Transient changes in amphetamine (AMPH) responsivity are observed in the first days after unilateral brain damage produced by infusion of 6-hydroxydopamine (6-OHDA) into the substantia nigra to deplete dopamine (DA) or by cortical ablation [Paquette et al., 2004, SfN Abstracts, 30]. We hypothesized that DA synthesis is altered during this early, transient period. To test this, we conducted dose-response studies of the effects of DA synthesis inhibitors on AMPH-evoked rotation 24 hr after unilateral brain damage. Specifically, we assessed: 1) the effects of the tyrosine hydroxylase (TH) inhibitor a-methylparatyrosine (a-MPT; 0, 10, 32, 56, 100, or 320 mg/kg, i.p.) after nigral or cortical damage, or 2) the effects of the dopa decarboxylase inhibitor m-hydroxybenzylhydrazine (NSD-1015; 0, 10, 32, or 100 mg/kg, i.p.) after nigral damage only. One day after 6-OHDA treatment, AMPH-evoked rotation was contraversive to the lesion and was resistant to synthesis inhibition by a-MPT and NSD-1015 at all doses. Howeve...