RATIONALE

There are conflicting reports as to whether alterations in tyrosine levels affect functional indices of striatal dopamine (DA) transmission. Since the DA antagonist haloperidol (HAL) increases striatal DA release and induces catalepsy through its actions on striatal DA systems, it provides a useful paradigm to assess both neurochemical and behavioral effects of lowering brain tyrosine levels.

OBJECTIVES

To determine how brain tyrosine depletion affects HAL-induced catalepsy and striatal DA release in awake, freely moving rats.

METHODS

In male rats, a control or tyrosine- and phenylalanine-free neutral amino acid solution NAA(-) (IP) was administered 30-60 min prior to HAL (IP). In one cohort, striatal microdialysate was assayed for DA levels. In a parallel cohort, catalepsy was measured using the bar test.

RESULTS

NAA (-) reduced striatal tyrosine levels by 60%. The latter did not affect basal striatal DA release, but consistently delayed the attainment of maximal HAL-induced (0.19 mg/kg and 0.25 mg/kg SC) striatal DA release; the latter was abolished by administration of tyrosine. NAA(-) also potentiated HAL-induced catalepsy.

CONCLUSIONS

Acute brain tyrosine depletion attenuates HAL-induced striatal DA release and potentiates haloperidol-induced catalepsy. Both effects can be reversed by administration of tyrosine. Overall, the data indicate that tyrosine depletion affects both neurochemical and behavioral indices of striatal DA release.