Differential effect of morphine on trigeminal nucleus versus reticular aversive stimulation: independence of negative effects from stimulation parameters.

Electrodes were implanted in mesencephalic, pontine, and bulbar reticular formation, and in spinal trigeminal nucleus and tract of rats. Central and peripheral aversive response thresholds were studied under normal conditions and with morphine. Peripherally elicited aversive reactions were assessed with tail-flick, hot-plate, and footshock responses.