Promotion of cAMP responsive element-binding protein activity ameliorates radiation-induced suppression of hippocampal neurogenesis in adult mice

The effect of piracetam on behavioral reactions of adult rats and morphological changes in the brain after whole body fractionated gamma irradiation: an exploratory study

This research was aimed at examining the effect of piracetam on behavioral reactions and morphological changes in the brain of adult rats after fractionated gamma irradiation with a total dose of 5 Gy. Fractionated gamma irradiation led to a decrease in freezing behavior in the Open Field and leukopenia. These behavioral and hematological disorders were accompanied by a cell decrease in the cross-sectional area of granular layer of the dentate gyrus, an increase in the number of Fluoro Jade B-positive cells, and an increase in the number of irreversible changes in the cerebral cortex. The administration of piracetam immediately after irradiation for 14 days maintained the freezing behavior at the level of intact animals and decreased in general motor activity. Also, an increase in morphometric parameters and a decrease of neurodegeneration were observed. We found a statistically significant decrease in the number of Fluoro Jade B-positive cells in comparison with the group of irradiated animals. The drug had no leukoprotective effect on laboratory animals, and led to the emergence of inconclusive trends in the alternation of the arms of the T-labyrinth. Piracetam application showed positive behavioral and morphological changes in rodents and might have a neuroprotective effect in brain tissue after gamma irradiation. Since it is the first experiment with piracetam we attempted, this exploratory study serves to provide more insight into the potential neuroprotection activity of piracetam, and following research is necessary.

Constitutive Activity of Serotonin Receptor 6 Regulates Human Cerebral Organoids Formation and Depression-like Behaviors

Serotonin receptor 6 (5-HT₆R), a typical G protein-coupled receptor (GPCR) mainly expressed in the neurogenic area with constitutive activity, is of particular interest as a promising target for emotional impairment. Here, we found that 5-HT₆R was highly expressed in human NSCs and activation of the receptor promoted self-renewal of human NSCs, and thus induced the expansion and folding of human cerebral organoids; dysfunction of receptor or inhibition of its constitutive activity resulted in the premature differentiation of NSCs, which ultimately depleted the NSC pool. The following mechanistic study revealed that EPAC-CREB signaling was involved in 5-HT₆R regulation. Furthermore, we showed that mice with genetic deletion of 5-HT₆R or knockin A268R mutant presented depression-like behaviors and impaired hippocampal neurogenesis for progressive decrease of the NSC pool. Thus, this study indicates that the modulation of 5-HT₆R and its constitutive activity may provide a therapeutic alternative to alleviate depression.

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5-HT₆R regulates human neural stem cell proliferation

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The constitutive activity of 5-HT₆R is essential for human neural stem cell's multipotency

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5-HT₆R modulates neurogenesis of human cerebral organoids

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Mice with reduced constitutive activity of 5-HT₆R show depression-like behaviors

Sodium butyrate prevents radiation-induced cognitive impairment by restoring pCREB/BDNF expression

Sodium butyrate is a histone deacetylase inhibitor that affects various types of brain damages. To investigate the effects of sodium butyrate on hippocampal dysfunction that occurs after whole-brain irradiation in animal models and the effect of sodium butyrate on radiation exposure-induced cognitive impairments, adult C57BL/6 mice were intraperitoneally treated with 0.6 g/kg sodium butyrate before exposure to 10 Gy cranial irradiation. Cognitive impairment in adult C57BL/6 mice was evaluated via an object recognition test 30 days after irradiation. We also detected the expression levels of neurogenic cell markers (doublecortin) and phosphorylated cAMP response element binding protein/brain-derived neurotrophic factor. Radiation-exposed mice had decreased cognitive function and hippocampal doublecortin and phosphorylated cAMP response element binding protein/brain-derived neurotrophic factor expression. Sodium butyrate pretreatment reversed these changes. These findings suggest that sodium butyrate can improve radiation-induced cognitive dysfunction through inhibiting the decrease in hippocampal phosphorylated cAMP response element binding protein/brain-derived neurotrophic factor expression. The study procedures were approved by the Institutional Animal Care and Use Committee of Korea Institute of Radiological Medical Sciences (approval No. KIRAMS16-0002) on December 30, 2016.

Nutrients, neurogenesis and brain ageing: From disease mechanisms to therapeutic opportunities

Appreciation of the physiological relevance of mammalian adult neurogenesis has in recent years rapidly expanded from a phenomenon of homeostatic cell replacement and brain repair to the current view of a complex process involved in high order cognitive functions. In parallel, an array of endogenous or exogenous triggers of neurogenesis has also been identified, among which metabolic and nutritional cues have drawn significant attention. Converging evidence from animal and in vitro studies points to nutrient sensing and energy metabolism as major physiological determinants of neural stem cell fate, and modulators of the whole neurogenic process. While the cellular and molecular circuitries underlying metabolic regulation of neurogenesis are still incompletely understood, the key role of mitochondrial activity and dynamics, and the importance of autophagy have begun to be fully appreciated; moreover, nutrient-sensitive pathways and transducers such as the insulin-IGF cascade, the AMPK/mTOR axis and the transcription regulators CREB and Sirt-1 have been included, beside more established "developmental" signals like Notch and Wnt, in the molecular networks that dictate neural-stem-cell self-renewal, migration and differentiation in response to local and systemic inputs. Many of these nutrient-related cascades are deregulated in the contest of metabolic diseases and in ageing, and may contribute to impaired neurogenesis and thus to cognition defects observed in these conditions. Importantly, accumulating knowledge on the metabolic control of neurogenesis provides a theoretical framework for the trial of new or repurposed drugs capable of interfering with nutrient sensing as enhancers of neurogenesis in the context of neurodegeneration and brain senescence.

Effects of total saponins of Panax notoginseng on immature neuroblasts in the adult olfactory bulb following global cerebral ischemia/reperfusion

The main active components extracted from Panax notoginseng are total saponins. They have been shown to inhibit platelet aggregation, increase cerebral blood flow, improve neurological behavior, decrease infarct volume and promote proliferation and differentiation of neural stem cells in the hippocampus and lateral ventricles. However, there is a lack of studies on whether total saponins of Panax notoginseng have potential benefits on immature neuroblasts in the olfactory bulb following ischemia and reperfusion. This study established a rat model of global cerebral ischemia and reperfusion using four-vessel occlusion. Rats were administered total saponins of Panax notoginseng at 75 mg/kg intraperitoneally 30 minutes after ischemia then once a day, for either 7 or 14 days. Total saponins of Panax notoginseng enhanced the number of doublecortin (DCX)⁺ neural progenitor cells and increased co-localization of DCX with neuronal nuclei and phosphorylated cAMP response element-binding/DCX⁺ neural progenitor cells in the olfactory bulb at 7 and 14 days post ischemia. These findings indicate that following global brain ischemia/reperfusion, total saponins of Panax notoginseng promote differentiation of DCX⁺ cells expressing immature neuroblasts in the olfactory bulb and the underlying mechanism is related to the activation of the signaling pathway of cyclic adenosine monophosphate response element binding protein.

Neonatal Irradiation Leads to Persistent Proteome Alterations Involved in Synaptic Plasticity in the Mouse Hippocampus and Cortex

Recent epidemiological data indicate that radiation doses as low as those used in computer tomography may result in long-term neurocognitive side effects. The aim of this study was to elucidate long-term molecular alterations related to memory formation in the brain after low and moderate doses of γ radiation. Female C57BL/6J mice were irradiated on postnatal day 10 with total body doses of 0.1, 0.5, or 2.0 Gy; the control group was sham-irradiated. The proteome analysis of hippocampus, cortex, and synaptosomes isolated from these brain regions indicated changes in ephrin-related, RhoGDI, and axonal guidance signaling. Immunoblotting and miRNA-quantification demonstrated an imbalance in the synapse morphology-related Rac1-Cofilin pathway and long-term potentiation-related cAMP response element-binding protein (CREB) signaling. Proteome profiling also showed impaired oxidative phosphorylation, especially in the synaptic mitochondria. This was accompanied by an early (4 weeks) reduction of mitochondrial respiration capacity in the hippocampus. Although the respiratory capacity was restored by 24 weeks, the number of deregulated mitochondrial complex proteins was increased at this time. All observed changes were significant at doses of 0.5 and 2.0 Gy but not at 0.1 Gy. This study strongly suggests that ionizing radiation at the neonatal state triggers persistent proteomic alterations associated with synaptic impairment.

Protective Effect of Administered Rolipram against Radiation-Induced Testicular Injury in Mice

Purpose

Pelvic irradiation for the treatment of cancer can affect normal cells, such as the rapidly proliferating spermatogenic cells of the testis, leading to infertility, a common post-irradiation problem. The present study investigated the radioprotective effect of rolipram, a specific phosphodiesterase type-IV inhibitor known to increase the expression and phosphorylation of the cyclic adenosine monophosphate response element-binding protein (CREB), a key factor for spermatogenesis, with the testicular system against pelvic irradiation.

Materials and Methods

Male C57BL/6 mice were treated with pelvic irradiation (2 Gy) and rolipram, alone or in combination, and were sacrificed at 12 hours and 35 days after irradiation.

Results

Rolipram protected germ cells from radiation-induced apoptosis at 12 hours after irradiation and significantly increased testis weight compared with irradiation controls at 35 days. Rolipram also ameliorated radiation-induced testicular morphological changes, such as changes in seminiferous tubular diameter and epithelial height. Additionally, seminiferous tubule repopulation and stem cell survival indices were higher in the rolipram-treated group than in the radiation group. Moreover, rolipram treatment counteracted the radiation-mediated decrease in the sperm count and mobility in the epididymis.

Conclusions

These protective effects of rolipram treatment prior to irradiation may be mediated by the increase in pCREB levels at 12 hours post-irradiation and the attenuated decrease in pCREB levels in the testis at 35 days post-irradiation in the rolipram-treated group. These findings suggest that activation of CREB signaling by rolipram treatment ameliorates the detrimental effects of acute irradiation on testicular dysfunction and the related male reproductive functions in mice.