Behavioral and endocrine adaptation, and up-regulation of NPY expression in rat amygdala following repeated restraint stress

A single 1h restraint increases experimental anxiety in the elevated plus-m aze through actions within the amygdala, while intra-amygdala administratio n of neuropeptide Y (NPY) has the opposite effect. Endogenous amygdala NPY expression is suppressed by single restraint, providing a possible mechanis m for the anxiety-promoting action of this stressor. Here, we examined whet her repeated stressor exposure might lead to an adaptation (habituation or sensitization) with regard to plus-maze behavior and glucocorticoid respons e, and whether this might be accompanied by altered effects of the stressor on NPY expression. Following repeated restraint (1h/day, 9-10 days), neith er an anxiogenic-like effect of the stressor nor a glucocorticoid response were present. This behavioral and endocrine adaptation was accompanied by a n upregulation of prepro-NPY mRNA and NPY peptide in amygdala but not in hy pothalamic or cortical extracts, an effect opposite to that previously seen after a single restraint session. Thus, an up-regulation of NPY expression in the amygdala complex may be an adaptive mechanism recruited to cope wit h a repeated stressor. (C) 1999 Lippincott Williams & Wilkins.