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EFFECTS OF 5‐HYDROXYTRYPTOPHAN ON SEROTONIN IN NERVE ENDINGS 1
Author(s) -
McBride W. J.,
Aprison M. H.,
Hingtgen J. N.
Publication year - 1974
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1974.tb04370.x
Subject(s) - diencephalon , cerebrum , serotonin , free nerve ending , chemistry , endocrinology , medicine , saline , 5 ht receptor , anatomy , biology , central nervous system , biochemistry , receptor
—Preparations of synaptosomes (P 2 ) from the telencephalon and from the diencephalon plus optic lobes of the pigeon and from the telencephalon of the rat were used to study the effects of 5‐hydroxytryptophan (5‐HTP) on (a) the levels of serotonin (5‐HT) in nerve endings and (b) the release of 5‐HT from nerve endings. The levels of 5‐HT were significantly higher (3.21 × 0.35 nmol/g original tissue weight) in the P 2 fraction isolated from the telencephalon of pigeons given intramuscular injections of 50mg/kg of d , l ‐5‐HTP in comparison to control values (1.42 ± 0.07). A similar twofold increase was observed with the P 2 fraction isolated from the diencephalon plus optic lobes. In addition, the levels of 5‐HTP and 5‐hydroxyindoleacetic acid also increased significantly in these P 2 fractions isolated from pigeons given d , l ‐5‐HTP injections in comparison to values obtained for pigeons given saline injections. In vitro studies using preparations of synaptosomes (from both pigeon and rat) labelled with [ 3 H]5‐HT indicated that 0.10 mil l ‐5‐HTP increased the release of [ 3 H]5‐HT twofold over control values. A concentration as low as 0.001 m m l ‐5‐HTP was tested on the P 2 fraction from the telencephalon of the pigeon and was found to significantly increase the release of [ 3 H]5‐HT over control values. This effect by l ‐5‐HTP was blocked if a decarboxylase inhibitor was added to the medium. l ‐5‐HTP at a concentration of 1.5 m m had no apparent effect on the release of [ 3 H]norepinephrine or [ 3 H]dopamine from synaptosomes prepared from the telencephalon of the rat or pigeon. The results are discussed in terms of the role of serotonin in producing certain types of behavioral depressions exhibited by pigeons and rats given injections of 5‐HTP.