VESTIBULAR COMPENSATION IN AGED RATS WITH UNILATERAL LABYRINTHECTOMY TREATED WITH DOPAMINERGIC DRUGS

Drugs acting as agonists (SKF38393 and quinpirol) or antagonists (SCH2 3390 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 cours e of vestibular compensation was evaluated by recording spontaneous ey e nystagmus and by scoring ambulation and rearing with the open field test and motor ability and coordination with the rotorod test. Treatme nt started 3 days prior to surgery and continued until day 7 after sur gery. The vestibular compensation of untreated young male rats was als o 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 b y sulpiride (D2 receptor antagonist) 4 mg kg(-1) day(-1), while the ot her drugs did not affect this parameter. After operation, ambulation a nd rearing of aged rats increased more slowly as compared to that of y oung animals. Moreover, motor performance and coordination in aged rat s improved less rapidly than those of young controls, Dopamine recepto r agonists increased ambulation and improved motor performance and coo rdination in aged rats, while dopamine receptor antagonists exerted op posite effects, Rearing was not affected by any kind of drug treatment . These results suggest that dopamine neurotransmission plays a role i n vestibular compensation process following unilateral labyrinthectomy in aged animals, and this may have clinical relevance in vestibular p athologies of peripheral origin that are associated to brain ageing. ( C) 1996 The Italian Pharmacological Society