Mismatch between BDNF mRNA and protein expression in the developing visualcortex: the role of visual experience

Brain-derived neurotrophic factor (BDNF) messenger RNA (mRNA) expression in the rat visual cortex of young and postnatal day 90 (P90) animals is devel opmentally regulated and influenced by visual experience. In the present pa per we compared the expression of BDNF mRNA to the actual changes of BDNF p rotein occurring during postnatal development and verified whether BDNF pro tein distribution is controlled by visual activity. To achieve this aim we analysed BDNF mRNA and/or BDNF protein cellular distribution in the rat vis ual cortex at different postnatal ages by using immunohistochemistry and hi ghly sensitive in situ hybridization. We found that before eye opening (P13 ), in all cortical layers a large number of visual cortical neurons contain BDNF mRNA with no detectable amount of BDNF protein. At later ages (P23 an d P90), the number of BDNF-immunostained cells increases; most neurons are double labelled for BDNF mRNA and protein, and a small group of neurons is labelled only for BDNF protein. The cellular increase of BDNF immunolabelli ng is blocked in animals deprived of visual experience from birth (dark rea ring), with a large population of neurons containing BDNF mRNA but not BDNF protein. This is similar to what is observed before eye opening. Exposure of dark-reared rats to a brief period (2 h) of light restores a good match between BDNF mRNA and BDNF protein cellular expression. We propose that vis ual experience controls the neuronal content of BDNF mRNA and BDNF protein in developing visual cortex.