Noggin expression in the adult rat brain.

Bone morphogenetic proteins (BMP) exert its biological functions by interacting with membrane bound receptors. However, functions of BMPs are also regulated in the extracellular space by secreted antagonistic regulators. Noggin is an extracellular BMP antagonist that binds BMP-2/4 with high affinity and thus interferes with binding to BMP receptors. Although noggin expression has been well described in the early development of the CNS, little information is available on its expression in the adult CNS. We, thus, investigated noggin expression in the adult rat CNS using immunohistochemistry. Noggin was intensely expressed in most neurons, and their axons. In addition, strong noggin expression was also observed in the neuropil of the gray matters where high plasticity is reported, such as the molecular layer of the cerebellum and the superficial layer of the superior colliculus. Furthermore, we found that astrocytes and ependymal cells also express noggin protein. These data indicate that noggin is more widely expressed throughout the adult CNS than previously reported, and its continued abundant expression in the adult brain strongly supports the idea that noggin plays pivotal roles also in the adult brain.