Effective stimulus for the Xenopus laevis lateral-line hair-cell system.

An in vitro preparation of the lateral-line organ of the African clawed toad Xenopus laevis was used to evaluate the properties of the physiological stimuli which are most effective in evoking neural responses in this simple hair-cell system. Changes in the mean firing rate and the amount of modulation of the neural activity in the fibers innervating the hair cells were determined during the presentation of well-controlled pressure or water-movement stimuli in a specially designed chamber that prevented movement and deformation of the organ during stimulation. It was shown that the most effective stimulus for the preparation was a varying flow of fluid past the organ. Sinusoidally varying water movements over a frequency range of 1 to 100 Hz were effective in evoking neural responses at stimulus amplitudes less than 10 mu peak-to-peak; in addition, a small response to a constant-velocity flow was found. Since no movement or deformation of the organ was present during the water-movement stimuli, it was concluded that these aspects of normal physiological stimuli were not necessary to evoke neural responses. Finally, it was demonstrated that the preparation was sensitive to neither constant nor varying-pressure stimuli.