Behaviorally selective cardiovascular hyperreactivity in spontaneously hypertensive rats. Evidence for hypoemotionality and enhanced appetitive motivation.

Abstract

Spontaneously hypertensive rats (SHRs) and Wistar Kyoto controls (WKYs) were chronically instrumented for computer-assisted recording of arterial pressure (AP) and heart rate (HR) and examined during classically conditioned emotional (fear) reactions or during the performance of a repertoire of natural behaviors, including eating, drinking, grooming, exploring, and resting. The purpose of the study was to determine whether exaggerated cardiovascular reactivity in SHRs during aversive stimulation: 1) can be coupled to stimuli that before conditioning elicited negligible changes in AP and HR; 2) is accompanied by a proportionately enhanced level of emotional arousal; and 3) is specific to aversive emotional arousal or is also present during natural behaviors. The conditioned blood pressure response (in mm Hg) was greater (p less than 0.01) in SHRs (peak response, 20 +/- 3) than in WKYs (peak response, 7 +/- 1). While the conditioned pressure response was SHRs (peak response, 17 +/- 7 bpm). Behavioral tests indicated reduced emotional reactions in SHRs: SHRs showed less (p less than 0.05) drink suppression (75 +/- 17 sec) than WKYs (111 +/- 10 sec) and SHRs showed less (p less than 0.01) suppression of exploratory activity (201 +/- 40 sec) than WKYs (499 +/- 70) in the presence of the conditioned emotional stimulus. The magnitude of blood pressure changes (in mm Hg) above resting baseline was not different in SHRs and WKYs during eating (SHR, 32 +/- 3; WKY, 28 +/- 2), grooming (SHR, 17 +/- 3; WKY, 14 +/- 2), or exploring (SHR, 17 +/- 2; WKY, 18 +/- 2), but was greater (p less than 0.01) during drinking in SHRs (48 +/- 4) than in WKYs (32 +/- 2). The amount of time (sec) spent grooming (SHR, 55 +/- 23; WKY, 38 +/- 15) and exploring (SHR, 187 +/- 33; WKY, 165 +/- 42) did not differ between the strains, but SHRs spent more time (p less than 0.01) eating (SHR, 1103 +/- 88); WKY, 800 +/- 114) and drinking (SHR, 119 +/- 18; WKY, 32 +/- 12). These findings demonstrate that: 1) exaggerated cardiovascular reactivity in SHRs is readily coupled through conditioning to otherwise benign stimuli; 2) conditioned cardiovascular hyperreactivity is accompanied by a reduced not an enhanced level of conditioned emotional arousal; 3) cardiovascular hyperreactivity is not specific to aversive arousal but is nevertheless a behaviorally-specific mode of response; and 4) SHRs and WKYs differ in the performance of natural as well as emotional behaviors.