Role of the Spinocerebellum in Adaptive Gain Control of Cat's Vestibulospinal Reflex

Abstract

In decerebrate cats, a 3-h period of sustained roll tilt of the head (at 0.15 Hz, ± 10°) leading to selective stimulation of labyrinth receptors, associated with a synchronous roll tilt of the body (at 0.15 Hz, ± 12.5°), leading to 2.5° out-of-phase neck rotation produced an adaptive increase in gain of the vestibulospinal reflex (VSR) elicited by roll tilt of the animal at 0.15 Hz, ± 10°. This increase reached the maximum at the end of the third h of stimulation and persisted unmodified during the first h after stimulation. Microinjection into zone B of the cerebellar anterior vermis of the GABA-A agonist muscimol (0.25 μl at 8 μg/μl saline), producing only a slight or negligible depression of the VRS gain in non-adaptive conditions, prevented the occurrence of the adapted increase in gain of the VSR following a 3-h period of sustained head-body rotation. Moreover, intravermal injection of the GABA-A agonist muscimol or the GARA-B agonist baclofen (0.25μl at 8 or 2μg/μl saline. respectively) suppressed the already adapted VSR gain. It is postulated that the adaptive increase in gain of the VSR following a sustained neck-vestibular stimulation depends on plastic changes which affect the Purkinje cells of the cerebellar anterior vermis.

Key Words:

• vestibulospinal reflex
• adaptation
• cerebellar cortex
• GABA agonists
• decerebrate cat