Aging but not estrogen alters regional [3H]5-HT binding in the CNS of female Fischer 344 rats.

Age-related changes in serotonergic regulation of neuroendocrine function were investigated in female Fischer 344 rats; serotonin ([3H]5-HT) binding sites were characterized in several brain regions. Neither the number (Bmax) nor the affinity (Kd) of [3H]5-HT sites were altered in the frontal cortex of reproductively young and senescent groups. However, a significant decline in receptor affinity was observed in the hypothalamus and midbrain dorsal raphe nucleus. An increase in the density of binding sites was also observed in the hypothalamus with advancing age. Acute 48 h exposure to estrogen failed to influence [3H]5-HT binding site characteristics in these brain regions. In summary, these results suggest that age-related changes in [3H]5-HT binding are regionally specific. Moreover, the observed changes in hypothalamic 5-HT function may underlie neuroendocrine aging events.