The effect of chronic voluntary exercise on induction of Fos expression in the rat brain by nonexercise stressor.

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We investigated the effect of voluntary wheel running training for 11-12 wks on induction of Fos expression, which is used as a marker of neuronal activation, in the hypothalamic paraventricular nucleus (PVN) of male rats by restrain stress (experiment 1). We also investigated the effect of running training on cardiovascular response to restrain stress (experiment 1 and 2). In addition, we examined the possibility that activation of opioid systems may be involved in the modified cardiovascular response to stress after running training (experiment 2). In experiment 1, trained (T) rats exhibited significantly (p<0.05) attenuated pressor response to restrain stress compared with control (C) rats. The number of Fos positive cells, which was analyzed quantitatively by immunohistochemistry, in the PVN following restrain stress was lower in T rats than that in C rats, although the difference did not reach statistical significance (p=0.069). In experiment 2, pressor response to restrain stress also tended to be attenuated in T rats. However, intravenous administration of opioid receptor antagonist, naloxone, had no effect on the pressor response to restrain stress in both C and T rats. To judge from these results, it was not clear whether running training, which had an effect in atteuating pressor response to stress, may attenuate neuronal activation in the PVN following nonexercise stressor. In addition, these results did not support the possibility that activation of opioid systems may be involved in the modified cardiovascular response to stress after running training.