Genetic analysis of the effects of morphine on plasma cyclic nucleotides and locomotor activity in male mice.

A biometric analysis of morphine-induced changes in locomotor activity and plasma cyclic nucleotide levels was conducted in two inbred strains of mice, DBA/2N and C57BL/6N, and their F1 hybrid and backcross progenies. C57BL/6N was partially dominant over DBA/2N for morphine-induced motor activity, whereas DBA/2N was partially dominant over C57BL/6N with respect to the effect of morphine on the cyclic nucleotides. The strain difference in the effect of morphine on motor activity and on plasma cyclic GMP was shown to be genetically determined, whereas the genetic influence on plasma cyclic AMP was statistically not confirmed. The number of gene pairs which regulate the effect of morphine on motor activity was assumed to be more than one; however, the contribution of more than one segregating unit in the effect of morphine on plasma cyclic GMP was not demonstrated.