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

Abstract

SUMMARY Spontaneously hypertensive rats (SHRs) and Wistar Kyoto controls (VVKYs) 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 < 0.01) in SHRs (peak response, 20 ± 3) than in WKYs (peak response, 7 ± 1). While the conditioned pressure response was accompanied by bradycardia in WKYs (peak response, -1 3 ± 5 bpm), tachycardia was present in SHRs (peak response, 17 ± 7 bpm). Behavioral tests indicated reduced emotional reactions in SHRs: SHRs showed less (p < 0.05) drink suppression (75 ± 17 sec) than WKYs (111 ± 10 sec) and SHRs showed less (p < 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 < 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 < 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. (Hypertension 4: 853-863, 1982) KEY WORDS • blood pressure • natural behavior • conditioned emotional responses • spontaneously hypertensive rats • classical conditioning A RTERIAL pressure (AP) changes associated with aversive emotional arousal are exaggerated in spontaneously hypertensive rats (SHRs) when compared with strain-matched WistarKyoto controls (WKYs): during the acute or chronic presentation of aversive stimuli, such as electric foot-

Sympathetic nerves and adrenal medulla: contributions to cardiovascular-conditioned emotional responses in spontaneously hypertensive rats.

“…4 In brief, at the time of conditioning, each rat was removed from its home cage and placed in a standard conditioning chamber enclosed by a sound attenuating cubicle. After 5 minutes of acclimation to the chamber, the tone conditioned emotional stimulus (CES) (800 Hz, 80 db, 10 sec) was presented through a speaker mounted in the chamber 40 times at an average intertrial interval of 150 seconds (range = 100-200 sec).…”

“…The elevated HR is consistent with our earlier finding that resting HR is elevated in conditioned SHR relative to unconditioned SHR, which did not differ from WKY. 4 …”

“…'~3 We have observed that during conditioned emotional (fear) responses and during drinking, but not during feeding, grooming, or exploration, greater increases in MAP occur in SHR than in Wistar-Kyoto (WKY) rats. 4 In the present study we have sought to determine the peripheral efferent mechanisms through which the exaggerated MAP changes associated with conditioned emotional responses in SHR are expressed. We have examined SHR and WKY subjected to classical fear conditioning and chronically implanted for computerassisted recording of MAP and heart rate (HR) while awake and unrestrained.…”

Paradoxical Hormonal and Behavioral Responses to Hypothyroid and Hyperthyroid States in the Wistar–Kyoto Rat

“…The WKY rat differs from the SHR not only with respect to resting blood pressure but it also displays smaller stress-induced increases in plasma cathecholamines (McCarty et al 1987), heart rate, and blood pressure (LeDoux et al 1982;Rettig et al 1986;Knardahl and Hendley 1990). In contrast, WKYs show larger endocrine and behavioral responses to stress compared not only to SHRs but also to Wistars and several other rat strains (Pare and Redei 1995).…”

Spontaneously hypertensive rats exhibit altered cardiovascular and neuronal responses to muscle contraction

“…In contrast, a similar yet independent study demonstrated no difference in basal firing rates of VLM neurons between SHRs and WKYs (Sun & Guyenet, 1986). However in the latter study, the relationship between discharge rate of ventrolateral medullary neurons and arterial pressure was shifted towards higher pressures in SHRs compared to WKYs (Sun & Guyenet, 1986 (Hallback, 1975;LeDoux et al 1982;Yamanioto et al 1987). The specific role of the central nervous system in generating the hyperresponsiveness to various autonomic stressors is relatively unknown.…”