Abstract
Previous studies conducted in our laboratory demonstrated that the vestibular system plays a significant role in controlling arterial pressure (AP) in conscious rats during transient conditions of microgravity. The vestibular system is known to be highly plastic, and on exposure to a different gravitational environment, the sensitivity of the vestibular system-mediated AP response might be altered. To test this hypothesis, rats were maintained in 3-G or a normal 1-G environment for 2 weeks, and the AP responses to free drop-induced microgravity were determined. In 1-G rats, the microgravity increased the AP by 37 ± 3 mmHg; this fluctuation in AP was significantly attenuated by vestibular lesion (VL) (24 ± 3 mmHg) or body stabilization (29 ± 2 mmHg). Thus, the microgravity-induced pressor response was mediated by both the vestibular and nonvestibular systems; the input of the latter system was blocked by body stabilization. In the 3-G rats, the pressor responses were significantly suppressed compared to those in the corresponding 1-G rats, i.e., the AP increased by 24 ± 2 mmHg in freely moving 3-G rats, by 10 ± 4 mmHg in 3-G rats with VL, and by 13 ± 4 mmHg in stabilized 3-G rats. Furthermore, there was no difference between the 1-G and 3-G rats in terms of the pressor response induced by stressors such as a loud noise or an air jet. These results indicate that pre-exposure to 3-G for 2 weeks induces plasticity in both vestibular- and nonvestibular-mediated AP responses to microgravity. [J Physiol Sci. 2007;57 Suppl:S196]
