The vestibulo-sympathetic reflex (VSR) increases blood pressure (BP) upon arising to maintain blood flow to the brain. The optimal directions of VSR activation and whether there are changes in heart rate (HR) are still not clear. This was studied with manually-driven translations, which had pulses and oscillatory linear accelerations of 0.2-2.5 g along the naso-occipital, interaural, and dorso-ventral axes in Isoflurane-anesthetized male, Long-Evans rats. BP and HR were recorded with intra-aortic sensors and accelerationd with 3-D linear accelerometer. Lineard regressions of changes in BP as a function of accelerations along the upward, downward and forward axes had slopes of ≈3-6 mmHg*g-1 (p<0.05). Lateral and backward accelerations did not produce consistent changes in BP. Thus, upward, downward, and forward translations were the directions that significantly altered BP. Heart rate (HR) was unaffected by these translations. The VSR sensitivity to oscillatory forward-backward translations was ≈6-10 mmHg*g-1 at frequencies of ≈0.1 Hz (0.2g) decreasing to zero at frequencies above 2 Hz (1.8g). Upward 70° tilts of an alert rat increased BP by 9 mmHg*g-1. The similarity in BP induced in alert and anesthetized rats indicates that anesthesia had not reduced the VSR sensitivity, which may be relatively insensitive to levels of alertness. The lack of effect on HR in the anesthetized rat indicates the VSR is likely to cause changes in BP through modification of peripheral vascular resistance, directed towards the cardiovascular system, in contrast to the responses in the alert state, which produce sweating, motion sickness, and alteration in BP and HR.
- Blood Pressure
- Heart Rate
- linear acceleration
- Copyright © 2016, Journal of Neurophysiology