Changes in pain reactivity induced by unconditioned and conditioned excitatory and inhibitory stimuli.
In three experiments we investigated the effects of aversive-conditioning components on the reactivity of rats to pain. After training in Experiment 1 with a discrete conditioned stimulus (CS) for a shock unconditioned stimulus (US), different groups were exposed to the CS, US, CS/Us compound, just the training context, or none of those immediately prior to a hot-plate test assessing the latency of a paw-lick response. Relative to no exposure and context alone, the CS produced a shorter latency--that is, an apparent sensitization effect--whereas the US produced a longer latency--that is, a hypoalgesic effect--that was actually augmented by the CS/US compound. Furthermore, whereas the US-induced hypoalgesia was unaffected by the opiate antagonist, naloxone, hypoalgesia produced by the CS/US compound was appreciably decremented by the drug. Experiment 2 showed the same effects with parameters more typical of conditioning research. Experiment 3 compared signals for the presence (CS+) and absence (CS-) of the US. The CS- did not itself affect pain reactivity, but in inhibited the effects of the CS+, US, and CS+/US compound. Collectively, the results suggest that a CS+sensitizes the animal to imminent events and also potentiates an opioid reaction that supplants the less effective nonopioid hypoalgesia induced by the US. In contrast, a CS- functions as a general moderator of excitation, inhibiting both sensitization and hypoalgesic effects, whether opioid or nonopioid.
Lysle
D T
DT
Department of Psychology, University of Pittsburgh, Pennsylvania 15260.
Fowler
H
H
D000818:Animals; D001143:Arousal / Q000187:drug effects; D001362:Avoidance Learning / Q000187:drug effects; D003214:Conditioning, Classical / Q000187:drug effects; D004597:Electroshock; D007266:Inhibition, Psychological; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D010146:Pain / Q000523:psychology*; D010147:Pain Measurement; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects
D009270:Naloxone