PGE2‐glycerol, a metabolite of the endocannabinoid 2‐arachidonyl glycerol, enhances neurotransmitter release at the vertebrate neuromuscular junction via activation of the TRPV1 receptor

Our lab has previously demonstrated that activation of muscarinic acetylcholine receptors at the lizard neuromuscular junction (NMJ) induces a biphasic modulation of evoked neurotransmitter release: an initial depression followed by a delayed enhancement. The depression is mediated by the release of the endocannabinoid 2‐Arachidonyl Glycerol (2‐AG) from the muscle and its binding to CB 1 receptors on the motor nerve terminal. The work presented here suggests that the delayed enhancement of neurotransmitter release is mediated by the glycerol ester of prostaglandin E2 (PGE 2 ‐G) that is produced through the metabolism of 2‐AG by cyclooxygenase (COX). Pre‐treatment with either Nimesulide or DuP 697, selective COX inhibitors, prevents the delayed increase in endplate potential (EPP) amplitude normally observed 30 minutes after the application of muscarine. Application of PGE 2 ‐G enhances EPP amplitude by an amount and with a time course similar to the muscarine‐induced enhancement of neurotransmitter release. Although application of PGE 2 ‐G increases the frequency of spontaneous miniature EPPs (MEPPs) it does not alter the mean amplitude of MEPPs, indicating that PGE 2 ‐G enhances the presynaptic evoked release of neurotransmitter. AH6809, an EP2 receptor antagonist, did not prevent the enhancement of EPP amplitude by PGE 2 ‐G; however, the TRPV1 antagonist capsazepine completely abolished the PGE 2 ‐G effect. Taken together, these results suggest that the delayed muscarine‐induced enhancement of synaptic transmission at the vertebrate NMJ is caused by the conversion of 2‐AG to PGE 2 ‐G and the latter acts via a TRPV1 receptor to enhance evoked neurotransmitter release.