Postnatal expression of AMPA receptor subunits and glutamate transporter EAAC1 in saccule-related vestibular nuclear neurons in rats

Abstract

To investigate the maturation profile of AMPA receptor subunits (GluR1-4) and the glutamate transporter (EAAC1) in saccule-related neurons within the vestibular nucleus and its subgroups, immunohistochemcial experiments were performed in Sprague-Dawleys rats (P4–adults). All conscious rats were subjected to sinusoidal linear acceleration along the vertical plane, thereby activating the saccule of the inner ear. Controls showed only sporadically scattered Fos-labeled neurons in the vestibular nuclei, confirming the saccular origin of c-fos expression. Functionally activated Fos-labeled neurons expressing either EAAC1 or AMPA receptor subunits were first identified at P7 in medial vestibular nucleus (MV), spinal vestibular nucleus (SpV) and group x. Such double-labeled neurons were however not observed in group y until P9. Despite the increase in Fos-labeled neurons with age, Fos/EAAC1 double-labeled neurons in SpV, MV, group x, and group y progressively decreased from 80% of Fos-labeled neurons to 30% in the adult. While 80% of the neurons in MV, SpV, and group x co-expressed Fos and AMPA receptor subunits in all age groups, those in group y decreased after the second postnatal week, reaching 10-30% in the adult. Our findings suggest that neurons in different vestibular subnuclei utilize different postsynaptic mechanisms to process gravity-related vertical spatial information. Supported by HK RGC