.t A ,. r" r . I ELSEVIER Molecular Brain Research 28 (1995) 231-238 MOLECULAR BRAIN RESEARCH Research report NGFR-mRNA expression in sciatic nerve: a sensitive indicator of early stages of axonopathy M.D. Roberson a, A.D. Toews a,c, T.W. Bouldin b,c, j. Weaver c, N.D. Goines c, p. Morell a,c,. a Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA b Department of Pathology, University of North Carolina, Chapel Hill, NC 27599, USA c Brain and Development Research Center, University of North Carolina, Chapel Hill, NC 27599, USA Accepted 13 September 1994 Abstract Expression of the low-affinity nerve growth factor receptor (NGFR) in the sciatic nerve (particularly Schwann cells) is high during development but is downregulated upon establishment of the mature axon-Schwann cell relationship. NGFR is re-expressed by Schwann cells if this relationship is altered by degeneration of axons (axotomy) or myelin (tellurium intoxication). To determine the sensitivity of NGFR expression to axonal injury, we have assayed NGFR-mRNA levels in proximal and distal regions of nerves exposed to the axonopathic agents acrylamide and isoniazid, as well as in proximal and distal stumps of axotomized nerves. NGFR-mRNA was elevated in all three models and correlated regionally with sites of axonal perturbation. In distal regions of acrylamide- and isoniazid-intoxicated nerves, NGFR-mRNA was elevated at least 2 days prior to visible signs of axonal degeneration as assayed by morphological techniques utilizing light microscopy. NGFR-mRNA was also elevated in proximal regions of axotomized and acrylamide-intoxicated nerves prior to signs of axonal degeneration. In these models, increased mRNA expression correlated with alterations in the size distribution of axonal cross sections. The common response in all of these situations indicates that NGFR expression, in addition to being a marker for axonal degeneration, is also a sensitive indicator of less profound perturbations in normal axon-Schwann cell interactions, including early stages of axonopathy. We suggest that assay for NGFR-mRNA may be utilized as a rapid and simple method (relative to more labor-intensive morphological methods) to screen for peripheral neurotoxicity. Additionally, regional analysis (distal versus proximal) may give insight into the sequence of events involved in the neuropathology of such disorders. Keywords: Acrylamide; Isoniazid; Axotomy 1. Introduction The level of messenger RNA for the low-affinity nerve growth factor receptor (NGFR-mRNA) is nor- mally very low in sciatic nerve but is markedly upregu- lated in distal stumps of transected nerves [8,26,27]. In this model, all myelinating Schwann ceils demyelinate, and upregulation for NGFR-mRNA is coincident with downregulation for mRNA for myelin specific proteins, such as P0 and myelin basic protein (MBP) [6,16,17,31]. The induced NGFR-mRNA is present in all Schwann ceils distal to the transection [27], and is presumed to * Corresponding author. 321 BSRC, CB# 7250, University of North Carolina, Chapel Hill, NC 27599, USA. Fax: (1) (919) 966-1844; E-maih PIERRE@CSS.UNC.EDU. 0169-328X/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0169-328X(94)0021 1-8 be a response to axonal degeneration and subsequent myelin degeneration. NGFR-mRNA is also upregulated in the primary demyelination induced by tellurium feeding [3,28]. Tel- lurium feeding inhibits synthesis of cholesterol (a major component of the myelin sheath) and myelin biosyn- thesis, as assayed by P0 mRNA levels, is downregulated to some degree in all Schwann cells [29,30]. However, only a minority of these cells undergo complete de- myelination, and NGFR-mRNA upregulation is re- stricted to those Schwann cells with at least some demyelination. In those Schwann cells which have only partially demyelinated internodes, newly synthesized NGFR protein is targeted to the areas where there is myelin loss [29]. This implies that NGFR-mRNA up- regulation in Schwann cells occurs as an early response to alterations at the axon-Schwann cell interface. We