INNERVATION OF A VESTIBULAR RECEPTOR IN THE FROG - EXISTENCE OF A FEEDBACK LOOP

In the frog, Rana esculenta, when the influence of the efferent vestibular system was eliminated, the spontaneous activity of single afferent fibres recorded from one branch of the nerve of the horizontal semicircular canal (HC) or of the nerve of the vertical anterior canal (VAC) was inhibited in 16-17% of the cases when stimulating electrically the other branch of the same ampullary nerve. Moreover, the spontaneous activity of about 200 afferent fibres was recorded from the nerves of the HC and VAC in three experimental situations. In the first one, the brain was destroyed, or the left vestibular nerve cut as it enters the brain stem, and all the branches of the left vestibular nerve were cut except for the one recorded (VAC or HC nerve); in the second one, recordings were made on the peripheral end of the ampullary nerve previously cut near the ampulla; in the third situation they were made on the ampullary nerve after having cut the vestibular nerve between the periphery and Scarpa's ganglion close to Scarpa's ganglion. Statistical comparisons of the distribution of the spontaneous frequencies and of the mean activities between the experimental situations show that the activities were greater in the second or third experimental situations than in the first one. These results could be explained by the existence of an inhibitory feedback loop outside the brain including Scarpa's ganglion and mediated by receptor-receptor fibres. © 1979 Springer-Verlag.