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Muscle satellite cell (SC) regulation is a complex process involving many key signalling molecules. Recently, the neurotrophinbrain-derived neurotropic factor (BDNF) has implicated in SC regulation in animals. To date, little is known regarding the roleof BDNF in human SC function in vivo. Twenty-nine males (age, 21 ± 0.5 years) participated in the study. Muscle biopsies from thethigh were obtained prior to a bout of 300 maximal eccentric contractions (Pre), and at 6 h, 24 h, 72 h, and 96 h postexercise.BDNF was not detected in any quiescent (Pax7+/MyoD−) SCs across the time-course. BDNF colocalized to 39% ± 5% of proliferating(Pax7+/MyoD+) cells at Pre, which increased to 84% ± 3% by 96 h (P < 0.05). BDNF was only detected in 13% ± 5% of differentiating(Pax7−/MyoD+) cells at Pre, which increased to 67% ± 4% by 96 h (P < 0.05). The number of myogenin+ cells increased 95% from Pre(1.6 ± 0.2 cells/100 myofibres (MF)) at 24 h (3.1 ± 0.3 cells/100 MF) and remained elevated until 96 h (cells/100 MF), P < 0.05. Theproportion of BDNF+/myogenin+ cells was 26% ± 0.3% at Pre, peaking at 24 h (49% ± 3%, P < 0.05) and remained elevated at 96 h(P < 0.05). These data are the first to demonstrate an association between SC proliferation and differentiation and BDNFexpression in humans in vivo, with BDNF colocalization to SCs increasing during the later stages of proliferation and earlydifferentiation. [ABSTRACT FROM AUTHOR]

The percutaneous muscle biopsy procedure is an invaluable tool for characterizing skeletal muscle and capillarization. Little is known about methodological or biological variation stemming from the technique in heterogeneous muscle. Five muscle biopsies were taken from the vastus lateralis of a group of young men (n = 29, 22 ± 1 years) over a 96-h period. We investigated the repeatability of fibre distribution, indices of muscle capillarization and perfusion, and myofibre characteristics. No differences between the biopsies were reported in myofibre type distribution, cross-sectional area (CSA), and perimeter. Capillary-to-fibre perimeter exchange index and individual capillary-fibre contacts were unchanged with respect to the location of the muscle biopsy and index of capillarization. The variability in the sampling distribution of fibre type specific muscle CSA increased when fewer than 150 muscle fibres were quantified. Variability in fibre type distribution increased when fewer than 150 muscle fibres were quantified. Myofibre characteristics and indices of capillarization are largely consistent throughout the vastus lateralis when assessed via the skeletal muscle biopsy technique. Novelty Markers of muscle capillarization and perfusion were unchanged across multiple sites of the human vastus lateralis. Myofibre characteristics such as muscle cross-sectional area, perimeter, and fibre type distribution were also unchanged. Variation of muscle CSA was higher when fewer than 150 muscle fibres were quantified. [ABSTRACT FROM AUTHOR]

Aging gradually renders bone marrow hematopoietically inactive. Endurance exercise reverses this phenotype in young mice. Here, we determine the effects in aged mice. Twenty-two month old mice ( n = 6) underwent a progressive exercise training protocol. In appendicular bones, marrow cellularity increased by 51% ( p < 0.05) and marrow CFU, CFU-GM, and CAFC increased by 12%, 71%, and 86%, respectively ( p < 0.05). Vertebral cellularity remained unchanged. The mechanical forces associated with treadmill exercise training may be responsible for these observations. [ABSTRACT FROM AUTHOR]