Do Central Terminals of Intact Myelinated Primary Afferents Sprout into the Superficial Dorsal Horn of Rat Spinal Cord after Injury to a Neighboring Peripheral Nerve? SAFA ALDEEN S. SHEHAB, 1 * ROSEMARY C. SPIKE, 2 AND ANDREW J. TODD 2 1 Department of Anatomy, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates 2 Spinal Cord Group, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom ABSTRACT In order to investigate whether normal myelinated primary afferent axons sprout into the territories of adjacent injured peripheral nerve fibers in the superficial dorsal horn of the spinal cord, adult rats underwent either sectioning of the saphenous or femoral nerves on one side, or else unilateral denervation of the skin of the posterior thigh. Two weeks later cholera toxin B subunit (CTb), which is normally transported selectively by myelinated somatic primary affer- ents, was injected into the ipsilateral (intact) sciatic nerve. The relationship between CTb, vasoactive intestinal peptide (VIP), and binding of Bandeiraea simplicifolia isolectin B4 (IB4) was then examined in the ipsilateral dorsal horn of the second to fifth lumbar spinal segments (L2–L5). Sectioning of the femoral or saphenous nerves resulted in a reduction of IB4 binding in laminae I–II in the medial third of the dorsal horn of L2, L3, and the upper part of L4. VIP-immunoreactivity was upregulated in exactly the same regions in which IB4-binding was reduced. These correspond to the areas that were previously innervated by unmyelinated affer- ents in the sectioned nerves. CTb-labeling was detected in regions known to receive input from myelinated sciatic afferents: lamina I and a band extending from the inner part of lamina II (IIi) to lamina V in the L3–5 segments, and the deepest part of the dorsal horn in L2. Importantly, no CTb-labeling was detected in the outer part of lamina II (IIo) in the denervated areas. Sectioning of branches of the posterior cutaneous nerve of the thigh resulted in a reduction of IB4-binding and upregulation of VIP-immunoreactivity in the lateral part of the superficial dorsal horn of caudal L4 and L5. Again, CTb-immunoreactivity showed the normal sciatic pattern in L4 –L5, with no labeling detected in lamina IIo in the denervated region. These results do not support the suggestion that the central terminals of intact myelinated afferents sprout into regions of lamina II occupied by adjacent nerves that have been axotomized peripherally. J. Comp. Neurol. 474: 427– 437, 2004. © 2004 Wiley-Liss, Inc. Indexing terms: axotomy; sprouting; cholera toxin B subunit; VIP; IB4; spinal cord The B subunit of cholera toxin (CTb) binds to the GM1 ganglioside, which is normally present on the surface of myelinated, but not unmyelinated, somatic primary affer- ents (Robertson and Grant, 1989). When CTb is injected into a peripheral somatic nerve, it is selectively taken up by myelinated afferents and transported to their cell bodies in the dorsal root ganglia and to their central terminals in lamina I and deeper laminae (IIi–VII, IX) of the spinal cord (Robertson and Grant, 1985; Rivero-Melian and Grant, 1990, 1991; LaMotte et al., 1991; Rivero-Melian et al., 1992; Woolf et al., 1995). In marked contrast, very little CTb labeling is normally detected in the outer part of lamina II (IIo), where Grant sponsor: Faculty of Medicine and Health Sciences of the United Arab Emirates University; Grant sponsor: Wellcome Trust. *Correspondence to: Safa Shehab, Department of Anatomy, Faculty of Medicine and Health Sciences, United Arab Emirates University, PO Box 17666, Al-Ain, UAE. E-mail: s.shehab@uaeu.ac.ae Received 25 November 2003; Revised 5 February 2004; Accepted 6 Feb- ruary 2004 DOI 10.1002/cne.20147 Published online in Wiley InterScience (www.interscience.wiley.com). THE JOURNAL OF COMPARATIVE NEUROLOGY 474:427– 437 (2004) © 2004 WILEY-LISS, INC.