Regional changes in monoamine metabolism in the aging constant estrous rat.

Studies were undertaken to determine levels of monoamines and their metabolites in brain regions in young (3-4 months) normally cycling and old (25-26 month) constant estrous female rats. Dopamine (DA) concentrations were reduced in old rats in the median eminence (ME), medial basal hypothalamus (MBH), preoptic area-anterior hypothalamus (POA-AH) and the striatum. Similarly, concentrations of dihydroxyphenylacetic acid (DOPAC), the major acid metabolite of DA, were reduced significantly in all 4 regions. In the ME, a strong positive correlation was observed between DA and DOPAC concentrations in both young and old rats. Concentrations of norepinephrine (NE) were reduced in old rats in the MBH and POA-AH but not in the ME or striatum. Concentrations of serotonin (5HT) and its major metabolite, 5-hydroxyindoleacetic acid (5HIAA) were generally unchanged with age in all of the regions examined. These studies indicate the age-related regional alterations in DA and 5HT metabolism can be monitored by methods which quantitate monoamines and their metabolites.