Localization of N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD) expression in mouse brain: A new perspective on N-acylethanolamines as neural signaling molecules.

N-acylethanolamines (NAEs) are membrane-derived lipids that are utilized as signaling molecules in the nervous system (e.g., the endocannabinoid anandamide). An N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD) that catalyzes formation of NAEs was recently identified as a member of the zinc metallohydrolase family of enzymes. NAPE-PLD(-/-) mice have greatly reduced brain levels of long-chain saturated NAEs but wild-type levels of polyunsaturated NAEs (e.g., anandamide), suggesting an important role for NAPE-PLD in the biosynthesis of at least a subset of endogenous NAEs in the mammalian nervous system. To provide a neuroanatomical basis for investigation of NAPE-PLD function, here we have analyzed expression of NAPE-PLD in the mouse brain using mRNA in situ hybridization and immunocytochemistry. NAPE-PLD(-/-) mice were utilized to establish the specificity of probes/antibodies used. The most striking feature of NAPE-PLD expression in the brain was in the dentate gyrus, where a strong mRNA signal was detected in granule cells. Accordingly, immunocytochemical analysis revealed intense NAPE-PLD immunoreactivity in the axons of granule cells (mossy fibers). Intense NAPE-PLD immunoreactivity was also detected in axons of the vomeronasal nerve that project to the accessory olfactory bulb. NAPE-PLD expression was detected in other brain regions (e.g., hippocampus, cortex, thalamus, hypothalamus), but the intensity of immunostaining was weaker than in mossy fibers. Collectively, the data obtained indicate that NAPE-PLD is expressed by specific populations of neurons in the brain and targeted to axonal processes. We suggest that NAEs generated by NAPE-PLD in axons may act as anterograde synaptic signaling molecules that regulate the activity of postsynaptic neurons.