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N-Methyl-D-aspartic Acid (NMDA) in the nervous system of the amphioxus Branchiostoma lanceolatum

DOI: 10.1186/1471-2202-8-109

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Abstract:

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).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.Synthetic N-methyl-D-aspartic acid (NMDA) is widely known for its property to be an agonist of the L-glutamate receptor of the NMDA-type. Among the three families of glutamate receptor proteins identified, one is activated by NMDA. The subunits of this receptor (NR1, NR2A, NR2B, NR2C and NR2D of the ligand-gated ionic channels) are collectively referred to as glutamate receptors of the NMDA-type. Another receptor family, known as AMPA-type, is activated by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and by kainate. The third family of glutamate receptors consists of G-protein coupled receptors, the so-called matabotropic receptors (mGluR1-8) [1,2] for its widespread activity, among which one of the most important is to induce hormone release in the hypothalamus and pituitary gland [3-6]. NMDA was first isolated as endogenous compound in the marine mollusk Scapharca brougtonii in 1987, by cation exchange chromatography [7], and later by HPLC methods [8]. Recently, using a novel strategy consisting in the purification of the tissue sample with o-phthaldialdehyde (OPA) associated with an enzymatic HPLC method, we demonstrated that NMDA is present in neuroendocrine tissues of rat [9,10], of the protochordate Ciona intestinalis [1

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