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

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.