CYCLIC CHANGES IN THE RELEASE OF NOREPINEPHRINE AND DOPAMINE IN THE MEDIAL BASAL HYPOTHALAMUS - EFFECTS OF AGING

Push-pull perfusion and HPLC were used to measure the release of norep inephrine (NE) and dopamine (DA) in the medial basal hypothalamus of y oung (4-5 months old), middle-aged (8-10 months old), and old (22-24 m onths old) rats. In the young animals, the afternoon of proestrus was characterized by a gradual increase in NE release and a simultaneous g radual decrease in DA release. The peak in NE release and the nadir in DA release occurred at about the time when the proestrous surges in s erum LH and PRL are known to occur. No changes in NE and DA releases o ccurred in the afternoon of diestrus when serum LH and PRL are known t o remain stable. In the middle-aged proestrous animals, the patterns o f NE and DA releases were similar to those in the young proestrous ani mals, but the peak in NE release was attenuated and did not reach stat istical significance. This corresponded with the reported attenuation in the LH surge in middle age. In the old persistently diestrous anima ls, NE and DA were released at constant rates, which correlated with t he well-documented constant levels of serum LH and PRL in old age. The se data provide an explanation for the simultaneous proestrous surges of LH and PRL and lead us to conclude that NE plays a facilitatory rol e in the LH surge, while DA, through its inhibitory action, regulates the PRL surge. These studies, by monitoring NE and DA releases from ad ulthood through middle-age to old age, indicated that cyclicity in cat echolamine (CA) activities begins to be dampened in middle-age and eve ntually completely disappears in the acyclic period of old age which i s also characterized by a marked deficiency in CA activities.