Chapter 10 Neuropeptides in morphologically and functionally identified primary afferent neurons in dorsal root ganglia: substance P, CGRP and somatostatin

This chapter discusses the neuropeptides in morphologically and functionally identified primary afferent neurons in dorsal root ganglia (DRG): substance P, CGRP, and somatostatin. Peptides can be released from the central and/or peripheral terminals of primary afferent neurons and can have important effects on the functioning of spinal neurons and/or peripheral tissues. For a full understanding of the functional significance of the peptides including the circumstances of their release, information about the types and properties of primary afferent neurons that secrete and release these peptides is essential. Their features including morphology, cell size, conduction velocity, and sensory receptor type can categorize DRG neurons. These categories and the way in which they relate to each other are first introduced in order to examine the relationship between them and peptide content. Many different neuropeptides are expressed in these neurons, including substance P (SP), neurokinin A, calcitonin generelated peptide (CGRP), somatostatin (SOM), vasoactive intestinal peptide (VIP), galanin, opioid peptides, and atrial natriuretic peptide. This chapter examines the properties of DRG neurons expressing substance P, CGRP, and SOM.