Genetically encoded sensors enable micro- and nano-scopic decoding of transmission in healthy and diseased brains

Abstract

Neural communication orchestrates a variety of behaviors, yet despite impressive effort, delineating transmission properties of neuromodulatory communication remains a daunting task due to limitations of available monitoring tools. Recently developed genetically encoded neurotransmitter sensors, when combined with superresolution and deconvolution microscopic techniques, enable the first micro- and nano-scopic visualization of neuromodulatory transmission. Here we introduce this image analysis method by presenting its biophysical foundation, practical solutions, biological validation, and broad applicability. The presentation illustrates how the method resolves fundamental synaptic properties of neuromodulatory transmission, and the new data unveil unexpected fine control and precision of rodent and human neuromodulation. The findings raise the prospect of rapid advances in the understanding of neuromodulatory transmission essential for resolving the physiology or pathogenesis of various behaviors and diseases.

The Property-Based Practical Applications and Solutions of Genetically Encoded Acetylcholine and Monoamine Sensors

“…The finding of restricted neuromodulatory transmission has multiple implications. Like several other transmission parameters, such as the amount of released transmitter, width of synaptic clefts, and location of postsynaptic transmitter receptors across various synapses (Savtchenko and Rusakov, 2007;Savtchenko et al, 2013;Haas et al, 2018), spatial spread length constants of neurotransmitters (i.e., glutamate, ACh, monoamines, and neuropeptides) are almost identical across various cell types (Lin et al, 2021;Zhu et al, 2020). These results support the idea that synapses optimize their nanoscale presynaptic and postsynaptic organizational elements to maximize efficacy and precision.…”

“…Indeed, initial experimental work validates that genetically encoded sensors, when combined with superresolution and deconvolution microscopic analysis, can decode the fundamental synaptic properties of neuromodulatory transmission (Borden et al, 2020;Lin et al, 2021;Zhu et al, 2020). It is important to note that both high-performing sensors and good practical solutions are critical for the success of biological applications (Lin et al, 2021;Zhu et al, 2020). We discussed how genetically encoded neuromodulatory transmitter sensors might advance our understanding of Alzheimer's disease, sleep-wake cycle and related sleep disorders, and tumorigenesis.…”

“…Moreover, iAChSnFRs had a large response dynamic range, allowing further improvement of fluorescence response (Borden et al, 2020). Notably, iAChSnFRs exhibited sufficient spatial and temporal resolution to allow characterization of fundamental synaptic properties of cholinergic transmission, including transmitter diffusion extent, number of release sites, release pool size, release probability, quantal size, and refilling rate, in various preparations (Borden et al, 2020;Lin et al, 2021;Zhu et al, 2020).…”

“…However, small and rapidly desensitizing neuromodulatory currents make electrophysiology an ineffective approach to determine synaptic parameters of neuromodulatory transmission. Some genetically encoded transmitter sensors possess kinetics fast enough to follow slow neuromodulatory synaptic releases evoked by moderate (actually, more physiological) rates of stimulation over a prolonged period (Borden et al, 2020;Lin et al, 2021;Zhu et al, 2020). This should permit reasonably accurate estimation of neuromodulatory synaptic properties (e.g., number of release sites, release pool size, release probability, quantal size, and refilling rate) (Neher, 2015;Pulido and Marty, 2017).…”

GESIAP: A Versatile Genetically Encoded Sensor-based Image Analysis Program

“…Recently developed genetically encoded sensors for neuromodulatory transmitters provide new opportunities to monitor and quantitate neuromodulation (Sabatini and Tian, 2020; Labouesse and Patriarchi, 2021; Lin et al, 2021; Wu et al, 2022). Indeed, both theoretical (Lin et al, 2021) and preliminary experimental (Zhu et al, 2020) analyses have shown that several genetically encoded transmitter sensors emit a large number of photons following transmitter binding to enable high-resolution visualization of the process. However, most genetically encoded transmitter sensors remain underused, due mainly to the lack of user-friendly analysis programs for high-sensitivity, high-resolution visualization of transmitter release.…”