However, comprehensive understanding of the biological activity of flavanols including their mechanisms of action in humans is still enigmatic. Over the past years, in vitro and in vivo studies have shown that polyphenols modulate the activity of cell signalling proteins, transcription factors and consequently the expression of both, mRNA and miRNA. For example, in animal models, supplementation of a diet with quercetin, naringenin or curcumin at nutritionally relevant doses altered the expression of hundreds of genes in lung, aorta or liver. In vitro, polyphenols impact the expression of genes in various cell types. It has been demonstrated that flavanone metabolites at physiological concentrations can modulate the expression of genes involved in inflammation in tumor necrosis factor -astimulated human umbilical vein endothelial cells. Exposure of human monocytes to green tea polyphenols affected the expression of genes related to atherosclerosis development, such as CD36, LXR-a, MYC or LDL-R. In human hepatocytes polyphenols from red grape juice were able to counteract the LDL-induced changes in gene expression of the LDL receptor, hydroxymethylglutaryl-CoA reductase and the transcription factor sterol regulatory element-binding protein -1, a key regulator of lipid homeostasis. Also genes such as ICAM1, MCP1, IL6 or IL1b of which expression is controlled by nuclear factor kappa B and of which transcriptional activation is critical in a number of pathologies, including cardiovascular diseases, are differentially expressed in the presence of polyphenols. However, only a few studies have been published up to now describing the genomic impact of polyphenols and polyphenol-rich foods in humans. It has been observed that the daily intake of 150 mg quercetin for 2 weeks significantly affected the expression of 788 genes in CD14-positive monocytes, genes related to immune system, apoptosis or cell signalling pathways. Consumption of orange juice rich in hesperidin or hesperidin alone for 4 weeks by healthy, middleaged, moderately overweight men significantly affected over 3000 and 1800 genes respectively. These genes were involved in the regulation of chemotaxis, cell adhesion, lipid transport and their expression profile could be considered as anti-inflammatory and anti-atherogenic. More recently, in a double-bind, randomized cross-over trial in menopausal women isoflavones affected in peripheral blood mononuclear cells the expression of 357 genes which are involved in inflammation, oxidative phosphorylation and cell cycle. In addition to the impact of polyphenols on the expression of genes, recent data suggest that polyphenols could also modulate DNA methylation at multiple levels. Furthermore, different lifestyle factors such as diet and smoking have been associated with DNA methylation changes in cancer and chronic inflammation related diseases such as metabolic syndrome.

To our knowledge, it is the first study directly comparing the effects of DA on AMPA/KA and NMDA receptors-mediated components of the ECSCs showing that DA exerted a stronger inhibition of NMDA than AMPA/KA receptor-mediated EPSCs. The latter finding supports the idea that there is direct D1-NMDA receptors interaction at cellular level. In addition, a recent study suggests a dopamine triggered heterosynaptic plasticity mechanism, likely mediated presynaptically located D1 recetors and expressed by presynaptic inhibition of GABA release. Most studies that have examined the effects of DA on glutamatergic neurotransmission in the nAcb have found a D1like receptors-mediated depression of excitatory responses in agreement with our results. In vitro experiments have shown that this inhibition was mediated by presynaptic dopaminergic receptors located on glutamatergic terminals and are consistent with the demonstration that DA inhibited glutamate release in nAcb. DA receptors are distributed on both presynaptic glutamatergic terminals and postsynaptic membrane of MS neurons in the nAcb. Therefore, DA may have exerted its inhibitory action on EPSCs by acting at pre- and/or postsynaptic mechanisms. We examined the changes in PPR produced during DA application as an indication of pre- or postsynaptic mechanism. We found that bath application of DA greatly reduced the EPSCs but the inhibition was less on EPSC2 than on EPSC1 resulting in an increase in PPR, suggesting that DA acted presynaptically to reduce the probability of glutamate release from presynaptic terminals. We have also found that DA did not change membrane conductance nor that it affected the extrinsic glutamate-induced currents also arguing in favor of presynaptic mechanisms. This conclusion is also consistent with that of previous investigators studying DA inhibition on EPSCs in the nAcb as well as in the nucleus of the solitary tract, the subiculum, the supraoptic nucleus and the parabrachial nucleus. In other studies, DA has also been shown to produce postsynaptic effects in MS neurons but we and others failed to observe postsynaptic effects. In the present study, we added QX314 to the recording pipette solution in order to prevent voltage-sensitive Na + channels from generating action potentials. QX314 as well as other local anaesthetics have been shown to interfere with G protein-coupled receptors as well as with other second messenger systems and it is likely to have occluded the expression of dopaminergic postsynaptic effects. QX314 is also known to interfere with cholinergic muscarinic receptors. In a previous study we found that postsynaptic action mediated by muscarinic receptor was observed only when QX314 was omitted from the recording pipette. In addition, QX-314 is also known to inhibit Gprotein-gated K + conductances and this may have also occluded dopaminergic postsynaptic effects on K + conductance reported by others.