OCCURRENCE AND BIOSYNTHESIS OF ENDOGENOUS CANNABINOID PRECURSOR, N-ARACHIDONOYL PHOSPHATIDYLETHANOLAMINE, IN RAT-BRAIN

It has been suggested that anandamide (N-arachidonoylethanolamine), an endogenous cannabinoid substance, may be produced through Ca2+-stimul ated hydrolysis of the phosphatidylethanolamine (PE) derivative N-arac hidonoyl PE. The presence of N-arachidonoyl PE in adult brain tissue a nd the enzyme pathways that underlie its biosynthesis are, however, st ill undetermined. We report here that rat brain tissue contains both a nandamide (11 +/- 7 pmol/gm wet tissue) and N-arachidonoyl PE (22 +/- 16 pmol/gm), as assessed by gas chromatography/mass spectrometry. We d escribe a N-acyltransferase activity in brain that catalyzes the biosy nthesis of N-arachidonoyl PE by transferring an arachidonate group fro m the sn-1 carbon of phospholipids to the amino group of PE. We also s how that sn-1 arachidonoyl phospholipids are present in brain, where t hey constitute similar to 0.5% of total phospholipids. N-acyltransfera se activity is Ca2+ dependent and is enriched in brain and testis. Wit hin the brain, N-acyltransferase activity is highest in brainstem; int ermediate in cortex, striatum, hippocampus, medulla, and cerebellum; a nd lowest in thalamus, hypothalamus, and olfactory bulb. Pharmacologic al inhibition of N-acyltransferase activity in primary cultures of cor tical neurons prevents Ca2+-stimulated N-arachidonoyl PE biosynthesis. Our results demonstrate, therefore, that rat brain tissue contains th e complement of enzymatic activity and lipid substrates necessary for the biosynthesis of the anandamide precursor N-arachidonoyl PE. They a lso suggest that biosynthesis of N-arachidonoyl PE and formation of an andamide are tightly coupled processes, which may concomitantly be sti mulated by elevations in intracellular Ca2+ occurring during neural ac tivity.