Involvement Of Adrenomedullin In The Development Of Bone Cancer Pain And Neuropathic Pain And Its Underlying Mechanisms

Adrenomedullin (AM) is newly confirmed a pronociceptive mediator which belongs to calcitonin gene-related peptide (CGRP) family. Widely exists in the spinal dorsal horn and the peptide and non-peptide neurons in dorsal root ganglia (DRG). Studies have shown that AM is a pronociceptive mediatorare, but the mechanism of AM participating in chronic hyperalgesia is not yet clear. Designed to reveal the role of AM in neuropathic and the relationship between AM and CGRP, IL-1β, NO in chronic neuropathic pain. This study based on bone cancer pain, sciatic nerve ligation models, introducing experimental techniques like imaging, behavioral, immunohistochemistry and quantitative real-time polymerase chain reaction (qRT-PCR) to investigate (1)the changes of hyphology and behavioristics cause from bone cancer (2)the effect of bone cancer pain on the expressions of AM、AM receptor、CGRP and nNOS in spinal dorsal horn and DRG (3)the effect of AM specific receptor antagonist AM22-52(10nM/10 μl) on threshold of pain and the expression of AM、CGRP、nNOS (4)the effect of peripheral nerve injury on mechanical withdrawal threshold and the expression of AM、CGRP、IL-1β in rats (5)the effect of AM22-52(20 nM/10 μl) on behavior in SNL rats (6)the effect of AM22-52 on the expression of AM、CGRP、IL-1β in DRG and spinal dorsal horn in SNL rats. Results showed as follows:(1) On the 7th day after bone cancer surgery, there has been appearing weight loss, bone destruction, mechanical hyperalgesia and thermal hyperalgesia obviously;(2) Bone cancer pain resulted in significantly increased expressions of AM、AM receptor、CGRP and nNOS in spinal dorsal horn and DRG, and staining showed that the majority of AM is located in the small diameter neurons in DRG;(3) Bone cancer pain-induced hyperalgesia in paw was reversed by intrathecal ad ministration of AM22-52(10 nM/10μl), Furthermore, AM22-52 also reduced the expression of AM, CGRP, nNOS in the spinal dorsal horn and DRG;(4) The paw withdraw pressure threshold dropped to about 50% of the baseline latency on 10th day after spinal nerve ligation, and the expression of AM、 CGRP、IL-1β in spinal dorsal horn and DRG were increased significantly;(5) Intrathecal administration of AM22-52(20 nM/10μl) can relieve the threshold respectively caused by SNL;(6) Intrathecal administration of AM22-52, expressions of CGRP in DRG and spinal dorsal horn were inhibited significantly, while AM and IL-1β were increasing;These results show that bone cancer and nerve injury could increase the AM synthesis, while blocking AM receptor can obviously relieve the pain. AM could be the upstream of pronociceptive mediator CGRP and pro-inflammatory cytokines as IL-1β and nNOS in neuropathic pain-induced cell signaling cascades. At the same time, in addition to the AM and CGRP, there may be other signaling pathway which needed further study induced proinflammatory factor, as IL-1β to participate in the formation of hyperalgesia.