Copper is an endogenous modulator of neural circuit spontaneous activity

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 two-photon 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. Significance Copper is traditionally regarded as a static, tightly bound cofactor in enzymes, but emerging data link more-loosely bound pools to cell signaling. Here we use molecular imaging to identify a role for copper in the brain as a modulator of spontaneous activity of developing neural circuits. First, we directly visualized a labile, loosely bound copper pool in hippocampal neurons and retinal tissue with a newly developed Copper Fluor-3 (CF3) indicator. We then used two-photon calcium imaging as readout of spontaneous activity to show that disruption of labile copper stores by acute chelation or genetic knockdown of the CTR1 (copper transporter 1) copper channel alters the frequency and spatial propagation of neural activity. The results establish the requirement for copper in a fundamental, dynamic property of brain circuitry.