In vivo Ca2+ imaging was applied to the cricket median giant interneuron (MGI), to visualize the dendritic processing of mechanosensory signals. Wind stimulation (air-puff) to the cerci induced a transient increase in the cytosolic Ca2+ concentration ([Ca2+](i)) in the MGI with a latency of a few seconds, suggesting the release of Ca2+ from the intracellular store site in the MGI. The amplitude of the transient increase in [Ca2+](i) in the dendrites depended on the direction of the air-puff, and the increase in [Ca2+](i) evoked by the air-puff was suppressed by the hyperpolarizing current injection which blocked the generation of action potentials. These results indicate that the action potential is necessary to the direction-sensitive increase in [Ca2+](i) induced by wind stimulation. Copyright (C) 1999 Elsevier Science Ireland Ltd.
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