Chapter 11 Spinal cord projections and neuropeptides in visceral afferent neurons

Abstract

This chapter discusses the neuroanatomical experiments that examine the segmental distribution and the central projections of the afferent neurons innervating the urogenital system, large intestine, heart, and upper abdominal organs and the identity of the peptide neurotransmitters in visceral afferent pathways. Recently, developed neuroanatomical tracing methods have yielded important advances in the knowledge of the organization of visceral afferent pathways at various levels of the spinal cord. Horseradish peroxidase tracing experiments have shown that afferent projections from a number of visceral organs exhibit a similar pattern of termination in the spinal cord, and that this pattern is markedly different from that of the somatic afferent neurons that innervate the skin. In addition, neurochemical studies, in which the axonal tracing techniques were combined with immunocytochemistry, revealed that a large percentage of the visceral afferent neurons exhibit neuropeptide immunoreactivity. These findings raised the possibility that neuropeptides may be important transmitters or neuromodulators in the visceral afferent systems.