Action of brain-derived neurotrophic factor on function and morphology of visual cortical neurons

Brain-derived neurotrophic factor (BDNF) is known to play a role in experience-dependent plasticity of the developing visual cortex. For example, BDNF acutely enhances long-term potentiation and blocks long-term depression in the visual cortex of young rats. Such acute actions of BDNF suggested to be mediated mainly through presynaptic mechanisms. A chronic application of BDNF to the visual cortex of kittens is known to expand ocular dominance columns in the cortex. With the method of direct intranuclear injection of plasmid cDNAs of BDNF tagged with green fluorescence protein (GFP) we have demonstrated that BDNF-GFP is transferred from presynaptic axon terminals to postsynaptic neurons in an activity-dependent manner, suggesting the possibility that BDNF also has chronic postsynaptic actions. In this study, however, it was not clear whether endogenous BDNF exerts such a postsynaptic action, because BDNF-GFP is a kind of artificial protein. In a subsequent study, therefore, we tested whether endogenous BDNF has any effect on dendritic morphology of postsynaptic neurons in igchimera culture of visual cortical neurons prepared from two types of transgenic mice, GFP mice and BDNF knockout mice. Neurons derived from the former mice have endogenous BDNF as well as GFP. We found that neurons derived from the latter mice, BDNF (-/-) neurons, have relatively poor dendrites if they were not contacted by GFP-positive terminals, whereas BDNF (-/-) neurons had complex dendritic morphology if they were directly contacted by GFP-positive terminals and thus supplied with endogenous BDNF. These results indicate that endogenous BDNF play a role in development of dendrites of visual cortical neurons in an activity-dependent manner.