Stress and pain responses in rats lacking CCK1 receptors.

UNLABELLED CCK involvement in stress- and pain-responsiveness was examined by studying the behavior of infant (11-12-days-old) and adult OLETF rats that do not express CCK1 receptors. Infant odor- and texture-preferences were also assessed. We hypothesized that OLETF rats will show behavioral patterns similar to those previously observed after CCK1 antagonist administration. Rate of separation-induced ultrasonic vocalization was significantly greater in OLETF compared to controls, in two separate studies. Infant pups of the two strains did not differ in odor- and texture-preference tests. OLETF rats showed consistently longer hot-plate paw-lift (as infants, in two separate studies) and paw-lick (as adults) latencies. SUMMARY OLETF pups vocalized in isolation more than controls and showed relative hypoalgesic responses, evident also in adulthood, in concordance with the pharmacological literature.