasize the interactions between neuroblasts and astrocyte-like cells that release gamma-aminobutyric acid (GABA) and glutamate, respectively. However, we also raise several limitations to our knowledge on neurotransmitters in neurogenesis. The function of neurotransmitters in vivo remains largely unexplored. Neurotransmitter signaling has been viewed as uniform, which dramatically contrasts with the cellular and molecular mosaic nature of the SVZ. How neurotransmitters are integrated with other well-conserved molecules, such as sonic hedgehog, is poorly understood. In an effort to reconcile these differences, we discuss how specificity of neurotransmitter functions can be provided through their multitude of receptors and intracellular pathways in different cell types and their possible interactions with sonic hedgehog.

Glycine release from radial cells modulates the spontaneous activity and its propagation during early spinal cord development

Rhythmic electrical activity is a hallmark of the developing embryonic CNS and is required for proper development in addition to genetic programs. Neurotransmitter release contributes to the genesis of this activity. In the mouse spinal cord, this rhythmic activity occurs after embryonic day 11.5 (E11.5) as waves spreading along the entire cord. At E12.5, blocking glycine receptors alters the propagation of the rhythmic activity, but the cellular source of the glycine receptor agonist, the release mechanisms, and its function remain obscure. At this early stage, the presence of synaptic activity even remains unexplored. Using isolated embryonic spinal cord preparations and whole-cell patch-clamp recordings of identified motoneurons, we find that the first synaptic activity develops at E12.5 and is mainly GABAergic. Using a multiple approach including direct measurement of neurotransmitter release (i.e., outside-out sniffer technique), we also show that, between E12.5 and E14.5, the main source of glycine in the embryonic spinal cord is radial cell progenitors, also known to be involved in neuronal migration. We then demonstrate that radial cells can release glycine during synaptogenesis. This spontaneous non-neuronal glycine release can also be evoked by mechanical stimuli and occurs through volume-sensitive chloride channels. Finally, we find that basal glycine release upregulates the propagating spontaneous rhythmic activity by depolarizing immature neurons and by increasing membrane potential fluctuations. Our data raise the question of a new role of radial cells as secretory cells involved in the modulation of the spontaneous electrical activity of embryonic neuronal networks.

Gamma-aminobutyric acid and glutamate differentially regulate intracellular calcium concentrations in mouse gonadotropin-releasing hormone neurons

Multiple factors regulate the activity of the GnRH neurons responsible for controlling fertility. Foremost among neuronal inputs to GnRH neurons are those using the amino acids glutamate and gamma-aminobutyric acid (GABA). The present study used a GnRH-Pericam transgenic mouse line, enabling live cell imaging of intracellular calcium concentrations ([Ca(2+)](i)) to evaluate the effects of glutamate and GABA signaling on [Ca(2+)](i) in peripubertal and adult mouse GnRH neurons. Activation of GABA(A), N-methyl-d-aspartate, or alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate acid (AMPA) receptors was found to evoke an increase in [Ca(2+)](i), in subpopulations of GnRH neurons. Approximately 70% of GnRH neurons responded to GABA, regardless of postnatal age or sex. Many fewer (approximately 20%) GnRH neurons responded to N-methyl-d-aspartate, and this was not influenced by postnatal age or sex. In contrast, about 65% of adult male and female GnRH neurons responded to AMPA compared with about 14% of male and female peripubertal mice (P < 0.05). The mechanisms underlying the ability of GABA and AMPA to increase [Ca(2+)](i) in adult GnRH neurons were evaluated pharmacologically. Both GABA and AMPA were found to evoke [Ca(2+)](i) increases through a calcium-induced calcium release mechanism involving internal calcium stores and inositol-1,4,5-trisphosphate receptors. For GABA, the initial increase in [Ca(2+)](i) originated from GABA(A) receptor-mediated activation of L-type voltage-gated calcium channels, whereas for AMPA this appeared to involve direct calcium entry through the AMPA receptor. These observations show that all of the principal amino acid receptors are able to control [Ca(2+)](i) in GnRH neurons but that they do so in a postnatal age- and intracellular pathway-specific manner.

Early synapse formation in developing interneurons of the adult olfactory bulb

New olfactory bulb granule cells (GCs) are GABAergic interneurons continuously arising from neuronal progenitors and integrating into preexisting bulbar circuits. They receive both GABAergic and glutamatergic synaptic inputs from olfactory bulb intrinsic neurons and centrifugal afferents. Here, we investigated the spatiotemporal dynamic of newborn GC synaptogenesis in adult mouse olfactory bulb. First, we established that GABAergic synapses onto mature GC dendrites contain the GABA(A) receptor alpha2 subunit along with the postsynaptic scaffolding protein gephyrin. Next, we characterized morphologically and electrophysiologically the development of GABAergic and glutamatergic inputs onto newborn GCs labeled with eGFP (enhanced green fluorescent protein) using lentiviral vectors. Already when reaching the GC layer (GCL), at 3 d post-vector injection (dpi), newborn GCs exhibited tiny voltage-dependent sodium currents and received functional GABAergic and glutamatergic synapses, recognized immunohistochemically by apposition of specific presynaptic and postsynaptic markers. Thereafter, GABAergic and glutamatergic synaptic contacts increased differentially in the GCL, and at 7 dpi, PSD-95 clusters outnumbered gephyrin clusters. Thus, the weight of GABAergic input was predominant at early stages of GC maturation, but not later. Newborn GC dendrites first reached the external plexiform layer at 4 dpi, where they received functional GABAergic contacts at 5 dpi. Reciprocal synapses initially were formed on GC dendritic shafts, where they might contribute to spine formation. Their presence was confirmed ultrastructurally at 7 dpi. Together, our findings unravel rapid synaptic integration of newborn GCs in adult mouse olfactory bulb, with GABAergic and glutamatergic influences being established proximally before formation of output synapses by apical GC dendrites onto mitral/tufted cells.

Neurogenesis and astrogenesis contribution to recovery of vestibular functions in the adult cat following unilateral vestibular neurectomy: cellular and behavioral evidence

In physiological conditions, neurogenesis occurs in restricted regions of the adult mammalian brain, giving rise to integrated neurons into functional networks. In pathological or postlesional conditions neurogenesis and astrogenesis can also occur, as demonstrated in the deafferented vestibular nuclei after immediate unilateral vestibular neurectomy (UVN) in the adult cat. To determine whether the reactive cell proliferation and beyond neurogenesis and astrogenesis following UVN plays a functional role in the vestibular functions recovery, we examined the effects of an antimitotic drug: the cytosine-beta-d arabinofuranoside (AraC), infused in the fourth ventricle after UVN. Plasticity mechanisms were evidenced at the immunohistochemical level with bromodeoxyuridine, GAD67 and glial fibrillary acidic protein (GFAP) stainings. Consequences of immediate or delayed AraC infusion on the behavioral recovery processes were evaluated with oculomotor and posturo-locomotor tests. We reported that after UVN, immediate AraC infusion blocked the cell proliferation and decreased the number of GFAP-immunoreactive cells and GABAergic neurons observed in the vestibular nuclei of neurectomized cats. At the behavioral level, after UVN and immediate AraC infusion the time course of posturo-locomotor function recovery was drastically delayed, and no alteration of the horizontal spontaneous nystagmus was observed. In contrast, an infusion of AraC beginning 3 weeks after UVN had no influence neither on the time course of the behavioral recovery, nor on the reactive cell proliferation and its differentiation. We conclude that the first 3 weeks after UVN represent a possible critical period in which important neuroplasticity mechanisms take place for promoting vestibular function recovery: reactive neurogenesis and astrogenesis might contribute highly to vestibular compensation in the adult cat.

Ca(2+) signaling evoked by activation of Na(+) channels and Na(+)/Ca(2+) exchangers is required for GABA-induced NG2 cell migration

NG2 cells originate from various brain regions and migrate to their destinations during early development. These cells express voltage-gated Na(+) channels but fail to produce typical action potentials. The physiological role of Na(+) channels in these cells is unclear. We found that GABA induces membrane depolarization and Ca(2+) elevation in NG2 cells, a process requiring activation of GABA(A) receptors, Na(+) channels, and Na(+)/Ca(2+) exchangers (NCXs), but not Ca(2+) channels. We have identified a persistent Na(+) current in these cells that may underlie the GABA-induced pathway of prolonged Na(+) elevation, which in turn triggers Ca(2+) influx via NCXs. This unique Ca(2+) signaling pathway is further shown to be involved in the migration of NG2 cells. Thus, GABAergic signaling mediated by sequential activation of GABA(A) receptors, noninactivating Na(+) channels, and NCXs may play an important role in the development and function of NG2 glial cells in the brain.

GABA increases Ca2+ in cerebellar granule cell precursors via depolarization: implications for proliferation

The amino acids glutamate and gamma-aminobutyric acid (GABA) have primarily been characterized as the most prevalent excitatory and inhibitory, respectively, neurotransmitters in the vertebrate central nervous system. However, the role of these signaling molecules extends far beyond the synapse. GABA, glutamate, and their complement of receptors are essential signaling molecules that regulate developmental processes in both embryonic and young adult mammals. In this review, we describe the current knowledge on the role of GABA and glutamate in development, focusing on the perinatal cerebellum. We will then present novel data suggesting that GABA depolarizes granule cell precursors via GABA(A) receptors, which leads to calcium increases in these cells. Finally, we will consider the role of GABA and glutamate signaling on cell proliferation and perhaps neural cancers. From our review of the literature and these data, we hypothesize that GABA(A) receptors and metabotropic glutamate receptors may be a novel target for the pharmacological regulation of the cerebellar tumors, medulloblastomas.

GABA's control of stem and cancer cell proliferation in adult neural and peripheral niches

Aside from traditional neurotransmission and regulation of secretion, gamma-amino butyric acid (GABA) through GABA(A) receptors negatively regulates proliferation of pluripotent and neural stem cells in embryonic and adult tissue. There has also been evidence that GABAergic signaling and its control over proliferation is not only limited to the nervous system, but is widespread through peripheral organs containing adult stem cells. GABA has emerged as a tumor signaling molecule in the periphery that controls the proliferation of tumor cells and perhaps tumor stem cells. Here, we will discuss GABA's presence as a near-universal signal that may be altered in tumor cells resulting in modified mitotic activity.

Ion fluxes and neurotransmitters signaling in neural development

The brain develops and functions in a complex ionic milieu, which is a prerequisite for neurotransmitter function and neuronal signaling. Neurotransmitters and ion fluxes are, however, important not only in neuronal signaling, but also in the control of neural differentiation, and in this review, we highlight the recent advances in our understanding of how the gamma-amino butyric acid (GABA) neurotransmitter and ion fluxes are relevant for cell cycle control and neural differentiation. Conversely, proteins previously associated with ion transport across membranes have been endowed with novel ion-independent functions, and we discuss this in the context of gap junctions in cell adhesion and of the neuron-specific K(+)-Cl(-) cotransporter KCC2 in dendritic spine development. Collectively, these findings provide a richer and more complex picture of when ion fluxes are needed in neural development and when they are not.

The astrocyte odyssey

Neurons have long held the spotlight as the central players of the nervous system, but we must remember that we have equal numbers of astrocytes and neurons in the brain. Are these cells only filling up the space and passively nurturing the neurons, or do they also contribute to information transfer and processing? After several years of intense research since the pioneer discovery of astrocytic calcium waves and glutamate release onto neurons in vitro, the neuronal-glial studies have answered many questions thanks to technological advances. However, the definitive in vivo role of astrocytes remains to be addressed. In addition, it is becoming clear that diverse populations of astrocytes coexist with different molecular identities and specialized functions adjusted to their microenvironment, but do they all belong to the umbrella family of astrocytes? One population of astrocytes takes on a new function by displaying both support cell and stem cell characteristics in the neurogenic niches. Here, we define characteristics that classify a cell as an astrocyte under physiological conditions. We will also discuss the well-established and emerging functions of astrocytes with an emphasis on their roles on neuronal activity and as neural stem cells in adult neurogenic zones.

Etazolate, a neuroprotective drug linking GABA(A) receptor pharmacology to amyloid precursor protein processing

Pharmacological modulation of the GABA(A) receptor has gained increasing attention as a potential treatment for central processes affected in Alzheimer disease (AD), including neuronal survival and cognition. The proteolytic cleavage of the amyloid precursor protein (APP) through the alpha-secretase pathway decreases in AD, concurrent with cognitive impairment. This APP cleavage occurs within the beta-amyloid peptide (Abeta) sequence, precluding formation of amyloidogenic peptides and leading to the release of the soluble N-terminal APP fragment (sAPPalpha) which is neurotrophic and procognitive. In this study, we show that at nanomolar-low micromolar concentrations, etazolate, a selective GABA(A) receptor modulator, stimulates sAPPalpha production in rat cortical neurons and in guinea pig brains. Etazolate (20 nM-2 microM) dose-dependently protected rat cortical neurons against Abeta-induced toxicity. The neuroprotective effects of etazolate were fully blocked by GABA(A) receptor antagonists indicating that this neuroprotection was due to GABA(A) receptor signalling. Baclofen, a GABA(B) receptor agonist failed to inhibit the Abeta-induced neuronal death. Furthermore, both pharmacological alpha-secretase pathway inhibition and sAPPalpha immunoneutralization approaches prevented etazolate neuroprotection against Abeta, indicating that etazolate exerts its neuroprotective effect via sAPPalpha induction. Our findings therefore indicate a relationship between GABA(A) receptor signalling, the alpha-secretase pathway and neuroprotection, documenting a new therapeutic approach for AD treatment.

The chemokine stromal cell-derived factor-1 regulates GABAergic inputs to neural progenitors in the postnatal dentate gyrus

Stromal cell-derived factor-1 (SDF-1) and its receptor CXC chemokine receptor 4 (CXCR4) are important regulators of the development of the dentate gyrus (DG). Both SDF-1 and CXCR4 are also highly expressed in the adult DG. We observed that CXCR4 receptors were expressed by dividing neural progenitor cells located in the subgranular zone (SGZ) as well as their derivatives including doublecortin-expressing neuroblasts and immature granule cells. SDF-1 was located in DG neurons and in endothelial cells associated with DG blood vessels. SDF-1-expressing neurons included parvalbumin-containing GABAergic interneurons known as basket cells. Using transgenic mice expressing an SDF-1-mRFP1 (monomeric red fluorescence protein 1) fusion protein we observed that SDF-1 was localized in synaptic vesicles in the terminals of basket cells together with GABA-containing vesicles. These terminals were often observed to be in close proximity to dividing nestin-expressing neural progenitors in the SGZ. Electrophysiological recordings from slices of the DG demonstrated that neural progenitors received both tonic and phasic GABAergic inputs and that SDF-1 enhanced GABAergic transmission, probably by a postsynaptic mechanism. We also demonstrated that, like GABA, SDF-1 was tonically released in the DG and that GABAergic transmission was partially dependent on coreleased SDF-1. These data demonstrate that SDF-1 plays a novel role as a neurotransmitter in the DG and regulates the strength of GABAergic inputs to the pool of dividing neural progenitors. Hence, SDF-1/CXCR4 signaling is likely to be an important regulator of adult neurogenesis in the DG.

Tonic activation of GLUK5 kainate receptors decreases neuroblast migration in whole-mounts of the subventricular zone

In the postnatal subventricular zone (SVZ), neuroblasts migrate in chains along the lateral ventricle towards the olfactory bulb. AMPA/kainate receptors as well as metabotropic glutamate receptors subtype 5 (mGluR5) are expressed in SVZ cells. However, the cells expressing these receptors and the function of these receptors remain unexplored. We thus examined whether SVZ neuroblasts express mGluR5 and Ca(2+)-permeable kainate receptors in mouse slices. Doublecortin (DCX)-immunopositive cells (i.e. neuroblasts) immunostained positive for mGluR5 and GLU(K5-7)-containing kainate receptors. RT-PCR from approximately 10 GFP-fluorescent cell aspirates obtained in acute slices from transgenic mice expressing green fluorescent protein (GFP) under the DCX promoter showed mGluR5 and GLU(K5) receptor mRNA in SVZ neuroblasts. Patch-clamp data suggest that approximately 60% of neuroblasts express functional GLU(K5)-containing receptors. Activation of mGluR5 and GLU(K5)-containing receptors induced Ca(2+) increases in 50% and 60% of SVZ neuroblasts, respectively, while most neuroblasts displayed GABA(A)-mediated Ca(2+) responses. To examine the effects of these receptors on the speed of neuroblast migration, we developed a whole-mount preparation of the entire lateral ventricle from postnatal day (P) 20-25 DCX-GFP mice. The GABA(A) receptor (GABA(A)R) antagonist bicuculline increased the speed of neuroblast migration by 27%, as previously reported in acute slices. While the mGluR5 antagonist MPEP did not affect the speed of neuroblast migration, the homomeric and heteromeric GLU(K5) receptor antagonists, NS3763 and UB302, respectively, increased the migration speed by 38%. These data show that although both GLU(K5) receptor and mGluR5 activations increase Ca(2+) in neuroblasts, only GLU(K5) receptors tonically reduce the speed of neuroblast migration along the lateral ventricle.

GABAergic signalling to adult-generated neurons

New neurons are continuously generated in discrete regions of the adult brain. In the hippocampus, newly generated cells undergo a step-wise progression of maturation that is regulated at multiple stages by a variety of physiological and pathological stimuli. Neural progenitors and newborn neurons initially receive exclusively GABAergic synaptic input, and accumulating evidence suggests that depolarizing actions of GABA contribute to activity-dependent regulation. Here we provide a brief overview of GABAergic signalling to newborn neurons in the hippocampus and describe how it regulates adult neurogenesis.

Control of neuroblast production and migration by converging GABA and glutamate signals in the postnatal forebrain

The production of adult-born neurons is an ongoing process accounting for > 10,000 immature neurons migrating to the olfactory bulb every day. This high turnover rate necessitates profound control mechanisms converging onto neural stem cells and neuroblasts to achieve adequate adult-born neuron production. Here, we elaborate on a novel epigenetic control of adult neurogenesis via highly coordinated, non-synaptic, intercellular signalling. This communication engages the neurotransmitters GABA and glutamate, whose extracellular concentrations depend on neuroblast number and high affinity uptake systems in stem cells. Previous studies show that neuroblasts release GABA providing a negative feedback control of stem cell proliferation. Recent findings show an unexpected mosaic expression of glutamate receptors leading to calcium elevations in migrating neuroblasts. We speculate that stem cells release glutamate that activates glutamate receptors on migrating neuroblasts providing them with migratory and survival cues. In addition, we propose that the timing of neurotransmitter release and their spatial diffusion will determine the convergent coactivation of neuroblasts and stem cells, and provide a steady-state level of neuroblast production. Upon external impact or injury this signalling may adjust to a new steady-state level, thus providing non-synaptic scaling of neuroblast production.

GABA effects on neurogenesis: an arsenal of regulation

The well-known inhibitory neurotransmitter GABA is excitatory to immature neurons during development as well as to neural progenitor cells during adult neurogenesis. Recent evidence indicates that GABA plays a role in regulating neurogenesis in various situations. This journal club paper aims to provide a skeleton description of GABA regulation of neurogenesis, describing some of the disparate mechanisms and scenarios in which it is involved.

GABAA receptors, anesthetics and anticonvulsants in brain development

GABA, acting via GABA(A) receptors, is well-accepted as the main inhibitory neurotransmitter of the mature brain, where it dampens neuronal excitability. The receptor's properties have been studied extensively, yielding important information about its structure, pharmacology, and regulation that are summarized in this review. Several GABAergic drugs have been commonly used as anesthetics, sedatives, and anticonvulsants for decades. However, findings that GABA has critical functions in brain development, in particular during the late embryonic and neonatal period, raise worthwhile questions regarding the side effects of GABAergic drugs that may lead to long-term cognitive deficits. Here, we will review some of these drugs in parallel with the control of CNS development that GABA exerts via activation of GABA(A) receptors. This review aims to provide a basic science and clinical perspective on the function of GABA and related pharmaceuticals acting at GABA(A) receptors.

Influence of calcium on direct incorporation of membrane proteins into in-plane lipid bilayer

Reconstitution of transmembrane proteins by direct incorporation into supported lipid bilayers (SLBs) is a new method to provide suitable samples for high-resolution atomic force microscopy (AFM) analysis of membrane proteins. First experiments have reported successful incorporation of proteins into detergent-destabilized SLBs. Here, we analyzed by AFM the incorporation of membrane proteins in the presence of calcium, a divalent cation functionally important for several membrane proteins. Using lipid-phase-separated membranes, we first show that calcium strongly stabilizes the SLBs decreasing the insertion of low cmc detergents, dodecyl-beta-maltoside, dodecyl-beta-thiomaltoside, and N-hexadecylphosphocholine (Fos-Choline-16) and further insertion of proteins. However, high yield of protein insertion is recovered in the presence of calcium by increasing the detergent concentration in the solution. These data revealed the importance of the calcium in the structure of SLBs and provided new insights into the mechanism of protein insertion into these model membranes.