Responsiveness of thalamic neurons to rotational and translational motions in the horizontal plane

Abstract

To identify the thalamic region(s) that relays vestibular signals towards the cerebral cortex, immunostaining was performed on rats that were subjected to rotational or translational stimulation along the horizontal plane. Neuronal activation was defined by Fos expression. Both canal- and otolith-related neurons were found in the subparafascicular nucleus(SPF). Fos-immunoreactive(ir) neurons activated by horizontal canal or otolithic inputs were intermingled throughout the SPF, with a higher number in its middle portion. Stationary and labyrinthectomized controls showed only sporadically scattered Fos-ir neurons in the SPF. Given that vestibular inputs from both ears converge at the vestibular nucleus, experiments were designed to determine whether the vestibular thalamus on one side receive input from both inner ears. In rats with unilateral labyrinthectomy for 2 weeks, symmetric Fos pattern was found on both sides of the SPF after stimulations. Our findings suggest that horizontal head movement signals arising from one ear are processed in both sides of the SPF.