LAUSR

is an understudied and underappreciated endogenous amino acid in the brain. Its role in neuronal function has been understudied for years due to the difficulty in detecting it. There is recent work showing that D-cysteine and cell permeable derivatives such as D-cysteine ethyl ester plays a role in neural progenitor cell prolifera-tionandreversingopioidinducedrespiratorydepression.Theserecent studies, coupled with evidence that D-cysteine is highly regulated in the body by D-amino acid oxidase and possibly other mechanisms sug-gest that it is an active amino acid in the body, which could be involved in a variety of disease models.