Compositions that include peptides derived from glial-derived neurotrophic factor (GDNF) (e.g., substantially pure polypeptides comprising a fragment of a GDNF precursor protein) and biologically active variants thereof are provided. The compositions can include one or more types of peptides and can include other substances (e.g., pharmaceutically acceptable carriers or diluents or liposomes). Also provided are methods for using the compositions for treatment of neurological disorders (e.g., motor system disorders and sensory system disorders).