Voluntary running rescues the defective hippocampal neurogenesis and behaviour observed in lipocalin 2-null mice

The continuous generation of new neurons in the adult mammalian hippocampus is a form of neural plasticity that modulates learning and memory functions, and also emotion (anxiety and depression). Among the factors known to modulate adult hippocampal neurogenesis and brain function, lipocalin-2 (LCN2) was recently described as a key regulator of neural stem cells (NSCs) proliferation and commitment, with impact on several dimensions of behaviour. Herein, we evaluated whether voluntary running, a well-known regulator of cell genesis, rescue the deficient adult hippocampal neurogenesis observed in mice lacking LCN2. We observed that running, by counteracting oxidative stress in NSCs, reverses LCN2-null mice defective hippocampal neurogenesis, as it promotes NSCs cell cycle progression and maturation, resulting in a partial reduction in anxiety and improved contextual behaviour. Together, these findings demonstrate that running is a positive modulator of adult hippocampal neurogenesis and behaviour in mice lacking LCN2, by impacting on the antioxidant kinetics of NSCs.

Adult Hippocampal Neurogenesis Modulation by the Membrane-Associated Progesterone Receptor Family Member Neudesin

Neudesin (Neuron-derived neurotrophic factor, NENF), a membrane-associated progesterone receptor family (MAPR) member, is a neuron secreted protein with neurotrophic properties during embryonic stages. However, its role in the adult brain is still poorly addressed. In this study we have used neudesin-null (Nenf^−/−) mice and performed a characterization of the proliferation state of the adult neurogenic niches, the adult subventricular zone (SVZ) and the hippocampus subgranular zone (SGZ). Nenf^−/− males did not presented any deficits in proliferation in the SVZ neither in vivo nor in vitro. On the other hand a decrease in cell proliferation in the SGZ was observed, as well as a decrease in the number of newborn neurons in the dentate gyrus (DG) that was accompanied by impaired context discrimination in a contextual fear conditioning (CFC) task. Since NENF neurotrophic action is suggested to occur via the formation of a progesterone stability complex for the activation of non-genomic cascade, we further evaluated progesterone metabolism in the absence of NENF. Interestingly, expression of progesterone catabolic rate-determining enzyme, 5-α-reductase was upregulated in the DG of Nenf^−/−, together with a significant increase in the expression of the δGABA_A receptor gene, involved in DG tonic inhibition. Taken together, these findings add in vivo evidence on the neurotrophic properties of NENF in the adult brain. Furthermore, the mechanism of action of NENF in this process might implicate neurosteroids modulation, at least in the DG.

The dynamics of stress: a longitudinal MRI study of rat brain structure and connectome

Stress is a well-established trigger for a number of neuropsychiatric disorders, as it alters both structure and function of several brain regions and its networks. Herein, we conduct a longitudinal neuroimaging study to assess how a chronic unpredictable stress protocol impacts the structure of the rat brain and its functional connectome in both high and low responders to stress. Our results reveal the changes that stress triggers in the brain, with structural atrophy affecting key regions such as the prelimbic, cingulate, insular and retrosplenial, somatosensory, motor, auditory and perirhinal/entorhinal cortices, the hippocampus, the dorsomedial striatum, nucleus accumbens, the septum, the bed nucleus of the stria terminalis, the thalamus and several brain stem nuclei. These structural changes are associated with increasing functional connectivity within a network composed by these regions. Moreover, using a clustering based on endocrine and behavioural outcomes, animals were classified as high and low responders to stress. We reveal that susceptible animals (high responders) develop local atrophy of the ventral tegmental area and an increase in functional connectivity between this area and the thalamus, further spreading to other areas that link the cognitive system with the fight-or-flight system. Through a longitudinal approach we were able to establish two distinct patterns, with functional changes occurring during the exposure to stress, but with an inflection point after the first week of stress when more prominent changes were seen. Finally, our study revealed differences in functional connectivity in a brainstem-limbic network that distinguishes resistant and susceptible responders before any exposure to stress, providing the first potential imaging-based predictive biomarkers of an individual's resilience/vulnerability to stressful conditions.

Lipocalin-2 regulates adult neurogenesis and contextual discriminative behaviours

In the adult mammalian brain, newborn granule cells are continuously integrated into hippocampal circuits, and the fine-tuning of this process is important for hippocampal function. Thus, the identification of factors that control adult neural stem cells (NSCs) maintenance, differentiation and integration is essential. Here we show that the deletion of the iron trafficking protein lipocalin-2 (LCN2) induces deficits in NSCs proliferation and commitment, with impact on the hippocampal-dependent contextual fear discriminative task. Mice deficient in LCN2 present an increase in the NSCs population, as a consequence of a G0/G1 cell cycle arrest induced by increased endogenous oxidative stress. Of notice, supplementation with the iron-chelating agent deferoxamine rescues NSCs oxidative stress, promotes cell cycle progression and improves contextual fear conditioning. LCN2 is, therefore, a novel key modulator of neurogenesis that, through iron, controls NSCs cell cycle progression and death, self-renewal, proliferation and differentiation and, ultimately, hippocampal function.

The habenula as a critical node in chronic stress-related anxiety

The habenula is activated in response to stressful and aversive events, resulting in exploratory inhibition. Although possible mechanisms for habenula activation have been proposed, the effects of chronic stress on the habenular structure have never been studied. Herein, we assessed changes in volume, cell density and dendritic structure of habenular cells after chronic stress exposure using stereological and 3D morphological analysis. This study shows for the first time that there is a hemispherical asymmetry in the medial habenula (MHb) of the adult rat, with the right MHb containing more neurons than its left counterpart. Additionally, it shows that chronic stress induces a bilateral atrophy of both the MHb and the lateral habenula (LHb). This atrophy was accompanied by a reduction of the number of neurons in the right MHb and the number of glial cells in the bilateral LHb, but not by changes in the dendritic arbors of multipolar neurons. Importantly, these structural changes were correlated with elevated levels of serum corticosterone and increased anxious-like behavior in stressed animals. To further assess the role of the habenula in stress-related anxiety, bilateral lesions of the LHb were performed; interestingly, in lesioned animals the chronic stress protocol did not trigger increases in circulating corticosterone or anxious-like behavior. This study highlights the role of the habenula in the stress responses and how its sub-regions are structurally impacted by chronic stress with physiological and behavioral consequences.

Neudesin is involved in anxiety behavior: structural and neurochemical correlates

Neudesin (also known as neuron derived neurotrophic factor, Nenf) is a scarcely studied putative non-canonical neurotrophic factor. In order to understand its function in the brain, we performed an extensive behavioral characterization (motor, emotional, and cognitive dimensions) of neudesin-null mice. The absence of neudesin leads to an anxious-like behavior as assessed in the elevated plus maze (EPM), light/dark box (LDB) and novelty suppressed feeding (NSF) tests, but not in the acoustic startle (AS) test. This anxious phenotype is associated with reduced dopaminergic input and impoverished dendritic arborizations in the dentate gyrus granule neurons of the ventral hippocampus. Interestingly, shorter dendrites are also observed in the bed nucleus of the stria terminalis (BNST) of neudesin-null mice. These findings lead us to suggest that neudesin is a novel relevant player in the maintenance of the anxiety circuitry.

Lipocalin-2 is involved in emotional behaviors and cognitive function

Lipocalin-2 (LCN2), an iron-related protein well described to participate in the innate immune response, has been shown to modulate spine morphology and to regulate neuronal excitability. In accordance, LCN2-null mice are reported to have stress-induced anxiety. Here we show that, under standard housing conditions, LCN2-null mice display anxious and depressive-like behaviors, as well as cognitive impairment in spatial learning tasks. These behavioral alterations were associated with a hyperactivation of the hypothalamic-pituitary-adrenal axis and with an altered brain cytoarchitecture in the hippocampus. More specifically, we found that the granular and pyramidal neurons of the ventral hippocampus, a region described to be associated with emotion, were hypertrophic, while neurons from the dorsal hippocampus, a region implicated in memory and cognition, were atrophic. In addition, LCN2-null mice presented synaptic impairment in hippocampal long-term potentiation. Whether the LCN2 effects are mediated through modulation of the level of corticosteroids or through a novel mechanism, the present observations bring further into light this immune-related protein as a player in the fine-tuning of behavior and of synaptic activity.

The path from the choroid plexus to the subventricular zone: go with the flow!

In adult mammals, under physiological conditions, neurogenesis, the process of generating new functional neurons from precursor cells, occurs mainly in two brain areas: the subgranular zone in the dentate gyrus of the hippocampus, and the subventricular zone (SVZ) lining the walls of the brain lateral ventricles. Taking into account the location of the SVZ and the cytoarchitecture of this periventricular neural progenitor cell niche, namely the fact that the slow dividing primary progenitor cells (type B cells) of the SVZ extend an apical primary cilium toward the brain ventricular space which is filled with cerebrospinal fluid (CSF), it becomes likely that the composition of the CSF can modulate both self-renewal, proliferation and differentiation of SVZ neural stem cells. The major site of CSF synthesis is the choroid plexus (CP); quite surprisingly, however, it is still largely unknown the contribution of molecules specifically secreted by the adult CP as modulators of the SVZ adult neurogenesis. This is even more relevant in light of recent evidence showing the ability of the CP to adapt its transcriptome and secretome to various physiologic and pathologic stimuli. By giving particular emphasizes to growth factors and axonal guidance molecules we will illustrate how CP-born molecules might play an important role in the SVZ niche cell population dynamics.

Prevalence and spread of extended-spectrum beta-lactamase-producing Enterobacteriaceae in Europe

Extended-spectrum beta-lactamases (ESBLs) represent a major threat among resistant bacterial isolates. The first types described were derivatives of the TEM-1, TEM-2 and SHV-1 enzymes during the 1980s in Europe, mainly in Klebsiella pneumoniae associated with nosocomial outbreaks. Nowadays, they are mostly found among Escherichia coli isolates in community-acquired infections, with an increasing occurrence of CTX-M enzymes. The prevalence of ESBLs in Europe is higher than in the USA but lower than in Asia and South America. However, important differences among European countries have been observed. Spread of mobile genetic elements, mainly epidemic plasmids, and the dispersion of specific clones have been responsible for the increase in ESBL-producing isolates, such as those with TEM-4, TEM-24, TEM-52, SHV-12, CTX-M-9, CTX-M-14, CTX-M-3, CTX-M-15 and CTX-M-32 enzymes.