Stimulation by melanocortins of neurite outgrowth from spinal and sensory neurons in vitro.

Using ELISAs for B-50/GAP43 and neurofilament (NF), we tested ACTH(1-24), alpha-MSH, ACTH(4-10), and an ACTH(4-9) analogue (ORG2766) for their ability to induce sprouting and neuritogenesis from spinal and sensory neurons. Dissociated fetal rat spinal cord neurons or neonatal rat dorsal root ganglion (DRG) cells were cultured with peptide and assayed after 24, 48, or 96 h. In spinal neurons, alpha-MSH and ACTH(1-24) induced the expression of B-50 dose dependently. After 24 h alpha-MSH had a stimulatory effect (from 10 nM onwards), with a maximum at 100 microM (36% increase). After 96 h the maximal effect of 100 microM alpha-MSH on B-50/GAP43 was lower (19%). ACTH(1-24) (100 microM) stimulated B-50/GAP43 by 19%. Neurofilament levels (96 h) were elevated maximally by 64% at 100 microM alpha-MSH. In DRG neurons a bell-shaped dose-response curve was found for alpha-MSH, the maximal effect being observed after 48 h at 100 nM: 54% for B-50/GAP43 and 22% for NF. In both culture systems neither ACTH(4-10) nor ORG2766 was effective. We conclude that alpha-MSH stimulates the expression of B-50/GAP43 (sprouting) and the formation of NF (neurite elongation) and may therefore be considered a neurotrophic factor.