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Straka, Hans ORCID: 0000-0003-2874-0441; Beraneck, M.; Rohregger, M.; Moore, L. E.; Vidal, P. P.; Vibert, N. (2004): Second-order vestibular neurons form separate populations with different membrane and discharge properties. In: Journal of Neurophysiology, Vol. 92, No. 2: pp. 845-861
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Abstract

Membrane and discharge properties were determined in second-order vestibular neurons (2degreesVN) in the isolated brain of grass frogs. 2degreesVN were identified by monosynaptic excitatory postsynaptic potentials after separate electrical stimulation of the utricular nerve, the lagenar nerve, or individual semicircular canal nerves. 2degreesVN were classified as vestibulo-ocular or -spinal neurons by the presence of antidromic spikes evoked by electrical stimulation of the spinal cord or the oculomotor nuclei. Differences in passive membrane properties, spike shape, and discharge pattern in response to current steps and ramp-like currents allowed a differentiation of frog 2degreesVN into two separate, nonoverlapping types of vestibular neurons. A larger subgroup of 2degreesVN (78%) was characterized by brief, high-frequency bursts of up to five spikes and the absence of a subsequent continuous discharge in response to positive current steps. In contrast, the smaller subgroup of 2degreesVN (22%) exhibited a continuous discharge with moderate adaptation in response to positive current steps. The differences in the evoked spike discharge pattern were paralleled by differences in passive membrane properties and spike shapes. Despite these differences in membrane properties, both types, i.e., phasic and tonic 2degreesVN, occupied similar anatomical locations and displayed similar afferent and efferent connectivities. Differences in response dynamics of the two types of 2degreesVN match those of their pre- and postsynaptic neurons. The existence of distinct populations of 2degreesVN that differ in response dynamics but not in the spatial organization of their afferent inputs and efferent connectivity to motor targets suggests that frog 2degreesVN form one part of parallel vestibulomotor pathways.