Impulses from Sensory Nerves of Catfish

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Abstract
Records of impulses from the lateral-line nerves of catfish show that the lateral-line organs are in a state of continuous activity, producing a massive discharge of impulses. The discharge may be increased during the direct application of pressure on the skin over the lateral-line canal, by ripples in the water, by irregular currents of water, and by movements of the fish''s trunk. The asynchronously discharging lateral-line organs respond to vibratory stimuli from tuning forks by getting into phase with each other and by beating synchronously at frequencies ranging from 20 to 70 per sec. The frequency of beating for a given preparation is independent of the frequency of the tuning fork for the frequencies of 100, 200, and 250 dvs. which were used. The continuous discharge of the lateral-line system is markedly changed by alteration of temp. The frequency declines on lowering the temp. and rises on increasing it. Spinal and facial nerves in the catfish fail to yield nerve impulses in response to changes of the skin temp. between 0[degree] and 28[degree] C, although the intact animal is known to be sensitive to temp. differences. Receptors in the lips and barbels of the catfish, Ameiurus nebulosus (Les.) are very sensitive to mechanical stimuli, giving large rapid (A-type) impulses in fibers of the facial nerve in response to touching the receptive surfaces and to movements of the waters in which the preparation is immersed. The great sensitivity of the barbels and lips to currents of water and the bilateral symmetry of the distribution of sensitivity of the facial nerve may serve as a basis for observed rheotropic orientation in the catfish. Acetic acid, NaCl, and meat juice, dissolved in the water bathing the barbels and lips, set up impulses of very small and barely detectable potential in the fibers of the facial nerve. It is suggested that the specificity of impulses for the two sense modalities may be correlated with the large size of the cells of origin of the axons in the Gasserian ganglion supplying tactile receptors and the small size of the cells of origin in the geniculate ganglion sending axons to taste-buds.

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