A direct projection from the tuberomammillary nucleus to the spinal cord in the rat.

After injections of retrograde fluorescent tracers (True blue (TB), Diamidino yellow (DY) and Fluorogold) into the upper cervical segments of the rat spinal cord, a group of labeled neurons were consistently found bilaterally in the tuberomammillary nucleus (TM) of the hypothalamus with an ipsilateral predominance. The data from injections of two different tracers (TB and DY) in the same animal suggest that the vast majority of TM cells projecting to the spinal cord rarely give off divergent axon collaterals to the frontal/prefrontal cortices, striatum, amygdala and superior colliculus.