Functional properties of Mauthner cell in the tadpole Rana catesbeiana.

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Abstract
The Mauthner (M) cell of the bullfrog tadpole (R. catesbeiana) is sufficient and necessary to produce an early contralateral muscle response (ECMR) of the trunk and tail. This recognizable electrophysiological response is associated with a rapid flexion of the body and is an important component of a fast start behavior similar to that observed in teleosts. Direct intracellular stimulation followed at a short latency by the ECMR was employed as a physiological criterion for identification of the M-cell. The ECMR fatigued with repetitive intracellular stimulation of the M-cell at 0.1-10/s. Fatigue occurred within the spinal cord since the M-cell could be antidromically stimulated at 20/s and since muscle activity could be produced with ventral root stimulation at 10/s. Bilateral stimulation of the 8th nerves could produce simultaneous action potentials in both M-cells followed by bilateral ECMR; therefore, spinal inhibition does not appear to be as rapid as that of teleosts. Inhibition of the tadpole M-cell at the soma-axon hillock level appears not be as well developed as that of the teleost fish. Stimulation of the contralateral 8th nerve produced a delayed period of inhibition, which attenuated and eventually blocked the M-cell action potential produced by ipsilateral 8th nerve stimulation.