In the light of the various neurobiological effects of glutamate in brain development, although some embryonic cells are a probable source of glutamate involved in the development of precursor cells and/or immature neurons, little is known about when and where glutamate plays its crucial roles during corticogenesis. To investigate these roles, we focused on the developmental expression of vesicular glutamate transporter (VGLUT)1 and VGLUT2, which are regarded as the best markers for verifying glutamatergic neuron identity, especially the spatiotemporal distributions of their transcripts and proteins in the developing mouse cortex and hippocampus. In situ hybridization studies revealed that VGLUT1 mRNA is expressed in preplate and marginal zone cells at embryonic day (E)10 and in subplate cells by E13, whereas VGLUT2 mRNA is expressed in preplate and marginal zone cells at E10 and in cells of the subventricular zone by E13. Reverse transcriptase–polymerase chain reaction analysis detected full‐length VGLUT1 and VGLUT2 gene transcripts in the embryonic brain. By dual labeling combined with immunostaining for microtubule‐associated protein 2 (MAP2) or reelin, we showed that MAP2‐positive preplate and marginal zone neurons and subplate neurons express VGLUT1, while reelin‐positive preplate and marginal zone cells and MAP2‐negative subventricular zone cells express VGLUT2. The present study is the first to provide morphologically reliable evidence showing that Cajal–Retzius cells and subplate neurons are glutamatergic, and that the two cells differentially express VGLUT1 and VGLUT2, respectively, as the specific transport system of glutamate in some events orchestrated by these cells during the cortical development of mice.
We studied the effects of prenatal stress on early postnatal development of the brain in mouse pups (PS) whose dams had been exposed daily to restraint stress during pregnancy (gestational days 14-18), with special reference to the expression of corticotropin-releasing factor (CRH), vesicular glutamate transporters (VGLUT1 and VGLUT2), and a synaptic vesicle marker protein (SV2). In a comparison with age-matched control pups born of unstressed dams, in situ hybridization analysis revealed a statistically significant reduction of CRH gene expression in the hypothalamic paraventricular nucleus of the PS pups at postnatal days 10 (P10), suggesting a functional alteration in the core neuroendocrine circuit of the stress response mechanism. Immunohistochemical analysis of the medial habenular nucleus followed by semi-quantitative evaluation revealed that VGLUT1 staining, but not VGLUT2 staining, is markedly reduced in the P10 PS pups compared to controls of the same age, and that such a difference between PS and control pups becomes undetectable at P21. These findings suggest that the embryonic environment, at least during late pregnancy, alters the activity of the neuroendocrine system involved in the stress response and influences the early postnatal development of glutamatergic neurons in a particular brain region.
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