Immunoreactive enkephalin is contained within some trigeminal and spinal neurons projecting to the rat medial...

In order to determine whether enkephalin is contained within rat trigeminothalamic and spinothalamic neurons, we have combined the techniques of retrograde labeling and immunocytochemistry. Injection sites were limited to medial thalamic nuclei. Retrogradely labeled neurons were most often seen contralaterally in trigeminal and spinal laminae I, V, VI and VII. After immunocytochemical processing, about 10% of the retrogradely labeled cells exhibited enkephalin immunoreactivity. These double-labeled neurons were located in laminae VI and VII.