Fig. 3

Skeletal muscle properties of p75^NTR−/− mice. a Total protein samples of Gastrocnemius muscles from 2 to 4 months old WT and p75^NTR−/− (n = 4) mice were analyzed by Western blot using specific antibodies to detect myosin heavy chain (MyHC) and Troponin C (TnC). The levels of GAPDH were used as loading control. b Quantification of the relative levels of the sarcomeric proteins was performed by band intensity densitometry and expressed as a ratio of GAPDH band intensity. c Contraction force curve as a function of stimulation frequency (Hz) in isolated TA muscle. d Maximal isometric force was determined in WT (n = 6) and p75^NTR−/− (n = 4) mice. e Cross-sections of TA muscles from 2-months-old WT and p75−/− mice were evaluated by hematoxylin/chromotrope staining (H&C) and WGA plus DAPI staining. Bar: 50 μm. f The percentage of myofibers bearing central nuclei was quantified in WGA/DAPI-stained cryosections of TA muscles from WT (n = 8) and p75^NTR−/− (n = 8) mice. g Cross-sections of TA muscles from both genotypes were stained to analyze inter-fiber protein deposition. Bright field images (fist column) display DAPI nuclear (blue) plus BTX NMJ (magenta) staining. The same sections were processed for immunohistochemical detection of fibronectin (second column), as well as for the two-photon laser-based second harmonic generation technique (third column, SHG) to detect collagen fibers. The insets show high magnification images at the perimysium. The fourth column show the merged images. Bar: 50 μm. h Total protein samples of TA muscles from WT and p75^NTR−/− (n = 3) mice were analyzed by Western blot using a specific antibody to detect fibronectin. The levels of β-actin were used as loading control. i Quantification of the relative levels of fibronectin was performed by band intensity densitometry and expressed as a ratio of β-actin band intensity. j Cross-sections of TA muscles from both genotypes were histochemically stained to detect NADH-TR activity. Scale bar: 50 μm. k Quantification of fiber types in at least 400 fibers per WT or p75^NTR−/− mice. Results are expressed as a percentage of the total quantified fibers in a central region of interest. l Distribution histogram of the cross-sectional area (CSA) of slow-twitch fibers. m Distribution histogram of the CSA of fast-twitch fibers. The results represent the mean ± SEM of n = 8 (WT and p75^NTR−/−) mice by quantifying at least 100 fibers per mice. n.s., non-significant, *p < 0.5; **p < 0.1; ***p < 0.01, unpaired t-test (b, d, f, i) or two-way ANOVA (c, k–m)