Survival Of Newborn Cells Research Articles

Co-Treatment with Diazepam Prevents the Effects of Fluoxetine on the Proliferation and Survival of Hippocampal Dentate Granule Cells

Selective serotonin reuptake inhibitors (SSRI) often produce increased anxiety during the first weeks of treatment before the clinical antidepressant response, and these symptoms are commonly treated with benzodiazepines. Selective serotonin reuptake inhibitors increase proliferation of neuronal progenitors in rodent hippocampus after a delay of approximately 2 weeks. We have used this delayed increase in neurogenesis, as detected with both a rapid dot-blot method and with immunostaining, as a model of the delayed clinical antidepressant effects. Whereas the SSRI fluoxetine alone significantly increased both neurogenesis and survival of newborn cells when administered for 2-3 weeks, co-treatment with diazepam and fluoxetine completely blocked the increase in both neurogenesis and survival. Furthermore, neurogenesis was not increased when fluoxetine and diazepam were first co-administered for 2 weeks and then fluoxetine was given alone for 2 additional weeks. Moreover, we show that daily administration is necessary for neurogenesis, because injection of fluoxetine for up to 1 week failed to increase neurogenesis, when assayed at 14 days from the first injection. These results suggest that benzodiazepines might interfere with the clinical effects of fluoxetine or that increased neurogenesis is not a valid model for the delayed onset of the clinical antidepressant effects.

Chronic lithium treatment decreases NG2 cell proliferation in rat dentate hilus, amygdala and corpus callosum

An increasing number of investigations suggest volumetric changes and glial pathology in several brain regions of patients with bipolar disorder. Lithium, used in the treatment of this disorder, has been reported to be neuroprotective and increase brain volume. Here we investigate the effect of lithium on the proliferation and survival of glial cells positive for the chondroitin sulphate proteoglycan NG2 (NG2 cells); a continuously dividing cell type implicated in remyelination and suggested to be involved in regulation of neuronal signaling and axonal outgrowth. Adult male rats were treated with lithium for four weeks and injected with the proliferation marker bromodeoxyuridine (BrdU) before or at the end of the treatment period. Immunohistochemical analysis of brain sections was performed to estimate the number of newly born (BrdU-labeled) NG2 cells and oligodendrocytes in hippocampus, basolateral nuclei of amygdala and corpus callosum. Lithium significantly decreased the proliferation of NG2 cells in dentate hilus of hippocampus, amygdala and corpus callosum, but not in the molecular layer or the cornu ammonis (CA) regions of hippocampus. The effect was more pronounced in the corpus callosum. No effect of lithium on the survival of newborn cells or the number of newly generated oligodendrocytes could be detected. Our results demonstrate that in both white and gray matter brain regions implicated in the pathophysiology of bipolar disorder, chronic lithium treatment significantly decreases the proliferation rate of NG2 cells; the major proliferating cell type of the adult brain.

Opposite Effects of Early Maternal Deprivation on Neurogenesis in Male versus Female Rats

BackgroundMajor depression is more prevalent in women than in men. The underlying neurobiological mechanisms are not well understood, but recent data shows that hippocampal volume reductions in depressed women occur only when depression is preceded by an early life stressor. This underlines the potential importance of early life stress, at least in women, for the vulnerability to develop depression. Perinatal stress exposure in rodents affects critical periods of brain development that persistently alter structural, emotional and neuroendocrine parameters in adult offspring. Moreover, stress inhibits adult hippocampal neurogenesis, a form of structural plasticity that has been implicated a.o. in antidepressant action and is highly abundant early postnatally. We here tested the hypothesis that early life stress differentially affects hippocampal structural plasticity in female versus male offspring.Principal FindingsWe show that 24 h of maternal deprivation (MD) at PND3 affects hippocampal structural plasticity at PND21 in a sex-dependent manner. Neurogenesis was significantly increased in male but decreased in female offspring after MD. Since no other structural changes were found in granule cell layer volume, newborn cell survival or proliferation rate, astrocyte number or gliogenesis, this indicates that MD elicits specific changes in subsets of differentiating cells and differentially affects immature neurons. The MD induced sex-specific effects on neurogenesis cannot be explained by differences in maternal care.ConclusionsOur data shows that early environment has a critical influence on establishing sex differences in neural plasticity and supports the concept that the setpoint for neurogenesis may be determined during perinatal life. It is tempting to speculate that a reduced level of neurogenesis, secondary to early stress exposure, may contribute to maladaptation of the HPA axis and possibly to the increased vulnerability of women to stress-related disorders.

An Animal Model of a Behavioral Intervention for Depression

Although conditioned inhibition of fear (or learned safety) is a learning process critical for preventing chronic stress, a predisposing factor for depression and other psychopathologies, little is known about its functional purposes or molecular mechanisms. To obtain better insight into learned safety, we investigated its behavioral and molecular characteristics and found that it acts as a behavioral antidepressant in two animal models. Learned safety promotes the survival of newborn cells in the dentate gyrus of the hippocampus, while its antidepressant effect is abolished in mice with ablated hippocampal neurogenesis. Learned safety also increases the expression of BDNF in the hippocampus and leads to downregulation of genes involved in the dopaminergic and neuropeptidergic but not the serotonergic system in the basolateral amygdala. These data suggest that learned safety is an animal model of a behavioral antidepressant that shares some neuronal hallmarks of pharmacological antidepressants but is mediated by different molecular pathways.

Chronic fluoxetine treatment improves ischemia‐induced spatial cognitive deficits through increasing hippocampal neurogenesis after stroke

Cognitive deficits, including spatial memory impairment, are very common after ischemic stroke. Neurogenesis in the dentate gyrus (DG) contributes to forming spatial memory in the ischemic brain. Fluoxetine, a selective serotonin reuptake inhibitor, can enhance neurogenesis in the hippocampus in physiological situations and some neurological diseases. However, whether it has effects on ischemia-induced spatial cognitive impairment and hippocampal neurogenesis has not been determined. Here we report that fluoxetine treatment (10 mg kg(-1), i.p.) for 4 weeks promoted the survival of newborn cells in the ischemic hippocampus and, consequently, attenuated spatial memory impairment of mice after focal cerebral ischemia. Disrupting hippocampal neurogenesis blocked the beneficial effect of fluoxetine on ischemia-induced spatial cognitive impairment. These results suggest that chronic fluoxetine treatment benefits spatial cognitive function recovery following ischemic insult, and the improved cognitive function is associated with enhanced newborn cell survival in the hippocampus. Our results raise the possibility that fluoxetine can be used as a drug to treat poststroke spatial cognitive deficits.

Involvement of cyclooxygenase-2 in lipopolysaccharide-induced impairment of the newborn cell survival in the adult mouse dentate gyrus

There is growing evidence indicating that neurogenesis in adulthood is influenced by certain types of the central diseases such as neuroinflammation, however, its mechanism is not fully understood. This study was, therefore, designed to examine the effects of lipopolysaccharide (LPS), a bacterial endotoxin known to cause the neuroinflammation, on the neurogenesis in the dentate gyrus of adult mice using the bromodeoxyuridine (BrdU) –pulse chase method. LPS failed to affect the number of BrdU-labeled cells in the dentate gyrus 2 h after BrdU injection, indicating no effects of LPS on the proliferation of the neural stem cells (NSCs). On the other hand, we found that LPS dose-dependently (0.1, 0.5, 1 mg/kg) decreased the number of BrdU-labeled cells 7 and 21 days after BrdU injection. We also observed that LPS increased cell death in the dentate gyrus using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining, suggesting that LPS impaired the survival of newborn cells derived from the NSCs. The double-immunostaining for BrdU and specific cell type markers revealed that LPS did not alter the commitment of the NSCs to the neurons and astrocytes. The systemic injection of indomethacin, a non-selective cyclooxygenase (COX) inhibitor, and NS398, a selective COX-2 inhibitor, but not SC560, a selective COX-1 inhibitor, did not only ameliorate LPS-induced suppression of the newborn cell survival, they fully protected against the LPS effect. Furthermore, the central injection of NS398 also ameliorated LPS-induced suppression of the newborn cell survival in the dentate gyrus. The treatment with LPS increased the expression of COX-2 protein 7 h and 7 days after the injection in the dentate gyrus. These results suggest that LPS impairs the survival of newly generated cells derived from the NSCs in the dentate gyrus without affecting the differentiation fate, and these effects of LPS were mediated presumably by COX-2 expression in the dentate gyrus.

Prenatal Restraint Stress Generates Two Distinct Behavioral and Neurochemical Profiles in Male and Female Rats

Prenatal Restraint Stress (PRS) in rats is a validated model of early stress resulting in permanent behavioral and neurobiological outcomes. Although sexual dimorphism in the effects of PRS has been hypothesized for more than 30 years, few studies in this long period have directly addressed the issue. Our group has uncovered a pronounced gender difference in the effects of PRS (stress delivered to the mothers 3 times per day during the last 10 days of pregnancy) on anxiety, spatial learning, and a series of neurobiological parameters classically associated with hippocampus-dependent behaviors. Adult male rats subjected to PRS (“PRS rats”) showed increased anxiety-like behavior in the elevated plus maze (EPM), a reduction in the survival of newborn cells in the dentate gyrus, a reduction in the activity of mGlu1/5 metabotropic glutamate receptors in the ventral hippocampus, and an increase in the levels of brain-derived neurotrophic factor (BDNF) and pro-BDNF in the hippocampus. In contrast, female PRS rats displayed reduced anxiety in the EPM, improved learning in the Morris water maze, an increase in the activity of mGlu1/5 receptors in the ventral and dorsal hippocampus, and no changes in hippocampal neurogenesis or BDNF levels. The direction of the changes in neurogenesis, BDNF levels and mGlu receptor function in PRS animals was not consistent with the behavioral changes, suggesting that PRS perturbs the interdependency of these particular parameters and their relation to hippocampus-dependent behavior. Our data suggest that the epigenetic changes in hippocampal neuroplasticity induced by early environmental challenges are critically sex-dependent and that the behavioral outcome may diverge in males and females.

Developmental exposure to 3,4-methylenedioxymethamphetamine results in downregulation of neurogenesis in the adult mouse hippocampus

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is a powerful releaser of 5-HT and chronic use of this drug can cause depletion of monoamines. Recently, concerns about the risk of adult brain damage due to fetal exposure to MDMA have been raised. We investigated whether developmental MDMA exposure affected adult neurogenesis in C57 black/6 mice. MDMA (1.25 or 20 mg/kg, p.o.) or vehicle was administered daily to the mother from prenatal 6th day to postnatal 21st day. When the offspring were 11 weeks old, they were injected with 5-bromo-2′-deoxyuridine (BrdU) (120 mg/kg, i.p.) once a day for 4 days. After 24 h or 28 days, the animals were killed to count the BrdU-positive cells in the dentate gyrus. At 24 h after the last BrdU injection, the number of BrdU-positive cells in the offspring developmentally exposed to MDMA was significantly lower than that of the control group. At 28 days post-BrdU labeling, BrdU-positive cells in the dentate gyrus of female offspring with developmental exposure to high dose MDMA were significantly fewer compared with the control group. In addition, most BrdU-positive cells were co-labeled with the mature neuronal marker, neuronal nuclei, while a few BrdU-labeled cells were merged with an astrocyte marker. Our results suggest that developmental exposure to MDMA can result in decreases in the proliferation and survival of mature newborn cells in the adult dentate gyrus.

Sortilin-related Receptor with A-type Repeats (SORLA) Affects the Amyloid Precursor Protein-dependent Stimulation of ERK Signaling and Adult Neurogenesis

Sortilin-related receptor with A-type repeats (SORLA) is a sorting receptor that impairs processing of amyloid precursor protein (APP) to soluble (s) APP and to the amyloid beta-peptide in cultured neurons and is poorly expressed in patients with Alzheimer disease (AD). Here, we evaluated the consequences of Sorla gene defects on brain anatomy and function using mouse models of receptor deficiency. In line with a protective role for SORLA in APP metabolism, lack of the receptor results in increased amyloidogenic processing of endogenous APP and in aggravated plaque deposition when introduced into PDAPP mice expressing mutant human APP. Surprisingly, increased levels of sAPP caused by receptor deficiency correlate with pro-found stimulation of neuronal ERK signaling and with enhanced neurogenesis, providing in vivo support for neurotrophic functions of sAPP. Our data document a role for SORLA not only in control of plaque burden but also in APP-dependent neuronal signaling and suggest a molecular explanation for increased neurogenesis observed in some AD patients.

The Novel Impact Of Treadmill Exercise And Sex Difference On Cell Proliferation and Cell Survival In The Dentate Gyrus Of G93A Mice

Neurogenesis persists in the adult mammalian brain and can be regulated by physiological stressors influencing cell proliferation or cell survival. We investigated whether sex and treadmill running would affect cell proliferation and newborn cell survival in the dentate gyrus (DG) of G93A mice, a transgenic model over‐expressing mutant human Cu/Zn‐superoxide dismutase (SOD1) and leading to excessive oxidative stress. Proliferating and surviving cells were labeled with bromodeoxyuridine (BrdU) over 7‐days before sacrificing mice @ 1 and 3 weeks. Proliferating cells were significantly higher in males than in females (p=0.009) but cell survival tended to be higher in female vs. male G93A mice (p=0.057). Running G93A mice have less proliferating cells than sedentary G93A mice (p=0.056); however, running wild type mice have significantly more proliferating cells than sedentary wild type mice (p=0.036) and than running G93A mice (p=0.040). In addition, female running G93A mice displayed more surviving cells than male running G93A mice (p=0.033). Wild type running mice showed a significant increase in cell survival vs. sedentary wild type (p=0.028). These results suggested that running promotes cell proliferation in wild type mice, but inhibits cell proliferation in G93A mice. Running promotes cell survival in male and female wild type and only female G93A mice. The sex differences in cell proliferation and survival for the G93A mice are supportive of our previous observation that female G93A mice have better survival and resistance to excessive running stress as compared with males.

Chronic stress in adulthood followed by intermittent stress impairs spatial memory and the survival of newborn hippocampal cells in aging animals: prevention by FGL, a peptide mimetic of neural cell adhesion molecule

In this study, we examined whether chronic stress in adulthood can exert long-term effects on spatial-cognitive abilities and on the survival of newborn hippocampal cells in aging animals. Male Wistar rats were subjected to chronic unpredictable stress at midlife (12 months old) and then reexposed each week to a stress stimulus. When evaluated in the water maze at the early stages of aging (18 months old), chronic unpredictable stress accelerated spatial-cognitive decline, an effect that was accompanied by a reduction in the survival of newborn cells and in the number of adult granular cells in the hippocampus. Interestingly, spatial-memory performance in the Morris water maze was positively correlated with the number of newborn cells that survived in the dentate gyrus: better spatial memory in the water maze was associated with more 5-bromo-2-deoxyuridine (BrdU)-labeled cells. Administration of FGL, a peptide mimetic of neural cell adhesion molecule, during the 4 weeks of continuous stress not only prevented the deleterious effects of chronic stress on spatial memory, but also reduced the survival of the newly generated hippocampal cells in aging animals. FGL treatment did not, however, prevent the decrease in the total number of granular neurons that resulted from prolonged exposure to stress. These findings suggest that the development of new drugs that mimic neural cell adhesion molecule activity might be of therapeutic relevance to treat stress-induced cognitive impairment.

Mesenchymal stem cells promote proliferation of endogenous neural stem cells and survival of newborn cells in a rat stroke model

Mesenchymal stem cells (MSCs) secrete bioactive factors that exert diverse responses in vivo. In the present study, we explored mechanism how MSCs may lead to higher functional recovery in the animal stroke model. Bone marrow-derived MSCs were transplanted into the brain parenchyma 3 days after induction of stroke by occluding middle cerebral artery for 2 h. Stoke induced proliferation of resident neural stem cells in subventricular zone. However, most of new born cells underwent cell death and had a limited impact on functional recovery after stroke. Transplantation of MSCs enhanced proliferation of endogenous neural stem cells while suppressing the cell death of newly generated cells. Thereby, newborn cells migrated toward ischemic territory and differentiated in ischemic boundaries into doublecortin+ neuroblasts at higher rates in animals with MSCs compared to control group. The present study indicates that therapeutic effects of MSCs are at least partly ascribed to dual functions of MSCs by enhancing endogenous neurogenesis and protecting newborn cells from deleterious environment. The results reinforce the prospects of clinical application using MSCs in the treatment of neurological disorders.

Notch regulates cell fate and dendrite morphology of newborn neurons in the postnatal dentate gyrus

The lifelong addition of neurons to the hippocampus is a remarkable form of structural plasticity, yet the molecular controls over proliferation, neuronal fate determination, survival, and maturation are poorly understood. Expression of Notch1 was found to change dynamically depending on the differentiation state of neural precursor cells. Through the use of inducible gain- and loss-of-function of Notch1 mice we show that this membrane receptor is essential to these distinct processes. We found in vivo that activated Notch1 overexpression induces proliferation, whereas gamma-secretase inhibition or genetic ablation of Notch1 promotes cell cycle exit, indicating that the level of activated Notch1 regulates the magnitude of neurogenesis from postnatal progenitor cells. Abrogation of Notch signaling in vivo or in vitro leads to a transition from neural stem or precursor cells to transit-amplifying cells or neurons. Further, genetic Notch1 manipulation modulates survival and dendritic morphology of newborn granule cells. These results provide evidence for the expansive prevalence of Notch signaling in hippocampal morphogenesis and plasticity, suggesting that Notch1 could be a target of diverse traumatic and environmental modulators of adult neurogenesis.

Lithium regulates hippocampal neurogenesis by ERK pathway and facilitates recovery of spatial learning and memory in rats after transient global cerebral ischemia

Recent studies have demonstrated that lithium has a neuroprotective effect against brain ischemia. Whether this effect is mediated by hippocampal neurogenesis remains unknown. The ERK (extracellular signal-regulated kinase) pathway plays an essential role in regulating neurogenesis. The present study was undertaken to investigate whether lithium regulates hippocampal neurogenesis by the ERK pathway and improves spatial learning and memory deficits in rats after ischemia. Rats were daily injected with lithium (1 mmol/kg) and 2 weeks later subjected to 15-min ischemia induced by four-vessel occlusion method. 5-bromo-2′-deoxyuridine (Brdu; 50 mg/kg) was administrated twice daily at postischemic day 6, or for 3 days from postischemic day 6 to 8. We found that lithium increased the ERK1/2 activation after ischemia by western blotting analysis. There was a significant increase in Brdu-positive cells in the hippocampal dentate gyrus after lithium treatment, compared with ischemia group at postischemic days 7 and 21; furthermore, the survival rate of Brdu-positive cells was elevated by lithium. Inhibition of the ERK1/2 activation by U0126 diminished these effects of lithium. The percentages of Brdu-positive cells that expressed a neuronal marker or an astrocytic marker were not significantly influenced by lithium. Moreover, lithium improved the impaired spatial learning and memory ability in Morris water maze, and U0126 attenuated the behavioral improvement by lithium. These results suggest that lithium up-regulates the generation and survival of new-born cells in the hippocampus by the ERK pathway and improves the behavioral disorder in rats after transient global cerebral ischemia.

Alzheimer's-Type Amyloidosis in Transgenic Mice Impairs Survival of Newborn Neurons Derived from Adult Hippocampal Neurogenesis

Alzheimer's disease (AD) is characterized by severe neuronal loss in several brain regions important for learning and memory. Of the structures affected by AD, the hippocampus is unique in continuing to produce new neurons throughout life. Mounting evidence indicates that hippocampal neurogenesis contributes to the processing and storage of new information and that deficits in the production of new neurons may impair learning and memory. Here, we examine whether the overproduction of amyloid-beta (Abeta) peptide in a mouse model for AD might be detrimental to newborn neurons in the hippocampus. We used transgenic mice overexpressing familial AD variants of amyloid precursor protein (APP) and/or presenilin-1 to test how the level (moderate or high) and the aggregation state (soluble or deposited) of Abeta impacts the proliferation and survival of new hippocampal neurons. Although proliferation and short-term survival of neural progenitors in the hippocampus was unaffected by APP/Abeta overproduction, survival of newborn cells 4 weeks later was dramatically diminished in transgenic mice with Alzheimer's-type amyloid pathology. Phenotypic analysis of the surviving population revealed a specific reduction in newborn neurons. Our data indicate that overproduction of Abeta and the consequent appearance of amyloid plaques cause an overall reduction in the number of adult-generated hippocampal neurons. Diminished capacity for hippocampal neuron replacement may contribute to the cognitive decline observed in these mice.

Plant-Derived Flavanol (−)Epicatechin Enhances Angiogenesis and Retention of Spatial Memory in Mice

Diet and exercise have a profound impact on brain function. In particular, natural nutrients found in plants may influence neuronal survival and plasticity. Here, we tested whether consumption of a plant-derived flavanol, (-)epicatechin, enhances cognition in sedentary or wheel-running female C57BL/6 mice. Retention of spatial memory in the water maze was enhanced by ingestion of (-)epicatechin, especially in combination with exercise. Improved spatial memory was associated with increased angiogenesis and neuronal spine density, but not newborn cell survival, in the dentate gyrus of the hippocampus. Moreover, microarray analysis showed upregulation of genes associated with learning and downregulation of markers of neurodegeneration in the hippocampus. Together, our data show that ingestion of a single flavanol improves spatial memory retention in adult mammals.

Adult neurogenesis in serotonin transporter deficient mice

Serotonin (5-HT) is a regulator of morphogenetic activities during early brain development and neurogenesis, including cell proliferation, migration, differentiation, and synaptogenesis. The 5-HT transporter (5-HTT, SLC6A4) mediates high-affinity reuptake of 5-HT into presynaptic terminals and thereby fine-tunes serotonergic neurotransmission. Inactivation of the 5-HTT gene in mice reduces 5-HT clearance resulting in persistently increased concentrations of synaptic 5-HT. In the present study, we investigated the effects of elevated 5-HT levels on adult neurogenesis in the hippocampus of 5-HTT deficient mice, including stem cell proliferation, survival, and differentiation. Using an in vivo approach, we showed an increase in proliferative capacity of hippocampal adult neural stem cells in aged 5-HTT knockout mice (approximately 14.5 months) compared to wildtype controls. In contrast, in vivo and additional in vitro analyses of younger adult 5-HTT knockout mice (approximately 7 weeks and approximately 3.0 months) did not reveal significant changes in proliferation of neural stem cells or survival of newborn cells. We showed that the cellular fate of newly generated cells in 5-HTT knockout mice is not different with respect to the total number and percentage of neurons or glial cells from wildtype controls. Our findings indicate that elevated synaptic 5-HT concentration throughout early development and later life of 5-HTT deficient mice does not induce adult neurogenesis in adult mice, but that elevated 5-HT levels in aged mice influence stem cell proliferation.

Peripheral Infusion of Insulin-Like Growth Factor-I Increases the Number of Newborn Oligodendrocytes in the Cerebral Cortex of Adult Hypophysectomized Rats

We have previously shown that recombinant human (rh) IGF-I induces cell proliferation and neurogenesis in the hippocampus of hypophysectomized rats. In the current investigation, we determined the effects of rhIGF-I on proliferation and differentiation in the cerebral cortex. Adult hypophysectomized rats were injected with bromodeoxyuridine (BrdU) to label newborn cells (once a day for the first 5 d), and rhIGF-I was administered peripherally for 6 or 20 d. In the cerebral cortex, the number of BrdU-labeled cells increased after 20 d but not after 6 d of rhIGF-I infusion. This suggests that rhIGF-I enhances the survival of newborn cells in the cerebral cortex. Using BrdU labeling combined with the oligodendrocyte-specific markers myelin basic protein and 2',3'-cyclic nucleotide 3'-phosphodiesterase, we demonstrated an increase in oligodendrogenesis in the cerebral cortex. The total amount of myelin basic protein and 2',3'-cyclic nucleotide 3'-phosphodiesterase was also increased on Western blots of homogenates of the cerebral cortex, confirming the immunohistochemical findings. Also, we observed an increase in the number of capillary-associated BrdU-positive cells, although total capillary area was not increased. rhIGF-I treatment did not affect cortical astrogliogenesis and neurogenesis was not observed. The ability of rhIGF-I to induce cortical oligodendrogenesis may have implications for the regenerative potential of the cortex.

Systemically delivered Erythropoietin transiently enhances adult hippocampal neurogenesis

Erythropoietin is a primary regulator of erythropoiesis in the hematopoietic system. More recently erythropoietin has been shown to play a role in neurogenesis and provide neurotrophic support to injured CNS tissue. Here the effects of large systemic doses of erythropoietin on basal levels of adult hippocampal neurogenesis in mice were examined. A 7-day period of recombinant human erythropoietin (rhEPO) administration increased the number of bromodeoxyuridine [BrdU(+)] cells in the sub-granular zone (SGZ) by 30%. Analysis of cell phenotype revealed an increase in mitotically active doublecortin(+) neuronal progenitor cells and glial fibrillary acidic protein(+) SGZ radial astrocytes/stem cells but not mature S100beta(+) astrocytes. These effects appeared to be mediated, in part, by mitogen-activated protein kinase signaling and potentially regulated by suppressor of cytokine signaling-3. Hippocampal levels of phosphorylated extracellular signal-related kinase 42/44 and suppressor of cytokine signaling-3 were increased 2-6 h after a single systemic rhEPO injection. However, rhEPO had no observed effect on the long-term survival of new born cells in the SGZ, with similar numbers of BrdU(+) cells and BrdU(+)/NeuN(+) co-labeled cells after 4 weeks. Therefore, systemically delivered rhEPO transiently increased adult hippocampal neurogenesis without any apparent long-term effects.

Fluoxetine does not affect the ischemia-induced increase of neurogenesis in the adult rat dentate gyrus

Ischemic insult enhances the proliferation of precursor cells in the dentate subgranular zone. This study was performed to determine whether fluoxetine further promotes the neurogenesis induced by transient forebrain ischemia in the rat dentate gyrus. Transient forebrain ischemia was induced by four-vessel occlusion for 10 min. First, to investigate whether the short-term treatment of fluoxetine influences ischemia-induced cell proliferation, rats were administered fluoxetine (5 mg/kg, i.p.) or a vehicle on days three to nine post-ischemia, and 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdU, 75 mg/kg, i.p.) one hour after the last fluoxetine injection. On examination one day later, the number of BrdU-labeled cells was not significantly different between the fluoxetine- and vehicle-treated groups. Second, to identify whether the chronic treatment of fluoxetine has an effect on the survival of ischemia-induced newborn cells, rats were administered fluoxetine or a vehicle on days 3 to 23 post-ischemia, and BrdU (75 mg/kg, three times) nine days post-ischemia. On examination four weeks after the BrdU injection, the number of BrdU-labeled cells was not significantly different between the fluoxetine- and vehicle-treated groups. Also, the rate of neuronal maturation was not significantly different between the two groups. These results show that fluoxetine does not affect the ischemia-induced increase of neurogenesis in the dentate gyrus of the adult rat.