Abstract
Animals with lesions of the midbrain raphe nuclei showed a 75% reduction of synaptosomal uptake activity of 3H-serotonin (3H-5-HT), whereas animals with lesions of the lateral midbrain area exhibited the same uptake activity as unoperated control animals. The uptake activity of radioactive l-tryptophan, dopamine and l-norepinephrine in animals with raphe lesions was not reduced, suggesting that of the four compounds tested, only 5-HT was uniquely accumulated by nerve endings of the raphe neurons. The synaptosomal uptake of 3H-5-HT was inhibited by low temperature, dinitrophenol and ouabain and also by the tricyclic agents imipramine and desmethylimipramine, the former being 10 times more effective as an inhibitor than the latter. In some experiments, the concentrations of 5-HT in the incubation medium was varied from 10-9 to 10-6 M. Between 10-9 and 5 x 10-6 M concentrations of 5-HT, there was the maximal 75% reduction of uptake activity in animals with lesions as compared to that in controls. However, at 10-7 and 10-6 M 5-HT medium concentrations, there was only a 55% and 35% reduction of synaptosomal uptake in lesioned animals. These data are consistent with the previously suggested notion that at high concentrations, 5-HT is significantly accumulated by nonserotonergic nerve endings. The time course of reduction of synaptosomal uptake activity and 5-HT levels in the forebrain were measured at various intervals after placements of lesions and compared to the time course of reduction of forebrain tryptophan hydroxylase activity.
Footnotes
- Received August 30, 1971.
- Accepted January 1, 1972.
- © 1972, by The Williams & Wilkins Company
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|
