Presence of leucine-enkephalin in organotypic explants of fetal mouse spinal cord.

Spinal cord explants with attached dorsal root ganglia (DRGs), from 14-day fetal mice were fixed at 1-3 weeks in vitro and incubated for leucine-enkephalin (LE) immunoreactivity by the peroxidase-anti-peroxidase (PAP) immunohistochemical method. Results show long processes with labeled varicosities seen more often in dorsal regions of the cord explants. Stained punctate bodies and varicosities were often seen close to large cells in these cultures, whereas no label was detected in neuronal perikarya. A prominent laminar array of stained punctate bodies was noted in one cord explant, concentric with the perimeter of the explant. No LE label was detected in the neuritic outgrowths from the cord-DRG explants, whereas high levels of opiate receptors develop in these outgrowths, primarily on the DRG neurites, by 1-2 weeks in culture. The results indicate the presence of LE in explants of fetal mouse spinal cord with attached DRGs and offer an in vitro model system in which the onset and development of peptidergic neurons can be studied as they form functional cellular interrelationships with neurons bearing opioid and monoaminergic receptors in these organotypic cultures.