Effects of dexamethasone and locus caeruleus lesion on morphine analgesia, electro-acupuncture analgesia and stress analgesia

Morphine analgesia (MA), electro-acripuncture analgesia . (EAA) and stress analgesia (SA) were observed after electrolytic and kainic acid lesions of locus caeruleus and dexamethasone ip. Three different pain tests were used. MA, EAA and SA were all revealed by electrical stimulation-vocalization test, while tail flick test was ineffective in SA, and formalin test was ineffective in EAA. Dexamethasone blocked only SA, but not EAA nor MA. Both EAA and SA were diminished after electrolytic and kainic acid lesions of locus caeruleus. MA was decreased after electrolytic lesion, but not after kainic acid lesion of locus caeruleus. These results suggest that the three analgesic effects involve different endogenous analgesic systems.