N-methyl-D-aspartic acid (NMDA) in the nervous system of the amphioxus Branchiostoma lanceolatum

Background: NMDA (N-methyl-D-aspartic acid) is a widely known agonist for a class of glutamate receptors, the NMDA type. Synthetic NMDA elicits very strong activity for the induction of hypothalamic factors and hypophyseal hormones in mammals. Moreover, endogenous NMDA has been found in rat, where it has a role in the induction of GnRH (Gonadotropin Releasing Hormone) in the hypothalamus, and of LH (Luteinizing Hormone) and PRL (Prolactin) in the pituitary gland. Results: In this study we show evidence for the occurrence of endogenous NMDA in the amphioxus Branchiostoma lanceolatum. A relatively high concentration of NMDA occurs in the nervous system of this species (3.08 +/-0.37 nmol/g tissue in the nerve cord and 10.52 +/-1.41 nmol/g tissue in the cephalic vesicle). As in rat, in amphioxus NMDA is also biosynthesized from D-aspartic acid (D-Asp) by a NMDA synthase (also called D-aspartate methyl transferase). Conclusion: Given the simplicity of the amphioxus nervous and endocrine systems compared to mammalian, the discovery of NMDA in this protochordate is important to gain insights into the role of endogenous NMDA in the nervous and endocrine systems of metazoans and particularly in the chordate lineage.