LEVORPHANOL AND SWIM STRESS-INDUCED ANALGESIA IN SELECTIVELY BRED MICE - EVIDENCE FOR GENETIC COMMONALITIES

Two independent selective breeding programs have developed divergent l ines of mice expressing either high and low swim stress-induced analge sia (HA/LA lines; Jastrzebiec, Poland) or high and low levorphanol ana lgesia (HAR/LAR lines; Portland, OR). In the present study, mice from both programs were tested for both levorphanol analgesia (2 mg/kg) and an opioid-mediated swim stress-induced analgesia (3 min swimming in 3 2-degrees-C water) in the hot-plate test. Mice selected for high and l ow levorphanol analgesia displayed high and low swim stress-induced an algesia, respectively; mice selected for high and low swim stress-indu ced analgesia displayed high and low levorphanol analgesia, respective ly. This pattern of correlated responses suggests a high degree of com mon genetic determination in opiate and swim stress-induced analgesia. These findings also suggest that individual differences in analgesic responsiveness to opiate drugs result from genetically determined indi vidual differences in endogenous pain inhibitory mechanisms.