Glycine: Inhibition from the Sacrum to the Medulla

Abstract

From a theoretical point of view, the fact that glycine has many metabolic roles as well as a functional role in the CNS is extremely interesting to the neurobiologist. Glycine does not have an assymetric carbon atom nor is it an essential amino acid (except in the chick). It is found in most tissues and its synthesis has been demonstrated in animals, plants and microorganisms. It has also been shown to be present in varying amounts in the tissues of the central nervous system. Most standard textbooks of biochemistry indicate that glycine is metabolically active and is utilized in the formation of proteins, heme, purines, glutathione, hippuric acid, creatine, glycocholic acid, serine, formate (for the one-carbon pool), glucose and glycogen. However, although glycine is biosynthetically involved in these important metabolic processes, in 1965 and shortly thereafter, a series of papers from the laboratories of Aprison and Werman announced that glycine was a segmental inhibitory transmitter in the cat spinal cord and thus also had an important functional role in the CNS (Aprison and Werman, 1965; Graham et al., 1967; Davidoff et al., 1967a,b; Werman et. al., 1967, 1968). Thus, in addition to GABA, the role of glycine had to be considered in studying inhibitory processes of CNS functions.