Can the Sympathetic Nervous System Activation Contribute to “Context-Related” Modulations of the Stretch Reflex?
Sympathetic stimulation at frequencies within the physiological range, markedly depresses both the jaw jerk and the tonic vibration reflex in the jaw closing muscles of precollicular decerebrate rabbits. In particular, bilateral stimulation of the cervical sympathetic trunk reduces by 60–90% the force reflexly produced by the jaw closing muscles and strongly decreases or suppresses EMG activity on both sides. These effects are mainly mediated by α-adrenergic receptors, a modest contribution of the noradrenaline co-transmitter neuropeptide Y to the late component of the response not being excluded. In addition, the sympathetically-induced depression of the stretch reflex cannot be attributed to an action, direct or secondary to vasomotor changes, exerted by the adrenergic mediator either on jaw muscles contraction or on the central nervous structures mediating the studied reflexes.
Data reported in the present paper suggest that the sympathetic nervous system can influence the stretch reflex in the jaw closing muscles through an action exerted at the peripheral level, probably on spindle afferent information. The possible functional role of such sympathetic effect is discussed within the context of the numerous modulatory actions exerted on the stretch reflex gain by central command and sensory information during intentional movements.
KeywordsDepression Coherence Noradrenaline Catecholamine Acetylcholine
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