Effect of ageing on monoamine turnover in the prefrontal cortex of rats

Turnover of dopamine (DA), serotonin (5-hydroxytryptamine) (5-HT), noradrenaline (NA) and their metabolites has been measured in control and aged rats. In addition, tyrosine hydroxylase (TH) activity has been studied. After pargyline treatment, the turnover rates of DA, NA, 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), 5-HT and 5-hydroxy-3-indolacetic acid (5-HIAA) and TH activity increased in aged rats with respect to controls. At the same time the DA and 3-MT turnover increase are consistent with the hypothesis that enhanced release of DA may participate in some degenerative processes in ageing. After probenecid treatment, the turnover of homovanillic acid (HVA) was lower in aged rats than in controls. However, DOPAC turnover was higher in the aged rats. The DOPAC increase seems to indicate a reinforcement of this pathway in aged rats.