Type II glucocorticoid receptor immunoreactivity in the mossy cells of the rat and the mouse hippocampus

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Abstract
Hippocampal principal neurons, granule and pyramidal cells, are known to express type II glucocorticoid receptors (GR) and it is believed that glucocorticoids (GC) mediate at least some of their effects through GR. Under conditions of severe stress and trauma, these principal cells are vulnerable to damage and this mechanism may be exacerbated by GR. The mossy cell, an excitatory dentate gyrus neuron, is also damaged following trauma, with over 50% reported loss in rats after kainate‐induced seizures. However, it has not been determined if GC play any role in protecting or exacerbating damage to this important hippocampal cell type. In the present study, we have undertaken an evaluation of the presence of GR in mossy cells of the rat and mouse utilizing an immunocytochemical double‐labeling technique. To identify mossy cells in the rat, we utilized an antibody to the glutamate receptor subunit 2/3 (GluR2/3). In addition to GluR2/3 antibodies, in the mouse, an antibody to the calcium‐binding protein, calretinin (CR), to identify mossy cells was also employed. Our results show that GR immunoreactivity (IR) was colocalized with GluR2/3‐IR in approximately 90% of the rat and the mouse mossy cells. In addition, GR‐IR was identified in the CR‐IR mossy cells in the mouse hippocampus, whereas the CR‐IR interneurons of rat and mouse were negative for GR‐IR. The presence of GR on mossy cells may indicate the ability of GC to mediate cellular activity of these cells. Hippocampus 2003;13:59–66.