Vagal Afferent Projections in Rana pipiens, Rana catesbeiana, and Xenopus mülleri

The vagus nerve was transected proximal to the ganglion in Rana pipiens, Rana catesbeiana and Xenopus mülleri.Degeneration, seen with the Nauta and Fink-Heimer I methods, was identical in the two species of Rana and this pattern formed the major portion of that seen in Xenopus. The medial group of X nerve fibers entered the fasciculus solitarius, with some fibers ascending, but the majority descending to the level of the obex where some decussation was seen. The lateral group of X fibers descend within the descending trigeminal tract to cervical spinal levels, at which point fibers formed a cap over the dorsal horn. Terminals were seen adjacent to the dorsal horn. In addition, terminal degeneration was seen on small cells located just ventral to the descending trigeminal tract. These two components appear to constitute the afferent visceral and somatic components of the vagus.In Xenopus, whose adult form retains a lateral line, a third component was seen entering the dorsal zone of the area acoustico-lateralis and ascending to the cerebellar nucleus.