A direct projection from the ventromedial nucleus and retrochiasmatic area of the hypothalamus to the medulla and spinal cord of the rat.

After injections of the fluorescent retrograde tracers bisbenzimide, 'true blue', 'granular blue' and Evans blue in the medulla oblongata (centered in the solitary nucleus) or in upper thoracic spinal segments, a continuous group of labeled neurons was found scattered throughout the retrochiasmatic area and ventral parts of the ventromedial nucleus of the hypothalamus, predominantly on the side ipsilateral to the injection sites. Findings after injections of two different tracers in the same animal (bisbenzimide and 'true blue', Evans blue and 'granular blue') suggest that about 15% of the labeled neurons in the above areas distribute divergent axon collaterals to both the medulla and the spinal cord.