Repeated delivery of fast rise-time acoustic stimuli elicit cardiac changes in humans that reflect startle, orienting, and defense responses. To test the hypothesis that fast rise-time stimuli produce these responses in the rot, we evaluated magnitude, latency, and habituation of cardiovascular responses to brief airpuff stimuli in normotensive rats. We also evaluated airpuff-elicited cardiovascular responses in spontaneously hypertensive rats. In addition to a robust increase in blood pressure, airpuffs produced one or more of three sequential heart-rate responses in normotensive rats-first, short-latency tachycardia (latency 0.8 s), then rapidly habituating bradycardia (latency 2.2 s), then long-latency tachycardia (latency 3.5 s) - which likely reflected startle, orienting, and defense responses, respectively. Airpuffs rarely produced bradycardia in hypertensive rats, suggesting that this strain does not appropriately orient to sensory stimuli. In addition, compared to normotensive rats, hypertensive rats exhibited greater between-session habituation of long-latency tachycardia and blood pressure increases. This finding contrasts with the Folkow hypothesis, which assumes that, in subjects with a genetic predisposition to develop hypertension, sympathetic responses will remain exaggerated after repeated stimulation, thus contributing to thickening of the arterial vasculature.
- Defense reflex
- Orienting reflex
- Somatosympathetic response
- Spontaneously hypertensive rat
- Startle reaction