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 norepinephrine (NE) and dopamine (DA) in the medial basal hypothalamus of young (4-5 months old), middle-aged (8-10 months old), and old (22-24 months old) rats. In the young animals, the afternoon of proestrus was characterized by a gradual increase in NE release and a simultaneous gradual 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 serum LH and PRL are known to occur. No changes in NE and DA releases occurred in the afternoon of diestrus when serum LH and PRL are known to remain stable. In the middle-aged proestrous animals, the patterns of NE and DA releases were similar to those in the young proestrous animals, but the peak in NE release was attenuated and did not reach statistical significance. This corresponded with the reported attenuation in the LH surge in middle age. In the old persistently diestrous animals, NE and DA were released at constant rates, which correlated with the well-documented constant levels of serum LH and PRL in old age. These data provide an explanation for the simultaneous proestrous surges of LH and PRL and lead us to conclude that NE plays a facilitatory role in the LH surge, while DA, through its inhibitory action, regulates the PRL surge.(ABSTRACT TRUNCATED AT 250 WORDS)