A genetic analysis of morphine responses in mice

To investigate whether genetic factors may play a role in the difference of the responses to morphine between inbred strains of mice, we determined the effect of morphine on the plasma cyclic nucleotides, the motor activity and the rectal temperature in the 2 progenitor strains of mice, DBA and C57BL, their F1 and F2 hybrids, and the 2 backcross progenies between F1 and parental strains. C57BL was partially dominant over DBA concerning the motor activity induced by morphine, whereas DBA was partially dominant over C57BL in terms of the increase in plasma cyclic nucleotides and the hypothermia elicited by morphine. The biometric analysis suggested that the strain difference in the effects of morphine was genetically determined except for plasma cyclic AMP, and that among these quantitative traits, the effects of morphine on motor activity and rectal temperature were controlled by more than one allelic gene pairs.