Caged compounds for multichromic optical interrogation of neural systems

Abstract

Caged compounds have widely used by neurophysiologists to study many aspects of cellular signaling in glia and neurons. Biologically inert before irradiation, they can be loaded into cells via patch pipette or topically applied in situ to a defined concentration, photolysis releases the caged compound in a very rapid and spatially defined way. Since caged compounds are exogenous optical probes, they include not only natural products such neurotransmitters, calcium and IP3, but non-natural products such as fluorophores, drugs and antibodies. In this Technical Spotlight we provide a short introduction to the uncaging technique by discussing the nitroaromatic caging chromophores most widely used in such experiments (e.g. CNB1, DMNB, MNI and CDNI). We show that recently developed caging chromophores (RuBi and DEAC450) that are photolyzed with blue light (ca. 430–480 nm range) can be combined with traditional nitroaromatic caged compounds to enable two-color optical probing of neuronal function. For example, one-photon uncaging of either RuBi-GABA or DEAC450-GABA with a 473-nm laser is facile, and can block non-linear currents (dendritic spikes or action potentials) evoked by two-photon uncaging of CDNI-Glu at 720 nm. We also show that two-photon uncaging of DEAC450-Glu and CDNI-GABA at 900 and 720 nm, respectively, can be used to fire and block action potentials. Our experiments illustrate that recently developed chromophores have taken uncaging out of the “monochrome era”, in which it has existed since 1978, so as to enable multichromic interrogation of neuronal function with single synapse precision.

Calcium Uncaging with Visible Light

“…Subsequently several chromophores have been used for uncaging of biological signaling molecules with blue light 16–21 . Photochemical protecting groups sensitive to green light have also been reported 22–24 , but to our knowledge no biological studies have appeared with these probes.…”

Cloaked Caged Compounds: Chemical Probes for Two‐Photon Optoneurobiology

“…Since we have shown that DEAC450 uncaging is highly wavelength-selective for 2P excitation at 900 nm [27] , our data suggest the cloaked caged neurotransmitter G5-DEAC450-GABA could be very useful for chromatically selective, two-color optoneurobiology.…”

“…Prior irradiation of the apical dendrite with 900nm (3 × 3 ms, 50 mW) elicited pronounced hyperpolarization, which blocked the action potential, which was restored when only short wavelength irradiation was used ( Figure 5). Since we have shown that DEAC450 uncaging is highly wavelength-selective for 2P excitation at 900 nm [27] , our data suggest the cloaked caged neurotransmitter G5-DEAC450-GABA could be very useful for chromatically selective, two-color optoneurobiology.Certainly it is the first example of a caged GABA compound that is highly active to 2P …”

Medicinal chemistry of adenosine, P2Y and P2X receptors

“…The γ-thiophosphate group impedes (Malmsjö et al, 2003), but does not completely prevent its enzymatic hydrolysis. A caged form of ATP 69 , which regenerates ATP upon irradiation has been studied and is potentially useful for studies of P2Rs (Amatrudo et al ., 2015). Similarly, the 1-(3,4-dimethyloxy-6-nitro-phenyl)ethyl (DMNPE) group was used to block the β-phosphate of agonist 65 to abolish its activity at the P2Y 1 R and P2Y 12 R, and this activity could be recovered upon irradiation (Gao et al ., 2008).…”