EPV 16. Spatial orientation deficit in a rat model of acute bilateral vestibulopathy

Background and aim Characterisation of the spatial orientation and locomotion behaviour after bilateral vestibular labyrinthectomy in the rat. Methods Ten Sprague-Dawley rats underwent a bilateral labyrinthectomy (BL) by transtympanic injection of bupivacaine and arsenilate, 10 rats received a bilateral middle-ear injection of saline (sham) as a control group. Behavioural testing was performed 1 day before and at days 1, 2, 3, 7, 15, 30 and 60 after BL/sham injection as follows: (1) analysis of spatial exploration behaviour in a square open field by the Noldus EthoVision System; (2) quantitative analysis of locomotion pattern by the Noldus CatWalk System. Results At all time points, rats of the sham group showed a strategically distributed exploration pattern with a preferred movement along the lateral edges and a preferred position in the corners of the open field. The exploration behaviour was guided by head movements in the lateral direction. In contrast, rats of the BL group presented with a omnidirectional exploration strategy and stayed in the central parts of the open field significantly longer. This exploration pattern did not change over time. Lateral head and body turns were reduced relative to controls. Mean velocity during exploration in the open field was significantly higher in the BL than in the sham group until day 60, whereas mean velocity during CatWalk measurement adapted between groups after day 15 post BL/sham injection. Conclusions A bilateral vestibular lesion induces a persistent deficit in spatial exploration behaviour. The pathophysiological basis seems to be a disturbance of head direction cells in the hippocampal formation due to the lack of vestibular input.