Bone morphogenetic protein-2, 4, 6 and transforming growth factor-β1 are induced in rat facial nuclei following motoneuron axotomy

Abstract

Transection of the rat facial nerve (FN) leads to a series of retrograde changes within the facial nuclei, which has been called the axon reaction. This reaction includes the rapid activation of both astrocytes and microglia and a change in the gene expression in axotomized motoneurons. In the present study, we investigated the expression of the transforming growth factor-β (TGF-β) superfamily member [bone morphogenetic protein (BMP)-2, 4, 6 and TGF-β1] in the axotomized facial nuclei using in situ hybridization. The aim of the present study was to clarify whether the BMP-2, 4, 6 and TGF-β1 are related to the regenerative and degenerative processes in the axotomized facial nuclei. The results showed that BMP-2 and TGF-β1 mRNA increased gradually after axotomy, and reached the maximal values on day 7 post injury. BMP-6 was expressed abundantly in the facial motoneurons, and no obvious differences were shown in the gene expression after transection of FN. However, no significant signals for BMP-4 in motoneuron were detected at any time point. These results revealed that some members of the TGF-β superfamily such as BMP-2 and TGF-β1, might be involved in glial activation and motoneuron survival, and might be potential neurotrophic factors of FN.