Tangential migration and proliferation of intermediate progenitors of GABAergic neurons in the mouse telencephalon

Molecular and cellular dynamics of the developing human neocortex at single-cell resolution

The development of the human neocortex is a highly dynamic process and involves complex cellular trajectories controlled by cell-type-specific gene regulation1. Here, we collected paired single-nucleus chromatin accessibility and transcriptome data from 38 human neocortical samples encompassing both the prefrontal cortex and primary visual cortex. These samples span five main developmental stages, ranging from the first trimester to adolescence. In parallel, we performed spatial transcriptomic analysis on a subset of the samples to illustrate spatial organization and intercellular communication. This atlas enables us to catalog cell type-, age-, and area-specific gene regulatory networks underlying neural differentiation. Moreover, combining single-cell profiling, progenitor purification, and lineage-tracing experiments, we have untangled the complex lineage relationships among progenitor subtypes during the transition from neurogenesis to gliogenesis in the human neocortex. We identified a tripotential intermediate progenitor subtype, termed Tri-IPC, responsible for the local production of GABAergic neurons, oligodendrocyte precursor cells, and astrocytes. Remarkably, most glioblastoma cells resemble Tri-IPCs at the transcriptomic level, suggesting that cancer cells hijack developmental processes to enhance growth and heterogeneity. Furthermore, by integrating our atlas data with large-scale GWAS data, we created a disease-risk map highlighting enriched ASD risk in second-trimester intratelencephalic projection neurons. Our study sheds light on the gene regulatory landscape and cellular dynamics of the developing human neocortex.

Network-driven intracellular cAMP coordinates circadian rhythm in the suprachiasmatic nucleus

The mammalian central circadian clock, located in the suprachiasmatic nucleus (SCN), coordinates the timing of physiology and behavior to local time cues. In the SCN, second messengers, such as cAMP and Ca2+, are suggested to be involved in the input and/or output of the molecular circadian clock. However, the functional roles of second messengers and their dynamics in the SCN remain largely unclear. In the present study, we visualized the spatiotemporal patterns of circadian rhythms of second messengers and neurotransmitter release in the SCN. Here, we show that neuronal activity regulates the rhythmic release of vasoactive intestinal peptides from the SCN, which drives the circadian rhythms of intracellular cAMP in the SCN. Furthermore, optical manipulation of intracellular cAMP levels in the SCN shifts molecular and behavioral circadian rhythms. Together, our study demonstrates that intracellular cAMP is a key molecule in the organization of the SCN circadian neuronal network.

Molecular divergence of mammalian astrocyte progenitor cells at early gliogenesis

During mammalian brain development, how different astrocytes are specified from progenitor cells is not well understood. In particular, whether astrocyte progenitor cells (APCs) start as a relatively homogenous population or whether there is early heterogeneity remains unclear. Here, we have dissected subpopulations of embryonic mouse forebrain progenitors using single-cell transcriptome analyses. Our sequencing data revealed two molecularly distinct APC subgroups at the start of gliogenesis from both dorsal and ventral forebrains. The two APC subgroups were marked, respectively, by specific expression of Sparc and Sparcl1, which are known to function in mature astrocytes with opposing activities for regulating synapse formation. Expression analyses showed that SPARC and SPARCL1 mark APC subgroups that display distinct temporal and spatial patterns, correlating with major waves of astrogliogenesis during development. Our results uncover an early molecular divergence of APCs in the mammalian brain and provide a useful transcriptome resource for the study of glial cell specification.

Characterization and Stage-Dependent Lineage Analysis of Intermediate Progenitors of Cortical GABAergic Interneurons

Intermediate progenitors of both excitatory and inhibitory neurons, which can replenish neurons in the adult brain, were recently identified. However, the generation of intermediate progenitors of GABAergic inhibitory neurons (IPGNs) has not been studied in detail. Here, we characterized the spatiotemporal distribution of IPGNs in mouse cerebral cortex. IPGNs generated neurons during both embryonic and postnatal stages, but the embryonic IPGNs were more proliferative. Our lineage tracing analyses showed that the embryonically proliferating IPGNs tended to localize to the superficial layers rather than the deep cortical layers at 3 weeks after birth. We also found that embryonic IPGNs derived from the medial and caudal ganglionic eminence (CGE) but more than half of the embryonic IPGNs were derived from the CGE and broadly distributed in the cerebral cortex. Taken together, our data indicate that the broadly located IPGNs during embryonic and postnatal stages exhibit a different proliferative property and layer distribution.

Two-Phase Lineage Specification of Telencephalon Progenitors Generated From Mouse Embryonic Stem Cells

Proper brain development requires precisely controlled phases of stem cell proliferation, lineage specification, differentiation, and migration. Lineage specification depends partly on concentration gradients of chemical cues called morphogens. However, the rostral brain (telencephalon) expands prominently during embryonic development, dynamically altering local morphogen concentrations, and telencephalic subregional properties develop with a time lag. Here, we investigated how progenitor specification occurs under these spatiotemporally changing conditions using a three-dimensional in vitro differentiation model. We verified the critical contributions of three signaling factors for the lineage specification of subregional tissues in the telencephalon, ventralizing sonic hedgehog (Shh) and dorsalizing bone morphogenetic proteins (BMPs) and WNT proteins (WNTs). We observed that a short-lasting signal is sufficient to induce subregional progenitors and that the timing of signal exposure for efficient induction is specific to each lineage. Furthermore, early and late progenitors possess different Shh signal response capacities. This study reveals a novel developmental mechanism for telencephalon patterning that relies on the interplay of dose- and time-dependent signaling, including a time lag for specification and a temporal shift in cellular Shh sensitivity. This delayed fate choice through two-phase specification allows tissues with marked size expansion, such as the telencephalon, to compensate for the changing dynamics of morphogen signals.

The mammalian circadian pacemaker regulates wakefulness via CRF neurons in the paraventricular nucleus of the hypothalamus

In mammals, the daily rhythms of physiological functions are timed by the central circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Although the importance of the SCN for the regulation of sleep/wakefulness has been suggested, little is known about the neuronal projections from the SCN, which regulate sleep/wakefulness. Here, we show that corticotropin-releasing factor (CRF) neurons in the hypothalamic paraventricular nucleus mediate circadian rhythms in the SCN and regulate wakefulness. Optogenetic activation of CRF neurons promoted wakefulness through orexin/hypocretin neurons in the lateral hypothalamus. In vivo Ca2+ recording showed that CRF neurons were active at the initiation of wakefulness. Furthermore, chemogenetic suppression and ablation of CRF neurons decreased locomotor activity and time in wakefulness. Last, a combination of optical manipulation and Ca2+ imaging revealed that neuronal activity of CRF neurons was negatively regulated by GABAergic neurons in the SCN. Our findings provide notable insights into circadian regulation of sleep/wakefulness in mammals.

A Composite Sketch of Fast-Spiking Parvalbumin-Positive Neurons

Parvalbumin-positive neurons are inhibitory neurons that release GABA and are mostly represented by fast-spiking basket or chandelier cells. They constitute a minor neuronal population, yet their peculiar profiles allow them to react quickly to any event in the brain under normal or pathological conditions. In this review, we will summarize the current knowledge about the fundamentals of fast-spiking parvalbumin-positive neurons, focusing on their morphology and specific channel/protein content. Next, we will explore their development, maturation, and migration in the brain. Finally, we will unravel their potential contribution to the physiopathology of epilepsy.

Expression of ventral telencephalon transcription factors ASCL1 and DLX2 in the early fetal human cerebral cortex

In rodent ventral telencephalon, diffusible morphogens induce expression of the proneural transcription factor ASCL1, which in turn induces expression of the transcription factor DLX2 that controls differentiation of cortical interneuron precursors and their tangential migration to the cerebral cortex. RNAseq analysis of human fetal samples of dorsal telencephalon revealed consistently high cortical expression of ASCL1 and increasing expression of DLX2 between 7.5 and 17 post-conceptional weeks (PCW). We explored whether cortical expression of these genes represented a population of intracortically derived interneuron precursors. Immunohistochemistry revealed an ASCL1+ /DLX2+ population of progenitor cells in the human ganglionic eminences between 6.5 and 12 PCW, but in the cortex there also existed a population of ASCL1+ /DLX2- progenitors in the subventricular zone (SVZ) that largely co-expressed cortical markers PAX6 or TBR2, although a few ASCL1+ /PAX6- progenitors were observed in the ventricular zone (VZ) and ASCL1+ cells expressing the interneuron marker GAD67 were present in the SVZ. Although rare in the VZ, DLX2+ cells progressively increased in number between 8 and 12 PCW across the cortical wall and the majority co-expressed LHX6 and originated either in the MGE, migrating to the lateral cortex, or from the septum, populating the medial wall. A minority co-expressed COUP-TFII, which identifies cells from the caudal ganglionic eminence (CGE). By 19 PCW, a significant increase in expression of DLX2 and ASCL1 was observed in the cortical VZ with a small proportion expressing both proteins. The DLX2+ cells did not co-express a cell division marker, so were not progenitors. The majority of DLX2+ cells throughout the cortical plate expressed COUP-TFII rather than LHX6+ . As the VZ declined as a proliferative zone it appeared to be re-defined as a migration pathway for COUP-TFII+ /DLX2+ interneurons from CGE to cortex. Therefore, in developing human cortex, ASCL1 expression predominantly marks a population of intermediate progenitors giving rise to glutamatergic neurons. DLX2 expression predominantly defines post-mitotic interneuron precursors.

Monoamines Inhibit GABAergic Neurons in Ventrolateral Preoptic Area That Make Direct Synaptic Connections to Hypothalamic Arousal Neurons

The hypothalamus plays an important role in the regulation of sleep/wakefulness states. While the ventrolateral preoptic nucleus (VLPO) plays a critical role in the initiation and maintenance of sleep, the lateral posterior part of the hypothalamus contains neuronal populations implicated in maintenance of arousal, including orexin-producing neurons (orexin neurons) in the lateral hypothalamic area (LHA) and histaminergic neurons in the tuberomammillary nucleus (TMN). During a search for neurons that make direct synaptic contact with histidine decarboxylase-positive (HDC+), histaminergic neurons (HDC neurons) in the TMN and orexin neurons in the LHA of male mice, we found that these arousal-related neurons are heavily innervated by GABAergic neurons in the preoptic area including the VLPO. We further characterized GABAergic neurons electrophysiologically in the VLPO (GABA^VLPO neurons) that make direct synaptic contact with these hypothalamic arousal-related neurons. These neurons (GABA^VLPO→HDC or GABA^{VLPO→orexin} neurons) were both potently inhibited by noradrenaline and serotonin, showing typical electrophysiological characteristics of sleep-promoting neurons in the VLPO. This work provides direct evidence of monosynaptic connectivity between GABA^VLPO neurons and hypothalamic arousal neurons and identifies the effects of monoamines on these neuronal pathways.SIGNIFICANCE STATEMENT Rabies-virus-mediated tracing of input neurons of two hypothalamic arousal-related neuron populations, histaminergic and orexinergic neurons, showed that they receive similar distributions of input neurons in a variety of brain areas, with rich innervation by GABAergic neurons in the preoptic area, including the ventrolateral preoptic area (VLPO), a region known to play an important role in the initiation and maintenance of sleep. Electrophysiological experiments found that GABAergic neurons in the VLPO (GABA^VLPO neurons) that make direct input to orexin or histaminergic neurons are potently inhibited by noradrenaline and serotonin, suggesting that these monoamines disinhibit histamine and orexin neurons. This work demonstrated functional and structural interactions between GABA^VLPO neurons and hypothalamic arousal-related neurons.

Chromatin Remodeling Proteins in Epilepsy: Lessons From CHD2-Associated Epilepsy

The chromodomain helicase DNA-binding (CHD) family of proteins are ATP-dependent chromatin remodelers that contribute to the reorganization of chromatin structure and deposition of histone variants necessary to regulate gene expression. CHD proteins play an important role in neurodevelopment, as pathogenic variants in CHD1, CHD2, CHD4, CHD7 and CHD8 have been associated with a range of neurological phenotypes, including autism spectrum disorder (ASD), intellectual disability (ID) and epilepsy. Pathogenic variants in CHD2 are associated with developmental epileptic encephalopathy (DEE) in humans, however little is known about how these variants contribute to this disorder. Of the nine CHD family members, CHD2 is the only one that leads to a brain-restricted phenotype when disrupted in humans. This suggests that despite being expressed ubiquitously, CHD2 has a unique role in human brain development and function. In this review, we will discuss the phenotypic spectrum of patients with pathogenic variants in CHD2, current animal models of CHD2 deficiency, and the role of CHD2 in proliferation, neurogenesis, neuronal differentiation, chromatin remodeling and DNA-repair. We also consider how CHD2 depletion can affect each of these biological mechanisms and how these defects may underpin neurodevelopmental disorders including epilepsy.

Detachment of Chain-Forming Neuroblasts by Fyn-Mediated Control of cell-cell Adhesion in the Postnatal Brain

In the rodent olfactory system, neuroblasts produced in the ventricular-subventricular zone of the postnatal brain migrate tangentially in chain-like cell aggregates toward the olfactory bulb (OB) through the rostral migratory stream (RMS). After reaching the OB, the chains are dissociated and the neuroblasts migrate individually and radially toward their final destination. The cellular and molecular mechanisms controlling cell-cell adhesion during this detachment remain unclear. Here we report that Fyn, a nonreceptor tyrosine kinase, regulates the detachment of neuroblasts from chains in the male and female mouse OB. By performing chemical screening and in vivo loss-of-function and gain-of-function experiments, we found that Fyn promotes somal disengagement from the chains and is involved in neuronal migration from the RMS into the granule cell layer of the OB. Fyn knockdown or Dab1 (disabled-1) deficiency caused p120-catenin to accumulate and adherens junction-like structures to be sustained at the contact sites between neuroblasts. Moreover, a Fyn and N-cadherin double-knockdown experiment indicated that Fyn regulates the N-cadherin-mediated cell adhesion between neuroblasts. These results suggest that the Fyn-mediated control of cell-cell adhesion is critical for the detachment of chain-forming neuroblasts in the postnatal OB.SIGNIFICANCE STATEMENT In the postnatal brain, newly born neurons (neuroblasts) migrate in chain-like cell aggregates toward their destination, where they are dissociated into individual cells and mature. The cellular and molecular mechanisms controlling the detachment of neuroblasts from chains are not understood. Here we show that Fyn, a nonreceptor tyrosine kinase, promotes the somal detachment of neuroblasts from chains, and that this regulation is critical for the efficient migration of neuroblasts to their destination. We further show that Fyn and Dab1 (disabled-1) decrease the cell-cell adhesion between chain-forming neuroblasts, which involves adherens junction-like structures. Our results suggest that Fyn-mediated regulation of the cell-cell adhesion of neuroblasts is critical for their detachment from chains in the postnatal brain.

Excitation of GABAergic Neurons in the Bed Nucleus of the Stria Terminalis Triggers Immediate Transition from Non-Rapid Eye Movement Sleep to Wakefulness in Mice

Emotionally salient situations usually trigger arousal along with autonomic and neuroendocrine reactions. To determine whether the extended amygdala plays a role in sleep-wakefulness regulation, we examined the effects of optogenetic and pharmacogenetic excitation of GABAergic neurons in the bed nucleus of the stria terminalis (GABA^BNST neurons). Acute optogenetic excitation of these cells during nonrapid eye movement (NREM) sleep resulted in an immediate state transition to wakefulness, whereas stimulation during REM sleep showed no effect on sleep-wakefulness states in male mice. An anterograde tracing study suggested GABA^BNST neurons send axonal projections to several brain regions implicated in arousal, including the preoptic area, lateral hypothalamus, periaqueductal gray, deep mesencephalic nucleus, and parabrachial nucleus. A dual orexin receptor antagonist, DORA-22, did not affect the optogenetic transition from NREM sleep to wakefulness. Chemogenetic excitation of GABA^BNST neurons evoked a sustained wakefulness state, but this arousal effect was markedly attenuated by DORA-22. These observations suggest that GABA^BNST neurons play an important role in transition from NREM sleep to wakefulness without the function of orexin neurons, but prolonged excitation of these cells mobilizes the orexin system to sustain wakefulness.SIGNIFICANCE STATEMENT We examined the role of the bed nucleus of the stria terminalis (BNST) in the regulation of wakefulness. Optogenetic excitation of GABAergic neurons in the BNST (GABA^BNST neurons) during nonrapid eye movement (NREM) sleep in mice resulted in immediate transition to a wakefulness state without function of orexins. Prolonged excitation of GABA^BNST neurons by a chemogenetic method evoked a longer-lasting, sustained wakefulness state, which was abolished by preadministration of a dual orexin receptor antagonist, DORA-22. This study revealed a role of the BNST GABAergic system in sleep-wakefulness control, especially in shifting animals' behavioral states from NREM sleep to wakefulness, and provides an important insight into the pathophysiology of insomnia and the role of orexin in arousal regulation.

Corticofugal GABAergic projection neurons in the mouse frontal cortex

Cortical projection neurons are classified by hodology in corticocortical, commissural and corticofugal subtypes. Although cortical projection neurons had been regarded as only glutamatergic neurons, recently corticocortical GABAergic projection neurons has been also reported in several species. Here, we demonstrate corticofugal GABAergic projection neurons in the mouse frontal cortex. We employed viral-vector-mediated anterograde tracing, classical retrograde tracing, and immunohistochemistry to characterize neocortical GABAergic projection neurons. Injections of the Cre-dependent adeno-associated virus into glutamate decarboxylase 67 (GAD67)-Cre knock-in mice revealed neocortical GABAergic projections widely to the forebrain, including the cerebral cortices, caudate putamen (CPu), ventral pallidum (VP), lateral globus pallidus (LGP), nucleus accumbens, and olfactory tubercle (Tu). Minor GABAergic projections were also found in the mediodorsal thalamic nucleus, diagonal band of Broca, medial globus pallidus, substantial nigra, and dorsal raphe nucleus. Retrograde tracing studies also demonstrated corticofugal GABAergic projection neurons in the mouse frontal cortex. Further immunohistochemical screening with neurochemical markers revealed the majority of corticostriatal GABAergic projection neurons were positive for somatostatin (SS)-immunoreactivity. In contrast, corticothalamic GABAergic projection neurons were not identified by representative neurochemical markers for GABAergic neurons. These findings suggest that corticofugal GABAergic projection neurons are heterogeneous in terms of their neurochemical properties and target nuclei, and provide axonal innervations mainly to the nuclei in the basal ganglia.

Altered proliferative ability of neuronal progenitors in PlexinA1 mutant mice

Cortical interneurons are generated predominantly in the medial ganglionic eminence (MGE) and migrate through the ventral and dorsal telencephalon before taking their final positions within the developing cortical plate. Previously we demonstrated that interneurons from Robo1 knockout (Robo1(-/-)) mice contain reduced levels of neuropilin 1 (Nrp1) and PlexinA1 receptors, rendering them less responsive to the chemorepulsive actions of semaphorin ligands expressed in the striatum and affecting their course of migration (Hernandez-Miranda et al. [2011] J. Neurosci. 31:6174-6187). Earlier studies have highlighted the importance of Nrp1 and Nrp2 in interneuron migration, and here we assess the role of PlexinA1 in this process. We observed significantly fewer cells expressing the interneuron markers Gad67 and Lhx6 in the cortex of PlexinA1(-/-) mice compared with wild-type littermates at E14.5 and E18.5. Although the level of apoptosis was similar in the mutant and control forebrain, proliferation was significantly reduced in the former. Furthermore, progenitor cells in the MGE of PlexinA1(-/-) mice appeared to be poorly anchored to the ventricular surface and showed reduced adhesive properties, which may account for the observed reduction in proliferation. Together our data uncover a novel role for PlexinA1 in forebrain development.

Diversity of cortical interneurons in primates: the role of the dorsal proliferative niche

Evolutionary elaboration of tissues starts with changes in the genome and location of the stem cells. For example, GABAergic interneurons of the mammalian neocortex are generated in the ventral telencephalon and migrate tangentially to the neocortex, in contrast to the projection neurons originating in the ventricular/subventricular zone (VZ/SVZ) of the dorsal telencephalon. In human and nonhuman primates, evidence suggests that an additional subset of neocortical GABAergic interneurons is generated in the cortical VZ and a proliferative niche, the outer SVZ. The origin, magnitude, and significance of this species-specific difference are not known. We use a battery of assays applicable to the human, monkey, and mouse organotypic cultures and supravital tissue to identify neuronal progenitors in the cortical VZ/SVZ niche that produce a subset of GABAergic interneurons. Our findings suggest that these progenitors constitute an evolutionary novelty contributing to the elaboration of higher cognitive functions in primates.

The Role of Sonic Hedgehog in the Specification of Human Cortical Progenitors In Vitro

Impaired sonic hedgehog (Shh) signaling is involved in the pathology of cortical formation found in neuropsychiatric disorders. However, its role in the specification of human cortical progenitors is not known. Here, we report that Shh is expressed in the human developing cortex at mid-gestation by radial glia cells (RGCs) and cortical neurons. We used RGC cultures, established from the dorsal (cortical) telencephalon of human brain at mid-gestation to study the effect of Shh signaling. Cortical RGCs in vitro maintained their regional characteristics, expressed components of Shh signaling, and differentiated into Nkx2.1, Lhx6, and calretinin-positive (CalR(+)) cells, potential cortical interneuron progenitors. Treatment with exogenous Shh increased the pool of Nkx2.1(+) progenitors, decreased Lhx6 expression, and suppressed the generation of CalR(+) cells. The blockade of endogenous Shh signaling increased the number of CalR(+) cells, but did not affect Nkx2.1 expression, implying the existence of parallel Shh-independent pathways for cortical Nkx2.1 regulation. These results support the idea that, during human brain development, Shh plays an important role in the specification of cortical progenitors. Since direct functional studies in humans are limited, the in vitro system that we established here could be of great interest for modeling the development of human cortical progenitors.

The complexity of the calretinin-expressing progenitors in the human cerebral cortex

The complex structure and function of the cerebral cortex critically depend on the balance of excitation and inhibition provided by the pyramidal projection neurons and GABAergic interneurons, respectively. The calretinin-expressing (CalR⁺) cell is a subtype of GABAergic cortical interneurons that is more prevalent in humans than in rodents. In rodents, CalR⁺ interneurons originate in the caudal ganglionic eminence (CGE) from Gsx2⁺ progenitors, but in humans it has been suggested that a subpopulation of CalR⁺ cells can also be generated in the cortical ventricular/subventricular zone (VZ/SVZ). The progenitors for cortically generated CalR⁺ subpopulation in primates are not yet characterized. Hence, the aim of this study was to identify patterns of expression of the transcription factors (TFs) that commit cortical stem cells to the CalR fate, with a focus on Gsx2. First, we studied the expression of Gsx2 and its downstream effectors, Ascl1 and Sp8 in the cortical regions of the fetal human forebrain at midgestation. Next, we established that a subpopulation of cells expressing these TFs are proliferating in the cortical SVZ, and can be co-labeled with CalR. The presence and proliferation of Gsx2⁺ cells, not only in the ventral telencephalon (GE) as previously reported, but also in the cerebral cortex suggests cortical origin of a subpopulation of CalR⁺ neurons in humans. In vitro treatment of human cortical progenitors with Sonic hedgehog (Shh), an important morphogen in the specification of interneurons, decreased levels of Ascl1 and Sp8 proteins, but did not affect Gsx2 levels. Taken together, our ex-vivo and in vitro results on human fetal brain suggest complex endogenous and exogenous regulation of TFs implied in the specification of different subtypes of CalR⁺ cortical interneurons.

Tangential migratory pathways of subpallial origin in the embryonic telencephalon of sharks: evolutionary implications

Tangential neuronal migration occurs along different axes from the axis demarcated by radial glia and it is thought to have evolved as a mechanism to increase the diversity of cell types in brain areas, which in turn resulted in increased complexity of functional networks. In the telencephalon of amniotes, different embryonic tangential pathways have been characterized. However, little is known about the exact routes of migrations in basal vertebrates. Cartilaginous fishes occupy a key phylogenetic position to assess the ancestral condition of vertebrate brain organization. In order to identify putative subpallial-derived tangential migratory pathways in the telencephalon of sharks, we performed a detailed analysis of the distribution pattern of GAD and Dlx2, two reliable markers of tangentially migrating interneurons of subpallial origin in the developing forebrain. We propose the existence of five tangential routes directed toward different telencephalic regions. We conclude that four of the five routes might have emerged in the common ancestor of jawed vertebrates. We have paid special attention to the characterization of the proposed migratory pathway directed towards the olfactory bulbs. Our results suggest that it may be equivalent to the "rostral migratory stream" of mammals and led us to propose a hypothesis about its evolution. The analysis of the final destinations of two other streams allowed us to identify the putative dorsal and medial pallium of sharks, the regions from which the neocortex and hippocampus might have, respectively, evolved. Derived features were also reported and served to explain some distinctive traits in the morphology of the telencephalon of cartilaginous fishes.

An enhanced role and expanded developmental origins for gamma-aminobutyric acidergic interneurons in the human cerebral cortex

Human beings have considerably expanded cognitive abilities compared with all other species and they also have a relatively larger cerebral cortex compared with their body size. But is a bigger brain the only reason for higher cognition or have other features evolved in parallel? Humans have more and different types of GABAergic interneurons, found in different places, than our model species. Studies are beginning to show differences in function. Is this expanded repertoire of functional types matched by an evolution of their developmental origins? Recent studies support the idea that generation of interneurons in the ventral telencephalon may be more complicated in primates, which have evolved a large and complex outer subventricular zone in the ganglionic eminences. In addition, proportionally more interneurons appear to be produced in the caudal ganglionic eminence, the majority of which populate the superficial layers of the cortex. Whether or not the cortical proliferative zones are a source of interneurogenesis, and to what extent and of what significance, is a contentious issue. As there is growing evidence that conditions such as autism, schizophrenia and congenital epilepsy may have developmental origins in the failure of interneuron production and migration, it is important we understand fully the similarities and differences between human development and our animal models.

The possible role of stem cells in acupuncture treatment for neurodegenerative diseases: a literature review of basic studies

This review reports on recent findings concerning the effects of acupuncture and electroacupuncture (EA) on stem cell mobilization and differentiation, in particular with regard to neurogenesis. Traditional Chinese acupuncture has a history of over 2,500 years and is becoming more popular worldwide. Evidence has demonstrated that acupuncture may be of benefit in stroke rehabilitation, parkinsonism, dementia, and depression. This article reviews recent studies concerning the effects of acupuncture/EA on stem cell mobilization and on progenitor cell proliferation in the CNS. The reviewed evidence indicates that acupuncture/EA has beneficial effects in several neurodegenerative diseases, and it may prove to be a nondrug method for mobilizing stem cells in the CNS.

GABAergic neurons in the preoptic area send direct inhibitory projections to orexin neurons

Populations of neurons in the hypothalamic preoptic area (POA) fire rapidly during sleep, exhibiting sleep/waking state-dependent firing patterns that are the reciprocal of those observed in the arousal system. The majority of these preoptic "sleep-active" neurons contain the inhibitory neurotransmitter GABA. On the other hand, a population of neurons in the lateral hypothalamic area (LHA) contains orexins, which play an important role in the maintenance of wakefulness, and exhibit an excitatory influence on arousal-related neurons. It is important to know the anatomical and functional interactions between the POA sleep-active neurons and orexin neurons, both of which play important, but opposite roles in regulation of sleep/wakefulness states. In this study, we confirmed that specific pharmacogenetic stimulation of GABAergic neurons in the POA leads to an increase in the amount of non-rapid eye movement (NREM) sleep. We next examined direct connectivity between POA GABAergic neurons and orexin neurons using channelrhodopsin 2 (ChR2) as an anterograde tracer as well as an optogenetic tool. We expressed ChR2-eYFP selectively in GABAergic neurons in the POA by AAV-mediated gene transfer, and examined the projection sites of ChR2-eYFP-expressing axons, and the effect of optogenetic stimulation of ChR2-eYFP on the activity of orexin neurons. We found that these neurons send widespread projections to wakefulness-related areas in the hypothalamus and brain stem, including the LHA where these fibers make close appositions to orexin neurons. Optogenetic stimulation of these fibers resulted in rapid inhibition of orexin neurons. These observations suggest direct connectivity between POA GABAergic neurons and orexin neurons.

Non-epithelial stem cells and cortical interneuron production in the human ganglionic eminences

GABAergic cortical interneurons underlie the complexity of neural circuits and are particularly numerous and diverse in humans. In rodents, cortical interneurons originate in the subpallial ganglionic eminences, but their developmental origins in humans are controversial. We characterized the developing human ganglionic eminences and found that the subventricular zone (SVZ) expanded massively during the early second trimester, becoming densely populated with neural stem cells and intermediate progenitor cells. In contrast with the cortex, most stem cells in the ganglionic eminence SVZ did not maintain radial fibers or orientation. The medial ganglionic eminence exhibited unique patterns of progenitor cell organization and clustering, and markers revealed that the caudal ganglionic eminence generated a greater proportion of cortical interneurons in humans than in rodents. On the basis of labeling of newborn neurons in slice culture and mapping of proliferating interneuron progenitors, we conclude that the vast majority of human cortical interneurons are produced in the ganglionic eminences, including an enormous contribution from non-epithelial SVZ stem cells.

Nuclear receptor COUP-TFII-expressing neocortical interneurons are derived from the medial and lateral/caudal ganglionic eminence and define specific subsets of mature interneurons

Neocortical GABAergic interneurons in rodents originate from subpallial progenitor zones. The majority of mouse neocortical interneurons are derived from the medial and caudal ganglionic eminences (MGE and CGE, respectively) and the preoptic area (POA). It is controversial whether the lateral ganglionic eminence (LGE) also generates neocortical interneurons. Previously it was shown that the transcription factor COUP-TFII is expressed in the CGE; here we show that COUP-TFII is also expressed in the dorsal MGE, dorsal LGE (dMGE and dLGE, respectively), and POA. In the adult neocortex, COUP-TFII+/somatostatin (SOM)+ interneurons are mainly located in layer V. Using a genetic fate-mapping approach (Shh-Cre and Nkx2.1-Cre), we demonstrate that the POA and ventral MGE do not give rise to COUP-TFII+ neocortical interneurons, suggesting that the dMGE is the source of COUP-TFII+/SOM+ neocortical interneurons. We also observed a migratory stream of COUP-TFII+/Sp8+ cells emanating from the dLGE and CGE to the neocortex mainly through the subventricular zone at later embryonic stages. Slice culture experiments in which dLGE progenitors were labeled with BrdU provided additional evidence that the dLGE generates neocortical interneurons. While earlier-born dMGE-derived COUP-TFII+ interneurons occupy cortical layer V, later-born dLGE- and CGE-derived COUP-TFII+ ones preferentially occupy superficial cortical layers. A similar laminar distribution was observed following neonatal transplantation of embryonic day (E)14.5 dMGE and E15.5 dLGE. These results provide novel information about interneuron fate and position from spatially and temporally distinct origins in the ganglionic eminences.

Limk2 mediates semaphorin signalling in cortical interneurons migrating through the subpallium

En route to the neocortex, interneurons migrate around and avoid the developing striatum. This is due to the chemorepulsive cues of class 3 semaphorins (Sema3A and Sema3F) acting through neuropilin and plexin co-receptors expressed in interneurons. In a recent genetic screen aimed at identifying novel components that may play a role in interneuron migration, we identified LIM-kinase 2 (Limk2), a kinase previously shown to be involved in cell movement and in Sema7A-PlexinC1 signalling. Here we show that Limk2 is differentially expressed in interneurons, with a higher expression in the subpallium compared to cortex, suggesting it may play a role in their migration through the subpallium. Chemotactic assays, carried out with small interfering RNAs (siRNAs), revealed that Limk2-siRNA transfected interneurons are less responsive to Sema3A, but respond to Sema3F. Lack of responsiveness to Sema3A resulted in their aberrant invasion of the developing striatum, as demonstrated in brain slice preparations and in in utero electroporated mouse embryos with the same siRNAs. Our results reveal a previously unknown role for Limk2 in interneuron migration and Sema3A signalling.

Amygdala kindling induces nestin expression in the leptomeninges of the neocortex

Nestin is an intermediate filament found in neurogenic progenitors and non-neuronal cells. Nestin-immunoreactivity (IR) in the brain often increases after brain damage. Here we show that amygdala kindling, which mimics the epileptic seizures, also induces nestin expression in the brain. Nestin-IR was greatly enhanced in the leptomeninges (pia and arachnoid maters) and neocortical parenchyma, but not much in the SVZ around the lateral ventricle, SGZ in the dentate gyrus, or the endothelial progenitor cells of blood vessels, fimbria, or choroid plexus after kindling. Electron microscopy revealed that nestin-IR in the leptomeninges was localized to granule cells, where it co-localized with GAD67-IR after electrical stimulation. The nestin-positive granule cells in the leptomeninges, especially around the emissary vein, were proliferative. However, nestin-IR in the neocortical parenchyma was expressed in NG2 glia and did not co-localize with GAD67-IR. Deletion of nestin-positive cells resulted in a high susceptibility to electrical stimulation. Consequently, almost all of the mice died or dropped out during kindling progression in 20 days, from naturally generated epileptic seizure or exhaustion. We speculate that the nestin-positive cells activated by amygdala kindling may involve in the protection of the brain from epilepsy.

Neurons on the move: migration and lamination of cortical interneurons

The modulation of cortical activity by GABAergic interneurons is required for normal brain function and is achieved through the immense level of heterogeneity within this neuronal population. Cortical interneurons share a common origin in the ventral telencephalon, yet during the maturation process diverse subtypes are generated that form the characteristic laminar arrangement observed in the adult brain. The long distance tangential and short-range radial migration into the cortical plate is regulated by a combination of intrinsic and extrinsic signalling mechanisms, and a great deal of progress has been made to understand these developmental events. In this review, we will summarize current findings regarding the molecular control of subtype specification and provide a detailed account of the migratory cues influencing interneuron migration and lamination. Furthermore, a dysfunctional GABAergic system is associated with a number of neurological and psychiatric conditions, and some of these may have a developmental aetiology with alterations in interneuron generation and migration. We will discuss the notion of additional sources of interneuron progenitors found in human and non-human primates and illustrate how the disruption of early developmental events can instigate a loss in GABAergic function.

A subpopulation of dorsal lateral/caudal ganglionic eminence-derived neocortical interneurons expresses the transcription factor Sp8

Cortical GABAergic interneurons in rodents originate from subpallial progenitors and tangentially migrate to the cortex. While the majority of mouse neocortical interneurons are derived from the medial and caudal ganglionic eminence (MGE and CGE, respectively), it remains unknown whether the lateral ganglionic eminence (LGE) also contributes to a subpopulation of cortical interneurons. Here, we show that the transcription factor Sp8 is expressed in one-fifth of adult cortical interneurons, which appear to be derived from both the dorsal LGE and the dorsal CGE (dLGE and dCGE, respectively). Compared with the MGE-derived cortical interneurons, dLGE/dCGE-derived Sp8-expressing (Sp8+) ones are born at later embryonic stages with peak production occurring at embryonic day 15.5. They tangentially migrate mainly along the subventricular/intermediate zone (SVZ/IZ) route; some continue to express mitotic markers (Ki67 and PH3) in the neonatal cortical SVZ/IZ. Sp8+ interneurons continue to radially migrate from the SVZ/IZ into the cortical layers at early postnatal stages. In contrast to MGE-derived interneurons, dLGE/dCGE-derived Sp8+ interneurons follow an outside-in layering pattern, preferentially occupying superficial cortical layers.