Accumulating evidence supports the role of astrocytes in endocannabinoid mediated modulation of neural activity. It has been reported that some astrocytes express the cannabinoid type 1 receptor (CB1-R), the activation of which is leading to Ca2+ mobilization from internal stores and a consecutive release of glutamate. It has also been documented that astrocytes have the potential to produce the endocannabinoid 2-arachidonoylglycerol, one of the best known CB1-R agonist. However, no relationship between CB1-R activation and 2-arachidonoylglycerol production has ever been demonstrated. Here we show that rat spinal astrocytes co-express CB1-Rs and the 2-arachidonoylglycerol synthesizing enzyme, diacylglycerol lipase-alpha in close vicinity to each other. We also demonstrate that activation of CB1-Rs induces a substantial elevation of intracellular Ca2+ concentration in astrocytes. Finally, we provide evidence that the evoked Ca2+ transients lead to the production of 2-arachidonoylglycerol in cultured astrocytes. The results provide evidence for a novel cannabinoid induced endocannabinoid release mechanism in astrocytes which broadens the bidirectional signaling repertoire between astrocytes and neurons.

The pedunculopontine nucleus (PPN) is known as the cholinergic part of the reticular activating system (RAS) and it plays an important role in transitions of slow-wave sleep to REM sleep and wakefulness. Although both exogenous and endocannabinoids affect sleep, the mechanism of endocannabinoid neuromodulation has not been characterized at cellular level in the PPN. In this paper, we demonstrate that both neurons and glial cells from the PPN respond to cannabinoid type 1 (CB1) receptor agonists. The neuronal response can be depolarization or hyperpolarization, while astrocytes exhibit more frequent calcium waves. All these effects are absent in CB1 gene-deficient mice. Blockade of the fast synaptic neurotransmission or neuronal action potential firing does not change the effect on the neuronal membrane potential significantly, while inhibition of astrocytic calcium waves by thapsigargin diminishes the response. Inhibition of group I metabotropic glutamate receptors (mGluRs) abolishes hyperpolarization, whereas blockade of group II mGluRs prevents depolarization. Initially active neurons and glial cells display weaker responses partially due to the increased endocannabinoid tone in their environment. Taken together, we propose that cannabinoid receptor stimulation modulates PPN neuronal activity in the following manner: active neurons may elicit calcium waves in astrocytes via endogenous CB1 receptor agonists. Astrocytes in turn release glutamate that activates different metabotropic glutamate receptors of neurons and modulate PPN neuronal activity.

The orbitofrontal cortex (OFC) has been implicated in a multiplicity of complex brain functions, including representations of expected outcome properties, post-decision confidence, momentary food-reward values, complex flavors and odors. As breathing rhythm has an influence on odor processing at primary olfactory areas, we tested the hypothesis that it may also influence neuronal activity in the OFC, a prefrontal area involved also in higher order processing of odors. We recorded spike timing of orbitofrontal neurons as well as local field potentials (LFPs) in awake, head-fixed mice, together with the breathing rhythm. We observed that a large majority of orbitofrontal neurons showed robust phase-coupling to breathing during immobility and running. The phase coupling of action potentials to breathing was significantly stronger in orbitofrontal neurons compared to cells in the medial prefrontal cortex. The characteristic synchronization of orbitofrontal neurons with breathing might provide a temporal framework for multi-variable processing of olfactory, gustatory and reward-value relationships.

Protein phosphatase‐1M (PP1M, myosin phosphatase) consists of a PP1 catalytic subunit (PP1c) and the myosin phosphatase target subunit‐1 (MYPT1). RhoA‐activated kinase (ROK) regulates PP1M via inhibitory phosphorylation of MYPT1. Using multidisciplinary approaches, we have studied the roles of PP1M and ROK in neurotransmission. Electron microscopy demonstrated the presence of MYPT1 and ROK in both pre‐ and post‐synaptic terminals. Tautomycetin (TMC), a PP1‐specific inhibitor, decreased the depolarization‐induced exocytosis from cortical synaptosomes. trans‐4‐[(1R)‐1‐aminoethyl]‐N‐4‐pyridinylcyclohexanecarboxamide dihydrochloride, a ROK‐specific inhibitor, had the opposite effect. Mass spectrometry analysis identified several MYPT1‐bound synaptosomal proteins, of which interactions of synapsin‐I, syntaxin‐1, calcineurin‐A subunit, and Ca2+/calmodulin‐dependent kinase II with MYPT1 were confirmed. In intact synaptosomes, TMC increased, whereas Y27632 decreased the phosphorylation levels of MYPT1Thr696, myosin‐II light chainSer19, synapsin‐ISer9, and syntaxin‐1Ser14, indicating that PP1M and ROK influence their phosphorylation status. Confocal microscopy indicated that MYPT1 and ROK are present in the rat ventral cochlear nucleus both pre‐ and post‐synaptically. Analysis of the neurotransmission in an auditory glutamatergic giant synapse demonstrated that PP1M and ROK affect neurotransmission via both pre‐ and post‐synaptic mechanisms. Our data suggest that both PP1M and ROK influence synaptic transmission, but further studies are needed to give a full account of their mechanism of action.