Anxiety-related behavior and biogenic amine pathways in the rat following bilateral vestibular lesions

Many clinical studies have reported that patients with vestibular disorders have a high rate of anxiety disorders and depression. By contrast, there have been few studies of affective behavior in animals following vestibular lesions. Recent studies using the vestibular impaired ci2/ci2 mutant rat strain have shown that rather than preferring the closed arm of the elevated plus maze, as rats would normally, they make more open-arm entries and spend more time on the open arms compared to wild-type controls. In the open-field maze, rather than preferring to explore the outer zone near the walls ("thigmotaxis"), ci2/ci2 rats prefer the inner region of the maze. In rats with bilateral vestibular deafferentation (BVD), similar results were obtained. Compared to sham controls, at 3 and 5 months post-op, BVD rats spent more time on the open arms of the elevated plus maze, more time in the inner zone of the open-field maze, and failed to learn inhibitory avoidance in the elevated T maze. They did not display increased hyponeophagia; however, they did exhibit a decrease in social interaction. Blood corticosterone levels were not significantly different from sham controls. At 6 months post-op, BVD rats demonstrated circumscribed changes in the expression of tyrosine hydroxylase, the serotonin transporter, and tryptophan hydroxylase, in various regions of the medial temporal and frontal lobes, suggesting changes in biogenic amine pathways.