VISCERAL AFFERENT AND EFFERENT COLUMNS IN THE SPINAL-CORD OF THE TELEOST, ICTALURUS-PUNCTATUS

In tetrapod vertebrates, neural circuitries subserving visceral and so matic reflexes are each represented in distinct columns of cells withi n the gray area of the spinal cord. To determine the location of visce ral elements of the spinal cord of a teleost fish, crystals of the car bocyanine dye 'dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI) , were placed on either the abdominal sympathetic (mesenteric) nerves, the coeliac ganglia, or on the rostral three somatic spinal nerves, i n fixed specimens of the channel catfish, Ictalurus punctatus. In fish in which DiI had been placed on the mesenteric nerves, labeled fibers coursed along the lateral margin of the dorsal horn within the first and second spinal segments, and appeared to terminate in a region at t he base of the dorsal horn. In contrast, when DiI crystals were placed on the somatic spinal nerves, labeled primary afferents terminated in the dorsalmost two thirds of the dorsal horn, as well as in ventral a nd ventromedial areas of;the medial funicular nuclear complex. Labeled somata (motor neurons) were situated in the: ventral horn. When DiI c rystals were placed bilaterally on the coeliac ganglia, labeled pirifo rm and fusiform preganglionic neurons occurred in intermediate positio ns adjacent to the central canal, corresponding to the paracentral nuc leus of Herrick, and in the lateral funiculus. These results demonstra te that somatic and visceral afferent and efferent functional columns are distinct in a teleost fish as they are in amniote vertebrates. (C) 1996 Wiley-Liss, Inc.