Abstract
To elucidate some of the mechanisms underlying the neuroendocrine and neurochemical changes associated with age in female rats, we administered the serotonin (5-HT) releaser and reuptake inhibitor, d-fenfluramine( d-FEN; 0.0 or 0.6 mg/kg/day, PO) for 30–38 days to young (4 month) and old (21 month) F-344 female rats. Animals were placed into a novel open field (OF) for 20 min before sacrifice. Control animals were sacrificed immediately upon removal from their home cage (HC). Old rats exhibited significantly ( p < 0.05) less exploratory behavior and a smaller CORT response to OF than young animals. rf-FEN treatment had no effect on plasma ACTH and CORT levels or exploratory behavior. The old HC rats had significantly ( p < 0.05) higher plasma levels of prolactin (PRL) than the young HC rats. A stress induced increase in PRL secretion was observed in the old rats only, which was attenuated by d-FEN treatment. In the OF groups, both the young and old rats showed elevated medial frontal cortex (MFC) dopamine turnover ( DOPAC DA ratio), but only the young rats exhibited an elevation in norepinephrine (NE) turnover ( MHPG NE ratio). d-FEN treatment blocked the stress-induced increase in NE turnover in the young rats and the increase in DA turnover in the old rats. These data suggest that 5-HT activity could be involved in the age-related changes in the MFC catecholamine and PRL responses to stress in female rats.
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