Tolerance to the neurotoxic effects of methamphetamine in young rats.

The present study examined whether exposure to methamphetamine during adolescence (as determined in post-natal day 40 rats) might alter its effects when used in young adulthood (as assessed in post-natal day 90 rats). Results confirm that high-dose methamphetamine administration (4x10 mg/kg/injection, s.c., 2-h intervals) decreases striatal dopamine uptake and transporter ligand binding in post-natal day 90 rats; effects that were blocked if animals received six biweekly methamphetamine pretreatments (15 mg/kg; s.c.) beginning at post-natal day 40. This neuroprotection was not likely due to pharmacokinetic tolerance, since brain methamphetamine concentrations did not differ 1 h after the high-dose methamphetamine regimen among treated rats regardless of pretreatment. The methamphetamine biweekly pretreatment attenuated the hyperthermia caused by the neurotoxic methamphetamine regimen; a phenomenon that may have contributed to the neuroprotection.