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Abstract:

Objective To investigate the expression and impact of the supraoptic hyperpolarization⁃activated cyclic nucleotide gated 2（HCN2）on chronic visceral hypersensitive（CVH）rats. Methods Neonatal male Sprague⁃ Dawley rats were randomly divided into sham operated（Sham）group，colorectal distention（CRD）group，Vehicle group，ZD7288 1 ng group，ZD7288 10 ng group and ZD7288 100 ng group. Neonatal CRD was enrolled to establish the rat models of CVH. ZD7288，the inhibitor HCN2，was stereotactically injected in supraoptic nuclei（SON）at the 8th postnatal week，and the effects of ZD7288 on visceral sensation were assessed via procedures of abdominal withdrawal reflex（AWR）score，visceral pain threshold and the electromyograph（EMG）of external oblique muscle discharge. All rats were sacrificed by 4% ⁃ paraformaldehyde perfusion or decapitation，and the brains and colons （between left curvature of colon and the pelvis）were collected for further detections. The hematoxylin⁃eosin（HE） staining of colon tissue was performed to avoid subjects with organic conditions. The supraoptic expression of HCN2 and c⁃Fos were detected by immunohistochemistry，immunofluorescence and Western blot. Results Morphological detection showed that there were no obvious morphological changes in rats with the use of colonic HE staining. Compared with Sham group，the expression of supraoptic HCN2 was significantly upregulated in CRD group by immunohistochemistry and Western Blot（P < 0.05）；the c⁃Fos positive cells in SON were significantly increased in CRD group by immunohistochemistry（P < 0.05）；the number of HCN2 and c⁃Fos co⁃labeled cells in SON were significantly increased by immunofluorescent（P < 0.05）. Behavioral and electrophysiological tests showed that the stereotactic injection of ZD7288 in SON dose⁃dependently increased the AWR scores and AUC，and decreased the visceral pain threshold compared with the Vehicle group（P < 0.05）. Conclusions SON inhibits the chronic visceral hypersensitivity via the upregulation of HCN2 in rats.

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