FMRFAMIDE IMMUNOREACTIVITY IN THE PERIPHERAL (ATRIAL) NERVOUS-SYSTEM OF AMPHIOXUS (BRANCHIOSTOMA)

Many of the components of the atrial nervous system of amphioxus (Bran chiostoma) are immunoreactive to antisera against the tetrapeptide FMR Famide. The atrial nervous system of the lancelet contains both motor and what are presumably sensory components, linked to the central nerv ous system via dorsal root nerves, but the role of many of these compo nents is still unclear. There are large numbers of FMRFamide-like posi tive multipolar neurons over the gut and its diverticulum, separated f rom the gut by a system of thin coelomic spaces. Because their axons p ass towards the central nervous system, they are presumably sensory. A gain, although the rich gill plexus is presumably involved in ciliary control, the frequent immunoreactive cells on the gill bars do not see m to be ciliary-motor. There is also a rich subendostylar plexus conta ining FMRFamide-like material, perhaps secretomotor. In fact, the only immunoreactive fibers the function of which is evident are those on t he pterygeal muscles flooring the atrium. The results are discussed in terms of the evolution of the vertebrate enteric nervous system.