A direct neural projection from the nucleus of the solitary tract to the subfornical organ in the rat.

A direct neuronal projection from the nucleus of the solitary tract (NTS) to the subfornical organ (SFO) in rats was demonstrated using the Phaseolus vulgaris leucoagglutinin (PHA-L) anterograde tracing technique. Small deposits of PHA-L were iontophoretically placed within the caudal parts of the nucleus of the solitary tract. Brain sections were processed for visualization of PHA-L using the avidin-biotin immunoperoxidase technique. PHA-L immunoreactive beaded axons were observed within the subependymal and central parts of the SFO. The results demonstrate an anatomical substrate for direct feedback from cardiovascular regions of the NTS to the SFO. This pathway may be important for relaying blood pressure and associated body fluid volume changes to the SFO.