Age-related changes in the metabolism of neurotransmitters and the effect of scavengers: an in vivo microdialysis study.
Brain microdialysis is a method to study the in vivo release and metabolism of neurotransmitters using freely-moving animals. We studied the changes in neurotransmitter metabolism from very young to the old rats (Sprague-Dawley). For brain microdialysis, a guide cannula, was implanted in the striatum (A +1.0, L +2.5, V -4.0). Extracellular content of neurotransmitters and their metabolites were detected with an electrochemical detector (ECD-100, EICOM Co.). The content was affected by KCl (100 mM), calcium-free Ringer and tetrodotoxin in a perfusion medium. Dopamine and its metabolites such as dihydroxyphenylacetic acid and homovanillic acid were significantly changed with age. The content of these metabolites were maximal around 2-3 months of age. In the case of serotonin metabolism, statisticaly no significant change was observed in the extracellular content of 5-hydroxyindoleacetic acid after sexual maturation (1.5 months of age). Potassium-induced dopamine release which is newly synthesized one, was maximum around 1.5 years of age and the content was about 50% lower in the old. The basal level of dopamine significantly decreased with age. Moreover, the inhibitory effect of pargyline, a monoamine oxidase inhibitor, was also decreased with age. On the basis of these results, it is suggested that the synaptic function shows postnatal development and reaches maximum at sexual maturation. Microdialysis could be a useful procedure for studying the in vivo metabolism of neurotransmitters.
Nakano
M
M
Hitomi
E
E
Mizuno
T
T