Subcellular Topography of Visually Driven Dendritic Activity in the Vertebrate Visual System

Neural pathways projecting from sensory organs to higher brain centers form topographic maps in which neighbor relationships are preserved from a sending to a receiving neural population. Sensory input can generate compartmentalized electrical and biochemical activity in the dendrites of a receiving neuron. Here, we show that in the developing retinotectal projection of young Xenopus tadpoles, visually driven Ca(2+) signals are topographically organized at the subcellular, dendritic scale. Functional in vivo two-photon Ca(2+) imaging revealed that the sensitivity of dendritic Ca(2+) signals to stimulus location in visual space is correlated with their anatomical position within the dendritic tree of individual neurons. This topographic distribution was dependent on NMDAR activation, whereas global Ca(2+) signals were mediated by Ca(2+) influx through dendritic, voltage-dependent Ca(2+) channels. These findings suggest a framework for plasticity models that invoke local dendritic Ca(2+) signaling in the elaboration of neural connectivity and dendrite-specific information storage.