The effect of exposure to positive space charge on aversive responses to noxious stimuli in rats.

Exposure of rats to positive atmospheric ions for four days or longer results in an increase in aversive response times (tail flick and hot-plate). While these effects are similar to those produced after opiate administration, they could not be inhibited by naloxone treatment. Prompt reversal of the positive ion analgesic effect, however was brought about by treatment with parachlorophenylalanine which lowers brain serotonin levels. The data suggest that the action of positive ions on the pain inhibitory system is dependent upon an intact serotonin pathway and that the effects on this system are mediated via central rather than peripheral neural mechanisms.