Abstract
Effects of scopolamine (0.5 mg/kg, s.c.) on ambulatory activity were investigated in 6 strains of mice (dd, ICR, BALB, C57BL, C3H and DBA). Scopolamine increased ambulatory activity, and the sensitivities were in the order of ICR>C3H>BALB>DBA>C57BL>dd. This was different from that produced by methamphetamine (2 mg/kg, s.c.) where the order was ICR>dd>DBA>C3H>C57BL>BALB. A tolerance to the ambulation-increasing effect of scopolamine was progressively produced in dd, ICR, C57BL and DBA strains, but not in BALB and C3H strains, when the drug was administered 5 times at intervals of 3-4 days. The repeated scopolamine treatment elicited a major enhancement of the sensitivity to the ambulation-increasing effect of methamphetamine (2 mg/kg, s.c.) in BALB and C3H strains and a minor enhancement in the C57BL strain, whereas dd, ICR and DBA strains did not exhibit a marked change in the sensitivity to methamphetamine even after the same treatment with scopolamine. These results suggest that the ambulation-increasing effect of scopolamine is different from that of methamphetamine and that the interaction between scopolamine and methamphetamine varies among different strains of mice.
