Using novel and validated tools to study the distribution and biosynthesis of brain-derived neurotrophic factor in the rodent brain

Brain-derived neurotrophic factor (BDNF) is a critical modulator of neuronal survival, synaptic transmission, and activity-dependent plasticity. In humans, a single nucleotide polymorphism in the BDNF pro-domain is associated with reduced memory performance, whereas deletion of a single BDNF allele results in mental retardation, increased food intake and abnormal weight gain. As the enhancement of BDNF signalling is an attractive therapeutic prospect in the context of brain dysfunction, there is a need for a better understanding of the brain circuitry using BDNF as a quasi-neurotransmitter. The lack of sufficient knowledge about the localisation of BDNF in the brain is largely due to its very low abundance and the lack of reliable tools faithfully reporting its localisation. To circumvent these difficulties, validated BDNF antibodies were used here that reliably detected BDNF expression in the CNS. These antibodies were first used to examine the biosynthesis of the endogenous protein in cultured neurons. The biosynthesis of the wildtype protein was then compared with tagged versions of BDNF using in vitro expression systems. These experiments revealed that the addition of large probes widely used in the BDNF field impaired the biological processing and secretion of the mature protein. These in vitro experiments also included the validation of a novel Bdnf cDNA construct, that was next utilised in vivo to generate a viable and fertile mouse model that reports Bdnf translation using green fluorescent protein (GFP). Using a novel BDNF localisation strategy, the detection of endogenous BDNF in the neural circuits relevant to spatial memory was also achieved in the rat brain. The contribution of past and present tools toward developing a better understanding of the biology of BDNF in neural circuits is also discussed