Genetic influences on brain stimulation-produced analgesia in mice: II. Correlation with brain opiate receptor concentration.

The analgesic effect of electrical stimulation of the periaqueductal gray matter (PAG) was studied in 4 strains of mice: C57BL/6By (C57), BALB/cBy (BALB), CXBH, and CXBK. These strains are known to have high (CXBH), low (CXBK), and intermediate (C57 and BALB) concentrations of brain opiate receptors. The current intensity required for stimulation-produced analgesia (SPA) did not differ among strains. Naloxone attenuated SPA in CXBH, C57 and BALB mice, but was ineffective in the opiate receptor deficient CXBK mice. The results suggest that genetic differences in opiate receptor density can influence the degree to which opioid mechanisms are involved in SPA from the PAG.