Objective To evaluate the role of cerebrospinal fluid-contacting nuclei (CSF-CN) in maintenance of chronic itch in rats.Methods Forty-two adult male Sprague-Dawley rats,aged 3 months,weighing 240-280 g,were used in the study.The experiment was performed in two parts.Part Ⅰ Forty-two Sprague-Dawley rats were randomly divided into 3 groups (n =14 each):control group (C group),acetone group (A group) and oxazolone group (O group).0.5％ oxazolone 15 μl was applied to the neck and back of rats in group O,while the equal volume of normal saline and acetone was applied in groups C and A,respectively.Application of the drug mentioned above was repeated on day 7,9,13,16,17,18,21 and 23 after the first stimulation in each rat in each group.Scratching behaviors were oberserved within 30 min after each stimulaiton.Six rats in each group were chosen and sacrificed after the last application of oxazolone,and the brains were obtained for determination of c-Fos expression in CSF-CN.Part Ⅱ Twenty-four rats were randomly divided into 3 groups (n =8 each):control group (C1 group),chronic itch group (group CI),and chronic itch + lesion group (CI + KA group).Chronic itch was induced by repeated application of oxazolone as previously described in CI and CI + KA groups.The chemical lesion of CSF-CN was performed at 6 h after 8th application of the drug.Then the scratching behaviors were observed within 30 min after 9th application of the drug.Results Part Ⅰ Compared with C group,the scratching behaviors were increased significantly at T4-8 in A group,and at T1-8 in O group (P ＜ 0.05),and the expression of c-Fos was up-regulated in O and A groups (P ＜ 0.05).Compared with A group,the scratching behaviors were increased significantly at T1-8 and the expression of c-Fos was up-regulated in O group (P ＜ 0.05).Part Ⅱ Compared with C1 group,the scratching behaviors were significantly increased in CI and CI + KA groups (P ＜ 0.05).The scratching behaviors were significantly reduced in CI + KA group compared with CI group (P ＜ 0.05).Conclusion CSF-CN is involved in the maintenance of chronic itch in rats.

Objective To investigate the effect of sciatic nerve injection of dexmedetomidine on the nociceptive behavior and spi-nal c-fos expression in formalin mice .Methods Adult male Kunming mice ,20-25 g ,were divided into 4 groups randomly :mice in group A and D were given an injection of NS (10 μL) and 0 .1 μg dexmedetomidine in 10 μL adjacent to the right sciatic nerve , sepretely .Mice in group B received intacutaneous injection of 10μL formalin(5% ) in the right hindpaws .Mice in group C were giv-en an injection of 0 .1 μg dexmedetomidine in 10 μL adjacent to the right sciatic nerve 15 min before formalin injection in the right hindpaws .Paw licking/biting time was counted every 5 min for an hour after hindpaw injections ,calculated pain score .1 hour after behavior tests ,the L4-5 of spinal cord were harvested to immunofluorescence for c-fos expression in the dorsal corn of spinal cord . Results Mice in group A、C and D showed no obvious foot licking/biting behaviors and a low level of c-fos expression in the dorsal corn of spinal cord .Compared with group A ,mice in group B displayed obvious two phases foot licking/biting behaviors(P<0 .05 , both in Phase Ⅰ and Phase Ⅱ) and a significant increasing expression of c-fos(P<0 .05) .Compared with group B ,dexmedetomi-dine injected to the adjacent of right sciatic nerve decreased the pain score and spinal c-fos expression in goup C(P<0 .05) .Conclu-sion Injection of dexmedetomidine to the right sciatic nerve alleviated intraplantar injected formalin-induced acute inflammatory pain ,and reduced the expression of spinal c-fos protein .