Neuropeptide Y-immunoreactive spinal neurons make close appositions on axons of primary sensory afferents

The dorsal cells in the lamprey are primary sensory neurons located in a parasagittal region of the spinal cord. In the same plane neuropeptide Y (NPY) immunoreactivity has been described. To investigate if the dorsal cells were in contact with NPY-immunoreactive (ir) fibers and cell bodies, intracellular injections of Lucifer yellow into identified dorsal cells were combined with NPY immunohistochemistry. NPY-ir varicosities were found to be in close apposition to both the descending and the ascending axon of dorsal cells. No NPY-ir boutons were seen in close contact with the dorsal cell bodies.