Changes in endogenous monoamines in aged rats

1. It has been documented that ageing may alter endogenous neurotransmitter s, However, these results are controversial. Thus, in the present study, ce rebral cortex and plasma from male Wistar rats aged 8 weeks and 6, 12 or 24 months were used to investigate the changes in monoamines using electroche mical detection. 2. A marked decrease in L-dihydroxyphenylalanine (L-DOPA) was observed in a ged rats, Like the decrease in dopamine (DA), levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindolacetic acid (5-HIAA), the major metabolite of 5-H T, in aged rats were decreased in the cerebral cortex and plasma. Plasma le vels of noradrenaline and levels of adrenaline in the cerebral cortex were also decreased in aged rats. Moreover, levels of 3,4-dihydroxyphenylacetic acid (DOPAC), a metabolite of DA, in the cerebral cortex and plasma were re duced by ageing. The level of homovanillic acid (HVA) in all samples was ma rkedly increased with ageing. 3. The ratio of DOPAC/DA and 5-HIAA/5-HT, being closely linked with the act ivity of monoamine oxidase, was increased in the cerebral cortex and plasma with ageing. The ratio of HVA/DOPAC, an index of the activity of catechol- O-methyltransferase, was also higher in the cerebral cortex and plasma of a ged rats. 4. These data suggest that ageing may alter endogenous monoamines in both t he brain and peripheral tissues.