Effects of nitric oxide on the vestibular functional recovery after unilateral labyrinthectomy

The effects of nitric oxide on the vestibular function recovery following unilateral labyrinthectomy were studied. Male Sprague-Dawley rats treated with N-omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, were subjected to destruction of the unilateral vestibular apparatus and spontaneous nystagmus was observed. To explore the role of nitric oxide on the potassium current, the whole cell patch clamp technique was applied on isolated medial vestibular nuclear neurons. The frequency of spontaneous nystagmus that appeared in L-NAME-treated rats was higher and maintained longer than in control animals. Potassium currents in the isolated medial vestibular nucleus were inhibited by nitric oxide liberating agents, sodium nitroprusside and S-nitroso-N-acetylpenicillamine. After blockade of calcium dependent potassium currents by high EGTA (11 mM)-containing pipette solution, sodium nitroprusside did not inhibit the outward potassium currents. 8-Bromoguanosine 3,5-cyclic monophosphate, a membrane-permeable cGMP analogue, produced similar effects to inhibit the outward potassium currents as sodium nitroprusside. These results suggest that nitric oxide production after unilateral labyrinthectomy would help to facilitate vestibular compensation by inhibiting calcium-dependent potassium currents through increasing intracellular cyclic GMP, thereby increasing excitability in ipsilateral vestibular nuclear neurons.