IMPACT OF SHOCK ON PAIN REACTIVITY .2. EVIDENCE FOR ENHANCED PAIN

Shocked rats (Rattus norvegicus) often exhibit longer tail withdrawal latencies to radiant heat, which suggests that exposure to shock reduc es pain. But at the same time, rats appear hyperreactive to shock, sug gesting that pain is enhanced. Experiment 1 replicated these findings and showed that when tail movement was monitored, shocked rats were le ss responsive to heat and hyperreactive to shock even when the same be havioral criteria were used. When latency to vocalize was measured, sh ocked rats appeared hyperreactive to both test stimuli (Experiments 2 and 3). Prior exposure to shock also enhanced the acquisition of condi tioned fear in a different context (Experiment 4) and the speed with w hich rats learned a response to avoid a thermal stimulus (Experiment 5 ). The results suggest that exposure to shock enhances pain.