A novel role of cannabinoids in synaptogenesis

Abstract

Synapses play a major role in signalling transduction in the nervous system. They display extensive activity-driven plasticity during development, learning and memory. Here we have explored a new role of endogenous cannabinoids and their CHI receptors in synapse formation, remodelling, and maintenance. Endogenous cannabinoids and their CHI receptors have been known to regulate neurotransmitter release at the level of the synapse and have also been implicated in several developmental events. Recent/y, if was reported that endogeneous cannabinoids decrease functional synapses in pyramidal neurons. We show here that endogenous cannabinoids and their CHI receptors regulate the dendritic and axonal filopodia formation (synapse precursors) and synaptogenesis obtained from embryonic mice cortical cultures. Stimulating the cortical cultures with the synthetic CHI receptor agonist, arachidonyl-2'-chloroethylamide (ACEA), produces a significant decrease in filopodia number at DIV8, and subsequently a lower synaptic contact density at DIV10 compared with the control group. On the other hand, inhibiting the action of endogenous cannabinoids and their CHI receptors by the inverse agonist AM251 or by the pure antagonist 02050 increases filopodia density at DIV8, and elevates synaptic density formation at DIV10. Furthermore, we found that this increase was reversed when cultures were pre-treated with H89, KT5720 (both inhibitors of Prote in Kinase A (PKA)) or DCCjb antibody, (an antibody which blocks the function of Deleted in Colorectal Cancer Receptor). Interestingly, a decrease of DCC receptors present at the surface of the neurons was observed when treated with ACEA. Conversely, an externalisation of DCC was observed when CHI receptors were antagonised by AM251 or 02050 and this effect was prevented when neurons were pretreated using H89, KT5720. This confirms the previous observations showing that the activation of adenylate cyclase and P KA pathway produces a netrinl-DCC dependent increase in synaptogenesis.