Postnatal Neuronal Development Research Articles

Microglia shape AgRP neuron postnatal development via regulating perineuronal net plasticity.

The hypothalamus plays a crucial role in controlling metabolism and energy balance, with Agouti-related protein (AgRP) neurons and proopiomelanocortin (POMC) neurons being essential components of this process. The proper development of these neurons is important for metabolic regulation in later life. Microglia, the resident immune cells in the brain, have been shown to significantly influence neurodevelopment. However, their role in shaping the postnatal development of hypothalamic neural circuits remains underexplored. In this study, we investigated the dynamic changes of microglia in the hypothalamic arcuate nucleus (ARC) during lactation and their impact on the maturation of AgRP and POMC neurons. We demonstrated that microglial depletion during a critical period of ARC neuron maturation increases the number of AgRP neurons and fiber density, with less effect on POMC neurons. This depletion also resulted in increased neonatal feeding behavior. Mechanistically, microglia can engulf perineuronal net (PNN) components surrounding AgRP neurons both in vivo and ex vivo. The absence of microglia leads to increased PNN formation and enhanced leptin sensitivity in ARC. Our findings suggest that microglia participate in the postnatal development of AgRP neurons by regulating the plasticity of PNN formation. This study contributes to a better understanding of microglia's role in shaping hypothalamic neural circuits during postnatal development and their impact on metabolism regulation.

A single-cell genomic atlas for maturation of the human cerebellum during early childhood.

Inflammation early in life is a clinically established risk factor for autism spectrum disorders and schizophrenia, yet the impact of inflammation on human brain development is poorly understood. The cerebellum undergoes protracted postnatal maturation, making it especially susceptible to perturbations contributing to the risk of developing neurodevelopmental disorders. Here, using single-cell genomics of postmortem cerebellar brain samples, we characterized the postnatal development of cerebellar neurons and glia in 1 to 5 year-old children, comparing individuals who had died while experiencing inflammation to those who had died as a result of an accident. Our analyses revealed that inflammation and postnatal cerebellar maturation are associated with extensive, overlapping transcriptional changes primarily in two subtypes of inhibitory neurons: Purkinje neurons and Golgi neurons. Immunohistochemical analysis of a subset of these postmortem cerebellar samples revealed no change to Purkinje neuron soma size but evidence for increased activation of microglia in those children who had experienced inflammation. Maturation-associated and inflammation-associated gene expression changes included genes implicated in neurodevelopmental disorders. A gene regulatory network model integrating cell type-specific gene expression and chromatin accessibility identified seven temporally specific gene networks in Purkinje neurons and suggested that inflammation may be associated with the premature downregulation of developmental gene expression programs.

Shank3a/b isoforms regulate the susceptibility to seizures and thalamocortical development in the early postnatal period of mice

Epileptic seizures are distinct but frequent comorbidities in children with autism spectrum disorder (ASD). The hyperexcitability of cortical and subcortical neurons appears to be involved in both phenotypes. However, little information is available concerning which genes are involved and how they regulate the excitability of the thalamocortical network. In this study, we investigate whether an ASD-associated gene, SH3 and multiple ankyrin repeat domains 3 (Shank3), plays a unique role in the postnatal development of thalamocortical neurons. We herein report that Shank3a/b, the splicing isoforms of mouse Shank3, were uniquely expressed in the thalamic nuclei, peaking from two to four weeks after birth. Shank3a/b-knockout mice showed lower parvalbumin signals in the thalamic nuclei. Consistently, Shank3a/b-knockout mice were more susceptible to generalized seizures than wild-type mice after kainic acid treatments. Together, these data indicate that NT-Ank domain of Shank3a/b regulates molecular pathways that protect thalamocortical neurons from hyperexcitability during the early postnatal period of mice.

Transient neurochemical features of the perigeniculate neurons during early postnatal development of the cat.

The thalamic reticular nucleus receives axons from the thalamic sensory nuclei and the cerebral cortex. The visual part of this nucleus in carnivores is the perigeniculate nucleus located dorsal to the lateral geniculate nucleus. The perigeniculate nucleus participates in the modulation of visual processing and in the transition of synchronized slow rhythmicity during sleep into desynchronized high-frequency activity during arousal and consists of inhibitory neurons. The main neurochemical markers for perigeniculate neurons are glutamic acid decarboxylase and Ca2+ -binding protein parvalbumin. Previous studies of postnatal development focused on the morphological features of the perigeniculate nucleus; however, its neurochemistry remains poorly understood. In this study, we focused on the postnatal development of perigeniculate neurons using immunohistochemical labeling of parvalbumin, two related Ca2+ -binding proteins (calretinin and calbindin), glutamic acid decarboxylase, and a common neuronal protein, NeuN, in kittens that were 0-123 days old and in adult cats. In parallel with the well-known dominant neuronal populations expressing parvalbumin and GAD67 and persisting until adulthood, transient populations expressing calretinin and calbindin were observed. The calbindin-positive neurons were similar to the main perigeniculate population and showed close morphological features and parvalbumin coexpression. In contrast, the calretinin-positive neurons differed in their morphological characteristics and did not express GAD67, thus distinguishing them from the majority of perigeniculate neurons. A possible link between these populations was revealed, and the development of thalamocortical processing is discussed.

M6A Modification Involves in Enriched Environment-Induced Neurogenesis and Cognition Enhancement.

Although previous studies have shown that an enriched environment (EE) promotes neurogenesis and alters DNA and histone modifications, it remains largely unknown whether an EE affects epitranscriptome in the context of neuronal development. Here, we showed that EE exposure enhanced the pool of adult neural stem/progenitor cells (aNSPCs) and promoted neuronal differentiation of aNSPCs. EE exposure also improved cognitive capabilities and altered the expression of genes relating to neuronal development, neurogenesis, and memory. N 6-Methyladenosine (m6A) immunoprecipitation combined with deep sequencing (MeRIP-seq) data analysis revealed that EE exposure increased the global level of m6A and led to differential m6A mRNA modification. Differential m6A modification-associated genes are involved in neuronal development, neurogenesis, and so on. Notably, EE exposure decreased the protein level of m6A eraser Fto, but did not affect the protein level of m6A writers METTL3 and METTL14. Taken together, our results suggest that enriched environment exposure induces differential m6A mRNA modification and adds a novel layer to the interaction between the environment and epigenetics in the context of postnatal neuronal development.

The Role of ATF3 in Neuronal Differentiation and Development of Neuronal Networks in Opossum Postnatal Cortical Cultures.

Activating transcription factor 3 (ATF3), a member of the ATF/cAMP response element-binding (CREB) family, is upregulated by various intracellular and extracellular signals such as injury and signals related to cell proliferation. ATF3 also belongs to the regeneration-associated genes (RAG) group of transcription factors. RAG and ATF/CREB transcription factors that play an important role in embryonic neuronal development and PNS regeneration may also be involved in postnatal neuronal differentiation and development, as well as in the regeneration of the injured CNS. Here we investigated the effect of ATF3 in differentiation, neural outgrowth, network formation, and regeneration after injury using postnatal dissociated cortical neurons derived from neonatal opossums (Monodelphis domestica). Our results show that RAG and ATF genes are differentially expressed in early differentiated neurons versus undifferentiated neurospheres and that many members of those families, ATF3 in particular, are upregulated in cortical cultures obtained from younger animals that have the ability to fully functionally regenerate spinal cord after injury. In addition, we observed different intracellular localization of ATF3 that shifts from nuclear (in neuronal progenitors) to cytoplasmic (in more mature neurons) during neuronal differentiation. The ATF3 inhibition, pharmacological or by specific antibody, reduced the neurite outgrowth and differentiation and caused increased cell death in early differentiating cortical neuronal cultures, suggesting the importance of ATF3 in the CNS development of neonatal opossums. Finally, we investigated the regeneration capacity of primary cortical cultures after mechanical injury using the scratch assay. Remarkably, neonatal opossum-derived cultures retain their capacity to regenerate for up to 1 month in vitro. Inhibition of ATF3 correlates with reduced neurite outgrowth and regeneration after injury. These results indicate that ATF3, and possibly other members of RAG and ATF/CREB family of transcription factors, have an important role both during cortical postnatal development and in response after injury.

Protein Kinase B/Akt1 Phosphorylates Dysbindin-1A at Serine 10 to Regulate Neuronal Development

Schizophrenia is a neurodevelopmental disorder with dendrite and dendritic spine dysfunction. Dysbindin-1, a protein decreased in the brains of schizophrenia patients, is involved in the development of dendrites and spines. However, it is still unclear how the role of dysbindin-1 in neuronal development is regulated. Here, we showed protein kinase B/Akt1, a serine/threonine kinase implicated in schizophrenia, phosphorylated dysbindin-1A at serine 10 (S10). S10 phosphorylation of dysbindin-1A was increased during postnatal neuronal and synapse development stage, and was enriched in postsynaptic densities (PSDs). Furthermore, overexpressing wild type or S10 phospho-mimic mutant (S10D), but not S10 phospho-dead mutant (S10A) of dysbindin-1A rescued the dendrite and spine deficits in dysbindin-1A knockdown neurons. These results indicate S10 phosphorylation of dysbindin-1A by Akt1 is essential for neuronal development, providing a potential regulation mechanism for dysbindin-1A in neuronal development.

Sildenafil improves hippocampal brain injuries and restores neuronal development after neonatal hypoxia\u2013ischemia in male rat pups

The hippocampus is a fundamental structure of the brain that plays an important role in neurodevelopment and is very sensitive to hypoxia–ischemia (HI). The purpose of this study was to investigate the effects of sildenafil on neonatal hippocampal brain injuries resulting from HI, and on neuronal development in this context. HI was induced in male Long–Evans rat pups at postnatal day 10 (P10) by a left common carotid ligation followed by a 2-h exposure to 8% oxygen. Rat pups were randomized to vehicle or sildenafil given orally twice daily for 7 days starting 12 h after HI. Hematoxylin and eosin staining was performed at P30 to measure the surface of the hippocampus; immunohistochemistry was performed to stain neurons, oligodendrocytes, and glial cells in the hippocampus. Western blots of the hippocampus were performed at P12, P17, and P30 to study the expression of neuronal markers and mTOR pathway. HI caused significant hippocampal atrophy and a significant reduction of the number of mature neurons, and induced reactive astrocytosis and microgliosis in the hippocampus. HI increased apoptosis and caused significant dysregulation of the normal neuronal development program. Treatment with sildenafil preserved the gross morphology of the hippocampus, reverted the number of mature neurons to levels comparable to sham rats, significantly increased both the immature and mature oligodendrocytes, and significantly reduced the number of microglia and astrocytes. Sildenafil also decreased apoptosis and reestablished the normal progression of post-natal neuronal development. The PI3K/Akt/mTOR pathway, whose activity was decreased after HI in the hippocampus, and restored after sildenafil treatment, may be involved. Sildenafil may have both neuroprotective and neurorestorative properties in the neonatal hippocampus following HI.

Suppression of DNA Double-Strand Break Formation by DNA Polymerase β in Active DNA Demethylation Is Required for Development of Hippocampal Pyramidal Neurons.

Genome stability is essential for brain development and function, as de novo mutations during neuronal development cause psychiatric disorders. However, the contribution of DNA repair to genome stability in neurons remains elusive. Here, we demonstrate that the base excision repair protein DNA polymerase β (Polβ) is involved in hippocampal pyramidal neuron differentiation via a TET-mediated active DNA demethylation during early postnatal stages using Nex-Cre/Polβ fl/fl mice of either sex, in which forebrain postmitotic excitatory neurons lack Polβ expression. Polβ deficiency induced extensive DNA double-strand breaks (DSBs) in hippocampal pyramidal neurons, but not dentate gyrus granule cells, and to a lesser extent in neocortical neurons, during a period in which decreased levels of 5-methylcytosine and 5-hydroxymethylcytosine were observed in genomic DNA. Inhibition of the hydroxylation of 5-methylcytosine by expression of microRNAs miR-29a/b-1 diminished DSB formation. Conversely, its induction by TET1 catalytic domain overexpression increased DSBs in neocortical neurons. Furthermore, the damaged hippocampal neurons exhibited aberrant neuronal gene expression profiles and dendrite formation, but not apoptosis. Comprehensive behavioral analyses revealed impaired spatial reference memory and contextual fear memory in adulthood. Thus, Polβ maintains genome stability in the active DNA demethylation that occurs during early postnatal neuronal development, thereby contributing to differentiation and subsequent learning and memory.SIGNIFICANCE STATEMENT Increasing evidence suggests that de novo mutations during neuronal development cause psychiatric disorders. However, strikingly little is known about how DNA repair is involved in neuronal differentiation. We found that Polβ, a component of base excision repair, is required for differentiation of hippocampal pyramidal neurons in mice. Polβ deficiency transiently led to increased DNA double-strand breaks, but not apoptosis, in early postnatal hippocampal pyramidal neurons. This aberrant double-strand break formation was attributed to active DNA demethylation as an epigenetic regulation. Furthermore, the damaged neurons exhibited aberrant gene expression profiles and dendrite formation, resulting in impaired learning and memory in adulthood. Thus, these findings provide new insight into the contribution of DNA repair to the neuronal genome in early brain development.

Distinct Expression Patterns of Apoptosis and Autophagy-Associated Proteins and Genes during Postnatal Development of Spiral Ganglion Neurons in Rat.

Autophagy and apoptosis have a complex interplay in the early embryo development. The development of spiral ganglion neurons (SGNs) in addition to Corti's organ in the mammalian cochlea remains crucial in the first two-week postnatal period. To investigate the roles of apoptosis and autophagy in the development of SGNs, light microscopy was used to observe the morphological changes of SGNs. The number of SGNs was decreased from P1 to P7 and plateaued from P10 to P14. Immunohistochemistry results revealed positive expression of cleaved-caspase3, bcl-2, microtubule-associated protein light chain 3-II (LC3-II), Beclin1, and sequestosome 1 (SQSTM1/P62) in SGNs. The apoptotic bodies and autophagosomes and autolysosomes were also identified by transmission electron microscopy at P1 and P7. Real-time PCR and western blotting results revealed that the apoptotic activity peaked at P7 and the autophagy activity was gradually upregulated along with the development. Taken together, our results for the first time showed that autophagy and apoptosis in SGNs play distinct roles during specific developmental phases in a time-dependent manner.

Fto-modulated lipid niche regulates adult neurogenesis through modulating adenosine metabolism.

Adult neurogenesis is regulated by diverse factors including the local environment, i.e. the neurogenic niche. However, whether the lipid in the brain regulates adult neurogenesis and related mechanisms remains largely unknown. In the present study, we found that lipid accumulates in the brain during postnatal neuronal development. Conditional knockout of Fto (cKO) in lipid not only reduced the level of lipid in the brain but also impaired the learning and memory of mice. In addition, Fto deficiency in lipid did not affect the proliferation of adult neural stem cells (aNSCs), but it did inhibit adult neurogenesis by inducing cell apoptosis. Mechanistically, specific deleting Fto in lipid altered gene expression and increased adenosine secretion of adipocytes. The treatment of adenosine promoted the apoptosis of newborn neurons. As a whole, these results reveal the important function of the lipid niche and its associated mechanism in regulating adult neurogenesis.

Early postnatal development of pyramidal neurons across layers of the mouse medial prefrontal cortex

Mammalian neocortex is a highly layered structure. Each layer is populated by distinct subtypes of principal cells that are born at different times during development. While the differences between principal cells across layers have been extensively studied, it is not known how the developmental profiles of neurons in different layers compare. Here, we provide a detailed morphological and functional characterisation of pyramidal neurons in mouse mPFC during the first postnatal month, corresponding to known critical periods for synapse and neuron formation in mouse sensory neocortex. Our data demonstrate similar maturation profiles of dendritic morphology and intrinsic properties of pyramidal neurons in both deep and superficial layers. In contrast, the balance of synaptic excitation and inhibition differs in a layer-specific pattern from one to four postnatal weeks of age. Our characterisation of the early development and maturation of pyramidal neurons in mouse mPFC not only demonstrates a comparable time course of postnatal maturation to that in other neocortical circuits, but also implies that consideration of layer- and time-specific changes in pyramidal neurons may be relevant for studies in mouse models of neuropsychiatric and neurodevelopmental disorders.

The Role of the Microglial Cx3cr1 Pathway in the Postnatal Maturation of Retinal Photoreceptors.

Microglia are the resident immune cells of the CNS, and their response to infection, injury and disease is well documented. More recently, microglia have been shown to play a role in normal CNS development, with the fractalkine-Cx3cr1 signaling pathway of particular importance. This work describes the interaction between the light-sensitive photoreceptors and microglia during eye opening, a time of postnatal photoreceptor maturation. Genetic removal of Cx3cr1 (Cx3cr1GFP/GFP ) led to an early retinal dysfunction soon after eye opening [postnatal day 17 (P17)] and cone photoreceptor loss (P30 onward) in mice of either sex. This dysfunction occurred at a time when fractalkine expression was predominantly outer retinal, when there was an increased microglial presence near the photoreceptor layer and increased microglial-cone photoreceptor contacts. Photoreceptor maturation and outer segment elongation was coincident with increased opsin photopigment expression in wild-type retina, while this was aberrant in the Cx3cr1GFP/GFP retina and outer segment length was reduced. A beadchip array highlighted Cx3cr1 regulation of genes involved in the photoreceptor cilium, a key structure that is important for outer segment elongation. This was confirmed with quantitative PCR with specific cilium-related genes, Rpgr and Rpgrip1, downregulated at eye opening (P14). While the overall cilium structure was unaffected, expression of Rpgr, Rpgrip1, and centrin were restricted to more proximal regions of the transitional zone. This study highlighted a novel role for microglia in postnatal neuronal development within the retina, with loss of fractalkine-Cx3cr1 signaling leading to an altered distribution of cilium proteins, failure of outer segment elongation and ultimately cone photoreceptor loss.SIGNIFICANCE STATEMENT Microglia are involved in CNS development and disease. This work highlights the role of microglia in postnatal development of the light-detecting photoreceptor neurons within the mouse retina. Loss of the microglial Cx3cr1 signaling pathway resulted in specific alterations in the cilium, a key structure in photoreceptor outer segment elongation. The distribution of key components of the cilium transitional zone, Rpgr, Rpgrip1, and centrin, were altered in retinae lacking Cx3cr1 with reduced outer segment length and cone photoreceptor death observed at later postnatal ages. This work identifies a novel role for microglia in the postnatal maturation of retinal photoreceptors.

Gene expression profile associated with postnatal development of pyramidal neurons in the human prefrontal cortex implicates ubiquitin ligase E3 in the pathophysiology of schizophrenia onset

Schizophrenia is a neurodevelopmental disorder with the typical age of onset of overt symptoms and deficits occurring during late adolescence or early adulthood, coinciding with the final maturation of the cortical network involving the prefrontal cortex. These observations have led to the hypothesis that disturbances of the developmental events that take place in the prefrontal cortex during this period, specifically the remodeling of synaptic connectivities between pyramidal neurons, may contribute to the onset of illness. In this context, we investigated the gene expression changes of pyramidal neurons in the human prefrontal cortex during normal periadolescent development in order to gain insight into the possible molecular mechanisms involved in synaptic remodeling of pyramidal neuronal circuitry. Our data suggest that genes associated with the ubiquitination system, which has been implicated in the biology of synaptic plasticity, may play a major role. Among these genes, UBE3B, which encodes the ubiquitin ligase E3, was found to undergo periadolescent increase and was validated at the protein level to be upregulated during periadolescent development. Furthermore, we found that the density of UBE3B-immunoreactive pyramidal neurons was decreased in schizophrenia subjects, consistent with the result of a previous study of decreased UBE3B mRNA expression in pyramidal neurons in this illness. Altogether these findings point to the novel hypothesis that this specific ligase may play a role in the developmental pathogenesis of schizophrenia onset by possibly altering the synaptic remodeling process.

The Dynamic DNA Demethylation during Postnatal Neuronal Development and Neural Stem Cell Differentiation.

Background DNA demethylation, the conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC), plays important roles in diverse biological processes and multiple diseases by regulating gene expression. Methods In this study, utilizing DNA dot blot, immunofluorescence staining, and qRT-PCR, we studied the expression pattern of Tets, the enzymes governing DNA demethylation, and the levels of 5hmC, 5fC, and 5caC during the postnatal neuronal development of mice. Results It was found that 5hmC, 5fC, and 5caC were highly enriched in multiple brain regions and aNSCs and displayed temporal and spatial patterns during postnatal neuronal development and the differentiation of aNSCs. Consistently, the expression of Tets also exhibited temporal and spatial patterns. Conclusion DNA demethylation displayed dynamic features during postnatal neuronal development and the differentiation of aNSCs of mice, which could contribute to appropriate gene expression.

Neonatal hyperglycemia induces cell death in the rat brain.

Several studies have examined neonatal diabetes, a rare disease characterized by hyperglycemia and low insulin levels that is usually diagnosed in the first 6month of life. Recently, the effects of diabetes on the brain have received considerable attention. In addition, hyperglycemia may perturb brain function and might be associated with neuronal death in adult rats. However, few studies have investigated the damaging effects of neonatal hyperglycemia on the rat brain during central nervous system (CNS) development, particularly the mechanisms involved in the disease. Thus, in the present work, we investigated whether neonatal hyperglycemia induced by streptozotocin (STZ) promoted cell death and altered the levels of proteins involved in survival/death pathways in the rat brain. Cell death was assessed using FluoroJade C (FJC) staining and the expression of the p38 mitogen-activated protein kinase (p38), phosphorylated-c-Jun amino-terminal kinase (p-JNK), c-Jun amino-terminal kinase (JNK), protein kinase B (Akt), phosphorylated-protein kinase B (p-Akt), glycogen synthase kinase-3β (Gsk3β), B-cell lymphoma 2 (Bcl2) and Bcl2-associated X protein (Bax) protein were measured by Western blotting. The main results of this study showed that the metabolic alterations observed in diabetic rats (hyperglycemia and hypoinsulinemia) increased p38 expression and decreased p-Akt expression, suggesting that cell survival was altered and cell death was induced, which was confirmed by FJC staining. Therefore, the metabolic conditions observed during neonatal hyperglycemia may contribute to the harmful effect of diabetes on the CNS in a crucial phase of postnatal neuronal development.

Effects of prenatal binge-like ethanol exposure and maternal stress on postnatal morphological development of hippocampal neurons in rats

BackgroundAlcohol is one of the most commonly used drugs of abuse negatively affecting human health and it is known as a potent teratogen responsible for fetal alcohol syndrome (FAS), which is characterized by cognitive deficits especially pronounced in juveniles but ameliorating in adults. Searching for the potential morphological correlates of these effects, in this study, we compared the course of developmental changes in the morphology of principal hippocampal neurons in fetal-alcohol (A group), intubated control (IC group), and intact control male rats (C group) over a protracted period of the first two postnatal months. MethodsEthanol was administered to the pregnant Wistar dams intragastrically, throughout gestation days (GD) 7–20, at a total dose of 6g/kg/day resulting in the mean blood alcohol concentration (BAC) of 246.6±40.9mg/dl. Ten morphometric parameters of Golgi-stained hippocampal neurons (pyramidal and granule) from CA1, CA3, and DG areas were examined at critical postnatal days (PD): at birth (PD1), at the end of the brain growth spurt period (PD10), in juveniles (PD30), and in young adults (PD60). ResultsDuring postnatal development, the temporal pattern of morphometric changes was shown to be region-dependent with most significant alterations observed between PD1-30 in the CA region and between PD10-30 in the DG region. It was also parameter-dependent with the soma size (except for CA3 pyramids), number of primary dendrites, dendrite diameter, dendritic tortuosity and the branch angle demonstrating little changes, while the total dendritic field area, dendritic length, number of dendritic bifurcations, and spine density being highly increased in all hippocampal regions during the first postnatal month. Moderate ethanol intoxication and the maternal intubation stress during gestation, showed similar, transient effects on the neuron development manifested as a smaller soma size in granule cells, reduced dendritic parameters and lower spine density in pyramidal neurons at PD1. Full recovery from these effects took place within the first 10 postnatal days. ConclusionsThis study showed regional and temporal differences in the development of different morphometric features of principal hippocampal neurons in intact subjects over a protracted 2-months postnatal period. It also demonstrated an overlap in the effects of a moderate fetal ethanol intoxication and a mild maternal stress produced by the intragastric intubation, a commonly used method of ethanol administration to the pregnant dams. Fast recovery from the adverse effects on the soma size, dendritic arborization and spines density observed at birth indicates towards the fetal ethanol/stress induced developmental retardation.

Brain-derived neurotrophic factor signaling is altered in the forebrain of Engrailed-2 knockout mice

Engrailed-2 (En2), a homeodomain transcription factor involved in regionalization and patterning of the midbrain and hindbrain regions has been associated to autism spectrum disorders (ASDs). En2 knockout (En2−/−) mice show ASD-like features accompanied by a significant loss of GABAergic subpopulations in the hippocampus and neocortex. Brain-derived neurotrophic factor (BDNF) is a crucial factor for the postnatal development of forebrain GABAergic neurons, and altered GABA signaling has been hypothesized to underlie the symptoms of ASD. Here we sought to determine whether interneuron loss in the En2−/− forebrain might be related to altered expression of BDNF and its signaling receptors. We first evaluated the expression of different BDNF mRNA isoforms in the neocortex and hippocampus of wild-type (WT) and En2−/− mice. Quantitative RT-PCR showed a marked down-regulation of several splicing variants of BDNF mRNA in the neocortex but not hippocampus of adult En2−/− mice, as compared to WT controls. Accordingly, levels of mature BDNF protein were lower in the neocortex but not hippocampus of En2−/− mice, as compared to WT. Increased levels of phosphorylated TrkB and decreased levels of p75 receptor were also detected in the neocortex of mutant mice. Accordingly, the expression of low density lipoprotein receptor (LDLR) and RhoA, two genes regulated via p75 was significantly altered in forebrain areas of mutant mice. These data indicate that BDNF signaling alterations might be involved in the anatomical changes observed in the En2−/− forebrain and suggest a pathogenic role of altered BDNF signaling in this mouse model of ASD.

Altered expression of developmental regulators of parvalbumin and somatostatin neurons in the prefrontal cortex in schizophrenia

Dysfunction of prefrontal cortex (PFC) inhibitory neurons that express the calcium-binding protein parvalbumin or the neuropeptide somatostatin in schizophrenia may be related to disturbances in the migration, phenotypic specification, and/or maturation of these neurons. These pre- and postnatal developmental stages are regulated in a cell type-specific manner by various transcription factors and co-activators, fibroblast growth factor receptors (FgfR), and other molecular markers. Consequently, we used quantitative PCR to quantify mRNA levels for these developmental regulators in the PFC of 62 schizophrenia subjects in whom parvalbumin and somatostatin neuron disturbances were previously reported, and in antipsychotic-exposed monkeys. Relative to unaffected comparison subjects, subjects with schizophrenia exhibited elevated mRNA levels for 1) the transcription factor MafB, which is expressed by parvalbumin and somatostatin neurons as they migrate from the medial ganglionic eminence to the cortex, 2) the transcriptional coactivator PGC-1α, which is expressed postnatally by parvalbumin neurons to maintain parvalbumin levels and inhibitory function, and 3) FgfR1, which is required for the migration and phenotypic specification of parvalbumin and somatostatin neurons. Elevations in these markers were most prominent in younger schizophrenia subjects and were not present in antipsychotic-exposed monkeys. Finally, expression levels of other important developmental regulators (i.e. Dlx1, Dlx5, Dlx6, SATB1, Sip1/Zeb2, ST8SIA4, cMaf, Nkx6.2, and Arx) were not altered in schizophrenia. The over-expression of a subset of molecular markers with distinct roles in the pre- and postnatal development of parvalbumin and somatostatin neurons might reflect compensatory mechanisms to sustain the development of these neurons in the face of other insults.

Postnatal Excitability Development and Innervation by Functional Transient Receptor Potential Vanilloid 1 (TRPV1) Terminals in Neurons of the Rat Spinal Sacral Dorsal Commissural Nucleus: an Electrophysiological Study.

The sacral dorsal commissural nucleus (SDCN) in the spinal cord receives both somatic and visceral primary afferents. Transient receptor potential vanilloid 1 (TRPV1) channels are preferentially expressed in certain fine primary afferents. However, knowledge of the SDCN neurons postnatal excitability development and their contacts with TRPV1 fibers remains elusive. Here, whole-cell recordings were conducted in spinal cord slices to evaluate the postnatal development of SDCN neurons and their possible contacts with functional TRPV1-expressing terminals. SDCN neurons in neonatal (postnatal day (P) 1-2), young (P8-10), and adult rats (P35-40) have different electrophysiological properties. SDCN neurons in neonatal rats have higher frequency of spontaneous firing, higher resting membrane potential, and lower presynaptic glutamate release probability. However, no difference in quantal release was found. At all developmental stages, TRPV1 activation with the selective agonist capsaicin increases glutamate release in the presence of tetrodotoxin, which blocks action potential-dependent and polysynaptic neurotransmission, indicating that functional TRPV1 fibers innervate SDCN neurons directly. Capsaicin-induced presynaptic glutamate release onto SDCN neurons depends on external Ca2+ influx through TRPV1 channels; voltage-dependent calcium channels had a slighter impact. In contrast, capsaicin blocked C fiber-evoked synaptic transmission, indicating that TRPV1 activation has opposite effects on spontaneous asynchronous and action potential-dependent synchronous glutamate release. These data indicate that excitability of SDCN neurons undergoes a developmental shift, and these neurons receive functional TRPV1 terminals from early postnatal stage. The opposite action of capsaicin on asynchronous and synchronous glutamate release should be taken into account when TRPV1 channels are considered as therapeutic targets.