Replenishment by 5-hydroxytryptophan of the amine stores in the central 5-hydroxytryptamine neurons after depletion induced by reserpine or by an inhibitor of monoamine synthesis

Abstract A combined biochemical and histochemical analysis of central 5-hydroxytryptamine distribution has produced further evidence to support the theory that 5-hydroxytryptophan is specifically taken up and decarboxylated in 5-hydroxytryptamine neurons of rat brain. After treatment with an inhibitor of monoamine synthesis, α-propyldopacetamide, but not after treatment with reserpine, the intraneuronal 5-hydroxytryptamine stores could be replenished by injected 5-hydroxytryptophan. This appears to indicate that the uptake-storage mechanism of amines in the 5-hydroxytryptamine neurons is intact after α-propyldopacetamide. Pretreatment with a monoamine oxidase inhibitor, nialamide, allowed repletion of the intraneuronal 5-hydroxytryptamine stores by 5-hydroxytryptophan even after treatment with reserpine. This further stresses the importance of monoamine oxidase in regulating the amine levels of the 5-hydroxytryptamine neurons.