((4-aminobutyl)guanidine, NH2-CH2-CH2-CH2-CH2-NH-C(-NH2)(=NH)) is the decarboxylation product of the amino acid arginine and is an intermediate in polyamine biosynthesis. It is discussed as a putative neurotransmitter. It is synthesized in the brain, stored in synaptic vesicles, accumulated by uptake, released by membrane depolarization, and inactivated by agmatinase. binds to α2-adrenergic receptor and imidazoline binding sites, and blocks receptors and other cation ligand-gated channels. inhibits nitric oxide synthase (NOS), and induces the release of some peptide hormones.