Vestibular control of sympathetic activity

Abstract

It has been proposed that a vestibular reflex originating in the otolith organs and other body graviceptors modulates sympathetic activity during changes in posture with regard to gravity. To test this hypothesis, we selectively stimulated otolith and body graviceptors sinusoidally along different head axes in the coronal plane with off-vertical axis rotation (OVAR) and recorded sympathetic efferent activity in the peroneal nerve (muscle sympathetic nerve activity, MSNA), blood pressure, heart rate, and respiratory rate. All parameters were entrained during OVAR at the frequency of rotation, with MSNA increasing in nose-up positions during forward linear acceleration and decreasing when nose-down. MSNA was correlated closely with blood pressure when subjects were within +/-90 degrees of nose-down positions with a delay of 1.4 s, the normal latency of baroreflex-driven changes in MSNA. Thus, in the nose-down position, MSNA was probably driven by baroreflex afferents. In contrast, when subjects were within +/-45 degrees of the nose-up position, i.e., when positive linear acceleration was maximal along the naso-ocipital axis, MSNA was closely related to gravitational acceleration at a latency of 0.4 s. This delay is too short for MSNA changes to be mediated by the baroreflex, but it is compatible with the delay of a response originating in the vestibular system. We postulate that a vestibulosympathetic reflex, probably originating mainly in the otolith organs, contributes to blood pressure maintenance during forward linear acceleration. Because of its short latency, this reflex may be one of the earliest mechanisms to sustain blood pressure upon standing.

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“…In humans, caloric vestibular stimulation (Cui et al, 1997) and head pitch (Ray and Carter, 2003), as well as GVS (Bent et al, 2006; Grewal et al, 2009; James and Macefield, 2010) influence SNA. Similarly, activation of the otolith organs using OVAR produces an increase in muscle SNA in-phase with the head-up tilt component and a decrease corresponding to the head-down component (Kaufmann et al, 2002). Moreover, linear acceleration (which specifically stimulates the otolith organs) causes transient changes in blood pressure (Cui et al, 1999) that are attenuated in patients with bilateral vestibular deficits (Yates et al, 1999).…”

Vestibular Activation Habituates the Vasovagal Response in the Rat

“…The sinusoidal galvanic vestibular stimulation (sGVS) was generated by a computer-controlled stimulator (32–34, 41, 42). Currents were delivered via sub-dermal needle electrodes placed in the skin over the mastoids.…”

The function of the autonomic nervous system during spaceflight

“…Studies of neuro-vestibular function both during and after spaceflight have demonstrated abnormal otolith-ocular reflexes and spatial perception both during adaptation to microgravity as well as re-adaptation after return to Earth (8). In addition to its well-established role in spatial orientation, gaze control, and neuromotor function, recent work has demonstrated the presence of vestibulo-autonomic reflexes (32, 33, 36, 56, 57, 66). These excitatory vestibulo-autonomic reflexes are the earliest stimulation of sympathetic activity in response to changes of body position.…”