Maturation profile of inferior olivary neurons expressing ionotropic glutamate receptors in rats: role in coding linear accelerations.
Using sinusoidal oscillations of linear acceleration along both the horizontal and vertical planes to stimulate otolith organs in the inner ear, we charted the postnatal time at which responsive neurons in the rat inferior olive (IO) first showed Fos expression, an indicator of neuronal recruitment into the otolith circuit. Neurons in subnucleus dorsomedial cell column (DMCC) were activated by vertical stimulation as early as P9 and by horizontal (interaural) stimulation as early as P11. By P13, neurons in the β subnucleus of IO (IOβ) became responsive to horizontal stimulation along the interaural and antero-posterior directions. By P21, neurons in the rostral IOβ became also responsive to vertical stimulation, but those in the caudal IOβ remained responsive only to horizontal stimulation. Nearly all functionally activated neurons in DMCC and IOβ were immunopositive for the NR1 subunit of the NMDA receptor and the GluR2/3 subunit of the AMPA receptor. In situ hybridization studies further indicated abundant mRNA signals of the glutamate receptor subunits by the end of the second postnatal week. This is reinforced by whole-cell patch-clamp data in which glutamate receptor-mediated miniature excitatory postsynaptic currents of rostral IOβ neurons showed postnatal increase in amplitude, reaching the adult level by P14. Further, these neurons exhibited subthreshold oscillations in membrane potential as from P14. Taken together, our results support that ionotropic glutamate receptors in the IO enable postnatal coding of gravity-related information and that the rostral IOβ is the only IO subnucleus that encodes spatial orientations in 3-D.
Department of Physiology, LKS Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Hong Kong, People's Republic of China.
Chuan
C
Li
Lei
L
Han
Chun-Wai
CW
Ma
Suk-King
SK
Lai
Chun-Hong
CH
Lai
Daisy Kwok Yan
DK
Shum
Ying-Shing
YS
Chan
D000054:Acceleration; D000818:Animals; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D009847:Olivary Nucleus / Q000166:cytology / Q000196:embryology*; D009949:Orientation / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D058468:Receptors, Ionotropic Glutamate / Q000378:metabolism*
D058468:Receptors, Ionotropic Glutamate