THE EFFECTS OF INJECTIONS OF d,l‐5‐HYDROXY‐TRYPTOPHAN ON THE EFFLUX OF ENDOGENOUS SEROTONIN AND 5‐HYDROXYINDOLEACETIC ACID FROM A SYNAPTOSOMAL FRACTION

P. E. Penn, W. J. McBride

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

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 languageEnglish (US)
Pages (from-to)765-769
Number of pages5
JournalJournal of Neurochemistry
Volume28
Issue number4
DOIs
StatePublished - Apr 1977

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

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