Facilitation by drug states does not depend on acquired excitatory strength

Abstract

Three experiments examined the effects of drug-extinction when a drug state served as a conditional stimulus (CS) for sucrose delivery or as a positive feature for pairings between a discrete CS (e.g., 15-s light-on) and sucrose. Some conditioning models predict that drug state will facilitate the conditional response (CR) based on an association with sucrose whether the drug is trained as a CS or as a facilitator. If so, repeated presentation of the drug state alone (drug-extinction) should decrease the CR in both situations. Nicotine (0.4mg/kg), amphetamine (AMP, 1mg/kg), and chlordiazepoxide (CDP, 5mg/kg) facilitated a goal tracking conditioned response to the discrete CS; however, AMP and CDP did not evoke reliable responding without an interposed stimulus, suggesting that associations between these drug states and sucrose are not expressed as anticipatory food seeking (goal tracking). Repeated presentation of each drug state alone did not disrupt facilitation by nicotine, amphetamine, or CDP; suggesting that the drug states did not facilitate goal tracking based on a direct association with sucrose. This latter finding implicates a higher-order or non-associative mechanism for facilitation of anticipatory food seeking by drug states in this Pavlovian discrimination task.

Figure 1

(A) Mean elevation scores (±1 SEM) from discrimination training for rats in the Feature condition receiving the light or white noise target CS. (B) Mean dipper entry rates (±1 SEM) from discrimination training for rats in the CS condition. Mean dipper entry rates for EXT and RET groups during the drug extinction phase for rats in the Feature (C) and CS (D) conditions, respectively. + indicates elevation score for rats receiving the white noise CS differs significantly from rats receiving the light CS in the nicotine state, p<0.05. # indicates elevation score for rats receiving the white noise CS differs significantly from rats receiving the light CS in the saline state, p<0.05. ^* indicates dipper entry rate on drug session significantly differs from responding on corresponding saline session (B), or dipper entry for EXT group significantly differs from RET group (C & D), p<0.05.

Figure 2

(A) Mean elevation scores (±1 SEM) from the post-extinction test for rats in the Feature condition. For comparative purposes, baselines are included in the left-hand portion of the graph. These data points represent mean elevation scores from the first trial of the last nicotine and saline sessions for each group from Discrimination Training. Filled symbols represent elevation scores from nicotine trials, open symbols represent elevation scores from saline test trials. (B) Mean dipper entry rates (±1 SEM) from the post-extinction test for rats in the CS condition. Baselines are included in the left-hand portion of the graph; these data points represent means for each measure from the last nicotine and saline sessions of Discrimination Training. ^* indicates dipper entry rate on drug session differed significantly from dipper entry rate on saline session, p<0.05.

Figure 3

(A) Mean dipper entry rates (±1 SEM) from the Discrimination Training phase for rats in the Amphetamine group. (B) Mean dipper entry rates (±1 SEM) from the Discrimination Training phase for rats in the Chlordiazepoxide (CDP) group.

Figure 4

(A) Mean elevation scores (±1 SEM) from the discrimination training phase for rats in the AMP condition. (B) Mean elevation scores (±1 SEM) from the discrimination training phase for rats in the CDP condition. (C) Mean duration scores (±1 SEM) from the discrimination training phase for rats in the CDP condition. (D) Mean dipper entry rates (±1 SEM) from the drug extinction phase for EXT and RET groups from the AMP condition. (E) Mean dipper entry rates (±1 SEM) from the drug extinction phase for EXT and RET groups from the CDP condition. (F) Mean dipper entry proportions (±1 SEM) from the drug extinction phase for EXT and RET groups from the CDP condition.

Figure 5

(A) Mean elevation scores (±1 SEM) for EXT and RET groups from the post-extinction test for rats in the AMP condition of Experiment 2B. (B) Mean elevation scores (±1 SEM) for EXT and RET groups from the post-extinction test for rats in the CDP condition. (C) Mean duration scores (±1 SEM) for EXT and RET groups from the post-extinction test for rats in the CDP condition. Filled symbols represent elevation or duration scores from drug test trials, open symbols represent elevation or duration scores from saline test trials. Baselines are included in the left-hand portion of each panel; these data points represent mean elevation scores from the first trial of the last drug and saline sessions from the Discrimination Training phase.