Different expression pattern of NMDA and AMPA glutamate receptor subunits in group y neurons responsive to vertical linear acceleration

Abstract

AMPA receptors mediate fast voltage-independent synaptic response while NMDA receptors are crucial in modulating the efficiacy of synaptic transmission. To determine the relative importance of NMDA and AMPA glutamate receptors in the function of central vestibular neurons, the distribution of these receptors in functionally activated neurons was assessed. To achieve this, adult Sprague–Dawley rats were subjected to sinusoidal vertical linear acceleration that activated the saccules in the inner ear. Neuronal activation was denoted by the expression of Fos protein; Fos-positive neurons were evaluated also for co-localization with NMDA or AMPA receptor subunits. Sporadic Fos-immunoreactivity (For-ir) etected in neurons of the vestibular nuclei of both stationary controls and labyrinthectomized controls were considered as background expression. In normal rats subjected to the vertical stimulation, Fos-ir neurons were abundant in the spinal vestibular nucleus (SpVe) and group × subnucleus. Lower numbers were found in the medial vestibular nucleus (MVe) and group y subnucleus while only a few were found in the lateral vestibular nucleus and superior vestibular nucleus. Double-immunofluorescence study indicated that nearly 80% of Fos-ir neurons in the SpVe, MVe and group x expressed either NMDA (NR1, NR2A-B) or AMPA (GluR1–4) glutamate receptor subunits. In contrast, nearly 70% Fos-ir neurons in group y expressed NR1 or NR2A-B, while only 10–30% of the Fos-ir neurons expressed GluR1, 2, 2/3 or 4. Such a difference in the expression pattern of glutamate receptor subunits between saccule-related group y neurons and neurons of other vestibular subnuclei suggests that these neurons differ in postsynaptic processing of spatiotemporal information associated with vertical head movements relative to gravity. Acknowledgement: Supported by HK RGC grant.