Whole tissue and preparations of synaptosomes from the telencephalon of the pigeon were used to study the effects of α-methyl-m-tyrosine (α-MMT), α-methyl-m-tyramine (α-MMTA) and metaraminol on the metabolism, uptake and release of serotonin (5-HT). Approximately 3·5 hr after an intramuscular injection of α-MMT (100 mg/kg), the levels of 5-HT decreased from 5·95 to 4·90 nmol/g tissue and the levels of 5-hydroxyindoleacetic acid (5-HIAA) decreased from 1·57 to 1·09 nmol/g tissue. Using an incubated crude synaptosomal preparation, it appeared that neither the uptake of [14C]-5-HT nor its conversion to 5-HIAA was inhibited by α-MMT. In addition, α-MMT did not seem to have an effect on the release of [14C]-5-HT from synaptosomes preloaded with radioactive 5-HT. However, two metabolites of α-MMT, namely, α-MMTA and metaraminol, significantly increased the release of (14C]-5-HT. Individually, at concentrations of 0·25 mg/ml, these two metabolites increased the efflux of [14C]-5-HT 14-17 fold from isolated synaptosomes. In combination and at lower concentrations of 0·025 and 0·005 mg/ml, there was a 6- and 2-fold increase, respectively, in efflux of [14C]-5-HT from isolated synaptosomes. α-MMTA and metaraminol also decreased the efflux of [14C]-5-HIAA; α-MMT did not appear to have any noticeable effect on the release of 5-HIAA. The results are discussed in terms of the behavioral effects produced by α-MMT in pigeons working on a multiple FR 50 FI 10 schedule of reinforcement.
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience