The Journal of comparative neurology
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Amphibians have two auditory organs specialized for reception of airborne sounds: the amphibian papilla and the basilar papilla. In this report we examine the morphology of the ganglion cells and the afferent innervation of the sensory epithelium in both auditory organs of the leopard frog, Rana pipiens pipiens. Extracellular injections of either biocytin or horseradish peroxidase (HRP) were made into the VIII nerve; they labeled ganglion cells, their axons, and their terminal fibers within the papillae. ⋯ In the basilar papilla labeled fibers were thick (around 4 microns) and terminated on as many as nine hair cells. Consistent with studies from the bullfrog, Rana catesbeiana, our results suggest that the amphibian papilla of R. pipiens pipiens has a convergent innervation (i.e., multiple hair cells provide input to a single ganglion cell) and is topographically organized. However, in contrast to reports in other ranid species, a highly convergent innervation like that found in the amphibian papilla is also found in the basilar papilla.