Pavlovian Conditioning in Awake and Pentobarbital Anesthetized Rats

Abstract

Prior research shows that very intense noises can produce antinociception in awake rats. Experiment 1 examined the antinociceptive effects of a tone and a noise at various intensity levels on awake and pentobarbital anesthetized rats. Both the tone and noise reduced reactivity to a noxious thermal stimulus applied to the tail in both awake and anesthetized subjects. Experiment 2 examined whether Pavlovian conditioning can be established in pentobarbital anesthetized rats. Half of the subjects experienced an auditory cue (the conditioned stimulus, or CS) paired with an aversive tailshock (the conditioned stimulus, or US). The remaining subjects experienced the CS and US in an unpaired fashion. US intensity was set to a value known to induce a strong antinociception in both awake and anesthetized rats. CS intensity was set, based on the results from Experiment I, to a level that generated a weak antinociception. Rats trained while awake exhibited longer tail-flick responses in the presence of the context, but they did not appear to exhibit any conditioning to the auditory cues. Rats trained under anesthesia did not exhibit conditioning to the context, but did display reduced tail-flick latencies (conditioned hyperalgesia) to the paired auditory cues. Implications of the results are discussed.