Abstract
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.
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