Relation between methamphetamine-induced monoamine depletions in the striatum and sequential motor learning

Methamphetamine (METH) use results in depletion of monoamines in the striatum. The purpose of this study was to evaluate the relation between the degree of METH-induced monoamine depletion in the striatum and impairment on a striatally-dependent learning task in rats. Male Sprague-Dawley rats received four injections of METH (10 mg/kg) or saline at 2-h intervals. METH treatment produced a 38.5% (± 5.6) and 46.7% (± 6.7) dopamine (DA) depletion in the medial and lateral striatum, respectively. Serotonin (5-HT) was depleted 15.6% (± 10.4) and 21.1% (± 8.2) in the medial and lateral striatum, respectively. One month after treatment, rats were trained on a sequential-memory task on an 8-arm radial maze. METH-treated rats made significantly fewer direct movements between arms in the maze sequence across days of trials. The learning impairment was significantly correlated with the degree of DA depletion in the medial striatum, as well as serotonin tissue content in striatum. Only rats with a greater than 40% DA depletion in medial striatum showed significant impairments. These results provide additional evidence for METH-induced learning impairments and suggest that this impairment is dependent on the striatal monoamine loss, in general, and the degree of DA loss in medial striatum, in particular.