DOES A COULOMETRIC RELATION DETERMINE WHETHER ANALGESIA IN THE DECEREBRATE RAT IS OPIOID OR NONOPIOID IN FORM? M.W. Meagher, J.W. Grau, & R.A. King, Depts. of Psychology, Texas A&M University, College Station, TX 77843, and UNC, Chapel Hill, NC 27514.

Terman et al. (Science, 226: 1270, 1984) have suggested that the coulometric relation (mA*sec) determines whether shock directly activates an opioid or nonopioid analgesic system at the level of the brainstem: low coulometric products elicit and opioid analgesia, while high coulometric products elicit a nonopioid analgesia. Here we test this hypothesis by evaluating whether a coulometric relation determines the form of the analgesia (i.e. whether its opioid or nonopioid) observed in the decerebrate rat. We first identified the minimum coulometric products required to elicit analgesia in the decerebrate rat on the tail-flick test. We found that either 3, 25-sec, 0.5 mA or 3, 12.5-sec, 1.0 mA shocks were required. We then compared the form of analgesia elicited by these shock schedules to that elicited by 3, 25-sec, 1.0 mA shocks. (Elsewhere we have shown that the analgesia observed after these shock schedules depends upon supraspinal systems.) All 3 shock schedules induced significant antinociception. However, naltrexone (14 mg/kg) had no effect on the analgesia observed in any of the groups. This suggests that only the nonopioid brainstem analgesic systems may be directly activated by shock. Supported by NIDA grant DAO4259-01 to JWG.

Published in Society for Neuroscience Abstracts, 15, 1989.

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