Acute lithium administration selectively lowers tyrosine levels in serum and brain

Lithium exerts anti-dopaminergic behavioral effects. We examined whether some of these might be mediated by changes in brain levels of tyrosine (TYR), the precursor to dopamine. Lithium chloride (LiCl(2)) 3.0mEq/kg IP acutely lowered serum TYR and the ratio of serum TYR to other large neutral amino acids (LNAAs); it also selectively lowered striatum TYR levels as measured in tissue or in vivo. While LiCl(2) 3.0mEq/kg IP also augmented haloperidol (0.19mg/kg SC)-induced catalepsy, this lithium effect was not attenuated by administration of TYR 100mg/kg IP. We conclude that lithium acutely and selectively lowers brain TYR by lowering serum levels of tyrosine relative to the LNAAs that compete with it for transport across the blood-brain barrier. However, the lowering of TYR does not appear to significantly contribute to the ability of lithium to potentiate haloperidol-mediated catalepsy.