Time course of postnatal distribution of doublecortin immunoreactive developing/maturing neurons in the somatosensory cortex and hippocampal CA1 region of C57BL/6 mice

Prdm16 and Vcam1 regulate the postnatal disappearance of embryonic radial glia and the ending of cortical neurogenesis

Embryonic neural stem cells (NSCs, i.e., radial glia) in the ventricular-subventricular zone (V-SVZ) generate the majority of neurons and glia in the forebrain. Postnatally, embryonic radial glia disappear and a subpopulation of radial glia transition into adult NSCs. As this transition occurs, widespread neurogenesis in brain regions such as the cerebral cortex ends. The mechanisms that regulate the postnatal disappearance of radial glia and the ending of embryonic neurogenesis remain poorly understood. Here, we show that PR domain-containing 16 (Prdm16) promotes the disappearance of radial glia and the ending of neurogenesis in the cerebral cortex. Genetic deletion of Prdm16 from NSCs leads to the persistence of radial glia in the adult V-SVZ and prolonged postnatal cortical neurogenesis. Mechanistically, Prdm16 induces the postnatal reduction in Vascular Cell Adhesion Molecule 1 (Vcam1). The postnatal disappearance of radial glia and the ending of cortical neurogenesis occur normally in Prdm16-Vcam1 double conditional knockout mice. These observations reveal novel molecular regulators of the postnatal disappearance of radial glia and the ending of embryonic neurogenesis, filling a key knowledge gap in NSC biology.

Microglial control of neuronal development via somatic purinergic junctions

Microglia, the resident immune cells of the brain, play important roles during development. Although bi-directional communication between microglia and neuronal progenitors or immature neurons has been demonstrated, the main sites of interaction and the underlying mechanisms remain elusive. By using advanced methods, here we provide evidence that microglial processes form specialized contacts with the cell bodies of developing neurons throughout embryonic, early postnatal, and adult neurogenesis. These early developmental contacts are highly reminiscent of somatic purinergic junctions that are instrumental for microglia-neuron communication in the adult brain. The formation and maintenance of these junctions is regulated by functional microglial P2Y12 receptors, and deletion of P2Y12Rs disturbs proliferation of neuronal precursors and leads to aberrant cortical cytoarchitecture during development and in adulthood. We propose that early developmental formation of somatic purinergic junctions represents an important interface for microglia to monitor the status of immature neurons and control neurodevelopment.

Spatial and temporal changes in the PGE2 EP2 receptor in mice hippocampi during postnatal development and its relationship with cyclooxygenase-2

Objective(s):

Prostaglandin E2 E-prostanoid 2 receptor (PGE2 EP2), downstream of cyclooxygenase-2 (COX-2), plays an important role in inflammatory responses, but there are some reports about synaptic functions of COX-2 and PGE2 EP2 in the hippocampus.

Materials and Methods:

C57BL/6J mice were sacrificed at postnatal days (P) 1, 7, 14, 28, and 56 for immunohistochemical staining for EP2 and doublecortin as well as western blot for EP2. In addition, COX-2 knockout and its wild-type mice were euthanized for immunohistochemical staining for EP2.

Results:

EP2 immunoreactivity was observed in the majority of the cells in the dentate gyrus at P1 and P7, while at P14, it was detected in the outer granule cell layer and was confined to its subgranular zone at P28 and P56. EP2 protein levels in the hippocampal homogenates were also highest at P7 and lowest at P56. EP2 immunoreactivity was partially colocalized, with doublecortin (DCX)-immunoreactive neuroblasts appearing in the mid-zone of the granule cell layer at P14 and in the subgranular zone of the dentate gyrus at P28. Co-localization of EP2 and DCX was significantly decreased in the dentate gyrus in the P28 group compared with that in the P14 group. In COX-2 knockout mice, EP2 immunoreactivity was significantly decreased in the hippocampal CA1 region (P=0.000165) and dentate gyrus (P=0.00898).

Conclusion:

EP2 decreases with age, which is expressed in DCX-immunoreactive neuroblasts in the dentate gyrus. This suggests that EP2 is closely linked to structural lamination and adult neurogenesis in the dentate gyrus.

Postnatal changes in constitutive cyclooxygenase‑2 expression in the mice hippocampus and its function in synaptic plasticity

Although the expression of cyclooxygenase-2 (COX-2) is closely associated with inflammation in the brain, it is constitutively expressed in the brain, and its expression is regulated by synaptic activity. The present study investigated postnatal expression of COX-2 in the hippocampus in C57BL/6 mice at postnatal days (P) 1, 7, 14, 28, and 56. In addition, the presented study examined the effects of COX-2 on synaptic plasticity through Arc, phosphorylated cAMP response element-binding protein (pCREB), N-methyl-d-aspartate receptor 1 (GluN1), and GluN2A/2B immunohistochemistry, which was performed on COX-2 knockout (KO) and wild-type (WT) mice. Extremely weak COX-2 immunoreactivity was detected in the hippocampal CA1-3 areas in addition to the dentate gyrus at P1. Conversely, COX-2 immunoreactivity was observed in the stratum pyramidale of the CA1-3 regions and in the outer granule cell layer of the dentate gyrus at P7. Additionally, although peak COX-2 immunoreactivity was observed in all hippocampal sub-regions, including the dentate gyrus at P14, it was significantly decreased at P14. Finally, COX-2 immunoreactivity and the distribution pattern seen at P56 in the hippocampal CA1-3 regions were similar to those observed at P28, whereas, they were identified in the inner half of the granule cell layer of the dentate gyrus. The western blot analysis revealed that the COX-2 protein levels peaked at P14 and were decreased at P28 and P56. Additionally, the number of Arc and pCREB immunoreactive cells as well as GluN1 and GluN2A/2B immunoreactivity of COX-2 KO mice were significantly decreased in the dentate gyrus when compared with that in WT mice. Taken together, the results of the present study suggest that COX-2 serves an important role in synaptic plasticity in the dentate gyrus and changes in the levels of its constitutive expression are associated with the hippocampal dentate gyrus postnatal development.

Postnatal low-concentration arsenic exposure induces autism-like behavior and affects frontal cortex neurogenesis in rats

This study aimed to explore the effects of postnatal low-concentration arsenic exposure on learning, social skills and frontal cortex neurogenesis in rats. Water-based arsenic exposure rat models were established on postnatal days 4-10 (P4-P10). The experimental animals were divided into four groups: the control group, a 15 μg/L As₂O₃ water group, a 30 μg/L As₂O₃ water group, and a 45 μg/L As₂O₃ water group. Cognitive function was examined with the Morris water maze, anxiety-like behavior with the open field test and light-dark box test, and social skills with a social interaction test. The frontal cortices of pups from each experimental group were sectioned at various time points after arsenic exposure. The morphologies and neurogenesis of the neurons in the frontal cortices were observed by hematoxylin-eosin staining, Nissl staining, and doublecortin (DCX) immunostaining. Significant positive correlations between arsenic concentration and deficits in learning and social skills were found, and the arsenic exposure groups showed significant increases in anxiety-like behavior compared with the control group (all Ps<0.05). Abnormal morphologic changes in the external granular layer and external pyramidal layer were positively correlated with the water arsenic concentration in the acute phase of arsenic exposure. However, at five weeks after arsenic exposure, the frontal cortex morphology was restored. Moreover, immunohistochemistry revealed that compared to the control group, the groups that were exposed to arsenic exhibited significantly higher levels of DCX expression in the external granular and external pyramidal layers (all Ps<0.001). Furthermore, the 30 μg/L and 45 μg/L arsenic exposure groups still showed some DCX expression at five weeks after exposure. In conclusion, postnatal low-concentration arsenic exposure impaired learning and social skills and increased anxiety-like behaviors, and abnormal frontal cortex neurogenesis may be the mechanism underlying these effects.

Growth/differentiation factor 15 promotes EGFR signalling, and regulates proliferation and migration in the hippocampus of neonatal and young adult mice

The activation of epidermal growth factor receptor (EGFR) affects multiple aspects of neural precursor behaviour, including proliferation and migration. Telencephalic precursors acquire EGF responsiveness and upregulate EGFR expression at late stages of development. The events regulating this process and its significance are still unclear. We here show that in the developing and postnatal hippocampus (HP), growth/differentiation factor (GDF) 15 and EGFR are co-expressed in primitive precursors as well as in more differentiated cells. We also provide evidence that GDF15 promotes responsiveness to EGF and EGFR expression in hippocampal precursors through a mechanism that requires active CXC chemokine receptor (CXCR) 4. Besides EGFR expression, GDF15 ablation also leads to decreased proliferation and migration. In particular, lack of GDF15 impairs both processes in the cornu ammonis (CA) 1 and only proliferation in the dentate gyrus (DG). Importantly, migration and proliferation in the mutant HP were altered only perinatally, when EGFR expression was also affected. These data suggest that GDF15 regulates migration and proliferation by promoting EGFR signalling in the perinatal HP and represent a first description of a functional role for GDF15 in the developing telencephalon.

Melatonin improves D-galactose-induced aging effects on behavior, neurogenesis, and lipid peroxidation in the mouse dentate gyrus via increasing pCREB expression

Melatonin (N-acetyl-5-methoxytryptamine) has multiple functions. In this study, we investigated the effects of melatonin on memory, cell proliferation, and neuroblast differentiation in the dentate gyrus of a mouse model of D-galactose-induced aging. D-galactose was subcutaneously administered to 7-wk-old mice for 10 wk, and age-matched mice were used as controls. Seven weeks after D-galactose administration, vehicle (water) or melatonin (6 mg/L in water) was administered ad libitum to the mice for 3 wk. The administration of D-galactose significantly increased the escape latency compared with that in the control mice on days 1-3. In addition, cells in the subgranular zone and in the granule cell layer of the dentate gyrus showed severe damage (cytoplasmic condensation) in the D-galactose-treated mice. However, melatonin supplementation to these mice for 3 wk significantly ameliorated the D-galactose-induced increase in escape latency and neuronal damage compared with the vehicle-treated group. The administration of melatonin also significantly restored the D-galactose-induced reduction of proliferating cells (Ki67-positive cells) and differentiating neuroblasts (doublecortin-positive neuroblasts) in the dentate gyrus. Furthermore, the administration of melatonin significantly increased Ser133-phosphorylated cyclic AMP response element binding protein in the dentate gyrus. The administration of melatonin significantly reduced D-galactose-induced lipid peroxidation in the dentate gyrus. These results suggest that melatonin may be helpful in reducing age-related phenomena in the brain.