Facilitation of Pavlovian conditioned cardiodecelerations following preshock in immobilized rats

Abstract

Two experiments are reported that examine the effects of unsignalled, inescapable prior shock exposure (PSE) on shock-motivated Pavlovian conditioned heart rate (HR) decelerations in rats. Both studies involved 2 CS-US contingencies (paired and unpaired) and 2 preshock treatments (preshock and no preshock). The 2 designs differed in the type of immobilization procedures to which the rats were submitted and the number of conditioning sessions. In Experiment 1 rats were conditioned for 2 consecutive 35 trial sessions while physically restrained, whereas only one conditioning session was used in Experiment 2 on animals that were paralyzed with d-tubocurarine chloride (dTC). The results demonstrated that PSE augmented the magnitude of the HR conditioned response (CR) in both the physically restrained and paralyzed preparations. In addition, PSE improved the rate of acquisition of the conditioned cardiodeceleration in physically restrained rats and tended to facilitate reinstatement of the HR CR during the second conditioning session. These data support the notion that certain nonspecific stress processes that are relatively independent of the CS-US contingency but related to the occurrence of response suppression are intimately involved in Pavlovian HR conditioning.