Traumatic brain injury promotes neurogenesis at the cost of astrogliogenesis in the adult hippocampus of male mice.

Traumatic brain injury (TBI) can result in long-lasting changes in hippocampal function. The changes induced by TBI on the hippocampus contribute to cognitive deficits. The adult hippocampus harbors neural stem cells (NSCs) that generate neurons (neurogenesis), and astrocytes (astrogliogenesis). While deregulation of hippocampal NSCs and neurogenesis have been observed after TBI, it is not known how TBI may affect hippocampal astrogliogenesis. Using a controlled cortical impact model of TBI in male mice, single cell RNA sequencing and spatial transcriptomics, we assessed how TBI affected hippocampal NSCs and the neuronal and astroglial lineages derived from them. We observe an increase in NSC-derived neuronal cells and a concomitant decrease in NSC-derived astrocytic cells, together with changes in gene expression and cell dysplasia within the dentate gyrus. Here, we show that TBI modifies NSC fate to promote neurogenesis at the cost of astrogliogenesis and identify specific cell populations as possible targets to counteract TBI-induced cellular changes in the adult hippocampus.

Cannabinoid type 2 receptor inhibition enhances the antidepressant and proneurogenic effects of physical exercise after chronic stress.

Chronic stress is a major risk factor for neuropsychiatric conditions such as depression. Adult hippocampal neurogenesis (AHN) has emerged as a promising target to counteract stress-related disorders given the ability of newborn neurons to facilitate endogenous plasticity. Recent data sheds light on the interaction between cannabinoids and neurotrophic factors underlying the regulation of AHN, with important effects on cognitive plasticity and emotional flexibility. Since physical exercise (PE) is known to enhance neurotrophic factor levels, we hypothesised that PE could engage with cannabinoids to influence AHN and that this would result in beneficial effects under stressful conditions. We therefore investigated the actions of modulating cannabinoid type 2 receptors (CB2R), which are devoid of psychotropic effects, in combination with PE in chronically stressed animals. We found that CB2R inhibition, but not CB2R activation, in combination with PE significantly ameliorated stress-evoked emotional changes and cognitive deficits. Importantly, this combined strategy critically shaped stress-induced changes in AHN dynamics, leading to a significant increase in the rates of cell proliferation and differentiation of newborn neurons, overall reduction in neuroinflammation, and increased hippocampal levels of BDNF. Together, these results show that CB2Rs are crucial regulators of the beneficial effects of PE in countering the effects of chronic stress. Our work emphasises the importance of understanding the mechanisms behind the actions of cannabinoids and PE and provides a framework for future therapeutic strategies to treat stress-related disorders that capitalise on lifestyle interventions complemented with endocannabinoid pharmacomodulation.

Circadian glucocorticoid oscillations preserve a population of adult hippocampal neural stem cells in the aging brain.

A decrease in adult hippocampal neurogenesis has been linked to age-related cognitive impairment. However, the mechanisms involved in this age-related reduction remain elusive. Glucocorticoid hormones (GC) are important regulators of neural stem/precursor cells (NSPC) proliferation. GC are released from the adrenal glands in ultradian secretory pulses that generate characteristic circadian oscillations. Here, we investigated the hypothesis that GC oscillations prevent NSPC activation and preserve a quiescent NSPC pool in the aging hippocampus. We found that hippocampal NSPC populations lacking expression of the glucocorticoid receptor (GR) decayed exponentially with age, while GR-positive populations decayed linearly and predominated in the hippocampus from middle age onwards. Importantly, GC oscillations controlled NSPC activation and GR knockdown reactivated NSPC proliferation in aged mice. When modeled in primary hippocampal NSPC cultures, GC oscillations control cell cycle progression and induce specific genome-wide DNA methylation profiles. GC oscillations induced lasting changes in the methylation state of a group of gene promoters associated with cell cycle regulation and the canonical Wnt signaling pathway. Finally, in a mouse model of accelerated aging, we show that disruption of GC oscillations induces lasting changes in dendritic complexity, spine numbers and morphology of newborn granule neurons. Together, these results indicate that GC oscillations preserve a population of GR-expressing NSPC during aging, preventing their activation possibly by epigenetic programming through methylation of specific gene promoters. Our observations suggest a novel mechanism mediated by GC that controls NSPC proliferation and preserves a dormant NSPC pool, possibly contributing to a neuroplasticity reserve in the aging brain.

Insult-induced aberrant hippocampal neurogenesis: Functional consequences and possible therapeutic strategies.

Adult hippocampal neurogenesis plays a critical role in a wide spectrum of hippocampus-dependent functions. Brain pathologies that involve the hippocampus like epilepsy, stroke, and traumatic brain injury, are commonly associated with cognitive impairments and mood disorders. These insults can affect neural stem cells and the subsequent neurogenic cascade in the hippocampus, resulting in the induction of aberrant neurogenesis, which is thought to compromise hippocampal network function, thereby hampering hippocampus-dependent behavior. We here summarize recent preclinical literature on hippocampal insult-induced changes in neurogenesis and based on that, we propose that normalizing aberrant neurogenesis post-insult may help to prevent or rescue behavioral deficits which could help develop novel therapeutic strategies.

Configurations of the Re-scan Confocal Microscope (RCM) for biomedical applications.

The new high-sensitive and high-resolution technique, Re-scan Confocal Microscopy (RCM), is based on a standard confocal microscope extended with a re-scan detection unit. The re-scan unit includes a pair of re-scanning mirrors that project the emission light onto a camera in a scanning manner. The signal-to-noise ratio of Re-scan Confocal Microscopy is improved by a factor of 4 compared to standard confocal microscopy and the lateral resolution of Re-scan Confocal Microscopy is 170 nm (compared to 240 nm for diffraction limited resolution, 488 nm excitation, 1.49 NA). Apart from improved sensitivity and resolution, the optical setup of Re-scan Confocal Microscopy is flexible in its configuration in terms of control of the mirrors, lasers and filters. Because of this flexibility, the Re-scan Confocal Microscopy can be configured to address specific biological applications. In this paper, we explore a number of possible configurations of Re-scan Confocal Microscopy for specific biomedical applications such as multicolour, FRET, ratio-metric (e.g. pH and intracellular Ca2+ measurements) and FRAP imaging.

microRNAs and the regulation of neuronal plasticity under stress conditions.

In the brain, the connection between sensory information triggered by the presence of a stressor and the organism's reaction involves limbic areas such as the hippocampus, amygdala and prefrontal cortex. Consequently, these brain regions are the most sensitive to stress-induced changes in neuronal plasticity. However, the specific effects of stress on neuronal plasticity in these regions largely differ. Despite these regional differences, in many cases the steps leading to brain adaptation to stress involve highly coordinated changes in gene expression affecting cell metabolism, neuronal plasticity and synaptic transmission. In adult life the effects of stress on neuronal plasticity are largely reversible but stress in early life induces persistent changes in neuronal plasticity that increases vulnerability to develop psychopathologies and aging-related cognitive decline, suggesting the involvement of epigenetic mechanisms. A growing body of evidence demonstrates that microRNAs (miRs) are key players in epigenetic regulation. In this forefront review we present a critical look on the literature demonstrating the regulation of neuronal plasticity by miRs and the molecular mechanisms of target specificity in neurons. We propose that further progress in the identification of miR's function beyond single target identification would require a combination of developmental expression studies, bioinformatics and a deeper understanding of large networks of targets involved in epigenetic regulation. This will help to extend our understanding of the role miRs play in the regulation of stress-induced neuronal plasticity.

Knockdown of the glucocorticoid receptor alters functional integration of newborn neurons in the adult hippocampus and impairs fear-motivated behavior.

Glucocorticoids (GCs) secreted after stress reduce adult hippocampal neurogenesis, a process that has been implicated in cognitive aspects of psychopathology, amongst others. Yet, the exact role of the GC receptor (GR), a key mediator of GC action, in regulating adult neurogenesis is largely unknown. Here, we show that GR knockdown, selectively in newborn cells of the hippocampal neurogenic niche, accelerates their neuronal differentiation and migration. Strikingly, GR knockdown induced ectopic positioning of a subset of the new granule cells, altered their dendritic complexity and increased their number of mature dendritic spines and mossy fiber boutons. Consistent with the increase in synaptic contacts, cells with GR knockdown exhibit increased basal excitability parallel to impaired contextual freezing during fear conditioning. Together, our data demonstrate a key role for the GR in newborn hippocampal cells in mediating their synaptic connectivity and structural as well as functional integration into mature hippocampal circuits involved in fear memory consolidation.

Glucocorticoid signaling and stress-related limbic susceptibility pathway: about receptors, transcription machinery and microRNA.

BACKGROUND: Stress is essential for health, but if coping with stress fails, the action of the stress hormones cortisol and corticosterone (CORT) becomes dysregulated, precipitating a condition favorable for increased susceptibility to psychopathology. We focus on the question how the action of CORT can change from protective to harmful. APPROACH: CORT targets the limbic brain, where it affects cognitive processes and emotional arousal. The magnitude and duration of the CORT feedback signal depends on bio-availability of the hormone, the activity of the CORT receptor machinery and the stress-induced drive. If CORT action becomes dysregulated, we postulate that this is linked to compromised receptor regulation in the limbic brain's susceptibility pathway. RESULTS: CORT action on gene transcription is mediated by high affinity mineralocorticoid (MR) and 10 fold lower affinity glucocorticoid (GR) receptors that also can mediate fast non-genomic actions. MR and GR operate a feedback loop that involves access and binding to the receptors, activation and shuttling of the CORT receptor complexes, which require interaction with coregulators and transcription factors for transcriptional outcome. CORT modulates the expression of gene transcripts encoding specific chaperones, motor proteins and transcription factors as well as its own receptors. The emerging evidence of microRNAs operating translational control points to further fine-tuning in receptor signaling. CONCLUSION: Imbalance in MR:GR-mediated actions caused by receptor variants and epigenetic modulations have been proposed as risk factor in stress-related disease. We here provide key regulatory steps in the activation, transport and regulation of CORT receptors that may sensitize susceptibility pathways underlying psychopathology.

Identification of new Nerve Growth Factor-responsive immediate-early genes.

Stimulation of the PC12 pheochromocytoma cell line with the prototypical neurotrophin Nerve Growth Factor (NGF) induces a cellular response of neuronal differentiation and is therefore a widely used model to gain molecular insight into this process. Classically, the transcriptional response to extracellular stimuli such as NGF is divided in genes that require no protein synthesis prior to their induction (immediate-early genes) and genes that do (delayed-response genes). Because an increasing number of studies have reported important roles for immediate-early genes (IEGs) in neuronal differentiation, the goal of the present study was to identify previously unrecognized NGF-responsive IEGs. Stimulation with NGF for 15, 30, 60 and 120 min resulted in a typical transient induction of many known NGF-responsive IEGs. To identify candidate new genes, we analyzed 27000 measured expression profiles and selected 10 genes for further study. Five genes, including Cbp/p300-interacting transactivator 2 (Cited2), Kruppel-like factor 4 (Klf4), v-Maf musculoaponeurotic fibrosarcoma oncogene family, protein F (Maff), Kruppel-like factor 10 (Klf10 or Tieg) and Activating transcription factor 3 (Atf3) were selected and positively validated by qPCR. NGF-induced activation of all five genes seems to be mediated by MAPK and PI3K-mediated pathways. Additionally, we tested translation-independent induction and showed that NGF induced upregulation of these genes in both the subclonal Neuroscreen-1 PC12 and parental PC12 cell line. These 5 transcription factors have not been previously reported as NGF-responsive IEGs, however have previously been reported as important regulators of cell differentiation and proliferation in different systems. These observations may therefore provide important new information on the molecular mechanisms underlying NGF-induced differentiation.

Histamine deficiency induces tissue-specific down-regulation of histamine H2 receptor expression in histidine decarboxylase knockout mice.

Histidine decarboxylase (HDC) is the single enzyme responsible for histamine synthesis. HDC-deficient mice (HDC(-/-)) have no histamine in their tissues when kept on a histamine-free diet. Therefore, the HDC(-/-) mice provide a suitable model to investigate the involvement of histamine in the regulation of histamine receptor expression. Gene expression of H1 and H2 histamine receptors was studied in several organs of HDC(-/-) mice and compared to standard (HDC(+/+)) mice. In many tissues, prolonged absence of histamine induced down-regulation of the H2 receptor subtype. The expression of the H1 receptor was less sensitive to histamine deficiency. Exogenous histamine present in the diet abolished the differences observed in H2 receptor expression. These results suggest that the expression of mouse H2 receptor is under the control of histamine in a tissue-specific manner.

Histamine as an autocrine growth factor: an unusual role for a widespread mediator.

The involvement of histamine in cancer growth represents an old controversy and direct experimental evidence proving this hypothesis is not still available. In this paper we review the most relevant mechanisms referring to the role of histamine receptors, histidine decarboxylase and histamine release in the onset of an autocrine loop, that enables histamine to act as an autocrine growth factor. We postulate that this autocrine loop, that has been studied in an experimental mammary carcinoma model induced in rats, may be present in different human neoplasias. Therefore, the better understanding of this novel regulatory pathway that is controlled by histamine may contribute to identifying new therapeutic targets.

Histamine as an autocrine growth factor in experimental mammary carcinomas.

In order to determine the role of endogenous histamine in the regulation of cell growth, the in vitro action of fluoromethyl-histidine (MFMH) was studied in experimental mammary carcinomas induced in rats. Tumor cells were cultured in soft agar using the clonogenic agar technique. The MFMH was added in different concentrations (0.01-100 microM). The effect observed was a 60% inhibition on colony formation with a maximal effect at concentrations over 10 microM. This action was completely reverted by the H2 agonists dimaprit and arpromidine with an IC50 value of 1 microM. The action of the H2 agonists when added alone was a significant increase in cell proliferation (135%), while the H1 agonist produced a dose-dependent inhibition on cell growth. In these experimental carcinomas endogenous histamine is critical for cell proliferation and one of its major effects may be the stimulation of cell growth by acting on specific H2 membrane receptors.

Effect of histamine on growth and differentiation of the rat mammary gland.

The presence of H1 and H2 histamine receptors and their associated second messenger systems were studied during the development of the rat mammary gland. In the tissue of the young female, histamine presented a double receptor site as previously described for experimental mammary tumors, namely a high affinity H2 site (Kd = 10 +/- 2 nM, Bmax = 1068 +/- 71 fm/mg prot.), which mediated its effect via the products of phosphoinositide hydrolysis and a low affinity H1 receptor (Kd1 = 5 +/- 2 nM, Bmax = 188 +/- 33 fm/mg prot. and Kd2 = 41 +/- 20 nM, Bmax = 1980 +/- 790 fm/mg prot. when characterized with 3H-mepyramine), coupled to adenylyl cyclase activation. On the other hand, the mammary gland of the adult rat presented these receptors coupled to the classical second messenger systems described for mammalian cells, that is, the H2 receptor produced an increase in intracellular cAMP levels and the H1 receptor increased the phosphoinositide turnover. We conclude that histamine plays a critical role during development and differentiation of the normal rat mammary gland.

Hepatic metabolic function in patients receiving long-term methotrexate therapy: comparison with topically treated psoriatics, patient controls and cirrhotics.

Standard biochemical liver function tests and the clearances of antipyrine and indocyanine green have been compared in psoriatic patients taking methotrexate, psoriatic patients on topical treatment, patient controls and patients with hepatic cirrhosis. The methotrexate-treated patients showed significant elevations in alkaline phosphatase (p less than 0.025) and gamma glutamyl transpeptidase activities (p less than 0.05) compared to topically treated psoriatics and patient controls. The clearance of antipyrine was reduced in the methotrexate treated group but not significantly (p less than 0.1 greater than 0.05). In contradistinction, the weight-adjusted clearance of indocyanine green was significantly impaired in the methotrexate group in comparison with the topically treated psoriatics (p less than 0.01). The clearance of both antipyrine and indocyanine green were markedly lowered in the cirrhotics (p less than 0.001 against all other groups). These data suggest that the serial measurement of alkaline phosphatase and indocyanine green clearance may provide a non-invasive indicator of the development and progression of methotrexate-related liver injury.

The number and distribution of benign pigmented moles (melanocytic naevi) in a healthy British population.

Total body mole counts have been performed on 432 normal healthy Caucasian subjects aged 4 days to 96 years (204 males and 228 females). The mean total body mole count in the first decade of life is three for females and two for males, rising rapidly in the second decade to a mean of 23 for females and 18 for males. In the third decade numbers are highest, with a mean of 33 for females and 22 for males. Thereafter, numbers of moles slowly drop until in the eighth decade they have fallen to levels similar to those seen in pre-pubertal children. There is a significant association between the presence of naevi in early childhood (prior to 5 years of age) and the development in later life of large numbers of moles. In women there is no significant association between total mole counts and either parity or use of the oral contraceptive.