Acute sympathectomy by 6-hydroxydopamine in the adult rat: Effects on cardiovascular conditioning and fear retention.

Abstract

Curarized rats, chemically sympathectomized by 6-hydroxydopamine (6-OH), had lower base-line systolic blood pressures but equivalent heart rates to vehicle-injected controls. Maximum blood pressure increase in the vehicle group to unsignaled shock occurred about 2 sec. after shock onset, while in the 6-OH group the increase was smaller, reaching maximum 9 sec. after shock. Heart-rate increases to shock were also attenuated by sympathectomy. After 41 paired or random CS and shock presentations, only the paired vehicle group showed a biphasic pressure increase to the CS. The paired and random 6-OH-treated groups showed equivalent long-latency responses to the CS. No consistent group-conditioned heart-rate responses were observed. The vehicle-and the 6-OH-treated groups did not differ on retention of fear of the CS when tested by a CER procedure 5 days after curarization.

Heart rate and muscle tension correlates of conditioned suppression in humans.

“…This hypothesis has its origins in early formulations of two-process theory which stated that responses mediated by the autonomic and particularly the sympathetic nervous system (e.g., heart rate) were components of the fear response (e.g., Mowrer, 1947). Since these early formulations, a considerable body of evidence has indicated that surgically or drug induced modifications of the sympathetic nervous system do not necessarily lead to changes in aversively conditioned responses such as passive avoidance , active avoidance (Di Giusto & King, 1972), and conditioned suppression (Pappas, Di Cara, & Miller, 1972). While aversively conditioned sympathetic responses may not be a component of the fear response they may still index fear, and this view has wide acceptance in both experimental (Germana, 1969) and clinical (Wolpe, 1966) circles.…”