IGF-I (1-3) is a neuroactive peptide with a potent action on acetylcholine release. IGF-I (1-3)u is the N-terminal tripeptide of insulin-like growth factor-I. IGF-I (1-3) inhibits glutamate binds to N-methyl-D-aspartate (NMDA) receptor with an IC50 value of 14.7 μM. Gly-Pro-Glu can be used for the research of neuroprotection