Increase in neurogenesis and behavioural benefit after chronic fluoxetine treatment in Wistar rats

Objective –  Disturbances in hippocampal neurogenesis may be involved in the pathophysiology of depression and it has been argued that an increase in the generation of new nerve cells in the hippocampus is involved in the mechanism of action of antidepressants.
Materials and Methods –  Adult Wistar rats were treated with fluoxetine (10 mg/kg) 1 h, daily for 5 (subchronic) or 28 days (chronic) before the Novelty Suppressed Feeding test was performed. Cell proliferation and neurogenesis were analysed using the markers 5-bromo-deoxy-2'-uridine, Ki-67, and doublecortin.
Results –  A significant behavioural effect was found after 28 days of fluoxetine administration. However, no behavioural improvement was demonstrated after acute and subchronic treatment with fluoxetine. We further demonstrate that chronic antidepressant treatment increases cell proliferation as well as neurogenesis in the dentate gyrus, here using Wistar rats.
Conclusions –  In further development of antidepressants, neurogenesis may serve as an important parameter to examine the efficacy and mechanism of action of novel drugs.     

Dissociation between apoptosis, neurogenesis, and synaptic potentiation in the dentate gyrus of adrenalectomized rats

Removal of adrenal hormone corticosterone in rats aged 3-4 months results within 3 days in acceleration of apoptosis and proliferation of newborn cells in the dentate gyrus (DG). A critical question is whether such a shift in the maturity of dentate cells after adrenalectomy (ADX) affects synaptic plasticity. To address this question, male rats were adrenalectomized and synaptic potentiation was recorded in vitro in hippocampal slices, as well as in vivo, in response to high frequency stimulation of the perforant path, 3 days after ADX. At this time-point, cell loss was assessed and proliferation was examined. Based on two independent parameters, bromodeoxyuridine and Ki-67, we found that removal of the adrenal glands increases proliferation rate. This increase in proliferation was, in particular, evident in those animals that displayed substantial cell loss. The accelerated cell-turnover after ADX was accompanied by reduced synaptic potentiation, both when recorded in vitro and in vivo. Corticosterone replacement in vivo (in adrenalectomized animals), at levels that activate the mineralocorticoid receptor, prevented ADX-induced proliferation, apoptosis, and restored synaptic potentiation to control levels. Importantly, corticosterone applied to slices from adrenalectomized rats also normalized synaptic potentiation, despite increased proliferation. This suggests that changes in cell proliferation and apoptotic cell death in the DG are not necessarily key factors determining the efficacy of synaptic potentiation.     

Doublecortin expression levels in adult brain reflect neurogenesis

Progress in the field of neurogenesis is currently limited by the lack of tools enabling fast and quantitative analysis of neurogenesis in the adult brain. Doublecortin (DCX) has recently been used as a marker for neurogenesis. However, it was not clear whether DCX could be used to assess modulations occurring in the rate of neurogenesis in the adult mammalian central nervous system following lesioning or stimulatory factors. Using two paradigms increasing neurogenesis levels (physical activity and epileptic seizures), we demonstrate that quantification of DCX-expressing cells allows for an accurate measurement of modulations in the rate of adult neurogenesis. Importantly, we excluded induction of DCX expression during physiological or reactive gliogenesis and excluded also DCX re-expression during regenerative axonal growth. Our data validate DCX as a reliable and specific marker that reflects levels of adult neurogenesis and its modulation. We demonstrate that DCX is a valuable alternative to techniques currently used to measure the levels of neurogenesis. Importantly, in contrast to conventional techniques, analysis of neurogenesis through the detection of DCX does not require in vivo labelling of proliferating cells, thereby opening new avenues for the study of human neurogenesis under normal and pathological conditions.     

Effects of maternal behavior induction and pup exposure on neurogenesis in adult, virgin female rats

The states of pregnancy and lactation bring about a range of physiological and behavioral changes in the adult mammal that prepare the mother to care for her young. Cell proliferation increases in the subventricular zone (SVZ) of the female rodent brain during both pregnancy and lactation when compared to that in cycling, diestrous females. In the present study, the effects of maternal behavior induction and pup exposure on neurogenesis in nulliparous rats were examined in order to determine whether maternal behavior itself, independent of pregnancy and lactation, might affect neurogenesis. Adult, nulliparous, Sprague-Dawley, female rats were exposed daily to foster young in order to induce maternal behavior. Following the induction of maternal behavior each maternal subject plus females that were exposed to pups for a comparable number of test days, but did not display maternal behavior, and subjects that had received no pup exposure were injected with bromodeoxyuridine (BrdU, 90 mg/kg, i.v.). Brain sections were double-labeled for BrdU and the neural marker, NeuN, to examine the proliferating cell population. Increases in the number of double-labeled cells were found in the maternal virgin brain when compared with the number of double-labeled cells present in non-maternal, pup-exposed nulliparous rats and in females not exposed to young. No changes were evident in the dentate gyrus of the hippocampus as a function of maternal behavior. These data indicate that in nulliparous female rats maternal behavior itself is associated with the stimulation of neurogenesis in the SVZ.     

The dynamics of adult neurogenesis in human hippocampus

The phenomenon of adult neurogenesis is now an accepted occurrence in mammals and also in humans.At least two discrete places house stem cells for generation of neurons in adult brain. These are olfactory system and the hippocampus. In animals, newly generated neurons have been directly or indirectly demonstrated to generate a significant amount of new neurons to have a functional role. However, the data in humans on the extent of this process is still scanty and such as difficult to comprehend its functional role in humans. This paper explores the available data on as extent of adult hippocampal neurogenesis in humans and makes comparison to animal data.     

Impaired fear memory and decreased hippocampal neurogenesis following olfactory bulbectomy in rats

It has been proposed that a decrease in adult hippocampal neurogenesis provides a biological and cellular basis for major depression. The olfactory bulbectomy (OB) in rats is widely accepted as an animal model of depression. In the present study, we investigated the effect of OB on memory formation in the memory tasks related to the hippocampal function and adult hippocampal neurogenesis. OB induced a behavioural syndrome, which was characterized by an increased activity in the open-field test and impairment in passive avoidance behaviour and contextual fear conditioning. The behavioural changes, following OB, were accompanied by a decrease in the number of proliferating cells in the dentate gyrus. Furthermore, the differentiation of the newly born cells, into mature calbindin-positive neurons, was also retarded. Stereological analysis revealed a decrease in the total granule neuron numbers within the granule cell layer of the dentate gyrus, without a significant decrease in volume of the dentate gyrus. Although a relationship between altered neurogenesis and behavioural syndrome, induced by OB, is not established yet, our results suggest that decreased neurogenesis might at least partly contribute for behavioural deficits following OB.     

Glutamate enhances proliferation and neurogenesis in human neural progenitor cell cultures derived from the fetal cortex

Excitatory amino acids such as glutamate play important roles in the central nervous system. We previously demonstrated that a neurosteroid, dehydroepiandrosterone (DHEA), has powerful effects on the cell proliferation of human neural progenitor cells (hNPC) derived from the fetal cortex, and this effect is modulated through NMDA receptor signaling. Here, we show that glutamate can significantly increase the proliferation rates of hNPC. The increased proliferation could be blocked by specific NMDA receptor antagonists, but not other glutamate antagonists for kainate-AMPA or metabotropic receptors. The NR1 subunit of the NMDA receptor was detectable in elongated bipolar or unipolar cells with small cell bodies. These NR1-positive cells were colocalized with GFAP immunoreactivity. Detection of the phosphorylation of cAMP response element-binding protein (pCREB) revealed that a subset of NR1-positive hNPC could respond to glutamate. Furthermore, we hypothesized that glutamate treatment may affect mainly the hNPC with a radial morphology and found that glutamate as well as DHEA selectively affected elongated hNPC; these elongated cells may be a type of radial glial cell. Finally we asked whether the glutamate-responsive hNPC had an increased potential for neurogenesis and found that glutamate-treated hNPC produced significantly more neurons following differentiation. Together these data suggest that glutamate stimulates the division of human progenitor cells with neurogenic potential.     

Determinants of central nervous system adult neurogenesis are sex,hormones, mouse strain,age, and brain region

Multiple sclerosis is a sexually dimorphic (SD) disease that causes oligodendrocyte death, but SD of glial cells is poorly studied. Here, we analyze SD of neural progenitors in 6–8 weeks and 6–8 months normal C57BL/6, SJL/J, and BALB/c mice in the subventricular zone (SVZ), dorsolateral horn (DLC), corpus callosum (CC), and parenchyma. With a short 2‐h bromodeoxyuridine (BrdU) pulse, no gender and strain differences are present at 6–8 weeks. At 6–8 months, the number of BrdU⁺ cells decreases twofold in each sex, strain, and region, indicating that a common aging mechanism regulates BrdU incorporation. Strikingly, 2× more BrdU⁺ cells are found in all brain regions in 6–8 months C57BL/6 females versus males, no gender differences in 6–8 months SJL/J, and fewer BrdU⁺ cells in females versus males in BALB/cs. The number of BrdU⁺ cells modestly fluctuates throughout the estrous cycle in C57BL/6 and SJLs. Castration causes a dramatic increase in BrdU⁺ cells in SVZ and DLC. These findings indicate that testosterone is a major regulator of adult neural proliferation. At 6–8 months, the ratio of PDGFRα⁺ cells in the CC to BrdU⁺ cells in the DLC of both strains, sexes, estrous cycle, and castrated mice was essentially the same, suggesting that BrdU⁺ cells in the DLC differentiate into CC oligodendrocytes. The ratio of TUNEL⁺ to BrdU⁺ cells does not match proliferation, indicating that these events are differentially regulated. Differential regulation of these two processes leads to the variation in glial numbers between gender and strain. Explanations of neural proliferation based upon data from one sex or strain may be very misleading. © 2012 Wiley Periodicals, Inc.     

Gonadal hormone modulation of neurogenesis in the dentate gyrus of adult male and female rodents

Gonadal hormones modulate neurogenesis in the dentate gyrus differentially in male and female adult rodents. Neurogenesis is comprised of at least two components: cell proliferation (the production of new cells) and cell survival (the number of new neurons that survive to maturity). Previous studies have found sex differences in the level of cell proliferation in the dentate gyrus only when comparing females in a high estrogen state to males. This review focuses on the effects of acute and chronic levels of estrogens or androgens on hippocampal neurogenesis in the adult male and female rodent. Evidence is also reviewed for the co-localization of androgen receptors and estrogen receptors (ER) with markers for cell proliferation or immature new cell survival. Briefly, evidence suggests that acute estradiol initially enhances and subsequently suppresses cell proliferation in the dentate gyrus of adult female rodents but may have limited effects in male rodents. Both the two known ER subtypes, ER and β upregulate hippocampal neurogenesis via cell proliferation. Intriguingly, repeated exposure to estradiol modulates hippocampal neurogenesis and cell death in adult female, but not male, rodents. However short-term estradiol treatment (5 days) in male meadow voles enhances new cell survival in the dentate gyrus but only when administered during the ‘axon extension’ phase. Furthermore, evidence is also reviewed showing a difference in response to acute and chronic estradiol treatment in older female rats compared to younger female rats. Recent findings from our laboratory indicate that testosterone and dihydrotestosterone upregulate hippocampal neurogenesis (via cell survival), but not cell proliferation, in adult male rodents. Effects of endogenous fluctuations in gonadal hormones on adult neurogenesis are observed across the seasons in meadow voles and during pregnancy and lactation in the rat dam. Pregnancy and motherhood differentially regulate adult hippocampal neurogenesis in the adult female rodent, with primiparous rats displaying lower levels of hippocampal cell proliferation and survival after parturition. Few studies have compared males and females but existing research suggests a sex difference in the hormonal regulation of hippocampal neurogenesis in the adult. Clearly more work is needed to elucidate the effects of gonadal hormones on neurogenesis in the dentate gyrus of both male and female rodents across the lifespan, especially if we are to use our knowledge of how adult neurogenesis is regulated to develop strategies to repair neuron loss in neurodegenerative diseases.     

Prenatal exposure to ethanol affects postnatal neurogenesis in thalamus

The number of neurons in the ventrobasal thalamus (VB) in the adolescent rat is unaffected by prenatal exposure to ethanol. This is in sharp contrast to other parts of the trigeminal-somatosensory system, which exhibit 30–35% fewer neurons after prenatal ethanol exposure. The present study tested the hypothesis that prenatal ethanol exposure affects dynamic changes in the numbers of VB neurons; such changes reflect the sum of cell proliferation and death. Neuronal number in the VB was determined during the first postnatal month in the offspring of pregnant Long–Evans rats fed an ethanol-containing diet or pair-fed an isocaloric non-alcoholic liquid diet. Offspring were examined between postnatal day (P) 1 and P30. The size of the VB and neuronal number were determined stereologically. Prenatal exposure to ethanol did not significantly alter neuronal number on any individual day, nor was the prenatal generation of VB neurons affected. Interestingly, prenatal ethanol exposure did affect the pattern of the change in neuronal number over time; total neuronal number was stable in the ethanol-treated pups after P12, but it continued to rise in the controls until P21. In addition, the rate of cell proliferation during the postnatal period was greater in ethanol-treated animals. Thus, the rate of neuronal acquisition is altered by ethanol, and by deduction, there appears to be less ethanol-induced neuronal loss in the VB. A contributor to these changes is a latent effect of ethanol on postnatal neurogenesis in the VB and the apparent survival of new neurons.     

普伐他汀对脑缺血大鼠的神经保护及神经发生的作用(英文)

目的研究中枢神经系统缺血损伤后,普伐他汀的神经保护和促进神经发生作用。方法采用线栓法造成大鼠大脑中动脉的暂时性缺血,在以下时间点给予普伐他汀:伤后6 h,伤后每天直至伤后14 天。用神经学评分、平衡实验和旋转实验评价伤后神经学恢复情况。检测血清胆固醇和甘油三酯的含量,计算脑梗塞面积。通过三染色法(BrdU, DCX, NeuN染色)研究普伐他汀对神经发生的作用。结果各组间血清胆固醇和甘油三酯无显著性差异;与对照组相比,实验组动物术后旋转实验评分显著性增加,梗塞面积减小;普伐他汀显著增加了齿状回和脑室下区的BrdU阳性细胞数,并增加了齿状回、脑室下区和纹状体中的BrdU/DCX阳性细胞数。结论中枢神经系统损伤早期重复使用低剂量的普伐他汀是相对安全的,并能够显著改善伤后的神经功能恢复,减少梗死面积。普伐他汀能够诱导大鼠齿状回及脑室下区的神经发生并增加纹状体中迁移神经元的数量,这与普伐他汀的降脂作用无关。     

普伐他汀对脑缺血大鼠的神经保护及神经发生的作用

目的研究中枢神经系统缺血损伤后,普伐他汀的神经保护和促进神经发生作用。方法采用线栓法造成大鼠大脑中动脉的暂时性缺血,在以下时间点给予普伐他汀：伤后6h,伤后每天直至伤后14天。用神经学评分、平衡实验和旋转实验评价伤后神经学恢复情况。检测血清胆固醇和甘油三酯的含量,计算脑梗塞面积。通过三染色法（BrdU, DCX, NeuN染色）研究普伐他汀对神经发生的作用。结果各组间血清胆固醇和甘油三酯无显著性差异;与对照组相比,实验组动物术后旋转实验评分显著性增加,梗塞面积减小;普伐他汀显著增加了齿状回和脑室下区的BrdU阳性细胞数,并增加了齿状回、脑室下区和纹状体中的BrdU/DCX阳性细胞数。结论中枢神经系统损伤早期重复使用低剂量的普伐他汀是相对安全的,并能够显著改善伤后的神经功能恢复,减少梗死面积。普伐他汀能够诱导大鼠齿状回及脑室下区的神经发生并增加纹状体中迁移神经元的数量,这与普伐他汀的降脂作用无关。     

Enhanced neurogenesis in the olfactory bulb in adult mice after injury induced by acute treatment with trimethyltin

In adults, the subventricular zone is known to contain undifferentiated neural progenitor cells that proliferate and generate the olfactory bulb (OB) interneurons throughout life. We earlier showed that trimethyltin (TMT) causes neuronal damage in the granular cell layer of the OB in adult mice. In the current study, we examined neurogenesis in the OB in adult mice after injury induced by acute treatment with TMT. On day 2 post‐TMT treatment, enhanced incorporation of 5‐bromo‐2′‐deoxyuridine (BrdU) was seen in the granular cell layer of the OB. Many of the BrdU‐labeled cells were undifferentiated cells on day 2 post‐treatment. On day 30 post‐TMT treatment, BrdU‐labeled neuronal cells were dramatically increased in number in the granular cell layer of the OB. However, TMT treatment was ineffective in affecting the migration of BrdU‐labeled cells from the subventricular zone to the OB. The results of a neurosphere assay revealed that the number of neurospheres derived from the OB was significantly increased on day 2 post‐TMT treatment. The neurosphere‐forming neural progenitor cells derived from the OB of TMT‐treated animals were capable of differentiating into neuronal cells as well as into astrocytes. Taken together, our data suggest that the OB has the ability to undergo enhanced neurogenesis following TMT‐induced neuronal injury in adult mice. © 2009 Wiley‐Liss, Inc.     

Dopamine receptor activation promotes adult neurogenesis in an acute Parkinson model

Cell proliferation of neural progenitors in the subventricular zone (SVZ) of Parkinson disease (PD) patients and animal models is decreased. It was previously demonstrated that the neurotransmitter dopamine modulates cell proliferation in the embryonic brain. The aim of the present study was to analyze whether oral treatment with the dopamine receptor agonist pramipexole (PPX) modulates adult neurogenesis in the SVZ/olfactory bulb system in a dopaminergic lesion model. 6-Hydroxydopamine (6-OHDA) lesioned adult rats received either PPX (1.0 mg/kg) or PBS orally twice daily and bromodeoxyuridine (BrdU, a cell proliferation marker) for 10 days and were perfused immediately after treatment or 4 weeks after PPX withdrawal. Stereological analysis revealed a significant augmentation in SVZ proliferation by PPX. Consecutively, enhanced neuronal differentiation and more new neurons were present in the olfactory bulb 4 weeks after PPX withdrawal. In addition, dopaminergic neurogenesis was increased in the olfactory bulb after PPX treatment. Motor activity as assessed by using an open field paradigm was permanently increased even after long term PPX withdrawal. In addition, we demonstrate that D2 and D3 receptors are present on adult rat SVZ-derived neural progenitors in vitro, and PPX specifically increased mRNA levels of epidermal growth factor receptor (EGF-R) and paired box gene 6 (Pax6).Oral PPX treatment selectively increases adult neurogenesis in the SVZ–olfactory bulb system by increasing proliferation and cell survival of newly generated neurons. Analyzing the neurogenic fate decisions mediated by D2/D3 signaling pathways may lead to new avenues to induce neural repair in the adult brain.     

Impairment of hippocampal neurogenesis in streptozotocin-treated diabetic rats

Objectives –  Adult neurogenesis in dentate gyrus (DG) is an evolutionarily preserved trait in most mammals examined thus far. Neuronal proliferation and subsequent integration of new neurons into the hippocampal circuit are regulated processes that can have profound effects on an animal's behaviour. A streptozotocin model of type I diabetes, characterized by low insulin and high plasma glucose levels, affects not only body's overall metabolism but also brain activity.
Materials and methods –  Neurogenesis was measured within the DG of the hippocampus using immunohistochemical markers Ki67, Doublecortin, Calbindin (CaBP) and bromodeoxyuridine (BrdU).
Results –  Cell proliferation, measured with the endogenous marker Ki67, was reduced by 45%, and cell survival, measured with BrdU, was reduced by 64% of the control. Combined effects on proliferation and survival produced dramatically lower neuronal production. Among the surviving cells only 33% matured normally as judged by the co-labelling of BrdU and CaBP.
Conclusion –  Such a reduction lowered the number of surviving cells with neuronal phenotype by over 80% of the control values and this is expected to cause a significant functional impairment of learning and memory in diabetic animals. These results may shed light on causes of diabetic neuropathology and provide an explanation for the memory deficiencies seen in some diabetic patients.     

Therapeutic effects of lipo-prostaglandin E1 on angiogenesis and neurogenesis after ischemic stroke in rats

Previous studies have demonstrated that prostaglandin E1 (PGE1) has a neuroprotective effect on cerebral ischemia. However, it remains unknown whether PGE1 promotes angiogenesis and neurogenesis after ischemic stroke. In this study, adult male Sprague-Dawley rats were subjected to permanently distal middle cerebral artery occlusion (MCAO). Rats were treated with lipo-prostaglandin E1(lipo-PGE1, 10 μg/kg/d) or the same volume of 0.9% saline starting 24 hours after MCAO daily for 6 consecutive days. All rats were injected 5'-bromo-2'-deoxyuridine (BrdU, 50 mg/kg) intraperitoneally every 12 hours for 3 consecutive days before being sacrificed. At 7 and 14 days after MCAO or sham-operation, rats were sacrificed. Post-stroke neurological outcome, infarction volume, angiogenesis and neurogenesis were evaluated. Treatment with lipo-PGE1 significantly increased the vascular density in the peri-infarct areas at 7 and 14 days after MCAO. The lipo-PGE1 treatment significantly enhanced the proliferation and migration of endogenous neural stem cells in the ipsilateral subventricular zone. The neural stem cells associated with blood vessels closely within a neurovascular niche in lipo-PGE1-treated rats after stroke. The lipo-PGE1 treatment also significantly improved the neurological recovery after MCAO. These results indicate that treatment with lipo-PGE1 promotes post-stroke angiogenesis, neurogenesis and their interaction, which would contribute to neurological recovery after cerebral infarction. Our study provides novel experimental evidences for the neuroprotective roles of PGE1 in ischemic stroke.     

Role of nitric oxide in subventricular zone neurogenesis

A possible role of nitric oxide (NO) in adult neurogenesis has been suggested based on anatomical findings showing that subventricular zone (SVZ) neuroblasts are located close to NO-producing cells, and on the known antiproliferative actions of NO in many cell types.Experiments have been performed in rodents with systemic and intracerebroventricular administrations of the NO synthase (NOS) inhibitor L-NAME. NOS inhibition leads to significant increases in the number of proliferating cells in the SVZ and olfactory bulb (OB). NO exerts its cytostatic action preferentially on the cell population expressing nestin but not βIII-tubulin, which may correspond to the type C cells described in the SVZ. The negative effect of NO on SVZ cell proliferation has also been confirmed in SVZ primary cultures.An inhibition of the tyrosine kinase activity of the epidermal growth factor receptor (EGFR) is described as one of the molecular mechanisms responsible for the antiproliferative effect of NO in SVZ cells. Biochemical data supporting this conclusion has been obtained using the neuroblastoma cell line NB69, which endogenously expresses the EGFR. In these cells, the antimitotic action of NO occurs upon inhibition of the EGFR tyrosine phosphorylation, probably by a direct S-nitrosylation of the receptor.The latest published reports on NO and neurogenesis indicate that NO physiologically participates in the control of adult neurogenesis by modulating the proliferation and fate of the SVZ progenitor cells. These effects might be partially due to a direct inhibition of the EGFR by S-nitrosylation.     

Chronic repetitive transcranial magnetic stimulation increases hippocampal neurogenesis in rats

Aim: While the underlying therapeutic mechanisms of repetitive transcranial magnetic stimulation (rTMS) treatment for depression remain unclear, recent animal studies have suggested that hippocampal neurogenesis might be required for the effects of antidepressant treatments including antidepressant drugs and electroconvulsive therapy. The aim of this study was to examine chronic rTMS effects on hippocampal neurogenesis in rats. Methods: Using a 70‐mm figure‐of‐eight coil, the stimulating parameters were set to 25 Hz and 70% of the rTMS device's maximum power. For 14 consecutive days, bromodeoxyuridine (BrdU) and 1000 pulses of rTMS were administered daily. Cell proliferation in the dentate gyrus was examined with immunohistochemistry. Results: In the rTMS‐treated group, BrdU‐positive cells were significantly increased in the dentate gyrus. Conclusion: Our results suggest that hippocampal neurogenesis might be involved in the antidepressant effects of chronic rTMS.