To investigate the effect of calcium modulatol (chelator and channel blocker) on the processing of afferent inputs at the spinal cord (SC) level, the responses of spinal dorsal horn cells (DHC) to mechanical stimulation of the receptive field were determined in the cat before and after direct application of EDTA (ethylene diamine tetraacetic acid), Mn^(2+), verapamil and ryanodine to the sulrface (approximately 1cm²) of the SC around the recording electrode.
Also studied was the effect of calcium applied directly to the surface of the SC on the EDTA-induced suppression of DHC responses to natural stimuli. The responses of DHC to mechanical stimuli were suppressed strongly by EDTA and Mn^(2+), and moderately by verapamil. Ryanodine had no significant effect on the activity of DHC. When calcium was applied following EDTA application, the reduced responses of the wide dynamic range (WDR) cells to brush, pressure and pinch were recovered to 151.4%, 55.I% and 66.1% of the control value, respectively. Intravenous adnlinistration of meperidine resulted in a suppression of DHC response to natural stimuli and the supressed activities of these cells were further decreased by verapamil applied to SC.
The results suggest that calciunl modulator may exert analgesic effects by the reduction in release of transmitters as a result of dlecreased Ca^(2+) level of the spinal cells involved in transmission of nociceptive signals.
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