Serotonin receptors expressed by myelinating Schwann cells in rat sciatic nerve.

We have previously reported that Schwann cells cultured from rat sciatic nerves express 5-HT2A receptors. In this study we extend these in vitro observations to Schwann cells in situ. Since the serotonin (5-HT) levels in rat sciatic nerve are elevated following nerve injury, we examined Schwann cells in healthy and injured adult rat sciatic nerves. These nerves were double-labeled immunohistochemically with an anti-idiotypic antibody that recognizes 5-HT1B, 5-HT2A, and 5-HT2C receptors and an antibody against S100beta, a Schwann cell marker. 5-HT receptor labeling was observed in Schwann cells of healthy and regenerating nerves, but not of degenerating nerves, while S100beta labeling was observed in the Schwann cells of all nerves examined. The 5-HT receptor immunolabeling was cytoplasmic, as with the cultured Schwann cells. While staining was observed at the nodes of Ranvier, it was not restricted to these locations. These results suggest that myelinating rat Schwann cells normally express 5-HT receptors in vivo, and that receptor expression is reduced during times when 5-HT levels are elevated in the sciatic endoneurium.