Decrease in doublecortin expression without neuronal cell death in rat retrosplenial cortex after stress exposure

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Exposure to acute stress by forced swim impairs spatial learning and memory in rats. The retrosplenial cortex plays an important role in spatial learning and memory. A cell population that expresses immature neuronal markers, including doublecortin (DCX), plays a key role in plasticity of the adult brain through formation of new neurons. Here, we aimed to determine whether rats exposed to acute stress showed changes in DCX expression in retrosplenial cortex cells. Twelve male Sprague–Dawley rats were used. Six were subjected to acute stress by forced swim (group S), and the remaining six served as controls (group C). Immunohistochemical staining was performed for DCX, neuron-specific nuclear protein, parvalbumin, calbindin, calretinin, and somatostatin. Newly generated cells were immunohistochemically detected by daily administration of 5-bromo-2′-deoxyuridine for 1 week. Fluoro-Jade B staining was performed to detect cell death. Group S showed lower number of DCX-expressing cells than group C (P<0.001). The proportion of DCX-expressing cells showing neuron-specific nuclear protein co-localization (24% in group S; 27% in group C) or parvalbumin co-localization (65% in group S; 61% in group C) remained unchanged after acute stress exposure. Neither 5-bromo-2′-deoxyuridine-positive nor Fluoro-Jade B-positive cells were found in the retrosplenial cortex of groups S and C. DCX-expressing cells in the retrosplenial cortex decreases markedly without cell death after acute stress exposure. Neuronal differentiation of these cells toward gamma aminobutyric acidergic interneurons appears to be unaltered. The decrease in DCX expression may reduce plasticity potential within the retrosplenial cortex and attenuate spatial learning and memory function.

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