Neurochemical Changes in the Mouse Hippocampus Underlying the Antidepressant Effect of Genetic Deletion of P2X7 Receptors.

Recent investigations have revealed that the genetic deletion of P2X7 receptors (P2rx7) results in an antidepressant phenotype in mice. However, the link between the deficiency of P2rx7 and changes in behavior has not yet been explored. In the present study, we studied the effect of genetic deletion of P2rx7 on neurochemical changes in the hippocampus that might underlie the antidepressant phenotype. P2X7 receptor deficient mice (P2rx7-/-) displayed decreased immobility in the tail suspension test (TST) and an attenuated anhedonia response in the sucrose preference test (SPT) following bacterial endotoxin (LPS) challenge. The attenuated anhedonia was reproduced through systemic treatments with P2rx7 antagonists. The activation of P2rx7 resulted in the concentration-dependent release of [3H]glutamate in P2rx7+/+ but not P2rx7-/- mice, and the NR2B subunit mRNA and protein was upregulated in the hippocampus of P2rx7-/- mice. The brain-derived neurotrophic factor (BDNF) expression was higher in saline but not LPS-treated P2rx7-/- mice; the P2rx7 antagonist Brilliant blue G elevated and the P2rx7 agonist benzoylbenzoyl ATP (BzATP) reduced BDNF level. This effect was dependent on the activation of NMDA and non-NMDA receptors but not on Group I metabotropic glutamate receptors (mGluR1,5). An increased 5-bromo-2-deoxyuridine (BrdU) incorporation was also observed in the dentate gyrus derived from P2rx7-/- mice. Basal level of 5-HT was increased, whereas the 5HIAA/5-HT ratio was lower in the hippocampus of P2rx7-/- mice, which accompanied the increased uptake of [3H]5-HT and an elevated number of [3H]citalopram binding sites. The LPS-induced elevation of 5-HT level was absent in P2rx7-/- mice. In conclusion there are several potential mechanisms for the antidepressant phenotype of P2rx7-/- mice, such as the absence of P2rx7-mediated glutamate release, elevated basal BDNF production, enhanced neurogenesis and increased 5-HT bioavailability in the hippocampus

Differential and converging molecular mechanisms of antidepressants' action in the hippocampal dentate gyrus

Major depression is a highly prevalent, multidimensional disorder. Although several classes of antidepressants (ADs) are currently available, treatment efficacy is limited, and relapse rates are high; thus, there is a need to find better therapeutic strategies. Neuroplastic changes in brain regions such as the hippocampal dentate gyrus (DG) accompany depression and its amelioration with ADs. In this study, the unpredictable chronic mild stress (uCMS) rat model of depression was used to determine the molecular mediators of chronic stress and the targets of four ADs with different pharmacological profiles (fluoxetine, imipramine, tianeptine, and agomelatine) in the hippocampal DG. All ADs, except agomelatine, reversed the depression-like behavior and neuroplastic changes produced by uCMS. Chronic stress induced significant molecular changes that were generally reversed by fluoxetine, imipramine, and tianeptine. Fluoxetine primarily acted on neurons to reduce the expression of pro-inflammatory response genes and increased a set of genes involved in cell metabolism. Similarities were found between the molecular actions and targets of imipramine and tianeptine that activated pathways related to cellular protection. Agomelatine presented a unique profile, with pronounced effects on genes related to Rho-GTPase-related pathways in oligodendrocytes and neurons. These differential molecular signatures of ADs studied contribute to our understanding of the processes implicated in the onset and treatment of depression-like symptoms.Patricia Patricio, Antonio Mateus-Pinheiro, Monica Morais, and Nuno Dinis Alves received fellowships from the Portuguese Foundation for Science and Technology (FCT). Michal Korostynski and Marcin Piechota were funded by the POIG De-Me-Ter 3.1 and NCN 2011/03/D/NZ3/01686 grants. This study was co-funded by the Life and Health Sciences Research Institute (ICVS) and ON. 2-O NOVO NORTE-North Portugal Regional Operational Programme 2007/2013, of the National Strategic Reference Framework (NSRF) 2007/ 2013, through the European Regional Development Fund (ERDF) and by the SwitchBox Consortium (Contract FP7-Health-F2-2010-259772 from the European Union). The authors declare no conflict of interest

Endocytosis of Xanthomonas campestris pathovar campestris lipopolysaccharides in non-host plant cells of Nicotiana tabacum

Gross A, Kapp D, Nielsen T, Niehaus K. Endocytosis of Xanthomonas campestris pathovar campestris lipopolysaccharides in non-host plant cells of Nicotiana tabacum. New Phytologist. 2005;165(1):215-226.The specific recognition of phytopathogenic bacteria by plant cells is generally mediated by a number of signal molecules. The elicitor-active lipopolysaccharides (LPS) of the phytopathogenic bacterium Xanthomonas campestris pv. campestris (X.c.c) are recognized by its non-host plant Nicotiana tabacum (N.t.). This LPS was purified and labelled with fluorescein isothiocyanate (FITC) for monitoring the fate of these signal molecules in intact plant cells of tobacco. In this study we were able to show that the so-labelled LPS rapidly bound to the cell wall and was then internalized into the cells in a temperature- and energy-dependent way. This uptake of LPS could be outcompeted by the addition of an excess of unlabelled LPS. Furthermore, it was blocked by amantadine, an inhibitor of receptor-mediated endocytosis of mammalian cells. Immunolocalization experiments showed for the first time a significant co-localization of the LPS-elicitor with endosomal structures using an anti-Ara6 antibody. These observations suggest specific endocytosis of LPSX.c.c. into tobacco cells. The possibility for a receptor-mediated endocytosis comparable to the mammalian system will be discussed