CONTROLLABLE, BUT NOT UNCONTROLLABLE SHOCK ELICITS AN ANTINOCICEPTION IN SPINALIZED RATS. C.W. Parker III., P.A. Illich, J.W. Grau & M.W. Meagher*. Dept. of Psychology, Texas A&M Univ. College STation, TX 77843.
Prior work has shown that exposure to inescapable shock produces both short- and long-term analgesia. These effects are not observed in rats that experienced the same amount of shock, but can control its termination. It has been generally assumed that such effects are mediated by forebrain systems. However, we have recently shown that other antinociceptive phenomena thought to involve forebrain systems can be obtained in spinalized subjects. Here, we assess whether having control influences nociception in spinalized subjects. A day after rats received a spinal transection at T2, they were placed in restraining tubes and tested for baseline levels of nociception. Nociceptive thresholds were defined as the shock intensity needed to produce a leg flexion. Subjects were then given a 30 min training session in which they received 1.0 mA footshocks. Subjects were run in pairs. One rat could terminate the shock by flexing its lef (Exp). The other rat received the same shock irrespective of lef position (Yok). Exp, but not Yok subjects spent increasingly more time with their legs in a flexed position. Interestingly, after training, Exp subjects exhibited an increase in nociceptive threshold (antinociception), while Yok subjects showed a decrease in nociceptive threshold (hyperalgesia) (p <.01). The results suggest that controllability influences nociception in spinalized rats.
Published in Society for Neuroscience Abstracts, 18, 1992, 1026.