The present invention is directed to novel peptides and compositions capable of modulating viability and growth in neuronal cells, and to methods of modulating neuronal cell viability and growth employing the novel peptides and compositions of the invention. In one aspect, the invention is directed to novel peptide analogues of motoneuronotrophic factor 1 containing either a "WMLSAFS" or "FSRYAR domain," which is sufficient for neurotrophic or neurotropic function.