Satoshi Nakahara

Glossopharyngeal-hypoglossal nerve reflex of the frog in metamorphosis

In adult frogs, a reflex discharge is elicited from the hypoglossal nerve by mechanical and chemical stimuli to the centre of the tongue surface and electrical stimuli to the glossopharyngeal nerve innervating tongue. However, there has been no report concerning the embryological stage at which this reflex develops. The metamorphosis of a frog is divided into three parts, premetamorphic, metamorphic and climax stage. In the climax stage, the forelimbs are lengthened and the tail gradually shortened. The glossopharyngeal-hypoglossal nerve reflex arose in the early climax stage, during which the tongue appeared on the floor of the mouth. At this stage, the conduction velocities of the first compound action potential of the glossopharyngeal and hypoglossal nerves were about 8.7 and 9.3 m/s, respectively. The latency of the reflex was long, especially the central latency. The response of the glossopharyngeal nerve and the reflex discharge from the hypoglossal nerve upon mechanical stimulation of the tongue were smaller in the tadpole than in the adult frog. As metamorphosis proceeded, the conduction velocity of these nerves increased; the latency shortened, especially the central latency; the reflex response to mechanical stimulus increased. These results suggest that, although the glossopharyngeal-hypoglossal nerve reflex is developed in the early climax stage, it is completed only in the adult frog. Therefore, adult frogs living mainly on land may reject and swallow prey by this reflective tongue movement.

Tactile and taste sensory maturation of the frog larvae tongue.

The maturation process of organs in the oral cavity of the larvae of bullfrogs, Rana catesbeiana, corresponding to the larval stages XVIII to XXV distinguished by Taylor and Kallros Anat. Rec., 94 (1946) 7-25, were investigated. In this study, these larval stages were divided by the width of the mouth slit into A1, A2, B and C stages. The A1 and A2 stages corresponded to larval stages XVIII-XIX and XX, respectively. The B and C stages corresponded to stages XXI and XXII-XXV, respectively. In stage A1, mechanical and chemical stimulation of the tongue rudiment, in most larvae, failed to elicit afferent discharges in glossopharyngeal nerves. However, in a small number of larvae, obvious afferent discharges of these nerves were generated. In stage A2, glossopharyngeal nerves in most larvae began responding to the same stimulations. The amplitude increased with decreasing duration of afferent discharges, resembling those of the adult. In stage B, the first glossopharyngeal-hypoglossal nerve reflex (G-H reflex) was elicited by mechanical stimulation of the tongue. In stage C, the G-H reflex was also induced by chemical stimulation and the latency of the G-H reflex elicited by mechanical stimulation decreased. In this stage, expansion and extension of the tongue increased. Therefore, the natural function of this reflex for the intake of food may follow this stage.

Frog Taste Cells After Denervation

The structure of the taste organ and the physiological properties of the taste cell of the bullfrog (Rana catesbeiana) were investigated after glossopharyngeal nerve transection.