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The effect of systemic administration of the 5-HT precursor, 5-hydroxy-L-tryptophan (5-HTP) on the release of 5-HT in the lateral hypothalamus of the chloral hydrate-anaesthetized rat in vivo was examined using brain microdialysis. Administration of 5-HTP caused an immediate increase of 5-HT in dialysates, which was long lasting (greater than or equal to 140 min) and dose-dependent (30-100 mg/kg i.p.). When calcium was omitted from the perfusion medium, thereby limiting exocytosis, levels of basal 5-HT were significantly decreased and the 5-HTP-induced response of 5-HT was markedly attenuated. Administration of the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (0.25 mg/kg i.p.), which selectively inhibits serotoninergic neuronal activity by activation of the somatodendritic 5-HT autoreceptor, significantly decreased basal levels of 5-HT and markedly attenuated the 5-HTP-induced increase in 5-HT. The data demonstrate that systemic administration of 5-HTP caused an increase in the release of 5-HT in the hypothalamus. Furthermore, this release occurred by a calcium-dependent mechanism (probably exocytosis), was dependent on serotoninergic neuronal activity and predominantly derived from 5-HT neurones. The findings are discussed in relation to the behavioral and neuroendocrine effects of increasing availability of the 5-HT precursor.

Type

Journal article

Journal

Neuropharmacology

Publication Date

01/1992

Volume

31

Pages

9 - 14

Keywords

5-Hydroxytryptophan, 8-Hydroxy-2-(di-n-propylamino)tetralin, Animals, Calcium, Chromatography, High Pressure Liquid, Dendrites, Dialysis, Exocytosis, Hypothalamus, Male, Rats, Rats, Inbred Strains, Serotonin, Tetrahydronaphthalenes