Phylogeny of the central autonomic nervous system: comparative anatomy of preganglionic neurons

Abstract

The brainstem of mammals contains cranial motor nuclei composed of parasympathetic preganglionic neurons, which are distinct from the branchiomotor nuclei. In fish and amphibians, on the other hand, cranial preganglionic neurons form motor nuclei integrated with motor neurons innervating gill and branchiomotor muscles, and various tendencies for differentiation are observed within the nuclei. Reptilian and avian preganglionic neurons, as in mammals, separate from the branchiomotor nuclei to form the dorsal motor nucleus of the vagus and the salivary nuclei. The sympathetic preganglionic neurons in mammals are mediolaterally segregated to form multiple nuclei in the intermediate zone of the spinal cord. In other vertebrates, preganglionic neurons also form nuclei in the intermediate zone, but the main nucleus is located in the lateral region in amphibians, the medial region in teleosts and avians, and the intermediate region in reptiles.