Effect of the α4β2∗ nicotinic acetylcholine receptor partial agonist varenicline on dopamine release in β2 knock-out mice with selective re-expression of the β2 subunit in the ventral tegmental area

International audienceWe studied the effects of 1 mg/kg doses of nicotine and the alpha4beta2* nicotinic acetylcholine receptor (nAChR) partial agonist, varenicline, on extracellular dopamine (DA) levels in the nucleus accumbens (NuAcc) of lentivirally vectorized male mice. Three separate experimental groups were injected with a lentiviral vector transducing the ventral tegmental area (VTA): wild-type C57BL/6J mice with a vector expressing eGFP only, beta2 knock-out mice (beta2KO) with the eGFP-only vector, and beta2KO mice with a bicistronic vector reintroducing beta2 and eGFP into the VTA as recently described (Maskos et al., 2005). Our results suggest that the neurochemical effects of varenicline as measured by using microdialysis in awake, freely moving mice are mainly mediated via beta2* nAChR subunits localized in the VTA

N-Glycosylation Deficiency Reduces the Activation of Protein C and Disrupts Endothelial Barrier Integrity

International audiencePhosphomannomutase 2 (PMM2) deficiency is the most prevalent congenital disorder of glycosylation. It is associated with coagulopathy, including protein C deficiency. Since all components of the anticoagulant and cytoprotective protein C system are glycosylated, we sought to investigate the impact of an N-glycosylation deficiency on this system as a whole. To this end, we developed a PMM2 knockdown model in the brain endothelial cell line hCMEC/D3. The resulting PMM2low cells were less able to generate activated protein C (APC), due to lower surface expression of thrombomodulin and endothelial protein C receptor. The low protein levels were due to downregulated transcription of the corresponding genes (THBD and PROCR, respectively), which itself was related to downregulation of transcription regulators Krüppel-like factors 2 and 4 and forkhead box C2. PMM2 knockdown was also associated with impaired integrity of the endothelial cell monolayer—partly due to an alteration in the structure of VE-cadherin in adherens junctions. The expression of protease-activated receptor 1 (involved in the cytoprotective effects of APC on the endothelium) was not affected by PMM2 knockdown. Thrombin stimulation induced hyperpermeability in PMM2low cells. However, pretreatment of cells with APC before thrombin simulation was still associated with a barrier-protecting effect. Taken as a whole, our results show that the partial loss of PMM2 in hCMEC/D3 cells is associated with impaired activation of protein C and a relative increase in barrier permeability

Alpha7-nicotinic receptors modulate nicotine-induced reinforcement and extracellular dopamine outflow in the mesolimbic system in mice.

International audienceNicotine is the main addictive component of tobacco and modifies brain function via its action on neuronal acetylcholine nicotinic receptors (nAChRs). The mesolimbic dopamine (DA) system, where neurons of the ventral tegmental area (VTA) project to the nucleus accumbens (ACb), is considered a core site for the processing of nicotine's reinforcing properties. However, the precise subtypes of nAChRs that mediate the rewarding properties of nicotine and that contribute to the development of addiction remain to be identified.OBJECTIVES : We investigated the role of the nAChRs containing the α7 nicotinic subunit (α7 nAChRs) in the reinforcing properties of nicotine within the VTA and in the nicotine-induced changes in ACb DA outflow in vivo.METHODS : We performed intra-VTA self-administration and microdialysis experiments in genetically modified mice lacking the α7 nicotinic subunit or after pharmacological blockade of α7 nAChRs in wild-type mice.RESULTS : We show that the reinforcing properties of nicotine within the VTA are lower in the absence or after pharmacological blockade of α7 nAChRs. We also report that nicotine-induced increases in ACb DA extracellular levels last longer in the absence of these receptors, suggesting that α7 nAChRs regulate the action of nicotine on DA levels over time.CONCLUSIONS : The present results reveal new insights for the role of α7 nAChRs in modulating the action of nicotine within the mesolimbic circuit. These receptors appear to potentiate the reinforcing action of nicotine administered into the VTA while regulating its action over time on DA outflow in the ACb