5-HT2a receptors in rat sciatic nerves and Schwann cell cultures.

Pharmacological approaches and optical recordings have shown that Schwann cells of a myelinating phenotype are activated by 5-HT upon its interaction with the 5-HT(2A) receptor (5-HT(2A)R). In order to further characterize the expression and distribution of this receptor in Schwann cells, we examined rat sciatic nerve and cultured rat Schwann cells using probes specific to 5-HT(2A)R protein mRNA. We also examined the endogenous sources of 5-HT in rat sciatic nerve by employing both histochemical stains and an antibody that specifically recognizes 5-HT. Rat Schwann cells of a myelinating phenotype contained both 5-HT(2A)R protein and mRNA. In the healthy adult rat sciatic nerve, 5-HT(2A)Rs were evenly distributed along the outermost portion of the Schwann cell plasma membrane and within the cytoplasm. The most prominent source of 5-HT was within granules of the endoneurial mast cells, closely juxtaposed to Schwann cells within myelinating sciatic nerves. These results support the hypothesis that the 5-HT receptors expressed by rat Schwann cells in vivo are activated by the release of 5-HT from neighboring mast cells.