Investigating lactate dynamics in brain tissue is challenging, partly because in vivo data at cellular resolution are not available. We monitored lactate in cortical astrocytes and neurons of mice using the genetically encoded FRET sensor Laconic in combination with two-photon microscopy. An intravenous lactate injection rapidly increased the Laconic signal in both astrocytes and neurons, demonstrating high lactate permeability across tissue. The signal increase was significantly smaller in astrocytes, pointing to higher basal lactate levels in these cells, confirmed by a one-point calibration protocol. Trans-acceleration of the monocarboxylate transporter with pyruvate was able to reduce intracellular lactate in astrocytes but not in neurons. Collectively, these data provide in vivo evidence for a lactate gradient from astrocytes to neurons. This gradient is a prerequisite for a carrier-mediated lactate flux from astrocytes to neurons and thus supports the astrocyte-neuron lactate shuttle model, in which astrocyte-derived lactate acts as an energy substrate for neurons.

Background Basic and clinical studies report that the expression of Fibroblast Growth Factor-2 (FGF2) is decreased in the Prefrontal Cortex (PFC) of depressed subjects or rodents exposed to stress, and increased following antidepressant treatment. Here, we aim to determine if: 1) FGF2/FGF receptor signaling is sufficient and required for mediating an antidepressant response behaviorally and cellularly; and 2) if the antidepressant actions of FGF2 are mediated specifically by the PFC. Methods The role of FGF2 signaling in behavioral models of depression and anxiety was tested using chronic unpredictable stress (CUS)/sucrose consumption test (SCT), forced swim test (FST) and novelty suppressed feeding test (NSFT). We also assessed the number of bromodeoxyuridine labeled dividing glial cells in the PFC as a cellular index relevant to depression (i.e. decreased by stress and increased by antidepressant treatment). Results Chronic FGF2 infusions (i.c.v.) blocked the deficit in SCT caused by CUS. Moreover, the response to antidepressant treatment in the CUS/SCT, and FST, were abolished upon administration of an inhibitor of FGF receptor activity, SU5402. These results are consistent with the regulation of proliferating cells in the PFC, a portion of which are of oligodendrocyte lineage. Lastly, subchronic infusions of FGF2 into the PFC but not into dorsal striatum produced antidepressant- and anxiolytic-like effects on FST and NSFT respectively. Conclusions These findings demonstrate that FGF2-FGFR signaling is sufficient and necessary for the behavioral, as well as gliogenic actions of antidepressants and highlight the PFC as a brain region sensitive to the antidepressant actions of FGF2.

Vascular endothelial growth factor (VEGF) is a hypoxia-induced angiogenic protein that exhibits a broad range of neurotrophic and neuroprotective effects in the central nervous system. Given that neurogenesis occurs in close proximity to blood vessels, increasing evidence has suggested that VEGF may constitute an important link between neurogenesis and angiogenesis. Although it is known that VEGF can directly stimulate the proliferation of neuronal progenitors, the underlying signaling pathways responsible in this process are not fully understood. Thus, in the present study, we set out to examine the requirement of two downstream targets of the VEGF/Flk-1 signaling network, the phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) pathways, in producing the mitogenic effects of VEGF. Both in vivo and in vitro experiments showed that a single treatment of VEGF activated Erk1/2 and Akt signaling pathways in the adult rat hippocampus and in cultured hippocampal neuronal progenitor cells. This effect was blocked with the VEGF/Flk-1 inhibitor SU5416. Importantly, microinfusion of VEGF into the rat brain also induced pCREB expression in the dentate gyrus and increased the number of BrdU-labeled cells in the dentate subgranular zone. Double immunofluorescence labeling revealed that a large proportion of BrdU-labeled cells expressed activated forms of Flk-1, Erk1/2, and Akt. Interestingly, treatment with the SSRI fluoxetine, which is well known to stimulate neurogenesis and VEGF-signaling, also produced a similar expression pattern of Erk1/2 and Akt in proliferating cells. Finally, pharmacological experiments showed that administration of inhibitors of either MAPK/ERK (U0126) or PI3K (LY294002) blocked VEGF-stimulation of hippocampal cell proliferation in vivo and in vitro. Taken together, our findings demonstrate that the proliferative actions of VEGF require activation of both ERK and Akt signaling cascades and that these intracellular pathways are stimulated almost exclusively in actively proliferating neuronal progenitor cells of the adult hippocampus.

In addition to its role as metabolic substrate that can sustain neuronal function and viability, emerging evidence supports a role for l-lactate as an intercellular signaling molecule involved in synaptic plasticity. Clinical and basic research studies have shown that major depression and chronic stress are associated with alterations in structural and functional plasticity. These findings led us to investigate the role of l-lactate as a potential novel antidepressant. Here we show that peripheral administration of l-lactate produces antidepressant-like effects in different animal models of depression that respond to acute and chronic antidepressant treatment. The antidepressant-like effects of l-lactate are associated with increases in hippocampal lactate levels and with changes in the expression of target genes involved in serotonin receptor trafficking, astrocyte functions, neurogenesis, nitric oxide synthesis and cAMP signaling. Further elucidation of the mechanisms underlying the antidepressant effects of l-lactate may help to identify novel therapeutic targets for the treatment of depression.

These data suggest that FGF2 levels are critically related to anxiety behavior and hypothalamic-pituitary-adrenal axis activity, likely through modulation of hippocampal glucocorticoid receptor expression, an effect that is likely receptor mediated, albeit not by FGFR1, FGFR2, and FGFR3.

Mental illnesses have long been perceived as the exclusive consequence of abnormalities in neuronal functioning. Until recently, the role of glial cells in the pathophysiology of mental diseases has largely been overlooked. However recently, multiple lines of evidence suggest more diverse and significant functions of glia with behavior-altering effects. The newly ascribed roles of astrocytes, oligodendrocytes and microglia have led to their examination in brain pathology and mental illnesses. Indeed, abnormalities in glial function, structure and density have been observed in postmortem brain studies of subjects diagnosed with mental illnesses. In this review, we discuss the newly identified functions of glia and highlight the findings of glial abnormalities in psychiatric disorders. We discuss these preclinical and clinical findings implicating the involvement of glial cells in mental illnesses with the perspective that these cells may represent a new target for treatment.

Spermines are naturally abundant polyamines that partially condense nucleic acids and exhibit the proton-sponge effect in an acidic environment. However, spermines show a limited efficiency for transfecting nucleic acids because of their low molecular weight. Therefore, spermines need to be modified to be used as nonviral vectors for nucleic acids. Here, we synthesized linear bisspermine as well as a linear and dendritic tetraspermine with different molecular architectures. These oligospermines were self-assembled into polyplexes with siRNA. The structure–activity relationship of the oligospermines was evaluated in terms of their efficiency for delivering siRNA into a nonsmall cell lung carcinoma cell line. Oligospermines displayed minimal cytotoxicity but efficient siRNA condensation and showed better stability against polyanions than polyethylenimine. The morphology of the polyplexes was strongly affected by the oligospermine architecture. Linear tetraspermine/siRNA polyplexes showed the best gene-silencing efficiency among the oligospermines tested at both the mRNA and protein expression levels, indicating the most favorable structure for siRNA delivery.

The extracellular matrix exhibits several nanostructures such as fibers, filaments, nanopores and ridges that can be mimicked by topographical and 3D substrates for cell and tissue cultures for an environment closer to in vivo conditions. This review summarizes and discusses a growing number of reports employing nanoimprint lithography to obtain such scaffolds. The different nanoimprint lithography methods as well as their advantages and disadvantages are described and special attention is paid to cell culture applications. We discuss the impact of materials, nanotopography, size, geometry, fabrication method, and cell type on growth guidance and differentiation. We present examples of cell guidance, inhibition of cell growth, cell pinning and engineering of 3D cell sheets or spheroids. As current applications are limited and not systematically compared for various cell types, this review only suggests promising substrates for particular applications. Future possible directions are also proposed in which this field may proceed.