Figure 1

Identification of neurotrophic factors and their receptors within native intervertebral disc tissue. Percentage expression is represented as the number of disc samples in each cohort that expressed the target gene, shown by the number above the bars. Bars represent the levels of mRNA expression seen in these samples. Expression of neurotrophic nerve growth factor (NGF) (A) and its receptor tropomyosin kinase (Trk)A (B), of brain-derived neurotrophic factor (BDNF) (C) and its receptor TrkB (D), and of neurotrophin 3 (NT3) (E) and its receptor TrkC (F) in human intervertebral discs graded histologically: grade 0 to 3, n = 8; grade 4 to 6, n = 12; grade 7 to 12, n = 20; infiltrated, n = 12 samples of intervertebral disc tissue. *Statistical significance between levels of gene expression: P ≤ 0.05. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.