Neurons compute using a vast array of diverse signals, in which millisecond-scale electrical pulses are complemented by slower membrane potential changes and by slower neuromodulator-driven signals that operate over a broad range of timescales (from seconds to hours), to govern neuroplasticity and neural information processing. Optogenetics (the use of light to control genetically-defined cells within neural tissue) has enabled control over fast electrical events, but has left control over neuromodulatory and slower events relatively unexplored. This deficiency in optogenetics represents an enormous unmet need, as neuromodulator-driven plasticity is likely to be important in Parkinson's Disease, addiction, depression, and many other neuropsychiatric processes, while transient electrical events simply do not capture the full complexity of neural information processing. Uncaging strategies can release second messengers such as Ca2+ and cAMP (just as glutamate uncaging can control fast electrical events);however, uncaging involves bulk application of synthetic UV-releasable compounds that are neither suitable for in vivo use, nor useful for driving genetically-targeted cell types. Moreover, key neuromodulators such dopamine and norepinephrine (which the brain delivers in temporally precise, pulsed, phasic or tonic patterns depending on the situation) do not recruit a single messenger, but rather act on target cells to recruit a complex fabric of intracellular messengers that would be impossible to recapitulate with current technologies. Thus, there is no temporally-precise method to control neuromodulation in defined cells within living animals.
In Aim 1, we will molecularly engineer novel versatile tools for optical recruitment of neuromodulatory signals, including those downstream of the G-protein coupled receptors linked to virtually every neuromodulator system.
In Aim 2, we will engineer strategies for long-timescale electrical control, focusing on identification and molecular optimization of proteins that provide for generation of stably modulated electrical states.
In Aim 3, we will adapt the novel tools from Aims 1 and 2 for targeting to specific locations in specific cell types, and in Aim 4, we will validate the novel tools, integrated with custom optical hardware in freely-moving mice, to test the causal roles of specific modulation patterns in behavioral conditioning. The new technologies, encompassing light sensor/effectors, devices, and targeting tools, will be 1) designed for versatile application across diverse fields;2) distributed to the scientific community, and 3) applied to mammalian models in our laboratory. This approach leverages our work on optical control of electrical events, but opens the door to a much broader landscape. Indeed, the anticipated impact is movement toward a network engineering approach that spans timescales and modalities, in which complex excitable-tissue function is understood in terms of system properties emerging from interacting electrical and biochemical signals.
We propose to develop a new generation of generalizable optical neuromodulatory technologies to directly address the need for both biochemical and electrical neuromodulation on long timescales. The tools developed and disseminated here should be applicable by neuroscientists to most cells, circuits, and animal models. Achieving this new perspective could help change the landscape of our understanding of normal physiology and neuroplasticity, and help move toward insights into the etiology and treatment of neuropsychiatric disease.
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