Effects of opioids and opioid peptide on the release of substance P-like material induced by tooth pulp stimulation in the trigeminal nucleus caudalis of the rabbit.
The superficial layer in subnucleus caudalis of the brain-stem trigeminal sensory nuclear complex (SpVc) in the rabbit was perfused with artificial cerebrospinal fluid using a push-pull perfusion cannula system. Immunoreactive substance P (iSP) and [Met5]enkephalin (iME) released into the perfusates following electrical stimulation of the lower incisor pulp were measured. An increase in the release of iSP and iME lasting for 1 h or more was observed following electrical stimulation with 40 V. The increase in iSP release depended on the intensity of stimulation. Systemic morphine (10 mg/kg i.v.) completely inhibited the stimulus-evoked iSP release and this inhibition was antagonized by pretreatment with naloxone (5 mg/kg i.v.). The stimulus-evoked iSP release was also inhibited by local application of morphine (10(-6) M) or the opioid peptide [D-Ala2,Met5]enkephalinamide (10(-4) M). However, the local application of naloxone (5 X 10(-7) M) only partially antagonized the inhibitory effects of locally applied morphine and the opioid peptide. These results suggest that there is a functional interaction between SP and enkephalin systems in the superficial layer of SpVc for the regulation of dental pain transmission.
D000818:Animals; D003782:Dental Pulp / Q000502:physiology*; D004558:Electric Stimulation; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology; D011817:Rabbits; D013373:Substance P / Q000378:metabolism*; D014278:Trigeminal Nuclei / Q000187:drug effects / Q000378:metabolism*
D013373:Substance P; D009270:Naloxone; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D009020:Morphine