Abstract
Vestibular dysfunction in humans is associated with a high rate of anxiety and depressive disorders. Although this may first appear to be due to the burden of living with a balance disorder, there is reason to think that there are deeper connections between the vestibular system and emotion. For example, there are important connections between the vestibular nucleus and the limbic system, and the vestibular system is known to regulate autonomic function. To the contrary, rats with bilateral vestibular lesions seem to show similar behaviours to rats with reduced anxiety, remaining in the open arms of the elevated plus and T mazes and the inner zone of the open field maze, for longer periods of time than controls. Since spatial deficits have been consistently observed in humans and rats with vestibular dysfunction, it is possible that the behaviours of bilateral vestibular deafferentated (BVD) rats in anxiety tasks are altered due to impaired spatial memory. Therefore, to investigate whether BVD rats are truly experiencing anxiety or whether spatial deficits are altering their behaviours, they were given the anxiolytic drug, buspirone, and the anxiogenic drug, FG-7142 and tested in a range of anxiety and spatial tasks. Twenty male Wistar rats were divided into BVD and sham groups (n = 10 per group). One month post-surgery, the animal were tested in the open field maze (OFM), elevated plus maze (EPM), and the elevated T-maze (ETM) to measure the level of anxiety, and in the spatial T-maze (STM) alteration task to assess their spatial learning and memory performance. A single dose of buspirone (0.3 mg/kg), FG-7142 (5 mg/kg) or respective vehicle was administered 30 min before each behavioural task using a 4 x 4 Latin square design. During the pre-drug trial, BVD rats spent more time in the inner zone of the OFM, spent similar percentage of time in the open arms and a similar number of open arm entries in the EPM, and had an impaired learnt inhibitory avoidance response in the ETM compared to sham rats during the pre-drug trials. Additionally, BVD rats were significantly impaired in spatial memory in the STM alteration task. However, neither drug treatment altered the anxiety-related behaviours in either BVD or sham animals, thereby, making it difficult to deciper if BVD rats were experiencing anxiety. The lack of drug effect in the STM alteration task revealed that spatial deficits in BVD rats might not be caused through anxiety. However, buspirone altered the exploratory behaviour of both BVD and sham rats in the OFM and in the EPM, therefore, suggesting a complex involvement between the vestibular system, hippocampal function and anxiety. Further studies are required to investigate the association between the ventral hippocampus and anxiety in BVD rats.