ASGSB 1999 Annual Meeting Abstracts

GRAVITY RECEPTOR POLARIZATION VECTORS EVIDENCED BY LINEAR VESTIBULAR EVOKED POTENTIALS (VsEP). T.A. Jones, P. Bell, and S.M. Jones. Departments of Surgery and Physiology, University of Missouri School of Medicine, Columbia.

The utricle and saccule are gravity receptor organs of the vestibular system. These receptors rely on a high-density otoconial membrane to detect linear acceleration and the position of the cranium relative to Earth’s gravitational vector. The linear VsEP has been shown to be an effective noninvasive functional test specifically for otoconial gravity receptors (Jones et al., 1999. Hearing Research, In Press). Moreover, there is some evidence that the VsEP can be used to independently test utricular and saccular function (Jones et al, 1998. Hearing Research (121)161-169; Taylor et al., 1997. Assoc. Res. Otolaryngol. Abs). Here we characterize compound macular polarization vectors for the utricle and saccule in hatchling chickens. Pulsed linear acceleration stimuli were presented in two axes, the cranio-caudal (CC, ±Z axis) to isolate the saccule, and the interaural (IA, ±Y axis) to isolate the utricle. Eighth nerve components of the VsEP were scored (P1, P1-N1). Traditional signal averaging was used to resolve responses recorded from the surface of the skull (gain 200K, 300-3KHz bandwidth, 256 responses averaged). Cochleas and maculae lagena were surgically removed in all animals. Gravity receptor responses exhibited clear preferences for one stimulus direction in each axis. With respect to each utricular maculae, lateral translation in the IA axis produced maximum ipsilateral response amplitudes with substantially greater amplitude-intensity slopes and intercepts than medially directed movement. Downward caudal motions in the CC axis produced substantially larger response slopes and intercepts. These data confirm and extend earlier work and support the hypothesis that maculae saccule and utricle can be selectively evaluated using the linear VsEP.

(Supported by NASA: NAG 5-4607 and NAGW 3910.)

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