Sympathetically-Induced Changes in the Spindle Afferent Response to Vibratory Stimuli Eliciting the TVR in Rabbit Jaw Closing Muscles

Abstract

Sympathetic nervous system activation can influence the stretch reflex in the jaw closing muscles of decerebrate rabbits through an action exerted at the peripheral level (Grassi, Deriu, Artusio & Passatore, 1993; Grassi, Deriu & Passatore, 1993). In particular, stimulation of the cervical sympathetic nerve (CSN), at frequencies within the physiological range, induces a marked depression, often preceded by a transient enhancement, of both the jaw jerk and the tonic vibration reflex (TVR) in the jaw closing muscles. This effect is mainly mediated by α₁-adrenergic receptors, though the noradrenaline co-transmitter NPY may make a small contribution. Indirect evidence supports the idea that the decrease in the stretch reflex induced by sympathetic stimulation is due to an action on muscle spindle afferents exerted by adrenergic mediators. We have tested this hypothesis by studying the sympathetically-induced changes in the spindle afferent response to vibratory stimuli eliciting the TVR.