Abstract
Background: Due to the paired structure of two labyrinths, their neural communication is conducted through the interconnected commissural pathway. Using the tight link, the neural responding characteristics are formed in vestibular nucleus, and these responses are initially generated by the mechanical movement of the hair cells in the semicircular canals and otoliths. Although the mechanism to describe the neuronal responses to the head movements was evident, few direct experimental data were provided, especially the directional preference of otolith-related neurons as one of critical responses to elucidate the function of the neurons in vestibular nucleus (VN). Experimental Approach: The directional preference of otolith-related neurons was investigated in VN. Also, a chemically induced unilateral labyrinthectomy (UL) was performed to identify the origin of the directional preference. For the model evaluation, static and dynamic behavioral tests were performed. Following the evaluation, an extracellular neural activity was recorded for the neuronal responses to the horizontal head rotation and the linear head translation. Results: Seventy seven neuronal activities were recorded from thirty SD rats (270-450 g, male), and total population was divided into three groups; left UL (20), sham (35), right UL (22). Based on the directional preference, two sub-groups were again classified as contra- and ipsi-preferred neurons. There was no significance in the number of those sub-groups (contra-: 15/35, 43%; ipsi-: 20/35, 57%) in the sham (p=0.155). However, more ipsi-preferred neurons (19/22, 86%) were observed after right UL (p=6.056×10-5) while left UL caused more contra-preferred neurons (13/20, 65%) (p=0.058). In particular, the convergent neurons mainly led this biased difference in the population (ipsi-: 100% after right UL & contra-: 89% after left UL) (p<0.002). Conclusion: The directional preference was evenly maintained under a normal vestibular function, and its unilateral loss biased the directional preference of the neurons, depending on the side of lesion. Moreover, the dominance of the directional preference was mainly led by the convergent neurons which had the neural information related with head rotation and linear translation.