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The Distribution of the Noiciceptin System in the Central Nervous System
Laboratory for Cellular Information Processing |
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The nociceptin system has the physiological function to facilitate the transmission of pain, whereas the opioid system has the function of reducing pain. In this way, their physiological functions are quite opposite. However, these two systems share many similarities. The nociceptin peptides and nociceptin receptors that constitute the nociceptin system have similar structures to the opioid peptides and opioid receptors respectively. In addition to their similarities in molecular structure, these two systems also share the same intra-cellular signal transduction pathways that inhibit neuronal activities as has been shown before by our laboratory. The reason why these similar systems are involved in quite opposite physiological functions has never been explained previously.
We have recently succeeded in elucidating the above problem by detailed analysis of the mRNA distribution of the nociceptin precursors and receptors in the central nervous system, thereby clarifying that the precursor mRNA is present mainly in inter-neurons while the receptor mRNA is homogeneously distributed in principle neurons. This characteristic distribution pattern was also observed in the relaying nuclei of the neural pathway regulating analgesia, which differed from the distribution pattern of the molecules in the opioid system. The descending analgesic pathway is usually inhibited by inter neurons but, when the opioid receptor is activated by an opioid release, the analgesic pathway is activated through the inhibition of inter neurons. On the other hand, nociceptin is released from the inter neurons and nociceptin receptors are shown to be present in the principle neurons of the analgesic pathway, so it is suggested that the activation of the nociceptin system results in the inhibition of the analgesic pathway. The reason why these two similar systems function differently is due to the differences in the distribution of their molecular components in the brain.
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Ikeda, K., Watanabe, M., Ichikawa, T., Kobayashi, T., Yano, R., Kumanishi, T.
Distribution of prepro-noiciception/orphanin FQ mRNA and its receptor mRNA in developing and adult mouse central nervous systems.
J. Comp. Neurol., 399, pp.139-151 (1988)
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Differences in the distribution of molecular components of the nociceptin and opioid systems in descending analgesic pathway
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