Fluorescent Biosensors for Neurotransmission and Neuromodulation: Engineering and Applications

Abstract

Understanding how neuronal activity patterns in the brain correlate with complex behavior is one of the primary goals of modern neuroscience. Chemical transmission is the major way of communication between neurons, however, traditional methods of detection of neurotransmitter and neuromodulator transients in mammalian brain lack spatiotemporal precision. Modern fluorescent biosensors for neurotransmitters and neuromodulators allow monitoring chemical transmission in vivo with millisecond precision and single cell resolution. Changes in the fluorescent biosensor brightness occur upon neurotransmitter binding and can be detected using fiber photometry, stationary microscopy and miniaturized head-mounted microscopes. Biosensors can be expressed in the animal brain using adeno-associated viral vectors, and their cell-specific expression can be achieved with Cre-recombinase expressing animals. Although initially fluorescent biosensors for chemical transmission were represented by glutamate biosensors, nowadays biosensors for GABA, acetylcholine, glycine, norepinephrine, and dopamine are available as well. In this review, we overview functioning principles of existing intensiometric and ratiometric biosensors and provide brief insight into the variety of neurotransmitter-binding proteins from bacteria, plants, and eukaryotes including G-protein coupled receptors, which may serve as neurotransmitter-binding scaffolds. We next describe a workflow for development of neurotransmitter and neuromodulator biosensors. We then discuss advanced setups for functional imaging of neurotransmitter transients in the brain of awake freely moving animals. We conclude by providing application examples of biosensors for the studies of complex behavior with the single-neuron precision.

Neuromodulatory pathways in learning and memory: Lessons from invertebrates

“…For example, novel neuropeptide vesicle exocytosis reporters that relay changes in acidity between the dense core vesicle lumen and the extracellular space were recently used to visualise neuropeptide release in Drosophila 90 and C. elegans 91 . GPCR‐based ligand sensors to visualise neuromodulator action at a cellular resolution have also been developed by various research groups 92,93 . Although they have yet to be applied in the study of learning circuits, these tools are certain to improve our understanding of neuromodulatory signalling within these circuits.…”

Defect Engineering in Ambipolar Layered Materials for Mode‐Regulable Nociceptor

“…Here, the laser spikes irradiating the PdSe 2 channel emulate the input stimulus from the presynapse and its controllable transconductance is analogized as the postsynaptic weight; the back gate bias in particular resembles the extra neuromodulator required to affect neuron activities via long‐range volume transmission (inset of Figure a). [ 48 ] The typical EPSC and IPSC can be triggered by input laser spike under modulation by different electrostatic gating signals (Figure 4a,c). Under the same irradiation conditions, the recorded currents increased under the bias condition of −30 V, while they decreased under the bias condition of −60 V; this mainly stemmed from the photo‐induced doping effect.…”

Neuronal Activity at Synapse Resolution: Reporters and Effectors for Synaptic Neuroscience

“…In recent years, genetic sensors for modulators, such as dopamine, norepinephrine, and others, have been reported. While they have been shown to detect neuromodulators release in vivo, their relatively low fluorescence has so far limited their use to whole-cell applications (Leopold et al, 2019). Hence, they do not seem to detect the release of neuromodulators at single synapses or release terminals.…”