Copper is an endogenous modulator of neural circuit spontaneous activity

Abstract

For reasons that remain insufficiently understood, the brain requires among the highest levels of metals in the body for normal function. The traditional paradigm for this organ and others is that fluxes of alkali and alkaline earth metals are required for signaling, but transition metals are maintained in static, tightly bound reservoirs for metabolism and protection against oxidative stress. Here we show that copper is an endogenous modulator of spontaneous activity, a property of functional neural circuitry. Using Copper Fluor-3 (CF3), a new fluorescent Cu + sensor for one-and twophoton imaging, we show that neurons and neural tissue maintain basal stores of loosely bound copper that can be attenuated by chelation, which define a labile copper pool. Targeted disruption of these labile copper stores by acute chelation or genetic knockdown of the CTR1 (copper transporter 1) copper channel alters the spatiotemporal properties of spontaneous activity in developing hippocampal and retinal circuits. The data identify an essential role for copper neuronal function and suggest broader contributions of this transition metal to cell signaling.copper signaling | fluorescent sensor | molecular imaging | neural activity

Voltage-sensitive rhodol with enhanced two-photon brightness

“…We reasoned that the conversion of fluorescein-based VF dyes into unsymmetrical rhodol-based reporters, in which one of the oxygen atoms at the 3′-and 6' positions of the xanthene chromophore is replaced by a substituted nitrogen (28), would improve photostability and two-photon absorbance (σ 2 ). Introduction of asymmetry in the chromophore axis increases the extent of intramolecular charge transfer, enhancing efficiency of σ 2 (measured in Göppert-Mayer units of 10 −50 cm 4 s photon −1 ·molecule −1 ) (27).…”

The Intestinal Copper Exporter CUA-1 Is Required for Systemic Copper Homeostasis in Caenorhabditis elegans

“…Staining with the Copper Probe CF4 and LysoTracker-The Copper Fluor-4 (CF4) sensor combines a piperidine-substituted rhodol with a trifluoromethyl-substituted bottom ring bearing a thioether receptor, along with a matched control Copper Fluor-4 (Control CF4) dye that lacks the copper-responsive receptor to help distinguish between copper-dependent and dye-dependent responses (30,63). Replacement of the thioether-rich receptor arms for copper recognition in CF4 by isostructural octyl groups in control CF4 provides a mimic of the size, shape, and hydrophobicity of thioethers but do not bind copper, offering a matched pair of probes to disentangle copper-dependent fluorescence responses from potential dyedependent ones.…”

Synthetic fluorescent probes for studying copper in biological systems

“…Of the five initial targets made, Copper Rhodol 3 (CR3) was the best performing dye in the series, exhibiting a 13-fold turn-on response to Cu(I) binding in vitro (Figure 3). 43 The substitution of a methyl group on the pendant aryl ring with a more bulky trifluoromethyl group afforded Copper Fluor-3 (CF3, Figure 3). This CH 3 to CF 3 substitution serves two purposes; first, it minimizes non-radiative decay from aryl-aryl rotations that may limit quantum yields, and second, it favours PET quenching in the unbound state by withdrawing electron density from the aryl ring.…”