Involvement of descending monoaminergic systems in the transmission of dental pain in the trigeminal nucleus caudalis of the rabbit.
Perfusates were taken from the superficial layers of the subnucleus caudalis of the trigeminal sensory nuclear complex (SpVc), the first relay station of dental pain, with a push-pull cannula system and were assayed for endogenous serotonin (5-HT) and catecholamines by high-pressure liquid chromatography with an electrochemical detection. Spontaneous release of 5-HT and epinephrine was observed, while that of norepinephrine was not. Tooth pulp stimulation (ST) tended to increase the level of 5-HT in the perfusates. Pretreatment with morphine at a dose of 10 mg/kg (i.v.) significantly enhanced the release of 5-HT. However, there was no significant difference in morphine effect on the 5-HT level between stimulated and non-stimulated animals. Systemic administration of morphine (10 mg/kg i.v.) completely inhibited the release of immunoreactive substance P from the superficial layers of SpVc evoked by ST, and this inhibition was antagonized by local application of methysergide (10(-4) M). These results suggest that in the superficial layers of SpVc, morphine may primarily activate the descending 5-HT pathway which serves to modulate dental pain transmission.
Yonehara
N
N
Department of Pharmacology, Faculty of Dentistry, Osaka University, Japan.
Shibutani
T
T
Imai
Y
Y
Inoki
R
R
D000818:Animals; D004837:Epinephrine / Q000378:metabolism*; D008297:Male; D009020:Morphine / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology*; D011817:Rabbits; D012701:Serotonin / Q000378:metabolism*; D014070:Tooth / Q000187:drug effects / Q000294:innervation*; D014279:Trigeminal Nucleus, Spinal / Q000378:metabolism / Q000503:physiopathology*
D012701:Serotonin; D009020:Morphine; D004837:Epinephrine