D-Aspartic acid (D-Asp, D-D) is an endogenous amino acid found in nervous and endocrine tissues in mammals including humans.
Embryos contain a high concentration of D-Asp which decreases after birth. D-Asp increases in testis just before birth and during maturation. In epinephrine-containing glandular tissue, in the adrenal medulla, D-Asp appears to regulate hormone synthesis and release. Mammalian cells can synthesize, release, take up, and degrade D-Asp. Recent findings suggest that D-Asp acts as a cellular messenger in the mammalian body. In 2011, Errico et al. observed that D-Asp activates N-methyl-D-aspartate receptors (NMDARs) by binding to the glutamate site on GluN2 subunits.
Adrenal Medulla
The adrenal medulla refers to the inner portion of the adrenal gland surrounded by the adrenal cortex. The adrenal gland synthesizes epinephrine (adrenalin), norepinephrine (noradrenaline) and some dopamine.
Reference
Errico, F., Nisticò, R., Di Giorgio, A., Squillace, M., Vitucci, D., Galbusera, A., … Usiello, A. (2014). Free D-aspartate regulates neuronal dendritic morphology, synaptic plasticity, gray matter volume and brain activity in mammals. Translational Psychiatry, 4(7), e417.