目的：通过抑制ＮＯ合酶，观察大鼠中缝背核５ＨＴ神经元免疫阳性反应的变化，旨在探讨脑内内源性ＮＯ与５ＨＴ神经元之间的关系。方法：应用免疫组织化学技术，观察大鼠腹腔给予ＮＯ合酶抑制剂—硝基左旋精氨酸（ＬＮＮＡ）后不同时间（１ｈ，２ｈ，４ｈ）中缝背核５ＨＴ神经元免疫阳性细胞数的变化。结果：给予ＬＮＮＡ后２～４ｈ，大鼠中缝背核５ＨＴ神经元阳性细胞数明显增多。与对照组比较，Ｐ＜００１。结论：内源性ＮＯ合成抑制可使中缝背核５ＨＴ神经元免疫阳性反应增强。提示中缝背核５ＨＴ神经元的功能活动可能与脑内ＮＯ有关。 OBJECTIVE: To observe the changes of 5-HT neurons in the dorsal raphe nucleus of rats by inhibiting NO synthase, and to explore the relationship between brain endogenous NO and 5HT neurons. Methods: Immunohistochemistry was used to observe the immunoreactivity of dorsaluclear 5HT neurons in different time (1h, 2h, 4h) after intraperitoneal administration of nitric-L-arginine (LNNA) Changes in cell number. Results: 2 ~ 4h after administration of LNNA, the number of 5HT neurons in dorsal raphe nucleus of rats increased significantly. Compared with the control group, P <001. Conclusion: Inhibition of endogenous NO synthesis can enhance the immunoreactivity of 5HT neurons in dorsal raphe nucleus. Tip dorsal raphe 5 HT neuronal function may be related to brain NO.