In both stimulation contexts, we show that bath application of D2-type DA receptor antagonist sulpiride and agonist quinpirole modulates nIRCat signals in a manner consistent with predicted effects of presynaptic D2 autoreceptor manipulation. Next, we use optogenetic stimulation to demonstrate selectivity of the nIRCat nanosensor response to dopaminergic over glutamatergic terminal stimulation. Second, we demonstrate that nIRCats exhibit a fractional change in fluorescence that has the dynamic range and signal-to-noise ratio to report DA efflux in response to brief electrical or optogenetic stimulation of dopaminergic terminals. nIRCats respond to DA with Δ F/ F of up to 24-fold in the fluorescence emission window of 1000 to 1300 nm ( 24), a wavelength range that has shown utility for noninvasive through-skull imaging in mice ( 25).įirst, we show in vitro characterization of the nanosensor’s specificity for the catecholamines DA and NE and demonstrate its relative insensitivity to the neurotransmitters GABA, GLU, and acetylcholine (ACH), as well as the neuromodulators histamine, serotonin, tyramine, and octopamine.
This technology makes use of an SWNT noncovalently functionalized with single-strand (GT) 6 oligonucleotides to form the nIR catecholamine nanosensor (nIRCat).
In this work, we describe the design, characterization, and implementation of a nanoscale nIR nongenetically encoded fluorescent reporter that allows precise measurement of catecholamine dynamics in brain tissue. nIR fluorescent, polymer-functionalized semiconducting single-wall carbon nanotubes (SWNTs) provide a versatile platform for optical probe synthesis to image a diverse set of biomolecular analytes, several of which have shown in vivo functionality ( 21– 23). To this end, we designed a synthetic optical probe that can report extracellular catecholamine dynamics with high spatial and temporal fidelity within a unique near infrared (nIR) spectral profile. To understand how neuromodulation sculpts brain activity, we sought to develop new tools that can optically report modulatory neurotransmitter concentrations in the brain extracellular space (ECS) in a manner that is compatible with pharmacology and other available tools to image neural structure and activity. However, the spatial limitations of fast-scan cyclic voltammetry (FSCV) and spatial and temporal limitations of microdialysis narrow our ability to interpret how neuromodulators affect the plasticity or function of individual neurons and synapses.
The absence of direct change in ionic flux across cell membranes, which is measurable using available tools such as electrophysiology or genetically encoded voltage indicators, has necessitated the use of methods borrowed from analytical chemistry such as microdialysis and amperometry to study the dynamics of neuromodulation. Thus, modulatory neurotransmitter activity extends beyond single synaptic partners and enables small numbers of neurons to modulate the activity of broader networks ( 20). In contrast, neuromodulators (catecholamines and neuropeptides) may diffuse beyond the synaptic cleft and act via extrasynaptically expressed metabotropic receptors ( 14– 19). In synaptic glutamatergic and GABAergic neurotransmission, neurotransmitter concentrations briefly rise in the synaptic cleft to mediate local communication between the pre- and postsynaptic neurons through the rapid activation of ligand-gated ion channels ( 13). Modulatory neurotransmission is thought to occur on a broader spatial scale than classic neurotransmission, the latter of which is largely mediated by synaptic release of the amino acids glutamate (GLU) and γ-aminobutyric acid (GABA) in the central nervous system.
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