Anserine (beta-alanyl-N-3-methylhistidine) is a dipeptide containing beta-alanine and 3-methylhistidine. It is a derivative of carnosine, which had been methylated. The methyl group of anserine is added to carnosine by the enzyme S-adenosylmethionine: carnosine N-methyltransferase (PMID: 29484990). The enzyme is closely related to histamine N-methyltransferase and appears to be present in a majority of anserine-producing species (PMID: 23705015). Anserine is a generally a more metabolically stable derivative of carnosine. Anserine can be found in the skeletal muscle and brain of certain mammals (rabbits, cattle), migratory fish and birds. This dipeptide is normally absent from human tissues and body fluids, and its appearance there is usually an artifact of diet. Anserine can also arise from serum carnosinase deficiency. (OMIM 212200). Anserine was first discovered in goose muscle in 1929, and was named after this extraction (anser is Latin for goose). Anserine, which is water-soluble, is found at high levels in the muscles of different non-human vertebrates, with poultry, rabbit, tuna, plaice, and salmon having generally higher contents than other marine foods, beef, or pork (PMID: 31908682). An increase of urinary anserine excretion has been found in humans after the consumption of chicken, rabbit, and tuna and has been associated with intake of chicken, salmon, and, to a lesser extent, beef (PMID: 31908682).  Anserine can undergo cleavage to give rise to 3-methylhistidine.(3-MH). The dipeptide balenine, common in some whales, cleaves to form 1-methylhistidine (1-MH) (PMID: 31908682).  There is considerable confusion with regard to the nomenclature of the methylated nitrogen atoms on the imidazole ring of histidine and other histidine-containing peptides such as anserine. In particular, older literature (mostly prior to the year 2000) designated anserine (N-pi methylated) as beta-alanyl-N1-methyl-histidine, whereas according to standard IUPAC nomenclature, anserine is correctly named as beta-alanyl-N3-methyl-histidine. As a result, many papers published prior to the year 2000 incorrectly identified 1MH as a specific marker for dietary consumption of certain foods or various pathophysiological effects when they really were referring to 3MH or vice versa (PMID: 24137022). In particular balenine (a whale or snake-specific dipeptide with 1MH) was often confused with anserine (the poultry dipeptide with 3MH). An animal model study of Alzheimer's disease using mice found that treatment with anserine reduced memory loss (PMID: 28974740). Anserine reduced glial inflammatory activity (particularly of astrocyte). The study also found that anserine-treated mice had greater pericyte surface area. The greater area of pericytes was commensurate with improved memory. The anserine-treated mice overall performed better on a spatial memory test (Morris Water Maze) (PMID: 28974740). A human study on 84 elderly subjects showed that subjects who took anserine and carnosine supplements for one year showed increased blood flow in the prefrontal cortex on MRI (PMID: 29896423).