CAREER:Modulation of the Presynaptic Action Potential Shape and Impact on Synaptic Function

Dartmouth College, Hanover NH

Investigators

Abstract

Everything animals see and do is controlled by electrical signals in their nerves and muscle. Ion channels, which function like tiny pores in the cell membrane, are crucial for sensing and generating electrical signals. The synaptic terminal connections between brain cells are where electrical signals initiate the release of neurotransmitters. Identifying the ion channels present at nerve terminals holds great promise for the development of future therapeutics. Measuring ion channels at nerve terminals is difficult due to their small size. The investigator has recently developed sensitive optical approaches that allow the measurement of electrical signals in nerve terminals with light. The goals of this project are to utilize this optical approach to: (1) identify ion channel compositions within nerve fibers crucial for sensing and generating electrical signals; (2) understand how the changing electrical signals alters synaptic communication; as well as (3) promote the understanding and use of quantitative fluorescent microscopy across undergraduate institutions in New Hampshire to foster innovation in the research workforce. Transfer of an electrical signal from one neuron to another (i.e. synaptic transmission) typically involves rapid depolarization of the presynaptic terminal, the entry of calcium ions, membrane fusion of vesicles that contain neurotransmitter signaling to the postsynaptic neuron. This sequence is set in motion by a rapid membrane depolarization, or action potential (AP), invading the presynaptic terminal. AP shape has often been ignored as a malleable signal at the subcellular level and is assumed to propagate as a uniform spike across thousands of synaptic contacts. This project will challenge this perception of the AP as an unchanging "all-or-none" waveform and address a fundamental gap in the understanding of axon physiology and synaptic transmission. The central hypothesis of this project is that after initiation, an AP is malleable and undergoes local "sculpting" during propagation throughout the axonal arborization, and this consequentially impacts presynaptic function. The investigator has developed sensitive optical approaches that allow the quantification of changes in membrane voltage using light that bypasses previous technical barriers to measure voltage in small cellular compartments such as the axon. Using these genetically encoded voltage indicators the PI will: (1) Determine how and where an AP is sculpted along the axon and pre-synaptic terminals; (2) Determine how AP shape drives calcium influx and activation of calcium sensors at the molecular level to impact vesicle fusion, using a combination of quantitative optical sensors. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.