Effects of L-tyrosine on brain monoamines in rats given intravenous amphetamine

A computer-controlled device was used to deliver intravenous injections of saline or d-amphetamine, in patterns resembling those of animals trained to self-administer the drug via lever pressing. Amphetamine, administered in this manner (over the course of an 8 hr test session), induced a 27% decrease in brain norepinephrine. The injection of the amino acid precursor L-tyrosine (100 mg/kg) prior to sacrifice abolished the decrements in brain norepinephrine. In animals administered i.v. saline, L-tyrosine treatment did not alter brain norepinephrine concentrations. Earlier clinical studies have suggested that the norepinephrine reuptake inhibitor desipramine is useful in controlling psychomotor stimulant abuse (the rationale being that this agent compensates for reduced levels of the amine). If this hypothesis is correct, L-tyrosine may be a safer method to replenish cerebral norepinephrine pools.