Strain differences in the hyperalgesic effect of a novel kappa receptor agonist, U-50488H in mice

The administration of a kappa agonist, U- 50488H produced reduction in jumping latencies in the hot plate test in Swiss and CBA strains of mice but not in CXBH , CXBK and C57BL strains. The hyperalgesia following U- 50488H in Swiss and CBA strains might possibly be related to the antagonism of endogenous substrates for kappa receptors released during the thermonociceptive stimuli. A detailed time-course study in Swiss Strain revealed that a significant hyperalgesia was observable from 10 min up to 2 h. The present results indicate that CXBH , CXBK and C57BL strains might be deficient in kappa ligands and/or receptor levels relevant to thermonociception .