In ovo neuromuscular stimulation alters the skeletal muscle phenotype of the chick

Abstract

4-aminopyridine (4-AP) is a drug that blocks the potassium channels in neurons and stimulates the release of the neurotransmitter acetylcholine (ACh), enhancing its availability at the synaptic cleft. The effects of 4-AP induced neuromuscular stimulation on skeletal muscle formation and development were investigated in embryonic chicks. Fertile white Leghorn eggs were incubated at 37.5 degrees C and windowed on day three of incubation. On embryonic days (E) 10, 11, 12 and 13 half of the eggs were injected with 100 microl of PBS buffer containing 0.2 microg 4-AP and the control group was administered 100 microl of PBS only. 4-AP treated (T) embryos showed at least a 10% increase in mean body mass relative to the controls (C) (P<0.05) at ages E14, E15 and E16. Tibia and femur lengths in the 4-AP treated embryos were significantly greater than the controls at E15 and E16 (P<0.05). The 4-AP treated animals had a 36.8% greater number of myofibres than the control animals at E20. Nuclear number per cross sectional area in the M. Semitendinosus was significantly greater (P<0.01) at E16 in the treated compared to the control embryos. The 4-AP treated group exhibited a greater percentage area of oxidative fibres in cross sections of M. Semitendinosus than the control group at E16 (P<0.01) and at E20 (P<0.05). It may be concluded from these results that 4-AP induced neuromuscular stimulation has a significant effect on skeletal muscle characteristics, leg bone length and overall body mass.

Neuromuscular stimulation causes muscle phenotype‐dependent changes in the expression of the IGFs and their binding proteins in developing slow and fast muscle of chick embryos

“…Taken together, these results suggest a down-regulation of the IGF actions in the fast muscle upon treatment, which is almost the opposite situation of that observed in the slow muscle. Based on the current knowledge of the IGF functions, a diminution of IGF bioavailability in the fast muscle would lead to impaired muscle development and growth, which is contradictory to the myotrophic effects of the drug as previously observed in the mixed semitendinosus muscle (Heywood et al, 2005). There is no clear explanation for this finding, but the data suggest that the effects of increased movement on muscle development and growth may be differently mediated in fast and slow muscles.…”

“…As IGF-1 is known to promote cell proliferation and differentiation, it thus appears that an up-regulation of this gene upon treatment may constitute a mechanism for the increased nuclear and fiber number previously reported (Heywood et al, 2005). The increase in IGF-1, however, was not accompanied by an increase in IGF-2 in the slow muscle, suggesting that the effect of movement on muscle development are unlikely to be directly mediated through IGF-2 expression levels.…”

“…Given that increased movement in ovo affects skeletal muscle development and growth (Heywood et al, 2005) and that the IGF system is largely involved in the regulation of myogenesis (Florini et al, 1996), we examined whether the effects of movement on muscle development could be partially mediated through the IGF system. We also took into account that the IGF system may respond differently to movement, depending on the phenotype of the muscle.…”

“…Our previous experiments have indicated that the developmental process of proliferation and differentiation during secondary myogenesis can be manipulated by means of the stimulation of movement in ovo during midembryogenesis and that excess movement in ovo increased the oxidative capacity as well as altered the fiber number immediately pre-hatch (Heywood et al, 2005). Studies in mammals have also shown that various factors, such as movement (Willis et al, 1998) and overloading of mature skeletal muscle (Awede et al, 1999), affect the regulation of the insulin-like growth factor (IGF) system.…”

Advances in research on the prenatal development of skeletal muscle in animals in relation to the quality of muscle-based food. I. Regulation of myogenesis and environmental impact

“…Fibre number and oxidative capacity were also increased in the Musculus semitendinosus (ST) of the stimulated chicks before hatching (Heywood et al, 2005). Neuromuscular stimulation caused muscle phenotype-dependent changes in the expression of the IGFs and their binding proteins in developing slow and fast muscle of chicken embryos (McEntee et al, 2006).…”