PROJECT SUMMARY Brain derived neurotrophic factor (BDNF) is a prevalent neurotrophin that modulates synaptic physiology and plasticity in the central nervous system. Multiple lines of evidence point towards its involvement in mental health disorders such as depression and schizophrenia, as well as the biological basis for an antidepressant effect. Yet despite its demonstrated involvement in neuropsychiatric diseases, very few studies have investigated how BDNF affects the presynaptic terminal, despite it being a fundamental component of neurotransmission. This is in part due to the difficulty of studying the presynapse and the lack of available technology to do so until more recently. Previously published work using viral manipulation in hippocampal slices demonstrates that BDNF acts upon the high affinity TrkB receptor at the presynapse to increase release probability, or the likelihood that a vesicle will be release in response to an action potential. With the resulting hypothesis that BDNF signaling specifically targets presynaptic function via TrkB signaling pathways, this proposal aims to investigate the molecular basis of BDNF’s effect at the presynapse. This will be done through the following: first, examining the effect of BDNF on excitatory neurotransmission (subaim 1.1). Preliminary data from subaim 1.1 show that in dissociated hippocampal cultures, release probability at excitatory synapses is increased in response to acute BDNF treatment in a manner dependent on TrkB activation. Subaim 1.2 will dissect the potential mechanisms underlying this effect through using pharmacological approaches to screen for potential downstream pathways that are involved in this effect. Because the spatiotemporal context of BDNF activity is critical in its effect, I will also use cTrkB KO hippocampal cultures to examine the spontaneous and evoked release events as a result of endogenous BDNF manipulation (subaim 1.3). Local calcium transients at synapses are strongly linked to neurotransmitter release, especially evoked release. I will thus investigate how presynaptic calcium transients are affected by exogenous BDNF (subaim 2.1), endogenous BDNF using cTrkB cultures (subaim 2.2), and whether BDNF utilizes calcium to modulate neurotransmission (subaim 2.3). The proposed studies will involve optical imaging of in vitro neuron cultures transfected or infected with fluorescent probes to study the presynase, as well as pharmacological and genetic manipulation tools to provide further mechanistic insight into findings. This research will further current understanding of the fundamental role of BDNF at the synapse, with implications for improving current therapeutics such as for antidepressants. The proposed research will be accomplished through a thoughtfully developed training plan that involves opportunities to further critical thinking skills, technical expertise, and scientific communication. Additionally, the research environment provided by the MSTP, Va...