TEMPERATURE-DEPENDENCE OF 2-TONE RATE SUPPRESSION IN THE NORTHERN LEOPARD FROG, RANA-PIPIENS-PIPIENS

The existence region of two-tone rate suppression in frog low-frequency auditory-nerve fibers was found to include a suppressive region below a fiber's characteristic frequency, contrary to previous reports. In response to a 3 degrees C rise in core temperature, the area and the best suppressive frequency (BSF) of the low-side suppressive region significantly increased. Increasing core temperature of the frog by 6 degrees C resulted in significant changes in the high-side suppressive region: Its area decreased, and its BSF and best suppressive threshold (BST) increased. Constant-temperature control trials were designed to partially simulate the relative movement of the probe tone within the excitatory tuning curve which occurred during temperature shifts. Lowering the probe tone by 0.5 oct had no effect on the low-side suppressive region, but significantly increased the area and lowered the BSF and BST of the high-side suppressive region. Temperature shifts in the frog appear to have a differential effect on the low-side and high-side suppressive areas of low-frequency auditory-nerve fibers. Moreover, excitation and suppression also respond differentially to temperature shifts.