Study on the presence of the specific substances participating in the transmission of particular kinds of sensation

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Since immunocytochemical analyses have demonstrated that many substances such as substance P(SP), enkephalin(Enk), calcitonin gene-related peptide(CGRP), somatostatin, etc. occur in the primary sensory neurons and the spinal dorsal horn, an involvement of these peptides in pain transmission arrest our sttentions. But it has't been made clear what role each peptide plays in the pain transmission. There is possibility that the specific substances which participate in the transmission of particular kinds of sensation may be released from the central endings of the primary sensory neurons in the spinal dorsal horn. On the basis of this assumption, the superficial layer in subnucleus caudalis of the brain-stem trigeminal sensory nuclear complex(SpVc-I,II), the first relay station for dental pain, was perfused with artificial cerebrospinal fluid using a push-pull perfusion cannula system. Immunoreactive peptides released into the perfusate following tooth pulp stimulation were measured to id … More entify substances transmitting dental pain sensation in SpVc-I,II.1. Electrical stimulation with 40V square wave of supramaximal intensity showed a significant increase in the release of SP and Met-Enk, and showed a tendency to increase in the release of CGRP. However, a stimulus-evoked release of neurokinin A, which is one of a family of tachykinins as wellas SP and coexists with SP in the primary sensory neurons, was not observed.2. The administration of opioids markedly inhibited the stimulus-evoked SP release and this inhibition was antagonized by the pretreatment with naloxone.3. The spontaneous release of serotonin and epinephrine were observed. And the release of not epinephrine but serotonin was remarkably increased by the pretreatment with morphine4. The stimulus-evoked SP release was inhibitd by local application of serotonin into SpVc-I,II through the push-pull cannula or an electrical stimulation of raphe magnus, the origin of the descending serotonergic system. These results indicate that SP is a potential transmitter which participate in the transmission of dental pain in SpVc-I,II, and the stimulus-evoked SP release may be regulated by enkephalinergic system(segmental inhibitory system) and serotonergic system(descending inhibitory system). Less