The effects of i.p. injections of 50 mg/kg D,L-5-hydroxytryptophan (5-HTP) and saline alone on the in vitro release of endogenous serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were studied using preparations of axon terminals (P2) isolated from the telencephalon of rats. The level of 5-HT was 2-fold greater and the level of 5-HIAA was 5-fold greater in the P2 fraction isolated from rats given the D,L-5-HTP injection than from rats given saline injections. At 37°C the in vitro efflux of 5-HT and 5-HIAA from the P2 fractions of animals injected with 5-HTP 30 min before killing was approx 3 times higher than the saline control group. The amount of 5-HT and 5-HIAA released at 37°C was 3-5 times higher than the amount released at 0°C for both the 5-HTP and saline injected rats. Increasing the concentration of potassium ions in the media for 55 mM significantly increased the release of 5-HT but not 5-HIAA in both groups of animals. The amount of 5-HT released by 55 mM-K+ was about 2-fold higher from the P2 fraction isolated from rats given 5-HTP injections with respect to those given saline injections. The potassium stimulated release of 5-HT was calcium dependent. The data thus indicate that injection of 50 mg/kg D,L-5-HTP in rats can cause an increase in the level of 5-HT and 5-HIAA in a crude synaptosomal fraction and that as a result of this increase, there is a temperature dependent increased release of 5-HT and 5-HIAA under normal resting membrane conditions. There is also an increased release of 5-HT as a result of membrane depolarizing conditions induced by elevated potassium levels which is calcium dependent.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of Neurochemistry|
|State||Published - Apr 1977|
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience