Teeth Clenching and Positive Acceleration-Induced Cerebral Arterial Hypotension in Rats

Abstract

High positive acceleration (+Gz) stress is known to cause cerebral hypoperfusion, resulting in brain insults. Muscular contraction is reported to induce a pressor response. The effects of teeth clenching on cerebral hypoperfusion were examined. The masseter muscle of anesthetized Sprague-Dawley rats was electrically stimulated to cause maximum clenching of the teeth. Arterial pressure at the level of the brain (APBr), heart rate, and central venous pressure were measured when rats were exposed to +1.5 Gz by using a centrifuge without an anti-C system. Acceleration of +1.5 Gz decreased APBr by 18.3 +/- 2.0 mmHg, which was reduced to 1.9 +/- 2.0 mmHg by masseter muscle contraction, but was not reduced by femoral muscle contraction. Stimulation of the masseter muscle but not the femoral muscle induced a pressor response of 11.8 +/- 2.1 mmHg, which was eliminated by dantrolene, a postsynaptic skeletal muscle relaxant. When masseter contraction was blocked by dantrolene, masseter stimulation did not reduce cerebral hypotension in the presence of +1.5-Gz acceleration (delta 18.9 +/- 2.6 mmHg). Our results suggest that teeth clenching induced a pressor response that prevented +Gz-induced cerebral hypotension, which suggests the possible development of a new anti-G method.