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This article belongs to the Special Issue Gut Microbiota and Immunity. ; Alcohol binge drinking (BD) and poor nutritional habits are two frequent behaviors among many adolescents that alter gut microbiota in a pro-inflammatory direction. Dysbiotic changes in the gut microbiome are observed after alcohol and high-fat diet (HFD) consumption, even before obesity onset. In this study, we investigate the neuroinflammatory response of adolescent BD when combined with a continuous or intermittent HFD and its effects on adult ethanol consumption by using a self-administration (SA) paradigm in mice. The inflammatory biomarkers IL-6 and CX3CL1 were measured in the striatum 24 h after BD, 3 weeks later and after the ethanol (EtOH) SA. Adolescent BD increased alcohol consumption in the oral SA and caused a greater motivation to seek the substance. Likewise, mice with intermittent access to HFD exhibited higher EtOH consumption, while the opposite effect was found in mice with continuous HFD access. Biochemical analyses showed that after BD and three weeks later, striatal levels of IL-6 and CX3CL1 were increased. In addition, in saline-treated mice, CX3CL1 was increased after continuous access to HFD. After oral SA procedure, striatal IL-6 was increased only in animals exposed to BD and HFD. In addition, striatal CX3CL1 levels were increased in all BD- and HFD-exposed groups. Overall, our findings show that adolescent BD and intermittent HFD increase adult alcohol intake and point to neuroinflammation as an important mechanism modulating this interaction. ; This research was funded by Spanish Ministry of Health, Social Affairs and Equality, Government Delegation for the National Drugs Plan (2018/013 to MRA and PNSD 2016I016 to JMa); Generalitat Valenciana, Conselleria de Educación, Dirección General de Universidades, Grupos de Investigación de excelencia, PROMETEOII/2018/132 to JMi; Ministerio de Economía y Competitividad' (FIS, PI14/00438) to JMa. Instituto de Salud Carlos III, Red de Trastornos Adictivos (RD16/0017/0007 to JMi) and Unión Europea, Fondos FEDER "una manera de hacer Europa". ; Peer reviewed

The neuropeptide oxytocin (OXT) plays a critical role in the regulation of social and emotional behaviors. OXT plays a role in stress response and in drug reward, but to date no studies have evaluated its implication in the long-lasting increase of the motivational effects of cocaine induced by repeated social defeat (RSD). During the social defeat procedure, 1 mg/kg of OXT was administered 30 min before each episode of RSD. Three weeks after the last defeat, the effects of cocaine on the conditioned place preference (CPP), locomotor sensitization and the self-administration (SA) paradigms were evaluated. The influence of OXT on the levels of BDNF in the prefrontal cortex (PFC), striatum and hippocampus was also measured. Our results confirm that raising the levels of OXT during social defeat stress can block the long-lasting effects of this type of stress. OXT counteracts the anxiety induced by social defeat and modifies BDNF levels in all the structures we have studied. Moreover, OXT prevents RSD-induced increases in the motivational effects of cocaine. Administration of OXT before each social defeat blocked the social defeat-induced increment in the conditioned rewarding effects of cocaine in the CPP, favored the extinction of cocaine-associated memories in both the CPP and SA, and decreased reinstatement of cocaine-seeking behavior in the SA. In conclusion, the long-lasting effects of RSD are counteracted by administering OXT prior to stress, and changes in BDNF expression may underlie these protective effects. ; This work was supported by the Ministerio de Economía y Competitividad, Dirección General de Investigación, [grant numbers PSI2014-51847-R and PSI 2017-83023-R]; Spanish Ministry of Economy, Innovation and Competiveness (SAF2016-75347-R). Instituto de Salud Carlos III, Red de Trastornos Adictivos (RTA) [grant numbers RETICS RD06/0001/1006; RD12/0028/0005; and RD/16/0017/0010] and Unión Europea, Fondos FEDER "A way to build Europe". The Department of Experimental and Health Sciences (UPF) is an "Unidad de Excelencia María de Maeztu" funded by the MINECO (Ref. MDM2014-0370). A.C-Z received CONACYT grant from the Government of Mexico. M.A.L. and C.F.P received FPU grant from the Spanish Ministry of Economy, Innovation and Competiveness (15/02492 and 14/02279).

Social stress in adulthood enhances cocaine self-administration, an effect that has been related with an increase in extracellular signal-regulated kinase and p38α mitogen-activated protein kinase phosphorylation. A detrimental effect of cocaine on blood-brain barrier (BBB) integrity has also been reported. This study evaluates the effects of repeated social defeat (RSD) during adolescence on the reinforcing and motivational effects of cocaine in adult mice and the changes induced by RSD on BBB permeability. Cocaine self-administration, conditioned place preference and quantitative analysis of claudin-5, laminin, collagen-IV and IgG immunoreactivity took place 3 weeks after RSD. Mice socially defeated during adolescence developed conditioned place preference and exhibited reinstated preference with a non-effective dose of cocaine (1 mg/kg). RSD mice needed significantly more sessions than control animals for the preference induced by 25 mg/kg of cocaine to be extinguished. However, acquisition of cocaine self-administration (0.5 mg/kg per injection) was delayed in the RSD group. Mice exposed to RSD displayed significant changes in BBB structure in adulthood, with a marked reduction in expression of the tight junction protein claudin-5 and an increase in basal laminin degradation (reflected by a decrease in laminin and collagen-IV expression) in the nucleus accumbens and hippocampus. The detrimental effect induced by cocaine (25 mg/kg) on collagen-IV expression in the hippocampus was more pronounced in RSD mice. In summary, our findings suggest that stress and cocaine can increase the long-term vulnerability of the brain to subsequent environmental insults as a consequence of a sustained disruption of the BBB. ; This work was supported by the Spanish Ministerio de Economía y Competitividad 'Instituto de Salud Carlos III', RETICS: RD12/0028/0005, RD12/0028/0023, RD12/0028/0002, PSI2011-24762, PSI2014-51847-R, SAF2011-29864 and SAF2013-40592-R. It is also supported by the Catalan Government (2014SGR1547) and the Valenciano Government (PROMETEOII/2014/063). The research leading to these results has also received funding from the European Community's Seventh Framework Programme (NEUROPAIN, HEALTH-F2-2013)