TRIGEMINAL, VAGAL, AND SPINAL PROJECTIONS OF SUPRAMEDULLARY CELLS IN THE PUFFER FISH, TAKIFUGU NIPHOBLES

The supramedullary cells (SMCs) of teleosts have been studied for near ly 100 years, but their peripheral connections have remained obscure. We examined the supramedullary cells of the puffer fish, Takifugu, nip hobles, using horseradish peroxidase transport. Horseradish peroxidase labeling was found bilaterally after application to the trigeminal, t he posterior branch of the vagal, and the spinal nerves. No labeled ne urons were found after application to the anterior or visceral branche s of the vagal nerve. Thus, labeled SMCs were found only after applica tion to the nerves containing cutaneous branches. Some rostrocaudal to pographical labeling was found after selective application to each of the four branches of the trigeminal nerve. Labeled neurons were more c ommon in the rostral than in the central or caudal part of the SMC reg ion. Some topographical labeling was also found after application to t he first, second, and third spinal nerves, but the topography was not very clear, and there was considerable overlap in the distribution of labeled cells. The sum total of labeled SMCs after unilateral horserad ish peroxidase application to each peripheral nerve was more than thre e times the total number of ipsilateral SMCs, indicating that a single SMC projects several peripheral processes into different nerves. From these results, and taking previous studies into consideration, we pro pose that supramedullary neurons have a phylogenetic relationship with the spinal dorsal cells of the lamprey and with the extramedullary ce lls of the amphibian embryo. (C) Wiley-Liss, Inc.