Reduced Numbers of Corticotropin-Releasing Hormone Neurons in Narcolepsy Type 1.

Narcolepsy type 1 (NT1) is a chronic sleep disorder correlated with loss of hypocretin(orexin). In NT1 post-mortem brains, we observed 88% reduction in corticotropin-releasing hormone (CRH)-positive neurons in the paraventricular nucleus (PVN) and significantly less CRH-positive fibers in the median eminence, whereas CRH-neurons in the locus coeruleus and thalamus, and other PVN neuronal populations were spared: that is, vasopressin, oxytocin, tyrosine hydroxylase, and thyrotropin releasing hormone-expressing neurons. Other hypothalamic cell groups, that is, the suprachiasmatic, ventrolateral preoptic, infundibular, and supraoptic nuclei and nucleus basalis of Meynert, were unaffected. The surprising selective decrease in CRH-neurons provide novel targets for diagnostics and therapeutic interventions. ANN NEUROL 2022;91:282-288.

Nf1 deletion results in depletion of the Lhx6 transcription factor and a specific loss of parvalbumin+ cortical interneurons.

Neurofibromatosis 1 (NF1) is caused by mutations in the NF1 gene, which encodes the protein, neurofibromin, an inhibitor of Ras activity. Cortical GABAergic interneurons (CINs) are implicated in NF1 pathology, but the cellular and molecular changes to CINs are unknown. We deleted mouse Nf1 from the medial ganglionic eminence, which gives rise to both oligodendrocytes and CINs that express somatostatin and parvalbumin. Nf1 loss led to a persistence of immature oligodendrocytes that prevented later-generated oligodendrocytes from occupying the cortex. Moreover, molecular and cellular properties of parvalbumin (PV)-positive CINs were altered by the loss of Nf1, without changes in somatostatin (SST)-positive CINs. We discovered that loss of Nf1 results in a dose-dependent decrease in Lhx6 expression, the transcription factor necessary to establish SST+ and PV+ CINs, which was rescued by the MEK inhibitor SL327, revealing a mechanism whereby a neurofibromin/Ras/MEK pathway regulates a critical CIN developmental milestone.

Interneuron Origins in the Embryonic Porcine Medial Ganglionic Eminence.

Interneurons contribute to the complexity of neural circuits and maintenance of normal brain function. Rodent interneurons originate in embryonic ganglionic eminences, but developmental origins in other species are less understood. Here, we show that transcription factor expression patterns in porcine embryonic subpallium are similar to rodents, delineating a distinct medial ganglionic eminence (MGE) progenitor domain. On the basis of Nkx2.1, Lhx6, and Dlx2 expression, in vitro differentiation into neurons expressing GABA, and robust migratory capacity in explant assays, we propose that cortical and hippocampal interneurons originate from a porcine MGE region. Following xenotransplantation into adult male and female rat hippocampus, we further demonstrate that porcine MGE progenitors, like those from rodents, migrate and differentiate into morphologically distinct interneurons expressing GABA. Our findings reveal that basic rules for interneuron development are conserved across species, and that porcine embryonic MGE progenitors could serve as a valuable source for interneuron-based xenotransplantation therapies.SIGNIFICANCE STATEMENT Here we demonstrate that porcine medial ganglionic eminence, like rodents, exhibit a distinct transcriptional and interneuron-specific antibody profile, in vitro migratory capacity and are amenable to xenotransplantation. This is the first comprehensive examination of embryonic interneuron origins in the pig; and because a rich neurodevelopmental literature on embryonic mouse medial ganglionic eminence exists (with some additional characterizations in other species, e.g., monkey and human), our work allows direct neurodevelopmental comparisons with this literature.

Interneuron Transplantation Rescues Social Behavior Deficits without Restoring Wild-Type Physiology in a Mouse Model of Autism with Excessive Synaptic Inhibition.

Manipulations that enhance GABAergic inhibition have been associated with improved behavioral phenotypes in autism models, suggesting that autism may be treated by correcting underlying deficits of inhibition. Interneuron transplantation is a method for increasing recipient synaptic inhibition, and it has been considered a prospective therapy for conditions marked by deficient inhibition, including neuropsychiatric disorders. It is unknown, however, whether interneuron transplantation may be therapeutically effective only for conditions marked by reduced inhibition, and it is also unclear whether transplantation improves behavioral phenotypes solely by normalizing underlying circuit defects. To address these questions, we studied the effects of interneuron transplantation in male and female mice lacking the autism-associated gene, Pten, in GABAergic interneurons. Pten mutant mice exhibit social behavior deficits, elevated synaptic inhibition in prefrontal cortex, abnormal baseline and social interaction-evoked electroencephalogram (EEG) signals, and an altered composition of cortical interneuron subtypes. Transplantation of wild-type embryonic interneurons from the medial ganglionic eminence into the prefrontal cortex of neonatal Pten mutants rescued social behavior despite exacerbating excessive levels of synaptic inhibition. Furthermore, transplantation did not normalize recipient EEG signals measured during baseline states. Interneuron transplantation can thus correct behavioral deficits even when those deficits are associated with elevated synaptic inhibition. Moreover, transplantation does not exert therapeutic effects solely by restoring wild-type circuit states. Our findings indicate that interneuron transplantation could offer a novel cell-based approach to autism treatment while challenging assumptions that effective therapies must reverse underlying circuit defects.SIGNIFICANCE STATEMENT Imbalances between neural excitation and inhibition are hypothesized to contribute to the pathophysiology of autism. Interneuron transplantation is a method for altering recipient inhibition, and it has been considered a prospective therapy for neuropsychiatric disorders, including autism. Here we examined the behavioral and physiological effects of interneuron transplantation in a mouse genetic model of autism. They demonstrate that transplantation rescues recipient social interaction deficits without correcting a common measure of recipient inhibition, or circuit-level physiological measures. These findings demonstrate that interneuron transplantation can exert therapeutic behavioral effects without necessarily restoring wild-type circuit states, while highlighting the potential of interneuron transplantation as an autism therapy.

Electroacupuncture Promotes the Survival of the Grafted Human MGE Neural Progenitors in Rats with Cerebral Ischemia by Promoting Angiogenesis and Inhibiting Inflammation.

Stem cells have the potential as a regenerative therapy for cerebral ischemia by improving functional outcomes. However, cell transplantation has some limitations, including a low rate of the grafted cell survival. There is still a major challenge of promoting the harmonious symbiosis between grafted cells and the host. Acupuncture can effectively improve the functional outcome after cerebral ischemia. The present study evaluated the therapeutic effects and explored the mechanism of combined medial ganglionic eminence (MGE) neural progenitors differentiated from human embryonic stem cells (hESCs) with electroacupuncture (EA) in a bilateral common carotid artery occlusion (2VO) rat model. The results showed that EA could promote the survival of the grafted MGE neural progenitors differentiated from hESCs and alleviate learning and memory impairment in rats with cerebral ischemia. This may have partially resulted from inhibited expression of TNF-α and IL-1ß and increased vascular endothelial growth factor (VEGF) expression and blood vessel density in the hippocampus. Our findings indicated that EA could promote the survival of the grafted MGE neural progenitors and enhance transplantation therapy's efficacy by promoting angiogenesis and inhibiting inflammation.

CTCF Governs the Identity and Migration of MGE-Derived Cortical Interneurons.

The CCCTC-binding factor (CTCF) is a central regulator of chromatin topology recently linked to neurodevelopmental disorders such as intellectual disability, autism, and schizophrenia. The aim of this study was to identify novel roles of CTCF in the developing mouse brain. We provide evidence that CTCF is required for the expression of the LIM homeodomain factor LHX6 involved in fate determination of cortical interneurons (CINs) that originate in the medial ganglionic eminence (MGE). Conditional Ctcf ablation in the MGE of mice of either sex leads to delayed tangential migration, abnormal distribution of CIN in the neocortex, a marked reduction of CINs expressing parvalbumin and somatostatin (Sst), and an increased number of MGE-derived cells expressing Lhx8 and other markers of basal forebrain projection neurons. Likewise, Ctcf-null MGE cells transplanted into the cortex of wild-type hosts generate fewer Sst-expressing CINs and exhibit lamination defects that are efficiently rescued upon reexpression of LHX6. Collectively, these data indicate that CTCF regulates the dichotomy between Lhx6 and Lhx8 to achieve correct specification and migration of MGE-derived CINs.SIGNIFICANCE STATEMENT This work provides evidence that CCCTC-binding factor (CTCF) controls an early fate decision point in the generation of cortical interneurons mediated at least in part by Lhx6. Importantly, the abnormalities described could reflect early molecular and cellular events that contribute to human neurological disorders previously linked to CTCF, including schizophrenia, autism, and intellectual disability.

Sp9 Regulates Medial Ganglionic Eminence-Derived Cortical Interneuron Development.

Immature neurons generated by the subpallial MGE tangentially migrate to the cortex where they become parvalbumin-expressing (PV+) and somatostatin (SST+) interneurons. Here, we show that the Sp9 transcription factor controls the development of MGE-derived cortical interneurons. SP9 is expressed in the MGE subventricular zone and in MGE-derived migrating interneurons. Sp9 null and conditional mutant mice have approximately 50% reduction of MGE-derived cortical interneurons, an ectopic aggregation of MGE-derived neurons in the embryonic ventral telencephalon, and an increased ratio of SST+/PV+ cortical interneurons. RNA-Seq and SP9 ChIP-Seq reveal that SP9 regulates MGE-derived cortical interneuron development through controlling the expression of key transcription factors Arx, Lhx6, Lhx8, Nkx2-1, and Zeb2 involved in interneuron development, as well as genes implicated in regulating interneuron migration Ackr3, Epha3, and St18. Thus, Sp9 has a central transcriptional role in MGE-derived cortical interneuron development.

Molecular control of two novel migratory paths for CGE-derived interneurons in the developing mouse brain.

GABAergic interneurons are highly heterogeneous and originate in the subpallium mainly from the medial (MGE) and caudal (CGE) ganglionic eminences according to a precise temporal sequence. MGE-derived cells disperse dorsally and migrate towards all regions of the cortex, but little is known about how CGE-derived cells reach their targets during development. Here, we unravel the existence of two novel CGE caudo-rostral migratory streams, one located laterally (LMS) and the other one more medially (MMS), that, together with the well-known caudal migratory stream (CMS), contribute to populate the neocortex, hippocampus and amygdala. These paths appear in a precise temporal sequence and express a distinct combination of transcription factors, such as SP8, PROX1, COUP-TFI and COUP-TFII. By inactivating COUP-TFI in developing interneurons, the lateral and medial streams are perturbed and expression of SP8 and COUP-TFII affected. As a consequence, adult mutant neocortices have laminar-specific alterations of distinct cortical interneuron subtypes. Overall, we propose that the existence of spatially and temporally regulated migratory paths in the subpallium contributes to the laminar distribution and specification of distinct interneuron subpopulations in the adult brain.

Remodeled cortical inhibition prevents motor seizures in generalized epilepsy.

OBJECTIVE: Deletions of CACNA1A, encoding the α1 subunit of CaV 2.1 channels, cause epilepsy with ataxia in humans. Whereas the deletion of Cacna1a in γ-aminobutyric acidergic (GABAergic) interneurons (INs) derived from the medial ganglionic eminence (MGE) impairs cortical inhibition and causes generalized seizures in Nkx2.1Cre ;Cacna1ac/c mice, the targeted deletion of Cacna1a in somatostatin-expressing INs (SOM-INs), a subset of MGE-derived INs, does not result in seizures, indicating a crucial role of parvalbumin-expressing (PV) INs. Here we identify the cellular and network consequences of Cacna1a deletion specifically in PV-INs. METHODS: We generated PVCre ;Cacna1ac/c mutant mice carrying a conditional Cacna1a deletion in PV neurons and evaluated the cortical cellular and network outcomes of this mutation by combining immunohistochemical assays, in vitro electrophysiology, 2-photon imaging, and in vivo video-electroencephalographic recordings. RESULTS: PVCre ;Cacna1ac/c mice display reduced cortical perisomatic inhibition and frequent absences but only rare motor seizures. Compared to Nkx2.1Cre ;Cacna1ac/c mice, PVCre ;Cacna1ac/c mice have a net increase in cortical inhibition, with a gain of dendritic inhibition through sprouting of SOM-IN axons, largely preventing motor seizures. This beneficial compensatory remodeling of cortical GABAergic innervation is mTORC1-dependent and its inhibition with rapamycin leads to a striking increase in motor seizures. Furthermore, we show that a direct chemogenic activation of cortical SOM-INs prevents motor seizures in a model of kainate-induced seizures. INTERPRETATION: Our findings provide novel evidence suggesting that the remodeling of cortical inhibition, with an mTOR-dependent gain of dendritic inhibition, determines the seizure phenotype in generalized epilepsy and that mTOR inhibition can be detrimental in epilepsies not primarily due to mTOR hyperactivation. Ann Neurol 2018;84:436-451.

Duration of culture and sonic hedgehog signaling differentially specify PV versus SST cortical interneuron fates from embryonic stem cells.

Medial ganglionic eminence (MGE)-derived GABAergic cortical interneurons (cINs) consist of multiple subtypes that are involved in many cortical functions. They also have a remarkable capacity to migrate, survive and integrate into cortical circuitry after transplantation into postnatal cortex. These features have engendered considerable interest in generating distinct subgroups of interneurons from pluripotent stem cells (PSCs) for the study of interneuron fate and function, and for the development of cell-based therapies. Although advances have been made, the capacity to generate highly enriched pools of subgroup fate-committed interneuron progenitors from PSCs has remained elusive. Previous studies have suggested that the two main MGE-derived interneuron subgroups--those expressing somatostatin (SST) and those expressing parvalbumin (PV)--are specified in the MGE from Nkx2.1-expressing progenitors at higher or lower levels of sonic hedgehog (Shh) signaling, respectively. To further explore the role of Shh and other factors in cIN fate determination, we generated a reporter line such that Nkx2.1-expressing progenitors express mCherry and postmitotic Lhx6-expressing MGE-derived interneurons express GFP. Manipulations of Shh exposure and time in culture influenced the subgroup fates of ESC-derived interneurons. Exposure to higher Shh levels, and collecting GFP-expressing precursors at 12 days in culture, resulted in the strongest enrichment for SST interneurons over those expressing PV, whereas the strongest enrichment for PV interneurons was produced by lower Shh and by collecting mCherry-expressing cells after 17 days in culture. These findings confirm that fate determination of cIN subgroups is crucially influenced by Shh signaling, and provide a system for the further study of interneuron fate and function.

Persistent seizure control in epileptic mice transplanted with gamma-aminobutyric acid progenitors.

OBJECTIVE: A significant proportion of the more than 50 million people worldwide currently suffering with epilepsy are resistant to antiepileptic drugs (AEDs). As an alternative to AEDs, novel therapies based on cell transplantation offer an opportunity for long-lasting modification of epileptic circuits. To develop such a treatment requires careful preclinical studies in a chronic epilepsy model featuring unprovoked seizures, hippocampal histopathology, and behavioral comorbidities. METHODS: Transplantation of progenitor cells from embryonic medial or caudal ganglionic eminence (MGE, CGE) were made in a well-characterized mouse model of status epilepticus-induced epilepsy (systemic pilocarpine). Behavioral testing (handling and open field), continuous video-electroencephalographic (vEEG) monitoring, and slice electrophysiology outcomes were obtained up to 270 days after transplantation (DAT). Post-hoc immunohistochemistry was used to confirm cell identity. RESULTS: MGE progenitors transplanted into the hippocampus of epileptic mice rescued handling and open field deficits starting at 60 DAT. In these same mice, an 84% to 88% reduction in seizure activity was observed between 180 and 210 DAT. Inhibitory postsynaptic current frequency, measured on pyramidal neurons in acute hippocampal slices at 270 DAT, was reduced in epileptic mice but restored to naïve levels in epileptic mice receiving MGE transplants. No reduction in seizure activity was observed in epileptic mice receiving intrahippocampal CGE progenitors. INTERPRETATION: Our findings demonstrate that transplanted MGE progenitors enhance functional GABA-mediated inhibition, reduce spontaneous seizure frequency, and rescue behavioral deficits in a chronic epileptic animal model more than 6 months after treatment. Ann Neurol 2017;82:530-542.

Brief Report: Robo1 Regulates the Migration of Human Subventricular Zone Neural Progenitor Cells During Development.

Human neural progenitor cell (NPC) migration within the subventricular zone (SVZ) of the lateral ganglionic eminence is an active process throughout early brain development. The migration of human NPCs from the SVZ to the olfactory bulb during fetal stages resembles what occurs in adult rodents. As the human brain develops during infancy, this migratory stream is drastically reduced in cell number and becomes barely evident in adults. The mechanisms regulating human NPC migration are unknown. The Slit-Robo signaling pathway has been defined as a chemorepulsive cue involved in axon guidance and neuroblast migration in rodents. Slit and Robo proteins expressed in the rodent brain help guide neuroblast migration from the SVZ through the rostral migratory stream to the olfactory bulb. Here, we present the first study on the role that Slit and Robo proteins play in human-derived fetal neural progenitor cell migration (hfNPC). We describe that Robo1 and Robo2 isoforms are expressed in the human fetal SVZ. Furthermore, we demonstrate that Slit2 is able to induce a chemorepellent effect on the migration of hfNPCs derived from the human fetal SVZ. In addition, when Robo1 expression is inhibited, hfNPCs are unable to migrate to the olfactory bulb of mice when injected in the anterior SVZ. Our findings indicate that the migration of human NPCs from the SVZ is partially regulated by the Slit-Robo axis. This pathway could be regulated to direct the migration of NPCs in human endogenous neural cell therapy. Stem Cells 2017;35:1860-1865.

Distribution and morphology of gonadotropin-releasing hormone neurons in the hypothalamus of an induced ovulator - The llama (Lama glama).

Gonadotropin-releasing hormone (GnRH) is a decapeptide involved in the regulation of reproduction in all mammals, but the distribution of GnRH neurons within the brain varies widely among species. The objective of the present study was to characterize the number and distribution of GnRH neurons in the hypothalamus and preoptic area of llamas, an induced ovulator. The brains of female llamas (n = 4) were fixed, frozen and sectioned serially every 50 µm in the transverse (coronal) plane. Every 10th section was stained for immunohistochemical detection of GnRH-positive neuron cell bodies and fibers by incubation with 3,3'-diaminobenzidine. The number of counted immunoreactive cells ranged from 222 to 250 (≈241 ±â€¯13 cells in the preoptic area and hypothalamus per animal) and were localized in the medio-basal hypothalamus (44.3%), anterior hypothalamus (27%), preoptic area (14.9%), diagonal band of Broca/medial septum (13.4%), and mammillary area (0.5%). The immunoreactive cells were not localized in specific hypothalamic nuclei, but rather appeared to be distributed diffusely. The highest concentration of immunoreactive neuron fibers was in the median eminence (P < 0.05), but fibers were identified in most of the areas analyzed, including the neurohypophysis. The GnRH neurons within the hypothalamus displayed monopolar (33%), bipolar (39%), and multipolar (28%) morphologies. The bipolar type was most common in the medio-basal region (40%; P < 0.05). We conclude that GnRH neurons and fibers form a network within the anterior and medio-basal hypothalamus of llamas, suggesting the central location of mechanisms controlling reproductive processes in llamas (i.e., induced ovulation).

Synergistic antipruritic effects of gamma aminobutyric acid A and B agonists in a mouse model of atopic dermatitis.

BACKGROUND: Despite recent insights into the pathophysiology of acute and chronic itch, chronic itch remains an often intractable condition. Among major contributors to chronic itch is dysfunction of spinal cord gamma aminobutyric acidergic (GABAergic) inhibitory controls. OBJECTIVES: We sought to test the hypothesis that selective GABA agonists as well as cell transplant-derived GABA are antipruritic against acute itch and in a transgenic mouse model of atopic dermatitis produced by overexpression of the TH2 cell-associated cytokine, IL-31 (IL-31Tg mice). METHODS: We injected wild-type and IL-31Tg mice with combinations of GABA-A (muscimol) or GABA-B (baclofen) receptor agonists 15 to 20 minutes prior to injection of various pruritogens (histamine, chloroquine, or endothelin-1) and recorded spontaneous scratching before and after drug administration. We also tested the antipruritic properties of intraspinal transplantation of precursors of GABAergic interneurons in the IL-31Tg mice. RESULTS: Systemic muscimol or baclofen are antipruritic against both histamine-dependent and -independent pruritogens, but the therapeutic window using either ligand alone was very small. In contrast, combined subthreshold doses of baclofen and muscimol produced a significant synergistic antipruritic effect, with no sedation. Finally, transplant-mediated long-term enhancement of GABAergic signaling not only reduced spontaneous scratching in the IL-31Tg mice but also dramatically resolved the associated skin lesions. CONCLUSIONS: Although additional research is clearly needed, existing approved GABA agonists should be considered in the management of chronic itch, notably atopic dermatitis.

Interneurons Differentially Contribute to Spontaneous Network Activity in the Developing Hippocampus Dependent on Their Embryonic Lineage.

Spontaneously generated network activity is a hallmark of developing neural circuits, and plays an important role in the formation of synaptic connections. In the rodent hippocampus, this activity is observed in vitro as giant depolarizing potentials (GDPs) during the first postnatal week. Interneurons importantly contribute to GDPs, due to the depolarizing actions of GABA early in development. While they are highly diverse, cortical interneurons can be segregated into two distinct groups based on their embryonic lineage from either the medial or caudal ganglionic eminences (MGE and CGE). There is evidence suggesting CGE-derived interneurons are important for GDP generation; however, their contribution relative to those from the MGE has never been directly tested. Here, we optogenetically inhibited either MGE- or CGE-derived interneurons in a region-specific manner in mouse neonatal hippocampus in vitro. In CA1, where interneurons are the primary source of recurrent excitation, we found that those from the MGE strongly and preferentially contributed to GDP generation. Furthermore, in dual whole-cell patch recordings in neonatal CA1, MGE interneurons formed synaptic connections to and from neighboring pyramidal cells at a much higher rate than those from the CGE. These MGE interneurons were commonly perisomatic targeting, in contrast to those from the CGE, which were dendrite targeting. Finally, inhibiting MGE interneurons in CA1 suppressed GDPs in CA3 and vice versa; conversely, they could also trigger GDPs in CA1 that propagated to CA3 and vice versa. Our data demonstrate a key role for MGE-derived interneurons in both generating and coordinating GDPs across the hippocampus. SIGNIFICANCE STATEMENT: During nervous system development, immature circuits internally generate rhythmic patterns of electrical activity that promote the establishment of synaptic connections. Immature interneurons are excitatory rather than inhibitory and actively contribute to the generation of these spontaneous network events, referred to as giant depolarizing potentials (GDPs) in the hippocampus. Interneurons can be generally separated into two distinct groups based on their origin in the embryo from the medial or caudal ganglionic eminences (MGE and CGE). Here we show that MGE interneurons play a dominant role in generating GDPs compared with their CGE counterparts. They accomplish this due to their high synaptic connectivity within the local circuitry. Finally, they can control network activity across large regions of the developing hippocampus.

Identification of an endocannabinoid system in the rat pars tuberalis-a possible interface in the hypothalamic-pituitary-adrenal system?

Endocannabinoids (ECs) are ubiquitous endogenous lipid derivatives and play an important role in intercellular communication either in an autocrine/paracrine or in an endocrine fashion. Recently, an intrinsic EC system has been discovered in the hypophysial pars tuberalis (PT) of hamsters and humans. In hamsters, this EC system is under photoperiodic control and appears to influence the secretion of hormones such as prolactin from the adenohypophysis. We investigate the EC system in the PT of the rat, a frequently used species in endocrine research. By means of immunocytochemistry, enzymes involved in EC biosynthesis, e.g., N-arachidonoyl-phosphatidylethanolamine-phospholipase D (NAPE-PLD) and diacylglycerol lipase α (DAGLα) and enzymes involved in EC degradation, e.g., fatty acid amide hydrolase (FAAH) and cyclooxygenase-2 (COX-2), were demonstrated in PT cells of the rat. Immunoreactions (IR) for FAAH and for the cannabinoid receptor CB1 were observed in corticotrope cells of the rat adenohypophysis; these cells were identified by antibodies against proopiomelanocortin (POMC) or adrenocorticotrophic hormone (ACTH). In the outer zone of the median eminence, numerous nerve fibers and terminals displayed CB1 IR. The majority of these were also immunolabeled by an antibody against corticotropin-releasing factor (CRF). These results suggest that the EC system at the hypothalamo-hypophysial interface affects both the CRF-containing nerve fibers and the corticotrope cells in the adenohypophysis. Our data give rise to the hypothesis that, in addition to its well-known role in the reproductive axis, the PT might influence adrenal functions and, thus, the stress response and immune system.

Transplantation of inhibitory precursor cells from medial ganglionic eminence produces distinct responses in two different models of acute seizure induction.

Medial ganglionic eminence (MGE) is one of the sources of inhibitory interneurons during development. Following transplantation in postnatal developing brain, MGE cells can increase local inhibition suggesting a possible protection to GABAergic dysfunction in brain disorders, such as epilepsy. Since it has been shown that MGE-derived cells harvested as neurospheres are able to suppress seizures, it might be important to investigate whether these protective effects would change in different seizure models. Here, we used pentylenetetrazole-(PTZ) and maximal electroshock (MES)-induced seizure models to test whether the transplantation of MGE cells would increase the threshold to trigger acute seizures. When transplanted into the neocortex (layers 3-4) of neonatal mice (postnatal days 3-4), MGE cells were able to survive and were mainly found in piriform cortex, fimbria, and ventricular wall regions. Additionally, the number of GFP+ cells found in the brains of mice induced with PTZ and MES differed significantly and suggests proliferation and larger survival rate of MGE-transplanted cells after PTZ, but not MES-induced seizures. Following transplantation, there was a reduction in the number of animals presenting mild and severe seizures induced by PTZ. Furthermore, MGE-cell transplantation was able to increase threshold to seizures induced by PTZ, but was not able to prevent seizure spread induced by MES.

Cortical plasticity induced by transplantation of embryonic somatostatin or parvalbumin interneurons.

GABAergic inhibition has been shown to play an important role in the opening of critical periods of brain plasticity. We recently have shown that transplantation of GABAergic precursors from the embryonic medial ganglionic eminence (MGE), the source of neocortical parvalbumin- (PV(+)) and somatostatin-expressing (SST(+)) interneurons, can induce a new period of ocular dominance plasticity (ODP) after the endogenous period has closed. Among the diverse subtypes of GABAergic interneurons PV(+) cells have been thought to play the crucial role in ODP. Here we have used MGE transplantation carrying a conditional allele of diphtheria toxin alpha subunit and cell-specific expression of Cre recombinase to deplete PV(+) or SST(+) interneurons selectively and to investigate the contributions of each of these types of interneurons to ODP. As expected, robust plasticity was observed in transplants containing PV(+) cells but in which the majority of SST(+) interneurons were depleted. Surprisingly, transplants in which the majority of PV(+) cells were depleted induced plasticity as effectively as those containing PV(+) cells. In contrast, depleting both cell types blocked induction of plasticity. These findings reveal that PV(+) cells do not play an exclusive role in ODP; SST(+) interneurons also can drive cortical plasticity and contribute to the reshaping of neural networks. The ability of both PV(+) and SST(+) interneurons to induce de novo cortical plasticity could help develop new therapeutic approaches for brain repair.

Synaptic integration of transplanted interneuron progenitor cells into native cortical networks.

Interneuron-based cell transplantation is a powerful method to modify network function in a variety of neurological disorders, including epilepsy. Whether new interneurons integrate into native neural networks in a subtype-specific manner is not well understood, and the therapeutic mechanisms underlying interneuron-based cell therapy, including the role of synaptic inhibition, are debated. In this study, we tested subtype-specific integration of transplanted interneurons using acute cortical brain slices and visualized patch-clamp recordings to measure excitatory synaptic inputs, intrinsic properties, and inhibitory synaptic outputs. Fluorescently labeled progenitor cells from the embryonic medial ganglionic eminence (MGE) were used for transplantation. At 5 wk after transplantation, MGE-derived parvalbumin-positive (PV+) interneurons received excitatory synaptic inputs, exhibited mature interneuron firing properties, and made functional synaptic inhibitory connections to native pyramidal cells that were comparable to those of native PV+ interneurons. These findings demonstrate that MGE-derived PV+ interneurons functionally integrate into subtype-appropriate physiological niches within host networks following transplantation.

RhoA and Cdc42 are required in pre-migratory progenitors of the medial ganglionic eminence ventricular zone for proper cortical interneuron migration.

Cortical interneurons arise from the ganglionic eminences in the ventral telencephalon and migrate tangentially to the cortex. Although RhoA and Cdc42, members of the Rho family of small GTPases, have been implicated in regulating neuronal migration, their respective roles in the tangential migration of cortical interneurons remain unknown. Here we show that loss of RhoA and Cdc42 in the ventricular zone (VZ) of the medial ganglionic eminence (MGE) using Olig2-Cre mice causes moderate or severe defects in the migration of cortical interneurons, respectively. Furthermore, RhoA- or Cdc42-deleted MGE cells exhibit impaired migration in vitro. To determine whether RhoA and Cdc42 directly regulate the motility of cortical interneurons during migration, we deleted RhoA and Cdc42 in the subventricular zone (SVZ), where more fate-restricted progenitors are located within the ganglionic eminences, using Dlx5/6-Cre-ires-EGFP (Dlx5/6-CIE) mice. Deletion of either gene within the SVZ does not cause any obvious defects in cortical interneuron migration, indicating that cell motility is not dependent upon RhoA or Cdc42. These findings provide genetic evidence that RhoA and Cdc42 are required in progenitors of the MGE in the VZ, but not the SVZ, for proper cortical interneuron migration.