Abstract
The relationship between electrical activity and spike‐induced Ca^2+^ increases in dendrites was investigated in the identified wind‐sensitive giant interneurons in the cricket. We applied a high‐speed Ca^2+^ imaging technique to the giant interneurons, and succeeded in recording the transient Ca^2+^ increases (Ca^2+^ transients) induced by a single action potential, which was evoked by presynaptic stimulus to the sensory neurons. The dendritic Ca^2+^ transients evoked by a pair of action potentials accumulated when spike intervals were shorter than 100 ms. The amplitude of the Ca^2+^ transients induced by a train of spikes depended on the number of action potentials. When stimulation pulses evoking the same numbers of action potentials were separately applied to the ipsi‐ or contra‐lateral cercal sensory nerves, the dendritic Ca^2+^ transients induced by these presynaptic stimuli were different in their amplitude. Furthermore, the side of presynaptic stimulation that evoked larger Ca^2+^ transients depended on the location of the recorded dendritic regions. This result means that the spike‐triggered Ca^2+^ transients in dendrites depend on postsynaptic activity. It is proposed that Ca^2+^ entry through voltage‐dependent Ca^2+^ channels activated by the action potentials will be enhanced by excitatory synaptic inputs at the dendrites in the cricket giant interneurons. © 2002 Wiley Periodicals, Inc. J Neurobiol 50: 234–244, 2002; DOI 10.1002/neu.10032