The D2 dopamine receptor and locomotor hyperactivity following bilateral vestibular deafferentation in the rat

Rats and mice with bilateral vestibular loss exhibit dramatic locomotor hyperactivity and circling behaviours, which to date cannot be explained. Dysfunction of the striatal dopaminergic system is responsible for a number of known movement disorders and the D2 dopamine receptor is known to be implicated. Therefore, it is possible that changes in striatal function are responsible for locomotor hyperactivity and circling following bilateral vestibular lesions. The aim of this study was to investigate the effects of the D2 receptor antagonist, eticlopride (0.02, 0.04 and 0.06 mg/kg; s.c.), on locomotor behaviour in rats at 5 months following bilateral vestibular deafferentation (BVD), using an open field maze. The levels of the D2 receptor protein in the striatum were measured at 1 and 6 months post-BVD using western blotting. BVD rats exhibited locomotor hyperactivity and circling, which eticlopride did not eliminate. However, BVD rats did exhibit a decreased response to the inhibitory effect of eticlopride compared to sham controls at the 0.02 mg/kg dose. There were no changes in the amount of the D2 receptor in the striatum at 1 or 6 months post-BVD; however, D2 receptor levels were significantly higher on the right side than the left in both sham and BVD animals. These results suggest that locomotor hyperactivity and circling behaviours following BVD are not due simply to changes in D2 receptor protein expression in the striatum and that other neurophysiological changes in the brain account for these behaviours following BVD.

► Bilateral vestibular loss causes hyperactivity and circling, implicating the striatum. ► The D2 dopamine antagonist, eticlopride, reduced these behaviours. ► There were no differences in D2 receptor expression in the striatum. ► These behaviours are not due simply to changes in striatal dopamine receptors.