Signaling Pathways Regulating Synaptic Vesicle Dynamics

Tufts University, Medford MA

Investigators

Abstract

Neurons communicate with one and other primarily by secreting chemical neurotransmitters that influence the electrical or biochemical activities of neighboring cells. These neurotransmitters are stored in small organelles called synaptic vesicles that are localized to presynaptic nerve endings. In order for neurotransmitter to be secreted, a synaptic vesicle must fuse with the surface membrane at the nerve terminal, which allows neurotransmitter to diffuse to the nearby target neurons. This tightly regulated fusion process is the fundamental event in interneuronal communication. Recent work has revealed that vesicle fusion is a low probability event related to the number of synaptic vesicles docked with the active zone, the site at which fusion occurs. A dynamic equilibrium exists between vesicles that are fusion-competent and the majority of vesicles that are held in reserve; this equilibrium is regulated in a Ca2+-dependent manner. The molecular basis for these Ca2+-dependent changes in the brain is incompletely understood, in part because billions of microscopic nerve terminals are distributed throughout the brain, making it difficult of impossible to synchronize the activity of the nerve terminals in an intact preparation. Work proposed by Dr. turner is designed to study the signaling pathways that regulate synaptic vesicle dynamics using synaptosomes, a preparation of isolated nerve terminals that is relatively uniform in composition. Dr. Turner's laboratory will use synaptosomes to measure biochemical changes in the activities of specific signaling pathways that have been implicated in regulating synaptic vesicle maturation, including Ca2+-regulated kinases and a monomeric GTP-binding known as Ral. In parallel, the relevance of these signaling pathways will be evaluatued by measuring the strength of synaptic transmission in a more intact preparation, the acute brain slice obtained from cerebellum. The parallel fiber to Purkinje cell synapse found in this preparation is a well-characterized excitatory synapse that should be representative of excitatory synapses found in all parts of the brain. Simultaneous measurements of neurotransmitter release and the attendant changes in cytoplasmic signaling pathways will advance a more detailed understanding of the mechanisms that underlie Ca2+-dependent changes in synaptic strength important to interneuronal signaling in the brain. The impact of this work will extend broadly throughout neuroscience because of the fundamental importance of synaptic transmission in information processing by the brain, for features including sensory reception, motor control, attention and decision, and learning and memory. In addition, this project will help launch the independent career of a young investigator.