THE IMPACT OF SCOPOLAMINE ON CONDITIONED AND SHOCK-INDUCED ANALGESIA. P.S. Chen*, P.A. Illich, M.W. Meagher and J.W. Grau. Department of Psychology, Texas A&M University, College Station, TX 77843.
Rats exposed to long shocks exhibit a nonopioid analgesia on the tail-flick test which is eliminated by spinal transection but not decerebration. It is currently unclear whether cholinergic systems play a role in this analgesia. We addressed thsi issue by testing the impact of the cholinergic antagonist scopolamine (1 mg/kg) on the analgesia observed after three 25 s, 1.0 mA, tail-shocks. Prior to shock, scopolamine treated subjects exhibited a significant hyperalgesia. The drug did not attenuate the analgesia observed after shock. In fact, when we controlled for the impact of scopolamine on baseline levels of pain reactivity, it actually potentiated shock-induced analgesia. Methylscopolamine, which does not cross the blood-brain barrier, had no effect. We also tested whether cholinergic systems play a role in conditioned analgesia. One stimulus (the CS+) was paired with shock while the other was presented alone (CS-). Each subject received 6 presentations of each stimulus spaced over 2 hr. TEsting was conducted 24 hr later. WE found that saline treated subjects were analgesic during the CS+ relative to the CS-. This conditioned analgesia was blocked by scopolamine but not methylscopolamine. Supported by BNS 881981 to J.W.G.
Published in Society for Neuroscience Abstracts, 16, 1990.