Restoration of analgesic response of C57BL/6J-bgJ (beige-J) mice to morphine by carbachol.

C57BL/6J-bgJ (beige-J) mice respond poorly to the analgesic effects of centrally administered (intracerebroventricular; i.c.v.) morphine in the tail-flick test. In the present study C57BL/6J-bgJ mice, their littermate (heterozygous) controls, and normal Swiss mice were given carbachol (200 micrograms/ml) in their drinking water for three weeks. Carbachol had no effect on control animals. However, the carbachol-treated beige-J mice responded to i.c.v.-administered morphine (1 microgram) significantly better than untreated beige-J mice and nearly as well as the normal mice.