HABITUATION OF AIRPUFF-ELICITED CARDIOVASCULAR-RESPONSES IN THE SPONTANEOUSLY HYPERTENSIVE RAT

Repeated delivery of fast rise-time acoustic stimuli elicit cardiac ch anges in humans that reflect startle, orienting, and defense responses . To test the hypothesis that fast rise-time stimuli produce these res ponses in the rat, we evaluated magnitude, latency, and habituation of cardiovascular responses to brief ah-puff stimuli in normotensive rat s. We also evaluated airpuff-elicited cardiovascular responses in spon taneously hypertensive rats. In addition to a robust increase in blood pressure, airpuffs produced one or more of three sequential heart-rat e responses in normotensive rats-first, short-latency tachycardia (lat ency 0.8 s), then rapidly habituating bradycardia (latency 2.2 s), the n long-latency tachycardia (latency 3.5 s)-which likely reflected star tle, orienting, and defense responses, respectively. Airpuffs rarely p roduced bradycardia in hypertensive rats, suggesting that this strain does not appropriately orient to sensory stimuli. In addition, compare d to normotensive rats, hypertensive rats exhibited greater between-se ssion habituation of long-latency tachycardia and blood pressure incre ases. This finding contrasts with the Folkow hypothesis, which assumes that, in subjects with a genetic predisposition to develop hypertensi on, sympathetic responses will remain exaggerated after repeated stimu lation, thus contributing to thickening of the arterial vasculature.