Orientation-specific maturation time and frequency responsiveness of utricle-related central neurons

Abstract

To determine the age when gravity-related horizontal orientations are first encoded in the vestibular nucleus (VN), Fos immuno-/ hybridization histochemistry was used in conscious rats (P5- adult) subjected to horizontal linear acceleration. In the medial (MV) and spinal vestibular nuclei, Fos neurons activated by transverse stimulation were first found at P7 whereas those by antero-posterior stimulation were from P9. In other vestibularrelated nuclei, neurons responding to the two directions showed no temporal disparity and Fos expression was observed between P9 and P14. Critical maturation times for the coding of horizontal head movement therefore differ among various nuclei. Neuronal distribution differed with stimulus frequency. The low but even distribution of Fos neurons observed at low acceleration contrasted the significant clustering found in the lateral part of MV at high acceleration. This shows the occurrence of histological segregation of otolith-related frequency information within the VN. [Supported by HKRGC]