Noninvasive recording of the Mauthner neurone action potential in larval zebrafish.

We describe the identification of Mauthner (M-) cell action potentials in an intact zebrafish larva, utilizing recording electrodes located outside the fish: 1. The externally recorded spike occurs at approximately the same time, and its waveform changes with recording site in the same way, as the extracellular M-spike recorded within the central nervous system. 2. The externally recorded M-spike may be readily distinguished from other forms of neural activity. 3. The M-spike can be identified in recordings from unrestrained larvae. This finding permits the direct study of M-cell function in the freely behaving animal.