Deafferentation and neurotrophin‐mediated intraspinal sprouting: a central role for the p75 neurotrophin receptor

Abstract

Axonal plasticity in the adult spinal cord is governed by intrinsic neuronal growth potential and by extracellular cues. The p75 receptor (p75(NTR)) binds growth-promoting neurotrophins (NTs) as well as the common receptor for growth-inhibiting myelin-derived proteins (the Nogo receptor) and so is well situated to gauge the balance of positive and negative influences on axonal plasticity. Using transgenic mice lacking the extracellular NT-binding domain of p75(NTR) (p75-/- mice), we have examined the influence of p75(NTR) on changes in the density of primary afferent (calcitonin gene-related peptide-expressing) and descending monoaminergic (serotonin- and tyrosine hydroxylase-expressing) projections to the dorsal horn after dorsal rhizotomy, with and without concomitant application of exogenous nerve growth factor and NT-3. We found that, in intact p75-/- mice, the axon density of all populations was equal to or less than that in wild-type mice but that rhizotomy-induced intraspinal sprouting was significantly augmented. Monoaminergic axon sprouting was enhanced in both nerve growth factor- and NT-3-treated p75-/- mice compared with similarly treated wild-type mice. Primary afferent sprouting was particularly robust in NT-3-treated p75-/- mice. These in vivo results illustrate the interactions of p75(NTR) with NTs, with their respective tropomyosin-related kinase receptors and with inhibitory myelin-derived molecules. Our findings illustrate the pivotal role of p75(NTR) in spinal axonal plasticity and identify it as a potential therapeutic target for spinal cord injury.

Calcitonin gene-related peptide immunoreactivity in chronic human spinal cord injury

“…A computerized program provided average density measurements for each 20-mm segment of the 720-mm long rectangular strip. To quantify CGRP-positive axon density in the spinal cord, we carried an automated thresholding procedure, 31,33,34 which first defines the thickest and brightest regions, and then, following application of a Laplacian omnidirectional edge-detection filter, the finer processes ( Figure 1, bottom). The edge-detection filter effectively normalizes the signal-to-noise ratio such that small variations in immunoreactivity across sections are eliminated.…”

Cell-Mediated Neuroprotection in a Mouse Model of Human Tauopathy

“…For threshold analysis, images were captured using Lucia or Leica software (Nikon) via a digital camera or a Zeiss AxioScope using AxioVision software and SigmaScan Pro (SPSS) was used for subsequent quantitative densitometric measurements of NeuN, bisbenzamide, and NF200, as detailed previously (Scott et al 2005;Hampton et al 2008). For NeuN and bisbenzamide, a percentage area of the cortex containing antibody signal was generated by dividing the number of positive readings by the total number of potential readings, multiplied by 100.…”

“…Sections for immunofluorescence were processed as described previously (Scott et al, 2005;Hampton et al, 2008). Primary antibodies used were as follows: monoclonal anti-NeuN (1:400, Millipore Bioscience Research Reagents); mouse monoclonal anti-phosphotau (AT8, 1:1000, Autogen Bioclear); monoclonal anti-GFAP (glial fibrillary acidic protein) clone GA5-Cy3 (1:500, Sigma); monoclonal anti-neurofilament NF200 (1:500, Sigma); polyclonal rabbit anti-NG2 (1:500, a kind gift from Prof. W. B. Stallcup, Burnham Institute, La Jolla, CA); polyclonal rabbit-anti-Olig-2 (1:200, Millipore Bioscience Research Reagents); polyclonal goat or rabbit anti-GFP (green fluorescent protein) (1:1000, Abcam and Invitrogen, respectively); biotinylated WFA (Wisteria floribunda agglutinin lectin) (1:200, Sigma); rabbit polyclonal anti-GDNF (glial-derived neurotrophic factor) (1:20, Abcam); rabbit polyclonal anti-BDNF (brain-derived neurotrophic factor) (1:100 Abcam); polyclonal anti-NGF (nerve growth factor) (1:100, Calbiochem); monoclonal anti-Reelin (1:250, Abcam); polyclonal rabbit anti-Cux1 (1:250, Calbiochem); and rabbit polyclonal anti-GABA (1: 500, Sigma).…”

Endogenous TrkB Ligands Suppress Functional Mechanosensory Plasticity in the Deafferented Spinal Cord

“…Quantitative analyses of terminal density in the dorsal horn were performed by measuring terminal density as a function of depth in the dorsal horn, as we have done previously (Ramer et al, 2001MacDermid et al, 2004;Scott et al, 2005). Densitometric analyses of vesicular glutamate transporter 1 (VGLUT1)-and CTB-positive terminals were performed within the consistent deafferentation gap apparent in C7 after C7/8 DRI.…”