Cannabidiol negatively modulates adenosine A2A receptor functioning in living cells.

OBJECTIVES: Cannabidiol (CBD) is a phytocannabinoid with great potential in clinical applications. The mechanism(s) of action of CBD require further investigation. Previous studies suggested that adenosine A2A receptors (A2ARs) could play a role in CBD-induced effects. Here, we evaluated the ability of CBD to modify the function of A2AR. METHODS: We used HEK-293T cells transfected with the cDNA encoding the human A2AR and Gαs protein, both modified to perform bioluminescence-based assays. We first assessed the effect of CBD on A2AR ligand binding using an A2AR NanoLuciferase sensor. Next, we evaluated whether CBD modified A2AR coupling to mini-Gαs proteins using the NanoBiT™ assay. Finally, we further assessed CBD effects on A2AR intrinsic activity by recording agonist-induced cAMP accumulation. RESULTS: CBD did not bind orthosterically to A2AR but reduced the coupling of A2AR to Gαs protein and the subsequent generation of cAMP. CONCLUSION: CBD negatively modulates A2AR functioning.

Unique effect of clozapine on adenosine A2A-dopamine D2 receptor heteromerization.

The striatal dopamine D2 receptor (D2R) is generally accepted to be involved in positive symptoms of schizophrenia and is a main target for clinically used antipsychotics. D2R are highly expressed in the striatum, where they form heteromers with the adenosine A2A receptor (A2AR). Changes in the density of A2AR-D2R heteromers have been reported in postmortem tissue from patients with schizophrenia, but the degree to which A2R are involved in schizophrenia and the effect of antipsychotic drugs is unknown. Here, we examine the effect of exposure to three prototypical antipsychotic drugs on A2AR-D2R heteromerization in mammalian cells using a NanoBiT assay. After 16 h of exposure, a significant increase in the density of A2AR-D2R heteromers was found with haloperidol and aripiprazole, but not with clozapine. On the other hand, clozapine, but not haloperidol or aripiprazole, was associated with a significant decrease in A2AR-D2R heteromerization after 2 h of treatment. Computational binding models of these compounds revealed distinctive molecular signatures that explain their different influence on heteromerization. The bulky tricyclic moiety of clozapine displaces TM 5 of D2R, inducing a clash with A2AR, while the extended binding mode of haloperidol and aripiprazole stabilizes a specific conformation of the second extracellular loop of D2R that enhances the interaction with A2AR. It is proposed that an increase in A2AR-D2R heteromerization is involved in the extrapyramidal side effects (EPS) of antipsychotics and that the specific clozapine-mediated destabilization of A2AR-D2R heteromerization can explain its low EPS liability.

Nanoscale alterations in GABAB receptors and GIRK channel organization on the hippocampus of APP/PS1 mice.

Alzheimer's disease (AD) is characterized by a reorganization of brain activity determining network hyperexcitability and loss of synaptic plasticity. Precisely, a dysfunction in metabotropic GABAB receptor signalling through G protein-gated inwardly rectifying K+ (GIRK or Kir3) channels on the hippocampus has been postulated. Thus, we determined the impact of amyloid-ß (Aß) pathology in GIRK channel density, subcellular distribution, and its association with GABAB receptors in hippocampal CA1 pyramidal neurons from the APP/PS1 mouse model using quantitative SDS-digested freeze-fracture replica labelling (SDS-FRL) and proximity ligation in situ assay (P-LISA). In wild type mice, single SDS-FRL detection revealed a similar dendritic gradient for GIRK1 and GIRK2 in CA1 pyramidal cells, with higher densities in spines, and GIRK3 showed a lower and uniform distribution. Double SDS-FRL showed a co-clustering of GIRK2 and GIRK1 in post- and presynaptic compartments, but not for GIRK2 and GIRK3. Likewise, double GABAB1 and GIRK2 SDS-FRL detection displayed a high degree of co-clustering in nanodomains (40-50 nm) mostly in spines and axon terminals. In APP/PS1 mice, the density of GIRK2 and GIRK1, but not for GIRK3, was significantly reduced along the neuronal surface of CA1 pyramidal cells and in axon terminals contacting them. Importantly, GABAB1 and GIRK2 co-clustering was not present in APP/PS1 mice. Similarly, P-LISA experiments revealed a significant reduction in GABAB1 and GIRK2 interaction on the hippocampus of this animal model. Overall, our results provide compelling evidence showing a significant reduction on the cell surface density of pre- and postsynaptic GIRK1 and GIRK2, but not GIRK3, and a decline in GABAB receptors and GIRK2 channels co-clustering in hippocampal pyramidal neurons from APP/PS1 mice, thus suggesting that a disruption in the GABAB receptor-GIRK channel membrane assembly causes dysregulation in the GABAB signalling via GIRK channels in this AD animal model.

ß-Catenin Role in the Vulnerability/Resilience to Stress-Related Disorders Is Associated to Changes in the Serotonergic System.

We previously reported that the inactivation (cKO) or the stabilization (cST) of ß-catenin in cells expressing the astrocyte-specific glutamate aspartate transporter (GLAST) is associated with the vulnerability or resilience to exhibit anxious/depressive-like behaviors, respectively, and to changes in hippocampal proliferation. Here, we used these cKO and cST ß-catenin mice to study the serotonergic system functionality associated with their behavioral/molecular phenotype. The activity of 5-HT1A receptors was assessed by (+)-8-OH-DPAT-induced hypothermia and [35S]GTPγS binding autoradiography. The animals' response to acute stress and the levels of extracellular serotonin (5-HT) in the medial prefrontal cortex (mPFC) were also assessed. cKO mice presented higher 5-HT1A autoreceptor functionality, lower 5-HT1A heteroreceptor functionality, and a decrease in extracellular 5-HT levels in the mPFC. These neurochemical changes were accompanied with a blunted physiological response to stress-induced hyperthermia. In contrast, cST mice showed a reduced 5-HT1A autoreceptor functionality and higher extracellular 5-HT levels in the mPFC after fluoxetine administration. Moreover, cST mice subjected to chronic corticosterone administration did not show a blunted response to fluoxetine. Our findings suggest the existence of a link between ß-catenin levels and 5-HT1A receptor functionality, which may be relevant to understand the neurobiological bases underlying the vulnerability or resilience to stress-related disorders.