In this study, we examined if glucocorticoids are required for the fasting-induced decrease of neuronal nitric oxide synthase (nNOS) in the magnocellular division of the paraventricular nucleus (PVN). Rats were adrenalectomized, subjected to 48 h of food deprivation with/without dexamethasone (5 mg/ kg, 4 subcutaneous injections with 12 h intervals), and the brain slices were processed for NADPH-diaphorase (NADPH- d) staining, a histochemical marker for nNOS in neuronal cells. In food deprived adrenalectomized rats, but not in free fed intact rats, dexamethasone significantly decreased NADPH-d staining in the magnocellular PVN. We previously reported that food deprivation decreases nNOS in the magnocellular PVN of intact rats. Thus, the present results together with our previous report suggest that although glucocorticoids are required for fasting-induced nNOS down-regulation in the magnocellular PVN, glucocorticoids may not be directly involved and some other molecular signals produced by food deprivation may play a pivotal role over glucocorticoid in the regulatory pathway for nNOS expression in this brain region.
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