Early Responsiveness to Stimuli Paired With Different Stages Within the State of Alcohol Intoxication

Abstract

Background: Infant rats quickly learn to avoid a sensory cue paired with alcohol as an unconditioned stimulus, particularly when the drug reaches peak blood concentrations. In this study, a tactile cue paired with the onset of alcohol intoxication preceded subsequent presentations of a gustatory conditioned stimulus (CS). The goal was to address the possibility of differential conditioning depending on when stimuli were introduced during the course of the toxic state. Methods: In experiment 1, rat pups received sequential presentations of a salient texture (sandpaper) and a gustatory cue (saccharin) while intoxicated with a 2.5 g/kg alcohol dose or after receiving saline. Texture location tests and saccharin intake assessments were then performed. A third modality of assessment was defined by a saccharin intake test while pups simultaneously experienced sandpaper. In experiment 2, alcohol-mediated conditioning was followed by tests similar to those of experiment 1, but after pups were re-exposed to either the tactile CS or the alcohol-unconditioned stimulus. Results: Conditioned taste aversions, due to pairing saccharin and the later stage of alcohol intoxication, were reliably established in both experiments. Also in both experiments, this excitatory aversive response was dramatically inhibited when the association between the texture CS and the earlier stage of alcohol intoxication was activated. There were no indications of conditioned motor responses to the tactile CS that might compete with intake behavior of saccharin or distort measurement of an appetitive memory derived from pairing the texture and the earlier stage of intoxication. Conclusions: Rat pups’ expression of an association between a taste signaling aversive consequences of alcohol was eliminated by the presence of a tactile stimulus that originally had signaled the absence of aversive consequences of alcohol intoxication. The results suggest the interaction of inhibitory and excitatory conditioning involving the aversive properties of alcohol.