Reciprocal changes in striatal dopamine and β-phenylethylamine induced by reserpine in the presence of monoamine oxidase inhibitors

Summary

Recent studies have demonstrated that selective monoamine oxidase inhibition may induce changes in brain β-phenylethylamine availability following lesions. The present study used this approach to re-assess the possible effects of reserpine on striatal concentrations of β-phenylethylamine and of other amines and selected metabolites. Mice were injected with pargyline (2,200 mg kg⁻¹, 4 h), clorgyline (2 mg kg⁻¹, 2 h) or (−)deprenyl (2 mg kg⁻¹, 2 h) alone or in combination with reserpine (1,10 mg kg⁻¹, 2 h). Increases in β-phenylethylamine accumulation were observed in the presence of both (−)deprenyl or pargyline respectively after reserpine except in the case of combined 200 mg kg⁻¹ of pargyline plus 1 mg kg⁻¹ of reserpine. In this condition, a minimal dopamine decrease was observed (to 80% of the concentration of pargyline-treated controls). Increases in β-phenylethylamine concentration were not observed with reserpine alone (1 or 10 mg kg⁻¹). In the latter condition, the concentrations of β-phenylethylamine remained at control values due to the activity of monoamine oxidase B. Changes in p-tyrosine, 5-hydroxytryptamine or tryptophan did not consistently accompany increases in β-phenylethylamine accumulation. Increased β-phenylethylamine accumulation was always accompanied by the decreases in dopamine induced by reserpine in mice with either non-selective (200 mg kkg⁻¹ pargyline) or type B monoamine oxidase inhibition (2 mg kg⁻¹ pargyline or deprenyl). These data suggest that although the changes in β-phenylethylamine accumulation may not be due simply to p-tyrosine availability they are related to dopamine levels in the intact striatum.