Autonomic mechanisms in fear-mediated behavior: the role of the adrenal medullae

Abstract

The purpose of the present rese arch was to assess the role of peripheral autonomic structures in fear-mediated behavior. A surgical procedure (apparent adrenaleotomy) which effectively demedullates the adrenal gland, but which requires no histological verification of demedullation is discussed. Two experiments investigating the role of autonomic structures in fear acquisition are reported. In Experiment 1, four groups of rats were trained in a conditioned emotional response task. Prior to training, the adrenal medullae of two of the groups were surgically removed. Either an apparent adrenalectomy procedure (N = 7) or the traditional demedullation operation (N = 8) was used. Two additional groups served as either sham-operated (N = 4) or normal control. (N = 4) groups. The Ss were given 12 days of conditioned emotional response training. Suppression ratios were calculated and these data were submit ted to an analysis of variance. No statistically reliable differences in rate of conditioned emotional response acquisition were found between any of the groups. Experiment 2 used a task in which no discrete CS was available to the animals. In such a task, epinephrine and norepinephrine are released from the adrenal medulla in considerable quantities. Three groups of rats sustained either adrenal demedullation and denervation (N = 6), sham operations (N = 8), or served as unoperated control animal a (N = 7). They were then trained to press a lever for food under a variable interval reinforcement schedule upon which a response contingent fixed interval shock schedule was superimposed. The results were analyzed in terms of lever presses emitted during each of six sessions of response contingent shock, number of shocks received, and reestablishment of the reinforcement baseline following no shock for six sessions. Analyses of variance indicated that there were no statistical.ly reliable differences between any of the groups. The results are discussed in terms of central nervous system structures which appear to be important in fear conditioning. Implications of these results for theoretical formulations which implicate the autonomic nervous system in fear acquisition are discussed.