The Neurochemical Systems that Mediate Antinociception in spinalized Rats

Program year: 1990/1991Digitized from print original stored in HDRWe have previously shown that exposure to three brief (2 sec) 3.0 mA shocks elicits an opioid hypoalgesia, and that exposure to longer (75 sec) tailshocks elicits a nonopioid hypoalgesia in spinalized rats. The present study explores whether cholinergic and noradrenergic systems play a role in the production of these antinociceptive effects. Experiment 1, showed that the cholinergic antagonist scopolamine elicits hyperalgesia in spinalized rats, but does not affect the magnitude of antinociception observed after either brief or long tailshocks. Experiment 2 showed that alpha-2- noradrenergic antagonist yohimbine does not affect baseline levels of pain reactivity. Yohimbine did, however, attenuate the antinociception observed after both shock schedules. Implications of the results are discussed