Modulation of responses to inflammatory mediators of nociceptive neurons by repeated cold stress loading

环境温度(SART)应激时特定节律的改变会导致痛觉过敏。前列腺素(PG)E2是一种在外周和中枢神经系统均可引起痛觉过敏的物质。我们以前的报告表明，PG EP3受体(EP3R)激动剂在体外利用犬睾丸-精索神经标本增强多模式受体(一种伤害性感受器)对缓激肽(BK)的反应。为了获得EP3R参与BK反应增敏的确凿证据，我们从犬背根神经节(DRG)中克隆并测序了EP3R基因。获得了两个编码具有不同C末端的异构体的不同的cDNA。EP3R激动剂可抑制Forsklin诱导的cAMP升高，而与百日咳毒素共同孵育可使其消失，提示EP3R的两种异构体的激活可通过Gi蛋白抑制Forsklin诱导的cAMP聚集。佐剂性炎症大鼠伤害性感受器的BK敏感性增加。免疫完全弗氏佐剂2周后，RT-PCR检测到大鼠背根神经节B2受体(B2R)mRNA的表达也增加。这一结果表明，慢性炎症增加了伤害性感受器对BK的敏感性，部分原因是BKB2R上调。在SART应激过程中，大鼠体重没有明显增加，机械痛阈值降低。SART应激大鼠下丘脑中促肾上腺皮质激素释放激素(CRH)的表达呈增加趋势。SART应激不会额外降低炎症大鼠的机械痛阈值。慢性炎症引起的痛敏反应可能已达到最大程度，CRH可能诱导了对炎症的部分耐受。

Specific alteration of rhythm in environmental temperature (SART) stress induces hyperalgesia. Prostaglandin (PG) E2 is a substance known to induce hyperalgesia both in the periphery and central nervous system. Our previous report showed that PG EP3 receptor (EP3R) agonist augmented the response of the polymodal receptor, a type of nociceptor, to bradykinin (BK), in vitro, using canine testis-spermatic nerve preparations. To obtain conclusive evidence that EP3R is involved in the sensitization of the response to BK, we cloned and sequenced EP3R cDNA from canine dorsal root ganglia (DRG). Two different cDNAs encoding the isoforms with different C-termini were obtained. EP3R agonist reduced forskolin-induced increase in cAMP in the cells stably expressing either of these variants, and this reduction was abolished by incubation with pertussis toxin, suggesting that the activation of the two isoforms of EP3R exerts an inhibitory effect on the forskolin-induced cAMP accumulation through Gi protein.Effects of SART stress were studied both in normal and in the adjuvant inflamed rats. BK sensitivity of nociceptors increases in adjuvant inflamed rats. The expression of B2 receptor (B2R) mRNA detected with RT-PCR also increased in rat DRG two weeks after inoculation of complete Freund's adjuvant. This result suggests that chronic inflammation increases BK sensitivity of nociceptors, in part with the up-regulation of BKB2R. During SART stress, the body weight of rats did not clearly increase and the mechanical pain threshold decreased. The expression of corticotrophin releasing hormone (CRH) mRNA tended to increase in the rat hypothalamus with SART stress. SART stress did not additionally decrease the mechanical pain threshold in inflamed rats. The hyperalgesia induced by chronic inflammation might have reached the maximum or some tolerance to inflammation might have been induced by CRH.