BDNF-mediated modulation of developing vestibular circuitry impacts on spatial learning

Abstract

 Vestibular information arising from the vestibular end organs, the otolith organs and the semi-circular canals, are crucial in providing sensory cues for spatial orientation. Labyrinthectomised rats showed impairments in spatial cognition. Brain-derived neurotrophic factor (BDNF) is known to play key roles in neural plasticity. It has been demonstrated BDNF contributes to the acquisition of graviceptive behaviour by modulating the maturation of GABAergic transmission within the developing vestibular network. However, the involvement of BDNF in spatial learning remains unclear. In this study, we investigated the effects of neonatal treatment of the vestibular nucleus (VN) with BDNF on the acquisition of spatial navigation in rats. With the use of dead reckoning as the behavioural indicator, we observed that rats pre-treated with BDNF on the first postnatal day exhibited impairments in spatial navigation at the adult stage. In the light probe test where visual cues are available, BDNF-treated rats required significantly longer time to search for the food pellet when compared with the sham controls. In the dark probe test where only idiothetic cues are available, BDNF-treated rats showed difficulties in directly returning to the home cage. In the new location test where a conflict between allothetic and idiothetic cues is induced, the BDNF-treated rats took significantly longer time to return to the home cage via a circuitous path. These findings indicate that BDNF modulates the central vestibular circuitry that impacts on spatial learning.