Neuropeptide Y innervation of nitric oxide-synthesizing sympathetic preganglionic neurons in humans.

We sought to determine whether neuropeptide Y (NPY) terminals are concentrated in the intermediolateral (IML) cell column and innervate human NADPH-diaphorase (NADPH-d)-reactive sympathetic preganglionic neurons (SPNs). Spinal cords were obtained at autopsy from one man and two women, cut into segments, and immersion fixed in 2% paraformaldehyde for 24 h. The T1, T3, T6 and T8 spinal cord segments were cut serially at 50 microns in the coronal, sagittal and horizontal planes. Alternating consecutive sections were double stained for NADPH-d and NPY or NPY alone. NPY-immunoreactive fibers were identified at all levels analyzed and varicosities appeared to run and cover the NADPH-d processes for long distances. NPY-immunoreactive varicosities were heavily concentrated around the soma and proximal dendrites of NADPH-d SPNs. NPY may exert many possible actions at the level of the IML cell column. Depletion of NPY-containing bulbospinal neurons may contribute to sympathetic failure in disorders such as multiple system atrophy.