Effects of brain‐derived neurotrophic factor on cell survival, differentiation and patterning of neuronal connections and Müller glia cells in the developing retina

The aim of the present study was to determine the influence of brain‐derived neurotrophic factor (BDNF) on survival, phenotype differentiation and network formation of retinal neurons and glia cells. To achieve a defined concentration and constant level of BDNF over several days, experiments were performed in an organotypic culture of the developing rat retina. After 6 days in vitro, apoptosis in the different cell layers was determined by TUNEL staining and cell‐type‐specific antibodies were used to identify distinct neuronal cell types and Müller cells. Cultured retinas treated with BDNF (100 ng BDNF/mL medium) were compared with untreated as well as with age‐matched in vivo retinas. Quantitative morphometry was carried out using confocal microscopy. BDNF promoted the in vitro development and differentiation of the retina in general, i.e. the number of cells in the nuclear layers and the thickness of the plexiform layers were increased. For all neurons, the number of cells and the complexity of arborizations in the synaptic layers were clearly up‐regulated by BDNF. In control cultures, the synaptic stratification of cone bipolar cells within the On‐ and Off‐layer of the inner plexiform layer was disturbed and a strong reactivity of Müller cell glia was observed. These effects were not present in BDNF‐treated cultures. Our data show that BDNF promotes the survival of retinal interneurons and plays an important role in establishing the phenotypes and the synaptic connections of a large number of neuronal types in the developing retina. Moreover, we show an effect of BDNF on Müller glia cells.