Vestibular compensation in aged rats with unilateral labyrinthectomy treated with dopaminergic drugs.

Drugs acting as agonists (SKF38393 and quinpirol) or antagonists (SCH23390 and sulpiride) on dopamine receptors were administered at various doses (1, 2 or 4 mg kg-1 day-1) to aged male rats of the Sprague-Dawley strain subjected to labyrinth unilateral lesion. The time course of vestibular compensation was evaluated by recording spontaneous eye nystagmus and by scoring ambulation and rearing with the open field test and motor ability and coordination with the rotorod test. Treatment started 3 days prior to surgery and continued until day 7 after surgery. The vestibular compensation of untreated young male rats was also studied with the same methods. The decline of spontaneous nystagmus in aged animals was slower than that of young rats and was facilitated by the large doses of quinpirol (D2 receptor agonist) and inhibited by sulpiride (D2 receptor antagonist) 4 mg kg-1 day-1, while the other drugs did not affect this parameter. After operation, ambulation and rearing of aged rats increased more slowly as compared to that of young animals. Moreover, motor performance and coordination in aged rats improved less rapidly than those of young controls. Dopamine receptor agonists increased ambulation and improved motor performance and coordination in aged rats, while dopamine receptor antagonists exerted opposite effects. Rearing was not affected by any kind of drug treatment. These results suggest that dopamine neurotransmission plays a role in vestibular compensation process following unilateral labyrinthectomy in aged animals, and this may have clinical relevance in vestibular pathologies of peripheral origin that are associated to brain ageing.