The sympathetic nervous system, which originates in the superior cervical ganglion (SCG) and is distributed in vestibular end organs, has been proposed to have some influence on vestibular function. The present investigation was conducted to assess the effects of unilateral electrical stimulation of the SCG, administration of a vasopressor drug, and introduction of KCl (0.7 M/ml) into the tympanic cavity on vestibular function in alert guinea pigs. Nystagmus was not observed as result of electrical irritation of the SCG (22 test animals), infusion of the KCl solution into the middle ear cavity (5 test animals), or the combination of SCG stimulation and vasopressor drug administration (7 test animals). However, when the SCG was stimulated electrically after introduction of the KCl solution into the ipsilateral cavity, nystagmus and postural deviation were observed (5 out of 12 animals). Furthermore, after the administration of a vasopressor drug to these 12 animals, irrespective of the manifestation of nystagmus, the same changes took place in response to the electrical stimulation (7 animals). These results suggest that SCB stimulation is a provocative factor for nystagmus, that infusion of KCl solution into the tympanic cavity induces a hypersensitive state in the inner ear, and that high blood pressure increases this hypersensitivity.
