NGF, BDNF, NT-3, and GDNF mRNA expression in rat skeletal muscle following denervation and sensory protection.

Poor muscle and nerve functional recovery after nerve damage is a serious clinical problem, particularly if there is prolonged delay before nerve-muscle contact is reestablished. Our previous studies showed that sensory nerve cross-anastomosis (sensory protection) provides support to the denervated muscle. In the present study, we analyzed neurotrophic factor mRNA expression by RT-PCR in denervated rat gastrocnemius muscle receiving sensory protection with the saphenous nerve, compared to normal innervated muscle, to denervated muscle, and to denervated muscle repaired immediately with the peroneal (motor) nerve, after periods of 3 days to 3 months. No significant differences in mRNA levels of beta-actin, nerve growth factor, brain-derived neurotrophic factor or neurotrophin-3 were found between the sensory protection treatment and the denervated or the motor repair groups. However, sensory protection resulted in levels of muscle glial cell line-derived neurotrophic factor mRNA expression that were lower than in denervated muscle and higher than in muscle given immediate motor repair. These results demonstrate that glial cell line-derived neurotrophic factor mRNA is elevated following denervation but is partially down-regulated by sensory protection. Our study suggests that sensory protection provides a modified trophic environment by modulating neurotrophic factor synthesis in muscle.