Effects of temperature on the response properties of auditory nerve fibers in the American toad ( Bufo americanus )

Abstract

While a number of studies have explored the effects of temperature on the electrical potentials in the inner ear, little is known about such effects on auditory nerve fibers. We therefore conducted a study of changes in the response properties of single auditory units in the VIIIth nerve of Bufo americanus as the animal's temperature was varied. Toads are opportune animals for such studies since they can tolerate a wide range of body temperature. While recording continuously from an individual fiber, the toad's temperature was varied by a Peltier plate to which it was secured. A total of 27 units in 4 animals was studied. As the animal's temperature was lowered, the best excitatory frequencies (BEF) of fibers from the amphibian papilla shifted downwards while their thresholds increased. In addition, both spontaneous activity and maximum firing rate to a tone at a unit's BEF decreased although its dynamic range remained approximately 30 dB above threshold, Fibers from the basilar papilla also showed a diminution in spontaneous activity and maximum firing rate. However, their BEF's and thresholds changed very little with temperature. These results suggest that the basis for frequency analysis differs between the two organs.