Hearing Research, 46 (1990) 63-82 Elsevier 63 HRR 01368 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Temperature-dependence of auditory nerve response properties in the frog Imme B. Stiebler and Peter M. Narins Department of Biology, University of California at LAX Angeles, Los Angeles, Califomra, U.S.A. (Received 8 September 1989; accepted 4 January 1990) Response properties of the auditory nerve fibers of the Pacific treefrog, Hyla regifla, were shown to be comparable to other Hylids at a standard temperature of 2O’C. This species from a rather variable thermal habitat was compared to the neotropical aboreal species, Eleutherodactylus coqui, in a study of auditory responses under conditions of changing temperatures. We found that as temperature increased: the center frequencies (CFs) of tuning curves remained constant for neurons from the basilar papilla but shifted to higher frequencies for neurons from the amphibian papilla (the amount of frequency shift decreased as CF increased); tone response thresholds decreased; phase-locking became stronger; the phase of the preferred response showed a lag in neurons with CFs below 500 Hz, a lead for CFs above 600 Hz, and almost no changes for CFs between 500 and 600 Hz; the variance of the click response and the average latency of the first spike in the response decreased. Threshold and vector strength measurements suggest a thermal optimum of about 20-22OC in H. regilla whereas this optimum in E. coqui seems to lie at 25’C or higher. Anura; Auditory system; Temperature effects; Tuning curves; Phase locking zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Introduction The inner ear of anurans (frogs and toads) is unusual in that it contains two organs which are specialized for the reception of airborne sounds. The amphibian papilla (a.p.) and the basilar papilla (b.p.) are anatomically distinct, spatially-separate organs each with its own complement of sensory hair cells and overlying tectorium. The a.p. is the anatomically more complex of the two structures, containing roughly 1000 tonotopically-arranged hair cells, stimulated by the tectorial membrane which presumably supports a travelling wave (Hil- lery and Narins, 1984; Lewis, 1984). In contrast, the b.p. is a simpler structure containing roughly 100 hair cells, which are innervated by auditory nerve fibers tuned to roughly the same frequency in an individual. Although these organs have been well-described anatomically (see Lewis et al., 1985 for review) and physiologically (see Fritzsch et al., 1988) the temperature-sensitivity of the response Correspondence to: Imme Stiebler, (Present address) Zentrum der Physiologie, Theodor-Stem-Kai 7, D-6000 Frankfurt 70, F.R.G. properties of the auditory nerve fibers originating from the two organs has not been documented in detail. This study is an attempt to describe the effects of temperature changes on the ability of the peripheral auditory system of anuran amphi- bians to perform spectral and temporal analyses of incoming sounds, and to relate these findings to the environmental conditions found in the animal’s natural habitat. Species chosen for this study were the Pacific tree frog (Hylu regilfu) and the Puerto Rican coqui (Eleutherodactylus coqui), primarily ‘because of the different range of temperatures to which each species is normally exposed. Although E. coqui is subjected to a wide range of temperatures in its natural habitat along an altitudinal gradient of over 1000 m (Narins and Smith, 1986) local populations at a given altitude experience little temperature variation during the course of the year. Males of this aboreal species produce a two-note advertisement call (Co-Qui). At the higher elevations the ‘Co’ note is a 100 ms, con- stant-frequency tone of about 1.1 kHz, and func- tions in male-male territorial interactions (Narins and Capranica, 1978). The ‘Co’ note is followed 037%5955/90/%03.50 0 1990 Elsevier Science Publishers B.V. (Biomedical Division)