Autocrine BDNF secretion enhances the survival and serotonergic differentiation of raphe neuronal precursor cells grafted into the adult rat CNS.

RN46A cells are a temperature-sensitive neuronal cell line derived from the E13 rat raphe nucleus. RN46A cells grafted into the adult rat hippocampus and cerebral cortex do not survive beyond 2 weeks. Brain-derived neurotrophic factor (BDNF) regulates the in vitro survival and serotonergic phenotype of RN46A cells, and we hypothesized that expression of BDNF in RN46A cells would potentiate their survival and serotonin (5HT) expression in vivo. The gene encoding rat BDNF was transfected into RN46A cells and the clonal 46A-B14 cell line isolated, 46A-B14 cells synthesize and secrete biologically active BDNF in vitro and synthesize 5HT following partial membrane depolarization. Two weeks following 46A-B14 cell transplantation into the adult rat cortex and hippocampus, there is a threefold increase in survival of 46A-B14 cells compared to RN46A cells transfected with the vector alone. The grafted 46A-B14 cells immunohistochemically stain for BDNF and 5HT, while RN46A cells transfected with vector only are negative for both BDNF and 5HT. In addition, 46A-B14 cells attain more morphologically complex phenotypes, indicating enhanced neuronal differentiation. Autocrine secretion of BDNF by RN46A cells thus potentiates survival and can be used to deliver both BDNF and 5HT in vivo.