Ontogeny of enkephalin- and VIP-containing neurons in dissociated cultures of embryonic mouse spinal cord and dorsal root ganglia.

The ontogeny of vasoactive intestinal polypeptide (VIP), and Met-enkephalin in primary cultures of spinal cord/dorsal root ganglia from 12-day mouse embryos was examined by radioimmunoassay and immunohistochemistry. Met-enkephalin levels rose from less than 5 to 700 pg/culture over 26 days and were half maximal by day 16-18 in culture. VIP levels rose from less than 1 to 30 pg/culture over the same period, but were already half maximal by day 9. Met-enkephalin immunoreactivity was localized in multipolar medium sized neurons while VIP immunoreactivity was visualized both in neurons with extensively branched processes and in bipolar cells some of which appeared to be dorsal root ganglion cells. Tetrodotoxin (TTX)-sensitive spontaneous release of both peptides developed in parallel with the ability to stimulate peptide release with elevated potassium. Factors affecting the ontogeny of neuropeptide expression in, and release from, spinal cord neurons can now be examined in vitro in a strictly defined neurochemical environment.