Postnatal expression of glutamate receptor subunits in rat inferior olivary neurons responsive to horizontal linear acceleration

Abstract

To investigate the developmental profile of ionotropic glutamate receptors in functionally activated otolith neurons within the inferior olive (IO), combined immuno- and hybridization histochemistry experiments were performed in conscious SpragueDawley rats (P9 to adult) that were subjected to sinusoidal linear acceleration along the horizontal plane. Neuronal activation was defined by the expression of Fos protein in cell nuclei. Only a few sporadically scattered Fos-labeled neurons were found in labyrinthectomized and static controls. During postnatal development, c-fos expression in subnuclei of the IO (viz. DMCC, IO ) was not observed until P11–13. Evidence of a gravity-related topographic spatial organization was found in these IO subnuclei along its rostrocaudal dimension. In DMCC, neurons responded only to interaural stimulation. In caudal IO , though neurons responsive to antero-posterior and interaural stimulations could both be found at a young age, only those responsive to antero-posterior movement persisted in number into the adult. In contrast, rostral IO neurons that were responsive to either direction increased with age, reaching the adult pattern around 1 month-old. In each age group, about 95–98% of Fos-labeled neurons responsive to horizontal interaural or antero-posterior stimulation also co-expressed NMDA (NR1, NR2A, NR2B) or AMPA (GluR2/3) receptor subunits. While the granule density of NR2B mRNAs decreased from P11, that of both NR1 and NR2A mRNA increased from P11 to P14 and then decreased afterwards. These findings suggest that dynamic changes in the expression of glutamate receptor subunits contribute to the maturation of otolith-related IO neurons in the coding of horizontal head movements. Acknowledgement: Supported by HK RGC.