The invention concerns in particular novel peptides and polypeptides comprising at least the following sequence in amino acids: -W-S-A1-C-S-A2-C-G- in which A1 and A2 are amino acid sequences comprising 1 to 5 amino acids, useful as medicines in therapeutic treatments involving the regeneration of the nervous system cells, for treating neuroblastomas, and also useful as additives in the culture of nervous cells.