The present invention relates to a peptide comprising an amino acid sequence identical to or substantially identical to an amino acid sequence represented by SEQ ID NO: 35 and having an ability of binding to a receptor protein comprising an amino acid sequence identical to or substantially identical to an amino acid sequence represented by SEQ ID NO: 1, SEQ ID NO: 2 or SEQ ID NO: 3, or a precursor thereof, its amide or ester, or a salt thereof. An inventive peptide-encoding DNA or equivalent can be employed in (1) a development of a receptor binding assay system using an expression system of a recombinant receptor protein and a screening for a pharmaceutical candidate compound, and (2) a development of a pharmaceutical having a reduced side effect such as a memory function improving agent, an appetite improving agent, an uterine, renal, prostatic, testicular or skeletal muscle function regulating agent.