Differential effects of systemic versus intracranial injection of opiates on central, orofacial and lower body nociception: somatotypy in bulbar analgesia systems.

1 microgram morphine sulfate or 30 microgram [D-Ala2]-met-enkephalin microcannulated into the bulbar nuclei reticularis gigantocellularis and paragigantocellularis produced profound analgesia for orofacial thermal nociception, while having a smaller analgesic effect on tail-flick latency, and no effect on aversive stimulation thresholds in midbrain and in the spinal trigeminal nucleus (subnucleus caudalis). Systemic morphine (10 mg/kg) producing equivalently profound orofacial analgesia, profoundly affected tail-flick latency and trigeminal nuclear stimulation thresholds, while still failing to affect aversive midbrain stimulation threshold.