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

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Abstract
Morphine sulfate [1 .mu.g] or [D-Ala2]-met-enkephalin [30 .mu.g] microcannulated into the bulbar nuclei reticularis gigantocellularis and paragigantocellularis of rats 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.