Methamphetamine Sensitization in Young Adult and Mature Adult Mice Assessed by Ambulation

Abstract

The dose-effect relationship for the ambulation increase caused by methamphetamine (1–8 mg kg−1, s.c.), and the sensitization following the 10-time repeated administrations of methamphetamine (2 mg kg−1) at 3- to 4-day intervals were investigated in young adult (7-weeks old) and mature adult (7–9-months old) mice. The mature adult mice showed higher activity counts after the administration of methamphetamine (1 and 2 mg kg−1, but not 4 and 8 mg kg−1) than the young adult mice, although there were no marked differences in the time-courses of change in the increased ambulation. The repeated administration of 2 mg kg−1 methamphetamine induced sensitization to its ambulation-increasing effect in both the young adult and mature adult mice. However, the established sensitization was more marked in the young adult mice than in the mature adult mice. These results may be caused by a difference in the dopaminergic neurotransmission, or learning and memory ability between young adult and mature adult mice.