Are interrelations between vestibular receptors mediated by Scarpa's ganglion? An electrophysiological study in the...

In the frog we have recorded, in "isolated head" preparations, the gross activity and single afferent fibre discharges from the ampullary nerve of the vertical anterior semicircular canal (VAC) in several experimental situations. In all the preparations the efferent vestibular fibres acting on the VAC were functionally eliminated by acute section of the vestibular nerve between Scarpa's ganglion and the brain stem (CVNa preparations) or, by section of the anterior branch of the vestibular nerve between Scarpa's ganglion and the peripheral receptors, close to the ganglion (SGE preparations) or, by section of the VAC ampullary nerve near the ampulla (PE preparations). 1) In CVNa preparations, mechanical stimulation of the horizontal canal was carried out by pressure exerted upon the ampulla in such a way that the cupula was deflected towards the utricle which elicited a long-lasting discharge on the whole VAC nerve which was detached from its ampulla. 2) In SGE and PE preparations, the mean frequencies of the spontaneous discharges calculated on more than 200 VAC afferent fibres had the same value; they were significantly higher than the mean frequency calculated in CVNa preparations. These results confirm the existence of interrelations between the vestibular receptors of the frog by means of receptor-receptor fibres. They also strongly suggest that Scarpa's ganglion is required for their action.