Electrophysiological evidence for the topographical arrangement of taste and tactile neurons in the facial lobe of the channel catfish.

Neural responses in the facial lobe of th channel catfish to chemical and mechanical stimulation of the external skin surface were studied electrophysiologically. Taste and tactile neurons in the lobe were organized in a somatotopic manner, which confirms the anatomical reports of the facial lobe in the bullhead catfish, but is markedly different from that of the Cyprinidae. The taste neurons were arranged generally in the more dorsal regions of the tactile sensitive areas and responded with highest frequency to L-alanine or L-arginine HCI among several amino acids tested. The mechanically responsive neurons in the deeper layer of the antero-medial portion of the lobe, possibly corresponding to the intermediate nucleus of the facial lobe, had large receptive fields ranging from 100 mm to the whole body surface; in addition, some of these neurons showed lateral inhibition. The present study revealed that the facial lobe of the channel catfish is a center not only for gustatory input, but also for tactile information.