Morphological evidence for a direct projection of trigeminal nerve fibers to the primary gustatory center in the sea catfish Plotosus anguillaris.

The central projections of the ramus mandibularis were examined in the Japanese sea catfish, Plotosus anguillaris by using the technique of transganglionic tracing with horseradish peroxidase (HRP). This ramus receives fibers from both the trigeminal and facial nerves and supplies primarily the two mandibular barbels. Two pathways for a direct trigeminal projection to the facial lobe (FL) were found: one from the main descending root of the Vth nerve (MRDV) to the medial portion of the FL, approximately midway between the rostro-caudal axis of the FL and a second, from deep RDV to the intermediate nucleus (NIF), beneath the medial lobule of the FL. The facial fibers project exclusively onto the medial portion of the FL and the NIF. The results show that fibers of these two cranial sensory nerves supplying the mandibular barbels converge centrally on the medial portion of the FL, indicating that the FL of the Japanese sea catfish is a highly differentiated center for both gustation and somatosensation.