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

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.

The responses of frogs to vestibular and visual stimulation in weightlessness.

The authors, using rotatory visual and vestibular stimulators, propose to perform an experiment to study the effect of long periods of weightlessness on vestibular and visual interactions in frogs. The results will be analysed within the Framework of sensory conflict theory. Preliminary experiments are in progress in order to determine the best method for containments of long duration.

Influence of the saccule, lagena and vertical posterior canal on the ipsilateral horizontal and vertical anterior semicircular canals in Rana esculenta: role of receptor-receptor fibres.

The influence of the efferent vestibular system being eliminated, the spontaneous activity of single afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By stimulating electrically the nerves of the vertical posterior canal, lagena or saccule as well as by sectioning these nerves and then using statistical methods, it is shown that the receptor-receptor fibres arising from the above mentioned receptors have generally an inhibitory influence on the afferent activity from the horizontal and vertical anterior canals.

Tonic influence of the efferent vestibular system on the spontaneous afferent activity from semicircular canals in the frog (Rana esculenta L.).

In the frog we have recorded the spontaneous activity of single afferent fibres of the ampullary nerves of the left horizontal semicircular canal (HC) and vertical anterior canal (VAC) in isolated head preparations. The recordings have been made in 4 experimental situations: intact preparations; preparations whose brain was destroyed; preparations whose contralateral vestibular nerve had been cut between Scarpa's ganglion and the brain; preparations where either an ampullary nerve (that of the HC or of the VAC) or the utricular nerve had been cut contralaterally. From our results, it appears that the efferent vestibular system has a tonic influence on the afferent activity from HC and VAC; the influence of the part of the efferent vestibular system (EVS) activity depending on contralateral vestibular inputs is inhibitory, while the influence of the part of the EVS activity depending on ipsilateral vestibular inputs might be facilitatory.

[Tonic conjugated action of receptor-receptor fibers and of the efferent vestibular system on the spontaneous afferene activity of a semicircular canal in the frog].

In the frog, the joint action of non-afferent vestibular systems [i.e. the efferent vestibular system and the receptor-receptor fibre system] on the afferent vestibular activity is null or very small.

[Action of vestibular receptors pn the spontaneous afferent activity of an ipsilateral semicircular canal in the frog].

In the frog, the influence of both the part of the efferent system which depends on ipsilateral vestibular inputs and the receptor-receptor fibre system on the afferent activity of semicircular canals is either null or facilitatory. The receptor-receptor fibre system being inhibitory, it seems that the part of the efferent vestibular activity which depends on ipsilateral vestibular inputs is facilitatory, which agrees with previous results.

Influence of receptor-receptor fibres on the spontaneous afferent activity from semicircular canals in the frog (Rana esculenta).

The influence of the efferent vestibular system having been eliminated, the spontaneous activity of afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By stimulating the ampullary nerve of one of these two canals while recording on the other, as well as by sectioning branches of the vestibular nerve and then using statistical methods, it is shown that receptor-receptor fibres have an inhibitory action on afferent activity from the horizontal and vertical anterior semicircular canals.

[Response of efferent vestibular fibers to horizontal rotation in frogs (Rana esculenta L.)].

The activity of efferent vestibular fibres has been recorded on the nerve of the left vertical anterior semicircular canal detached from its ampulla during rotations in the horizontal plane. Different types of responses have been found; they are noted in table I and pictured on fig. 2.

[Effect of some antibiotics on semi-circular canal activity in the frog (Rana esculenta)].

We have studied the action of two ototoxic antibiotics (streptomycin and gentamycin) on the activity of the horizontal semicircular canal in comparison with those of penicillin and 7 g/1 NaCl solution, all of them being injected into the labyrinthic cavity. Only streptomycin and gentamycin have a specific action, and the one of streptomycin is much more important than the one of gentamycin.