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.