Optofluidic control of rodent learning using cloaked caged glutamate

Abstract

Glutamate is the major excitatory neurotransmitter in the brain, and photochemical release of glutamate (or uncaging) is a chemical technique widely used by biologists to interrogate its physiology. A basic prerequisite of these optical probes is bio-inertness before photolysis. However, all caged glutamates are known to have strong antagonism toward receptors of γ-aminobutyric acid, the major inhibitory transmitter. We have developed a caged glutamate probe that is inert toward these receptors at concentrations that are effective for photolysis with violet light. Pharmacological tests in vitro revealed that attachment of a fifth-generation (G5) dendrimer (i.e., cloaking) to the widely used 4-methoxy-7-nitro-indolinyl(MNI)-Glu probe prevented such off-target effects while not changing the photochemical properties of MNI-Glu significantly. G5-MNI-Glu was used with optofluidic delivery to stimulate dopamine neurons of the ventral tegmental area of freely moving mice in a conditioned place-preference protocol so as to mediate Pavlovian conditioning.

Monitoring of uncaging processes by designing photolytical reactions

“…In particular, sophisticated photoremovable groups have been successfully used for in vivo neurophysiological studies. 42 Therefore, newer PPGs have been described with improved photophysical properties, especially shifting the absorption maxima further into the visible/NIR region and enhancing the uncaging efficiency. The transfer of the ''caged" compounds technique to near-infrared region is the cornerstone for in vivo applications.…”

In Vivo Photopharmacology Enabled by Multifunctional Fibers

“…To illuminate the molecular mechanisms underlying neuronal function, a number of chemical and genetic techniques have been developed to place cells under optical control. − As demonstrated by optogenetics, the enhanced spatiotemporal precision attained using an optical stimulus is enabling to understanding how specific circuits control behavior and animal physiology. , However, optogenetics has so far relied on exogenously expressed microbial rhodopsins, thus offering a means to investigate electrophysiological, but not molecular, mechanisms underlying neural dynamics and behavior. Light-controllable ligands present an attractive alternative to optogenetics, as they add an optical switch to a pharmacological agent to place cell signaling pathways under optical control . Of particular utility are azobenzene photoswitches, which can be synthetically incorporated into a small-molecule ligand. , Their activity can then be reversibly tuned using different wavelengths of light via trans/cis isomerization.…”

Neural and behavioral control in Caenorhabditis elegans by a yellow-light–activatable caged compound

“…Light irradiation induces photolysis of the caging groups to restore the bioactivity of these molecules. Since the initial applications of caged cyclic adenosine monophosphate (cAMP) (3) and caged adenosine triphosphate (ATP) (4) in biological experiments, caged compounds have been applied to cultured cells (1), brain slices (5,6), and living animals (7). Although the lightmediated delivery of chemical probes in vivo is challenging, there are reports of photoactivation of neurons in Drosophila by caged ATP (8,9) and photo-mediated gene activation in zebrafish by caged RNA/DNA (10,11).…”