Plasma corticosterone and free fatty acid responses and positive behavioral contrast

Corticosterone and free fatty acid (FFA) responses during water-reinforced operant sessions were examined in rats subjected to reinforcement schedule shifts which may elicit frustration-induced arousal reactions. Rats were trained on a multiple VI VI-30 sec schedule that was subsequently changed to a multiple VI EXT or multiple VI VI-60 sec schedule. The rats shifted to the multiple VI EXT schedule developed positive behavioral contrast. The corticosterone levels of both groups were elevated by the first postshift session, in which the frequency of reinforcement was halved, but returned to preshift levels by the 8th postshift session, which preceded discriminative performance in the Contrast group. The FFA levels of both groups were elevated by the Multiple VI VI-30 sessions (compared to presession basal levels), but the response decreased with the halving of the reinforcement rate. The present findings were interpreted as evidence that the psychological variables associated with the acquired emotional state of frustration influence the blood concentration of corticosterone, but not FFA. The findings are consistent with such explanations of positive behavioral contrast as positive induction or release-from-inhibition. No evidence was found for a direct energizing effect of frustration to account for positive contrast.