TEST TYPE INFLUENCES THE EXPRESSION OF LITHIUM CHLORIDE-INDUCED HYPERALGESIA

The hyperalgesic properties of the emetic drug lithium chloride (LiCl) were examined in eight experiments. At a dose of 63.6 mg/kg, LiCl pro duced hyperalgesia in the radiant-heat (Experiment la) and immersion ( Experiment Ib) tail-flick tests. At doses of 15.9, 31.8, 63.6, and 127 .2 mg/kg, LiCl failed to produce hyperalgesia during the delayed behav ioral response in the formalin test (Experiments 2a and 2b), but 63.6 mg/kg LiCl did produce hyperalgesia during the normally quiescent, int erphase period of formalin responding (Experiment 2c). At the dose of 63.6 mg/kg, LiCl did not produce hyperalgesia in the hotplate test (Ex periments 3a and 3b) and did not exert significant motoric effects in a step-down passive-avoidance task (Experiment 4). The results were di scussed with reference to the behavioral effects of LiCl and their imp lications for demonstrations of associatively mediated morphine analge sic tolerance. (C) 1998 Elsevier Science Inc.