Linkage of distal mouse chromosome 8 to U50,488 (50 mg/kg, i.p.) analgesia in female but not male B6D2F2 mice. (a) Male and female LOD score curves, showing the logarithm of the likelihood for a presence of a QTL at that location. A free genetic model yielded a peak LOD score of 2.7 in females; additive and recessive models also yielded significant LOD scores in this sex (2.3 and 2.4, respectively). The approximate locations of microsatellite markers used are shown below the ordinate. (b) Impact on U50,488 analgesia of inheritance of the three possible genotypes (B6/B6, homozygous for B6 allele; B6/D2, heterozygous; D2/D2, homozygous for D2 allele) at D8Mit56. The time course of U50,488 analgesia was identical in all groups (data not shown), peaking at 15 min postinjection. Bars represent mean ± SEM percent total analgesia (% analgesia) over the 60-min testing period. *, Significantly different from B6/B6 group, P < 0.05.