Immunocytochemical identification of long ascending, peptidergic lumbar spinal neurons terminating in either the medial or lateral thalamus in the rat.

The peptidergic content of rat spinothalamic tract neurons was investigated by combining the retrograde transport of the fluorescent dye Fluoro-gold with immunocytochemistry for enkephalin, dynorphin or vasoactive intestinal polypeptide. Evidence is presented for the existence of enkephalin and dynorphin in a subpopulation of spinothalamic neurons terminating in the medial thalamus and vasoactive intestinal polypeptide in a subpopulation terminating primarily in the lateral thalamus.