Dissociation of dorsal root ganglion neurons into afferent and efferent-like neurons

Although the textbook function of dorsal root ganglion neurons is to signal information to the brain, a group of C-fibre and some AG-fibre afferents have the capacity to release peptide transmitters from their peripheral terminations and thereby to regulate vascular and other tissue activities. Depending on the species under study, vasoactive dorsal root ganglion neurons in the skin belong to heat nociceptors or a subclass of polymodal nociceptors, and it has been a matter of long-standing discussion how the local effector role of dorsal root ganglion neurons is related to their afferent function. The observation that local vascular regulation may take place independently of nociception has commonly been explained by a number of transductional differences between peripheral peptide release and afferent nerve activity. However, the view that it is only one population of dorsal root ganglion neurons that can work in either mode is increasingly challenged, and after consideration of the available information we hypothesize that some dorsal root ganglion neurons are specialized in controlling peripheral effector mechanisms but have no role in sensation. These local effector neurons represent a novel class of autonomic neurons that lack a preganglionic input, but operate in an efferent-like mode after stimulation by internal or external stimuli. (C) 1998 IBRO. Published by Elsevier Science Ltd.