Sensory reinforcement as a predictor of cocaine and water self-administration in rats

Abstract

Rationale: The ability of locomotor activity in a novel environment (Loco) and visual stimulus reinforcement (VSR) to predict acquisition of responding for cocaine and water reinforcers in the absence of explicit audiovisual signals was evaluated.

Methods: In Experiment 1 (Exp 1), rats (n = 60) were tested for VSR, followed by Loco, and finally acquisition of responding for cocaine (0.3 mg/kg/inf). In Experiment 2 (Exp 2), rats (n = 32) were tested for VSR, followed by Loco, and finally acquisition of responding for water (0.01 mL/reinforcer).

Results: There were three main findings. First, Loco and VSR were significantly associated (Exp 1: r = 0.49, p < 0.00; Exp 2: r = 0.35, p < 0.05). Second, neither Loco (r = .00, p = 0.998) nor VSR (r = -0.12, p = 0.352) predicted acquisition of cocaine SA. Third, in the subgroup of animals that acquired cocaine SA, VSR (r = 0.41, p < 0.01) but not Loco (r = 0.28, p = 0.10) was positively associated with operant responding for cocaine. Both Loco and VSR (Loco: r = 0.37, p < 0.04; VSR: r = 0.51, p < 0.00) were positively associated with operant responding for water reinforcers.

Conclusions: The results indicate that VSR is at least as good a predictor of cocaine reinforced responding as Loco. VSR was predictive of operant responding for both drug and water reinforcers, while Loco was found to be predictive of responding only for water reinforcers. In studies that present visual stimuli in association with drug delivery, Loco may be predicting acquisition of responding for VSR rather than drug.

Fig 1

Illustration of the test panels used in visual stimulus reinforcement (a) and self-administration testing (b).

Fig. 2

This plot shows the distribution of cocaine infusions in the sixty animals tested for cocaine self-administration. The dotted line indicates the criterion used for acquisition. There was a bimodal distribution, with two distinct groups of rats.

Fig. 3

These plots show light reinforcement performance for all animals tested. The 10 sessions to the left of the dashed line were pre-exposure session during which responding had no effects. The 6 sessions to the right of the dashed line were visual stimulus reinforcement sessions where responses to the active alternative produced light onset according to a variable interval 1 minute schedule of reinforcement. The closed squares indicate the animals that met criterion for acquisition for cocaine self-administration (ACQ; n = 36), and the open circles indicate animals that failed to meet criterion for acquisition for cocaine self-administration (NON-ACQ; n = 24). Data are shown as group averages (± SEM). (a) The top panel shows total number of responses emitted during testing. (b) The bottom panel shows relative frequency of active responses. See text for detailed explanation.

Fig. 4

These plots show acquisition of cocaine SA for all animals tested. The closed squares indicate animals that met criterion for acquisition (ACQ; n = 36), and the open circles indicate animals that failed to meet criterion for acquisition (NON-ACQ; n = 24). Data are shown as group averages (± SEM). (a) The top panel shows number of cocaine infusions earned during 60 min test sessions. (b) The middle panel shows total number of responses emitted. (c) The bottom panel shows the relative frequency of active responses. See text for detailed explanation.

Fig. 5

These scatterplots show the relationships between cocaine self-administration and locomotor response to novelty, total visual stimulus reinforcement responses, and the relative frequency of active responses during visual stimulus reinforcement testing. (a) Shows a non-significant tendency for locomotor response to novelty to be associated with cocaine infusions. (b) Shows the positive association between total light reinforced responses and cocaine infusions. (c) Shows the lack of association between relative frequency of active light responses and cocaine infusions.

Fig. 6

These plots show light reinforcement performance for all water reinforcement animals tested. The 10 sessions to the left of the dashed line were pre-exposure sessions during which responding had no effects. The 6 sessions to the right of the dashed line were visual stimulus reinforcement sessions where responses to the active alternative produced light onset according to a VI 1 min schedule of reinforcement. Data are shown as group averages (± SEM). (a) The top panel shows total number of responses emitted during testing. (b) The bottom panel shows relative frequency of active responses. See text for detailed explanation.

Fig. 7

These plots show water reinforcement performance for all rats tested. (a) The top panel shows number of water reinforcers earned across days of acquisition. (b) The middle panel shows total number of responses emitted across test days. (c) The bottom panel shows relative frequency of active responses to the water reinforced alternative. Data are shown as group averages (± SEM).

Fig.8

These scatterplots show the relationships between water reinforcement and locomotor response to novelty, total visual stimulus reinforcement responses, and the relative frequency of active visual stimulus reinforcement responses. (a) Shows a significant positive association between locomotor response and water reinforcement. (b) Shows a significant positive association between total visual stimulus reinforcement responses and water reinforcement. (c) Shows a non-significant positive association between relative frequency of active visual stimulus responses and water reinforcement.