Effects of opioids on neuronal survival in culture of embryonic chick dorsal root ganglion neurons

We studied the effects of endogenous and synthetic opioids on survival of primary-cultured dorsal root ganglion neurons of 8-day chick embryos. In the basal growth medium containing nerve growth factor (NGF), [Leu 5]enkephalin, [Met 5]enkephalin or selective μ-agonist, [ d-Ala 2, N-Me-Phe 4, Gly 5-ol]enkephalin (DAMGO) produced significant increase of neuronal survival in a naloxone-reversible manner. On the other hand, dynorphin A (1–13), [ d-Pen 2, l-Pen 5] enkephalin (DPLPE) (a δ-agonist) and U-50,488 (a κ-agonist) showed no such effect. No viable neurons were observed in the absence of NGF in spite of the presence of any opioid peptides. These results suggest that [Leu 5]enkephalin and [Met 5]enkephalin might increase neuronal survival by stimulating μ-opioid receptors, and that these opioid peptides are working with other growth factors but, in and by themselves, do not promote survival.