Deciphering Ca-controlled biochemical computation governing neural circuit dynamics via multiplex imaging.

In dendrites and synapses in the neuronal circuit, temporal and spatial trains of Ca transients are triggered as a consequence of 4-dimensional patterns of synaptic transmission, local dendritic spikes and action potential firing. Among downstream Ca effectors, Ca/calmodulin-dependent kinase II (CaMKII) and Ca/calmodulin-dependent phosphatase calcineurin (CaN) interactively and competitively regulate essential neuronal functions, such as bidirectional synaptic plasticity, gene expression, learning and memory. New developments in optical imaging and local optical manipulation revealed distinctive spatiotemporal features of bidirectional dendritic spine structural plasticity that are co-regulated by CaMKII and CaN. We created a novel set of genetically-encoded fluorescent probes to specifically investigate key activation processes of CaMKII and CaN in living neurons. Multiplex FRET imaging approaches revealed distinct spatiotemporal properties of CaMKII and CaN co-activation in dendrites and synapses that likely underlie the biochemical machinery to decode information represented in the patterned neuronal input to decide properties of spine structural plasticity. We also created new orthogonal color variants of linearly performing Ca indicators XCaMPs that can be easily multiplexed with a number of other fluorescent probes. These advances facilitate future investigation on how biochemical decoding is achieved in neurons in the living brain, and will shed new light on complex brain information dynamics at the crossroad of neurochemistry, pathophysiology and neuro-inspired engineering.