The Distribution of Nitric Oxide Synthase Positive Cerebrospinal Fluid contacting Neurons in the Surrounding Region of the Third Ventricle in the Rat

Objective:To observe the morphology and dis tribution o f nitric oxide synthase(NOS) positive cerebrospinal fluid(CSF) contacting neuro ns in the surrounding region of the third ventricle in the rat. Methods: NADPH diaphorase histochemistry method was used to investi ga te the distribution of NOS positive CSF contacting neurons in the surrounding r egion of the third ventricle in the rat. Results:NOS positive CSF contacting neurons were scattered at the s ur rounding region of the third ventricle, from anterior ventral area to posterior d orsal area. These neurons could be classified in four types. They were located i n the ependymal layer, subependymal layer. Some of them were located where there was some distance to the ependyma, but they had some processes protruded into t he third ventricle. In the anterior parts of posterior magnocellar paraventricular nuclei and medial magnocellar paraventricular nuclei, there were a large number of NOS positive fibers extending to the third ventricle, mixing with or contacti ng processes of NOS positive CSF contacting neurons. Conclusion: NO S positive CSF contacting neurons in the surrounding re gion of the third ventricle were very close to the CSF. So, we suggested that th ese neurons may acquire information from the CSF and release NO into the CSF, an d play an important role in neurohumoral regulation.