Cycloserine was discovered simultaneously in 1954 by Eli Lilly and Merck. The drug was approved for the treatment of active pulmonary and extrapulmonary tuberculosis and marketed under the name Seromycin (among the others). Cycloserine suppresses the synthesis of bacterial wall by inhibitin two enzymes: alanine racemase and d-alanine ligase.

SERINE, D- (D-serine) is a non-essential amino acid occurring in natural form as the L-isomer. It is synthesized from glycine or threonine. It is involved in the biosynthesis of purines, pyrimidines and other amino acids. A considerable level of D-serine was discovered, surprisingly, in the mammalian brain in the early 1990s. Since then, D-serine has been considered to be a co-agonist of glutamate at the glycine site of NMDA receptors. D-serine plays an important role in the central nervous system as an endogenous ligand for the glycine site of glutamate N-Methyl-D-Aspartate (NMDA) receptors. D-serine is synthetized by racemization of L-serine in most neural and non-neural cells, and modulates a variety of physiological functions in mammals. D-Serine synthesis is attributed to Serine Racemase (SR), which catalyses the synthesis of D-serine from L-serine. D-serine may play a role in the pathophysiology of neuropsychiatric disorders, such as schizophrenia, which may be linked to NMDA receptor hypo-function. Studies in genetic and pharmacological animal models with decreased D-serine levels have shown that these animals displayed behavioural abnormalities similar to those seen in schizophrenia. Moreover, exogenous administration of D-serine and related compounds improved several phenotypes relevant to schizophrenia, which could have positive clinical implications in humans. The results of a clinical trial in Taiwanese schizophrenic patients who received D-serine as adjuvant treatment indicated that those patients who received D-serine treatment, improved positive, negative and cognitive symptoms seen in schizophrenia. In addition, this clinical trial showed that D-serine did not worsen side effects from other antipsychotics, which may be due to its selective action at the NMDA-glycine site. Therefore, D-serine could be considered as a therapeutic approach for schizophrenia, which is different from the dopaminergic approach. It has also been shown that exogenous d-serine administration can suppress appetite and alter food preference. Thus NMDA receptor and its co-agonist d-seine participate in the control of appetite and food preference, which can be used to suppress obesity. D-serine has been shown to have cognitive-enhancing properties in different brain disorders and in age-related cognitive decline. From a clinical perspective, it is important to highlight that in a recent double-blind placebo-controlled cross-over study our group observed that an acute oral administration of 30 mg/kg of d-serine improved spatial learning and problem solving. D-serine may be especially useful for depression because of its acute and chronic antidepressant effects,