Comparison of the conditioned reinforcing properties of a safety signal and appetitive stimulus: effects of d-amphetamine and anxiolytics

RATIONALE: Safety signals providing relief are hypothesised to possess conditioned reinforcing properties, supporting the acquisition of a new response (AnR) as seen with appetitive stimuli. Such responding should also be sensitive to the rate-increasing effects of d-amphetamine and to the anxiolytics 8-OH-DPAT and diazepam. OBJECTIVES: This study tests whether safety signals have conditioned reinforcing properties similar to those of stimuli-predicting reward. METHODS: Rats received Pavlovian conditioning with either appetitive stimuli (CS+) or safety signals (conditioned inhibitors, CIs) plus truly random control (TRC) stimuli. The appetitive group received a CS + paired with a sucrose pellet and the safety signal group, a stimulus paired with shock omission. Stimuli were tested using an AnR procedure and following systemic d-amphetamine, the 5HT-1A agonist 8-OH-DPAT and the benzodiazepine diazepam in a counterbalanced design. RESULTS: Effective conditioning selectively reduced contextual freezing during CI presentation in the safety signal group and increased food magazine responses (with respect to context and TRC) during CS + presentation in the appetitive group. The appetitive stimulus strongly supported AnR but the safety signal did not. Systemic d-amphetamine significantly potentiated lever pressing in the appetitive group but for the safety signal group, it either reduced it or had no effect, dependent on food deprivation state. 8-OH-DPAT and diazepam had no effect on responding in either group. CONCLUSIONS: The safety signal did not support AnR and, therefore, did not exhibit conditioned reinforcing properties. Furthermore, d-amphetamine decreased responding when the safety signal was presented as a consequence, whilst increasing responding with appetitive-conditioned reinforcement. These results are discussed in terms of implications for opponent motivational theory.