Clostridium ramosum regulates enterochromaffin cell development and serotonin release.

Peripheral serotonin (5-hydroxytryptamine: 5-HT) synthesized in the intestine by enterochromaffin cells (ECs), plays an important role in the regulation of peristaltic of the gut, epithelial secretion and promotes the development and maintenance of the enteric neurons. Recent studies showed that the indigenous gut microbiota modulates 5-HT signalling and that ECs use sensory receptors to detect dietary and microbiota-derived signals from the lumen to subsequently transduce the information to the nervous system. We hypothesized that Clostridium ramosum by increasing gut 5-HT availability consequently contributes to high-fat diet-induced obesity. Using germ-free mice and mice monoassociated with C. ramosum, intestinal cell lines and mouse organoids, we demonstrated that bacterial cell components stimulate host 5-HT secretion and program the differentiation of colonic intestinal stem progenitors toward the secretory 5-HT-producing lineage. An elevated 5-HT level regulates the expression of major proteins involved in intestinal fatty acid absorption in vitro, suggesting that the presence of C. ramosum in the gut promotes 5-HT secretion and thereby could facilitates intestinal lipid absorption and the development of obesity.

Cannabinoid receptor CB1 mediates baseline and activity-induced survival of new neurons in adult hippocampal neurogenesis.

BACKGROUND: Adult neurogenesis is a particular example of brain plasticity that is partially modulated by the endocannabinoid system. Whereas the impact of synthetic cannabinoids on the neuronal progenitor cells has been described, there has been lack of information about the action of plant-derived extracts on neurogenesis. Therefore we here focused on the effects of Delta9-tetrahydrocannabinol (THC) and Cannabidiol (CBD) fed to female C57Bl/6 and Nestin-GFP-reporter mice on proliferation and maturation of neuronal progenitor cells and spatial learning performance. In addition we used cannabinoid receptor 1 (CB1) deficient mice and treatment with CB1 antagonist AM251 in Nestin-GFP-reporter mice to investigate the role of the CB1 receptor in adult neurogenesis in detail. RESULTS: THC and CBD differed in their effects on spatial learning and adult neurogenesis. CBD did not impair learning but increased adult neurogenesis, whereas THC reduced learning without affecting adult neurogenesis. We found the neurogenic effect of CBD to be dependent on the CB1 receptor, which is expressed over the whole dentate gyrus. Similarly, the neurogenic effect of environmental enrichment and voluntary wheel running depends on the presence of the CB1 receptor. We found that in the absence of CB1 receptors, cell proliferation was increased and neuronal differentiation reduced, which could be related to CB1 receptor mediated signaling in Doublecortin (DCX)-expressing intermediate progenitor cells. CONCLUSION: CB1 affected the stages of adult neurogenesis that involve intermediate highly proliferative progenitor cells and the survival and maturation of new neurons. The pro-neurogenic effects of CBD might explain some of the positive therapeutic features of CBD-based compounds.

Arc/Arg3.1 is essential for the consolidation of synaptic plasticity and memories.

Arc/Arg3.1 is robustly induced by plasticity-producing stimulation and specifically targeted to stimulated synaptic areas. To investigate the role of Arc/Arg3.1 in synaptic plasticity and learning and memory, we generated Arc/Arg3.1 knockout mice. These animals fail to form long-lasting memories for implicit and explicit learning tasks, despite intact short-term memory. Moreover, they exhibit a biphasic alteration of hippocampal long-term potentiation in the dentate gyrus and area CA1 with an enhanced early and absent late phase. In addition, long-term depression is significantly impaired. Together, these results demonstrate a critical role for Arc/Arg3.1 in the consolidation of enduring synaptic plasticity and memory storage.

Running in pregnancy transiently increases postnatal hippocampal neurogenesis in the offspring.

Voluntary wheel running of mice in pregnancy and lactation led to a twofold increase in hippocampal precursor-cell proliferation and in the number of Prox1-expressing lineage-determined cells at postnatal day 8 (P8). At P36, the number of newly generated granule cells approximately doubled, resulting in a 40% higher total number of granule cells in pups from running dams as compared with controls. Cell proliferation at embryonic day 15 (E15), in contrast, was decreased in the progeny of exercising mice, and the birth weight was reduced. At P49, body weight had normalized, and hippocampal neurogenesis was not different between the two groups. mRNA for FGF2 was expressed at higher levels at E15 and P8 in runner pups, whereas VEGF was increased only at E15. Insulin-like growth factor did not show differences at any time point. At P36, no differences for any of the factors were found. Our data indicate that maternal behavior and physical activity affects infantile growth-factor expression and can transiently stimulate postnatal hippocampal development in the offspring.

Physical exercise prevents age-related decline in precursor cell activity in the mouse dentate gyrus.

Physical activity induces adult hippocampal neurogenesis. We here show that the acute up-regulating effect of voluntary wheel running on precursor cell proliferation decreases with continued exercise, but that continued exercise reduces the age-dependent decline in adult neurogenesis. Cell proliferation peaked at 3 days of running. After 32 days of exercise this response returned to baseline. Running-induced proliferation of transiently amplifying progenitor cells led to a consecutive increase in the number of more mature cells. Increasing age reduced adult neurogenesis at 9 months to 50% of the value at 6 weeks and to 17% at the age of 2 years. At both 1 and 2 years, precursor cell divisions remained inducible by physical activity. Exercise from 3 to 9 months of age significantly reduced the age-dependent decline in cell proliferation but (presumably in the absence of additional stimuli) did not maintain net neurogenesis at levels corresponding to a younger age. We propose that physical activity might contribute to successful aging by increasing the potential for neurogenesis represented by the pool of proliferating precursor cells.

Age-dependent expression of glucocorticoid- and mineralocorticoid receptors on neural precursor cell populations in the adult murine hippocampus.

Steroid hormones are regulators of adult hippocampal neurogenesis and are central to hypotheses regarding adult neurogenesis in age-related and psychiatric disturbances associated with altered hippocampal plasticity--most notably dementias and major depression. Using immunohistochemistry, we examined the expression of glucocorticoid (GR) and mineralocorticoid (MR) receptors during adult hippocampal neurogenesis. In young mice only 27% of dividing cells in the subgranular zone expressed GR, whereas 4 weeks after division 87% had become positive for GR and MR. GR was expressed by 50% of the radial glia-like type-1 and type-2a progenitor cells, whereas MR was expressed only by mature calbindin-positive granule cells. Doublecortin-positive neuronal progenitor cells (type-2b) and early postmitotic calretinin-positive neurons were devoid of GR and MR expression. Fifty per cent of the intermediate type-3 cells showed GR expression, possibly reflecting cells terminating maturation. Thus, all subpopulations of dividing precursor cells showed an identical receptor profile (50% GR, no MR), except for type-2b cells, which expressed neither receptor. There was also no overlap between calretinin and GR early postnatally (P8) or after physical activity or exposure to an enriched environment, both of which are potent neurogenic stimuli. In contrast, in old age calretinin-positive young neurons became GR and MR positive, suggesting increased steroid sensitivity. Age also increased the expression of GR in type-1 and type-2a precursor cells. Other intermediates were so rare in old age that they could not be studied. This course and variability of receptor expression in aging might help to explain differential vulnerability of adult neural precursor cells to corticoid-mediated influences.

Transient calretinin expression defines early postmitotic step of neuronal differentiation in adult hippocampal neurogenesis of mice.

We here show that the early postmitotic stage of granule cell development during adult hippocampal neurogenesis is characterized by the transient expression of calretinin (CR). CR expression was detected as early as 1 day after labeling dividing cells with bromodeoxyuridine (BrdU), but not before. Staining for Ki-67 confirmed that no CR-expressing cells were in cell cycle. Early after BrdU, CR colocalized with immature neuronal marker doublecortin; and later with persisting neuronal marker NeuN. BrdU/CR-labeled cells were negative for GABA and GABAA1 receptor, but early on expressed granule cell marker Prox-1. After 6 weeks, no new neurons expressed CR, but all contained calbindin. Stimuli inducing adult neurogenesis have limited (enriched environment), strong (voluntary wheel running), and very strong effects on cell proliferation (kainate-induced seizures). In these models the induction of cell proliferation was paralleled by an increase of CR-positive cells, indicating the stimulus-dependent progression from cell division to a postmitotic stage.