PHYSOSTIGMINES IMPACT ON BRIEF SHOCK-INDUCED HYPOALGESIA PARALLELS ITS EFFECT ON MEMORY

Past research indicates that the anticholinergic drug scopolamine disr upts memory and environmentally induced hypoalgesia in rats. The prese nt study examined the impact of the centrally active cholinesterase in hibitor physostigmine, which enhances memory and central cholinergic a ctivity, on brief shock-induced hypoalgesia on the tail-flick test usi ng Sprague-Dawley rats. It is reported that physostigmine (0.1 mg/kg) potentiates the magnitude of this hypoalgesia. Contrary to past resear ch, our results showed that omission of baseline testing did not elimi nate hypoalgesia or its potentiation by physostigmine. Similar to its effects on memory, physostigmine (0.04, 0.1, and 0.25 mg/kg) has a non monotonic impact on brief shock-induced hypoalgesia; low doses potenti ated hypoalgesia (0.1 mg/kg), whereas a high dose (0.25 mg/kg) disrupt ed it. These results provide further evidence that the cholinergic sys tem indirectly affects pain reactivity by modulating the memory of the aversive event. (C) 1998 Academic Press.