SOMATOTOPIC REPRESENTATION OF THE MEDULLARY FACIAL LOBE OF CATFISH SILURUS-ASOTUS AS REVEALED BY TRANSGANGLIONIC TRANSPORT OF HRP

The facial lobe (FL) of the catfish Silurus asotus is composed of pair ed structures which are anteriorly tapered and posteriorly swollen lon gitudinal columns. Two longitudinal columns (lobules) extend caudorost rally in the anterior one-third of the lobe. We studied the central pr ojections of seven major taste peripheral rami into the FL with horser adish peroxidase (HRP) transganglionic labeling methods. The facial af ferent fibers of the maxillary barbel ramus terminate over a large are a of the FL from anterior to posterior. Their terminal areas are distr ibuted in the medial lobule of the anterior FL, ventral half of the in termediate FL, and lateral portion of the posterior FL. The maxillary and mandibular fibers project, respectively, to the most lateral porti on and to the overall region of the caudal half of the FL. The recurre nt facial fibers project to the dorsolateral lobule of the anterior FL . The facial fibers of the hyomandibular and ophthalmic rami project t o the most lateral portions in the intermediate region of the rostroca udal extent of the FL. The intermediate nucleus of the FL which develo ps as a longitudinal column throughout the caudal two-thirds of the ve ntromedial portion of the FL receives projections from the maxillary b arbel, maxillary and mandibular rami. The present results show that ea ch peripheral taste ramus projects in a precise topographic fashion to the ipsilateral Fl, and that the two lobules, one for maxillary barbe l and the other for the trunk are present in the anterior one-third of the FL. The trigeminal fibers of the maxillary barbel, maxillary and mandibular rami project to certain areas of the FL where the facial fi bers of each ramus also project.