Skeletal muscles are a target for motoneurons and synthesize neurotrophins, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5). Both at the embryonic stage and the adult stage, the mRNA expression of neurotrophins in skeletal muscles of rats has been reported. However, little was known about the mRNA expression patterns of neurotrophins in skeletal muscles of rats at the young developmental stage. In this study, we investigated the mRNA expressions of BDNF and NT-3 in three different skeletal muscles in 4 - to 8 - week - old rats using the reverse transcriptional polymerase chain reaction (RT-PCR) method. The expression of BDNF mRNA in the soleus muscle gradually became higher with age from 5 to 8 weeks. But BDNF mRNA in the tibialis anterior and extensor digitorum longus muscles did not change with growth. The expression of NT-3 mRNA did not show a specific tendency during this period. The differences of muscle fiber types, recruitment patterns of the muscles, and roles of neurotrophins may cause these mRNA expression patterns.

Neurotrophins are target-derived, activity-dependent neurotrophic factors and are transported retrogradely. There is a possibility that the different expression patterns of neurotrophins in muscles may be involved in the maturation of neuromuscular function in different muscles during the young developmental period.