Axotomy of rat facial nerve induces TGF-beta and latent TGF-beta binding protein

Transforming growth factor-beta (TGF-beta) has been found to be abundantly and specifically expressed in the nervous system. However, the function of TGF-beta during nerve regeneration is still unknown. We have examined the expression of TGF-beta isoforms and the latent TGF-beta binding protein (LTBP) by immunohistochemistry in the rat facial nuclei after unilateral axotomy. An increased immunoreactivity for all the TGF-beta isoforms and the LTBP was observed in the facial nuclei of the injured side during the regeneration period examined until Day 24. These differences were tested statistically by nominal logistic regression analysis. When the intensity of the immunoreactivity in the injured side was compared to that of the contralateral side, significantly increasing differences were found for TGF-beta 2 (p < 0.003) and LTBP (p < 0.002). Strong immunostaining was detected in the neuronal perikarya and their axons. No clear immunoreactivity was seen in either microglia or astrocytes. The enhanced immunoreactivity was seen in the operated side already at Day 3, remaining at high level with some fluctuations until Day 12 or 24 after axotomy. These findings suggest that TGF-beta might play a functional role in the regeneration of motor neurons.