Background:It is well known that physical training can promote the development of muscle and nerve function in gross motor development period, but the mechanisms of what happened
inside the muscle and nerve structures still need to be further revealed. The aim of this study is to evaluate the effects and mechanisms of swimming in postnatal neuromuscular junction (NMJ)
development and to provide theoretical evidences for promotion effects of physical training in early stage after birth.
Methods:Neonatal Sprague-Dawley rats were divided into control group（group C）and training group（group T）. Rats in group T performed 3 weeks of swimming training (6 days per week,
10mins at the beginning gradually increased to 1h per day) and were fed in the same manner with rats in group C at the rest of the time. At the end of 3-week after birth which is also considered as
the end of gross motor development of rats, NMJ endplate area perimeters and square meters in frozen sections of gastrocnemius were observed and measured through α-BTX
(α-Bungarotoxin-tetramethylrhodamine) fluorescent staining. Expressions level of γ-, ε-and δ-nAchR (3 main subunits of n-acetylcholine receptors) as well as neuron-derived induced factor Agrin and its
receptor Musk, muscle-derived neurotrophic factor NT-3 were measured through fluorogenic quantitative PCR and compared between group T and C. Independent T-test was used to test the significance of
difference between groups.
Results:The perimeter and square meter of endplate area in gastrocnemius of group T were significantly larger and complex than that of group C. The expression level of ε-AchR subunit
(which is considered as mature type of n-AchR), neuron-derived induced factor Agrin and its receptor Musk were higher in group T than in group C as well. Expression level of other factors showed no
significant difference in this experiment.
Conclusions:Swimming can promote the development of NMJ in gastrocnemius both in form and main structural components in early stage after birth which is related to the development of
gross motor. The corresponding increased expression level of induced factor Agrin and its receptor Musk in muscle and nerve may act as one of the main mechanisms in this process.