Effects of previous curare-immobilization on Pavlovian conditioned heart decelerations in the curarized rat

Abstract

Recent evidence indicates that mechanisms other than the vagal-blocking properties of d-tubocurarine chloride (dTC) or inadequate respiration may account for the reports of invariant heart rate (HR) in curarized rats. Two experiments were conducted to determine if repeated dTC-paralysis facilitate acquisition of a Pavlovian HR conditioning in the dTC-paralyzed rat. In Experiment 1, Pavlovian HR conditioning was examined in curarized rats which had (1) experience with dTC-induced immobilization before conditioning, or (2) no experience with dTC-induced immobilization. The results showed that pronounced conditioned HR decelerations were observed only for the curare-experienced animals. Experiment 2 was conducted to determine if repeated curarization influenced tolerance to dTC-induced neuromuscular paralysis. No group differences in basal electromyographic (EMG) activity or time to recover from paralysis were found between the Non-Curare Adapted (NCA), and the Curare Adapted (CA) groups. The implications of the results are discussed in terms of the role of immobilization-induced stress on acquiring stimulus control over autonomic responses.