Increased Sensitivity to Arousal in Spontaneously Hypertensive Rats is Partially Dependent Upon the Amygdala

Abstract

This study was designed to determine the effects of behavioral arousal on baroreflex regulation of heart rate in stroke-prone SHR (spSHR) and to ascertain whether the integrity of the amygdala is necessary to mediate these effects. Heart rate responses to phenylephrine-induced increases in arterial pressure were used as an index of baroreflex sensitivity (BRS). spSHR had reduced BRS compared to WKR. Electrical stimulation of the amygdala suppressed BRS in conscious rats only at intensities that elicited behavioral arousal. When normalized for control bradycardic responses, the spSHR demonstrated a greater suppression of BRS upon amygdalar stimulation than Wistar-Kyoto rats (WKR). Confrontation with a mouse, used to elicit behavioral arousal, attenuated BRS in both spSHR and WKR. Ablation of the central nucleus of the amygdala and adjacent tissue prevented confrontation-induced suppression of BRS both in WKR and spSHR. These data suggest that spSHR are more sensitive to suppression of BRS due to arousal elicited by stimulation of the amygdala. Furthermore, the amygdala is necessary for arousal-induced suppression of BRS in WKR and spSHR.

Key Words:

• stroke-prone spontaneously hypertensive rat
• cardiac index of baroreflex sensitivity
• heart rate
• behavioral arousal