NADPH-diaphorase neurons contacting the cerebrospinal fluid in the ventricles of rat brain.

Two populations of scattered neurons containing nitric oxide synthase activity were detected in the wall of the third and lateral cerebral ventricles of rat brain, using histochemistry for NADPH-diaphorase activity. One type was multipolar and lay supraependymally, with dendrites oriented in the plane of the ependymal layer. The second type was bipolar and was situated subependymally, with dendrites extending in opposite directions, either into the surrounding brain tissue or to the ventricular surface. Moreover, multipolar neurons, situated in the corpus callosum and in the subcortical white matter, had long varicose dendrites extending toward the roof of the lateral ventricles. As a result, numerous NADPH-diaphorase neurites spread out on the free surface of the ependymal layer in contact with the CSF. These observations raise the possibility that periventricular nitrergic neurons play an essential role in registering the composition of the CSF and in modulating subcortical cerebral blood flow. A further possibility is that supraependymal nitrergic neuronal processes are effectors regulating activity of ependymal cells.