ABSTRACT
Acoustic response characteristics of single fibres were studied in the VIIIth cranial nerve of adult and early post-metamorphic bullfrogs (Rana catesbeiana). Based on the distribution of units’ best excitatory frequencies, three populations of auditory fibres were found in each group of frogs. The sharpness of the tuning curves and temporal firing patterns of primary fibres were similar in both adults and froglets. However, the distributions of the populations were different between the two groups, and it was found that froglets responded to higher frequencies than did adults. There were also differences in the distributions of thresholds of excitation between the froglets and adults. The excitation thresholds of low-frequency selective and high-frequency selective fibres tended to be higher in froglets. Low-frequency selective fibres in both groups of frogs exhibited two-tone inhibition, and the best inhibitory frequencies were higher in froglets than in adults. These results demonstrate that changes in the response properties of primary auditory fibres occur during the development of the bullfrog. These functional changes presumably reflect morphological changes which may occur in the peripheral auditory system.
