Metabotropic glutamate receptor 1-mediated calcium mobilization in the neonatal hippocampal marginal zone.

The hippocampal marginal zone contains Cajal-Retzius (C-R) cells and participates in the regulation of cortical development. Two subtypes of group I metabotropic glutamate receptors (mGluRs), mGluR1 and mGluR5, are found in the central nervous system and are considered to regulate neuronal excitability. The release of Ca from intracellular stores is thought to be a main consequence of activation of these receptor subtypes. In hippocampal C-R cells, the expression of mGluR1 has been showed using immunohistochemical techniques, but its function has not been elucidated. In this study, Ca mobilization through mGluR1 activation was demonstrated in the neonatal rat hippocampus. In marginal zone C-R cells, intracellular Ca elevation was detected by fluorescence imaging after the application of a group I mGluR-specific agonist. This response was prevented by application of an mGluR1 antagonist but was not changed by application of an mGluR5 antagonist. The intracellular Ca elevation induced by mGluR1 activation was still observed in Ca -free perfusate, indicating the release of Ca from intracellular stores. γ-Aminobutyric acid and ionotropic glutamate receptor-mediated intracellular Ca elevation was also detected in mGluR1-possessing neurons, although the former was much smaller than that mediated by mGluR1. These results indicate that mGluR1 is functionally expressed in C-R cells in the neonatal marginal zone and regulates cell function through the elevation of intracellular Ca .