Yatsenko N. Modulation of glycine receptors by cannabinoids in rat CNS neurons

The present work is devoted to the investigation of a novel direct modulation of glycine-activated chloride channels by cannabinoids in isolated hippocampal pyramidal and Purkinje neurons. Here, we demonstrate that cannabinoids may directly affect the functioning of inhibitory glycine receptor (GlyR) channels. In isolated hippocampal pyramidal and Purkinje cerebellar neurons, endogenous cannabinoids anandamide and 2-arachidonylglycerol, applied at physiological concentrations (0.2-2 µM), strongly inhibited the peak of the glycine-activated current (IGly) in a concentration-dependent manner. Meanwhile, the IGly onset and desensitization were accelerated in the presence of endocannabinoids. Endogenous cannabinoids significantly reduced peak of IGly at all tested holding potentials. However, the changes in the decay kinetics, induced by 2-AG, were more pronounced at positive membrane potentials. In contrast to endocannabinoids, the synthetic cannabinoid agonist WIN 55,212-2 (1 µM) cause significant potentiation of the IGly peak amplitude, observed at the lowest concentration of Gly. With increasing concentrations of agonist, the potentiation significantly decreased. The WIN 55,212-2-induced acceleration of desensitization and rise time of IGly exhibited clear concentration dependence. As in the case of endocannabinoids, prominent voltage dependence of the IGly desensitization observed in control conditions was practically eliminated in the presence of WIN 55,212-2. This corresponds to a much more pronounced effect of WIN 55,212-2 on the desensitization kinetics at depolarized potentials. The effects of cannabinoids on IGly were not attenuated in the presence of CB1R antagonists, vanilloid receptor 1 antagonists, and the G-protein inhibitor, suggesting that cannabinoid receptors activation are not involved in action of cannabinoids on GlyRs. We also demonstrate that, in the presence of a GABA(A) receptor antagonist, GlyRs may contribute to the generation of synchronous activity induced by short bursts of high-frequency stimulation of inputs to hippocampal CA1 region, because this activity was diminished by selective GlyR antagonists (strychnine and ginkgolides B and J). The GlyR-mediated rhythmic activity was also reduced by cannabinoids (anandamide) in the presence of a CB1 receptor antagonist. These results suggest that the direct inhibition of GlyRs by endocannabinoids can modulate the hippocampal network activity. Our findings suggest a fundamental importance of GlyR in hippocampal network activity and nominate GlyR as a novel target for endocannabinoid signaling.