Influence of environmental manipulation on exploratory behaviour in male BDNF knockout mice

It is widely accepted that brain derived neurotrophic factor (BDNF) plays a crucial role in mediating changes in learning and memory performance induced by environmental conditions. In order to ascertain whether BDNF modulates environmentally induced changes in exploratory behaviour, we examined mice carrying a deletion in one copy of the BDNF gene. Young heterozygous male BDNF knockout mice (BDNF+/-) and their wild-type (WT) controls were exposed to the enriched environment condition (EC) or the standard condition (SC) for 8 weeks. Exploratory behaviour was assessed in the open-field (OF) and hole-board (HB) test. Brains from EC and SC reared animals were processed for Golgi-Cox staining and the dendritic spine density in the dentate gyrus (DG) and CA1 hippocampal regions were examined. We found behavioural differences both due to the genetic modification and the environmental manipulation, with the BDNF+/- mice being more active in the OF whereas the EC mice had increased exploratory behaviour in the HB test. Environmental enrichment also led to an increase in dendritic spines in the hippocampal CA1 region and DG of the wild-type mice. This effect was also found in the enriched BDNF+/- mice, but was less pronounced. Our findings support the critical role of BDNF in behavioural and neural plasticity associated with environmental enrichment and suggest that besides maze learning performance, BDNF dependent mechanisms are also involved in other aspects of behaviour. Here we provide additional evidence that exploratory activity is influenced by BDNF.     

Neurogenesis in the R6/1 transgenic mouse model of Huntington's disease: effects of environmental enrichment

Previous work has demonstrated that the transgenic R6/1 mouse model of Huntington's disease has decreased proliferation of neural precursor cells (NPCs) in the dentate gyrus of the hippocampus. This study therefore examined the survival and differentiation of NPCs in presymptomatic and symptomatic R6/1 mice and the effects of environmental enrichment on these variables. Here it is demonstrated that the survival of bromodeoxyuridine-positive (BrdU+) NPCs in the dentate gyrus is decreased in the transgenic mice. In addition, the number of doublecortin-positive (DCX+) cells is greatly reduced in these mice, as is the total number of new mature neurons, while the proportion of BrdU+ cells differentiating into mature neurons was not significantly different between genotypes. Furthermore, the DCX+ cells in the R6/1 mice had smaller and irregular-shaped somas, shorter neurites, and migrated a shorter distance into the granular cell layer compared with wild-type mice. Older symptomatic mice housed in an enriched environment had an increased number of BrdU+ and DCX+ cells as well as longer neurites and increased migration of DCX+ cells. There was no significant difference between genotypes or environments in the number of BrdU+ cells in the subventricular zone. These results suggest that decreased neurogenesis might be responsible, in part, for the hippocampal deficits observed in these mice and that environmental enrichment produces morphological changes in newborn granule neurons in both wild-type and R6/1 mice, which could underlie some of the beneficial effects of enrichment.     

Granule cell dispersion and aberrant neurogenesis in the adult hippocampus of an LIS1 mutant mouse

Human type 1 lissencephaly is a severe brain malformation associated with cognitive dysfunction and intractable epilepsy. Mutant mice with a heterozygous deletion of LIS1 show varying degrees of hippocampal abnormality and enhanced excitability. Whether a reduction of LIS1 function affects adult hippocampal neurogenesis, and if so, whether aberrant neurogenesis contributes to the generation of a disorganized hippocampus remain unknown. Previous reports indicate the presence of multiple pyramidal cell layers and granule cell dispersion in LIS1 mutant mice. Here we observed disruption of the subgranular zone and glial fibrillary acidic protein-immunoreactive radial astrocytes in the dentate gyrus of adult LIS1 mice. Using pulse-chase bromodeoxyuridine (BrdU) labeling combined with neuronal and glial antibody staining we provide evidence for ectopic adult neurogenesis in LIS1 mice. A gradually decreased survival rate for these newborn granule cells was also demonstrated in LIS1 mice 7 days after BrdU injection. This reduced survival rate was associated with impaired neuronal differentiation 28 days after BrdU administration. Thus, LIS1 haploinsufficiency can lead to abnormal cell proliferation, migration and differentiation in the adult dentate gyrus.     

Prenatal choline availability modulates hippocampal neurogenesis and neurogenic responses to enriching experiences in adult female rats

Increased dietary intake of choline early in life improves performance of adult rats on memory tasks and prevents their age-related memory decline. Because neurogenesis in the adult hippocampus also declines with age, we investigated whether prenatal choline availability affects hippocampal neurogenesis in adult Sprague-Dawley rats and modifies their neurogenic response to environmental stimulation. On embryonic days (ED) 12-17, pregnant rats ate a choline-supplemented (SUP-5 g/kg), choline sufficient (SFF-1.1 g/kg), or choline-free (DEF) semisynthetic diet. Adult offspring either remained in standard housing or were given 21 daily visits to explore a maze. On the last ten exploration days, all rats received daily injections of 5-bromo-2-deoxyuridine (BrdU, 100 mg/kg). The number of BrdU+ cells was significantly greater in the dentate gyrus in SUP rats compared to SFF or DEF rats. While maze experience increased the number of BrdU+ cells in SFF rats to the level seen in the SUP rats, this enriching experience did not alter cell proliferation in DEF rats. Similar patterns of cell proliferation were obtained with immunohistochemical staining for neuronal marker doublecortin, confirming that diet and exploration affected hippocampal neurogenesis. Moreover, hippocampal levels of the brain-derived neurotrophic factor (BDNF) were increased in SUP rats as compared to SFF and DEF animals. We conclude that prenatal choline intake has enduring effects on adult hippocampal neurogenesis, possibly via up-regulation of BDNF levels, and suggest that these alterations of neurogenesis may contribute to the mechanism of life-long changes in cognitive function governed by the availability of choline during gestation.     

Increased neurogenesis and the ectopic granule cells after intrahippocampal BDNF infusion in adult rats

There is evidence that BDNF influences the birth of granule cells in the dentate gyrus, which is one of the few areas of the brain that demonstrates neurogenesis throughout life. However, studies to date have not examined this issue directly. To do so, we compared the effects of BDNF, phosphate-buffered saline (PBS), or bovine serum albumin (BSA) on neurogenesis after infusion into the hippocampus of the normal adult rat, using osmotic pumps that were implanted unilaterally in the dorsal hilus. BDNF, PBS, and BSA were infused for 2 weeks. The mitotic marker bromodeoxyuridine (BrdU) was administered twice daily during the 2-week infusion period. At least 1 month after infusion ended, brains were processed immunocytochemically using antibodies to BrdU, a neuronal nuclear protein (NeuN), or calbindin D28K (CaBP), which labels mature granule cells. Stereology was used to quantify BrdU-labeled cells in the dorsal hippocampus that were double-labeled with NeuN or CaBP. There was a statistically significant increase in BrdU(+)/NeuN(+) double-labeled cells in the granule cell layer after BDNF infusion relative to controls. The values for BrdU(+)/NeuN(+) cells were similar to BrdU(+)/CaBP(+) cells, indicating that most new neurons were likely to be granule cells. In addition, BrdU(+)/NeuN(+)-labeled cells developed in the hilar region after BDNF infusion, which have previously only been identified after severe continuous seizures (status epilepticus) and associated pathological changes. Remarkably, neurogenesis was also increased contralaterally, but BDNF did not appear to spread to the opposite hemisphere. Thus, infusion of BDNF to a local area can have widespread effects on hippocampal neurogenesis. The results demonstrate that BDNF administration to the dentate gyrus leads to increased neurogenesis of granule cells. They also show that ectopic granule cells develop after BDNF infusion, which suggests that ectopic migration is not necessarily confined to pathological conditions. These results are discussed in light of the evidence that BDNF increases neuronal activity in hippocampus. Thus, the mechanisms underlying neurogenesis following BDNF infusion could be due to altered activity as well as direct effects of BDNF itself, and this is relevant to studies of other growth factors because many of them have effects on neuronal excitability that are often not considered.     

Enriched environment and physical activity stimulate hippocampal but not olfactory bulb neurogenesis

Exposure to an enriched environment and physical activity, such as voluntary running, increases neurogenesis of granule cells in the dentate gyrus of adult mice. These stimuli are also known to improve performance in hippocampus-dependent learning tasks, but it is unclear whether their effects on neurogenesis are exclusive to the hippocampal formation. In this study, we housed adult mice under three conditions (enriched environment, voluntary wheel running and standard housing), and analysed proliferation in the lateral ventricle wall and granule cell neurogenesis in the olfactory bulb in comparison to the dentate gyrus. Using bromodeoxyuridine to label dividing cells, we could not detect any difference in the number of newly generated cells in the ventricle wall. When giving the new cells time to migrate and differentiate in the olfactory bulb, we observed no changes in the number of adult-generated olfactory granule cells; however, voluntary running and enrichment produced a doubling in the amount of new hippocampal granule cells. The discrepancy between the olfactory bulb and the dentate gyrus suggests that these living conditions trigger locally through an as yet unidentified mechanism specific to neurogenic signals in the dentate gyrus.     

Balance between neurogenesis and gliogenesis in the adult hippocampus: role for reelin

The extracellular matrix protein reelin is essential for the proper radial migration of cortical neurons. In reeler mice lacking reelin, there is a malformation of the radial glial scaffold required for granule cell migration. Immunostaining for glial fibrillary acidic protein (GFAP) reveals abundant radial glial cells with long fibers traversing the granular layer in the wild type, but almost exclusively astrocytes in the reeler mutant. With the concept that radial glial cells are precursors of neurons, we hypothesized that the balance between neurogenesis and gliogenesis is altered in the reeler mutant. To this end, adult reeler mutants and their wild-type littermates were injected with bromodeoxyuridine (BrdU), a marker of newly generated cells. When compared to wild-type animals, we found a reduction in the number of BrdU-labeled cells in the adult reeler dentate gyrus. Moreover, whereas there was a dramatic decrease in the number of newly generated granule cells identified by double labeling for BrdU and NeuN, the number of BrdU-labeled, GFAP-positive astrocytes had increased. Decreased neurogenesis in the adult reeler dentate gyrus was confirmed by immunostaining for doublecortin, a marker of newly generated neurons. These results indicate that adult neurogenesis is altered in the reeler dentate gyrus and that newly generated cells preferentially differentiate into astrocytes.     

Luteolin induces hippocampal neurogenesis in the Ts65Dn mouse model of Down syndrome

Studies have shown that the natural flavonoid luteolin has neurotrophic activity. In this study, we investigated the effect of luteolin in a mouse model of Down syndrome. Ts65 Dn mice, which are frequently used as a model of Down syndrome, were intraperitoneally injected with 10 mg/kg luteolin for 4 consecutive weeks starting at 12 weeks of age. The Morris water maze test was used to evaluate learning and memory abilities, and the novel object recognition test was used to assess recognition memory. Immunohistochemistry was performed for the neural stem cell marker nestin, the astrocyte marker glial fibrillary acidic protein, the immature neuron marker DCX, the mature neuron marker NeuN, and the cell proliferation marker Ki67 in the hippocampal dentate gyrus. Nissl staining was used to observe changes in morphology and to quantify cells in the dentate gyrus. Western blot assay was used to analyze the protein levels of brain-derived neurotrophic factor(BDNF) and phospho-extracellular signal-regulated kinase 1/2(p-ERK1/2) in the hippocampus. Luteolin improved learning and memory abilities as well as novel object recognition ability, and enhanced the proliferation of neurons in the hippocampal dentate gyrus. Furthermore, luteolin increased expression of nestin and glial fibrillary acidic protein, increased the number of DCX~+ neurons in the granular layer and NeuN~+ neurons in the subgranular region of the dentate gyrus, and increased the protein levels of BDNF and p-ERK1/2 in the hippocampus. Our findings show that luteolin improves behavioral performance and promotes hippocampal neurogenesis in Ts65 Dn mice. Moreover, these effects might be associated with the activation of the BDNF/ERK1/2 pathway.     

Early involvement of synapsin III in neural progenitor cell development in the adult hippocampus

Synapsin III is a synaptic vesicle-associated protein that is expressed in cells of the subgranular layer of the hippocampal dentate gyrus, a brain region known to sustain substantial levels of neurogenesis into adulthood. Here we tested the hypothesis that synapsin III plays a role in adult neurogenesis with synapsin III knockout and wild-type mice. Immunocytochemistry of the adult hippocampal dentate gyrus revealed that synapsin III colocalizes with markers of neural progenitor cell development (nestin, PSA-NCAM, NeuN, and Tuj1) but did not colocalize with markers of mitosis (Ki67 and PCNA). Because neurogenesis consists of a number of stages, the proliferation, survival, and differentiation of neural progenitor cells were systematically quantitated in the hippocampal dentate gyrus of adult synapsin III knockout and wild-type mice. We found a 30% decrease in proliferation and a 55% increase in survival of neural progenitor cells in synapsin III knockout mice. We also observed a 6% increase in the number of neural progenitor cells that differentiated into neurons. No difference in the volume of the dentate gyrus was observed between synapsin III knockout and wild-type mice. Collectively, our results demonstrate a novel role for synapsin III in regulating the proliferation of neural progenitor cells in the adult hippocampal dentate gyrus. These findings suggest a distinct function for this synaptic vesicle protein, in addition to its role in neurotransmission.     

Reduced hippocampal neurogenesis and number of hilar neurones in streptozotocin-induced diabetic mice: reversion by antidepressant treatment

Cerebral dysfunctions, including a high incidence of depression, are common findings in human type 1 diabetes mellitus. An association between depression and defective hippocampal neurogenesis has been proposed and, in rodents, antidepressant therapy restores neuronal proliferation in the dentate gyrus. Hippocampal neurogenesis is also deficient in diabetic mice, which led us to study whether the selective serotonin reuptake inhibitor fluoxetine influences cell proliferation in streptozotocin-diabetic animals. Diabetic and control C57BL/6 mice received fluoxetine (10 mg/kg/day, i.p., 10 days) and dentate gyrus cell proliferation was measured after a single injection of 5-bromo-2'-deoxyuridine (BrdU). Diabetic mice showed reduced cell proliferation. Fluoxetine treatment, although having no effect in controls, corrected this parameter in diabetic mice. The phenotype of newly generated cells was analysed by confocal microscopy after seven daily BrdU injections, using Tuj-1/beta-III tubulin as a marker for immature neurones and glial fibrillary acidic protein for astrocytes. In controls, the proportion of Tuj-1-BrdU-positive cells over total BrdU cells was approximately 70%. In vehicle-treated diabetic mice, immature neurones decreased to 56% and fluoxetine brought this proportion back to control values without affecting astrocytes. Therefore, fluoxetine preferentially increased the proliferation of cells with a neuronal phenotype. In addition, neurones were counted in the hilus of the dentate gyrus; a 30% decrease was found in diabetic mice compared with controls, whereas this neuronal loss was prevented by fluoxetine. In conclusion, fluoxetine treatment restored neuroplasticity-related hippocampal alterations of diabetic mice. These findings may be potentially important to counteract diabetes-associated depression in humans.     

Reduced hippocampal neurogenesis in R6/2 transgenic Huntington's disease mice

We investigated whether cell proliferation and neurogenesis are altered in R6/2 transgenic Huntington's disease mice. Using bromodeoxyuridine (BrdU), we found a progressive decrease in the number of proliferating cells in the dentate gyrus of R6/2 mice. This reduction was detected in pre-symptomatic mice, and by 11.5 weeks, R6/2 mice had 66% fewer newly born cells in the hippocampus. The results were confirmed by immunohistochemistry for the cell cycle markers Ki-67 and proliferating cell nuclear antigen (PCNA). We did not observe changes in cell proliferation in the R6/2 subventricular zone, indicating that the decrease in cell proliferation is specific for the hippocampus. This decrease corresponded to a reduction in actual hippocampal neurogenesis as assessed by double immunostaining for BrdU and the neuronal marker neuronal nuclei (NeuN) and by immunohistochemistry for the neuroblast marker doublecortin. Reduced hippocampal neurogenesis may be a novel neuropathological feature in R6/2 mice that could be assessed when evaluating potential therapies.     

Environmental enrichment promotes neurogenesis and changes the extracellular concentrations of glutamate and GABA in the hippocampus of aged rats

The aim of the present study was to investigate the effects of environmental enrichment on the neurogenesis and the extracellular concentrations of glutamate and GABA in the hippocampus of freely moving young and aged rats. Male Wistar rats of 2 (young) and 25 (old) months of age were housed during 8 weeks in an enriched environment; control rats were kept in individual plastic cages during that same period of time. Rats were injected intraperitoneally with bromodeoxyuridine (BrdU; 40 mg/kg; 7 days) during the fourth week of the housing period to detect neurogenesis in the dentate gyrus (DG) of the hippocampus. Rats were sacrified 6 weeks after the last injection of BrdU. During the last week of housing, rats were tested in the water maze for the evaluation of spatial learning. After the housing period, rats were stereotaxically implanted with guide-cannulas to accommodate microdialysis probes in the CA3 area of the hippocampus and the extracellular concentrations of glutamate and GABA were determined. Aged rats showed a decrease in the number of BrdU positive cells in the dentate gyrus compared to young rats. However, neurogenesis in the dentate gyrus of both young and old rats was increased in animals housed in an enriched environment. Microdialysis experiments in the CA3 area of the hippocampus showed that enriched housing conditions increased basal extracellular concentrations of glutamate in aged rats. Perfusion of KCl 100 mM produced a higher increase of extracellular glutamate and GABA in aged rats but not in young rats housed in an enriched environment compared to control rats. These results suggest that enriched housing conditions change both neurogenesis in the dentate gyrus and glutamate and GABA levels in the CA3 area of the hippocampus of aged rats.     

Adult neurogenesis produces a large pool of new granule cells in the dentate gyrus.

Knowing the rate of addition of new granule cells to the adult dentate gyrus is critical to understanding the function of adult neurogenesis. Despite the large number of studies of neurogenesis in the adult dentate gyrus, basic questions about the magnitude of this phenomenon have never been addressed. The S-phase marker bromodeoxyuridine (BrdU) has been extensively used in recent studies of adult neurogenesis, but it has been carefully tested only in the embryonic brain. Here, we show that a high dose of BrdU (300 mg/kg) is a specific, quantitative, and nontoxic marker of dividing cells in the adult rat dentate gyrus, whereas lower doses label only a fraction of the S-phase cells. By using this high dose of BrdU along with a second S-phase marker, [(3)H]thymidine, we found that young adult rats have 9,400 dividing cells proliferating with a cell cycle time of 25 hours, which would generate 9,000 new cells each day, or more than 250,000 per month. Within 5-12 days of BrdU injection, a substantial pool of immature granule neurons, 50% of all BrdU-labeled cells in the dentate gyrus, could be identified with neuron-specific antibodies TuJ1 and TUC-4. This number of new granule neurons generated each month is 6% of the total size of the granule cell population and 30-60% of the size of the afferent and efferent populations (West et al. [1991] Anat Rec 231:482-497; Mulders et al. [1997] J Comp Neurol 385:83-94). The large number of the adult-generated granule cells supports the idea that these new neurons play an important role in hippocampal function.     

The hydrophobic dipeptide Leu-Ile inhibits immobility induced by repeated forced swimming via the induction of BDNF

Depression has recently become a serious problem in society worldwide. However, we lack appropriate therapeutic tools, since the causes of depression remain unclear. Degeneration of neuronal cells and a decrease in neurogenesis have been suggested recently as two of the factors responsible for depression-like behavior. Furthermore, brain-derived neurotrophic factor (BDNF) is also suggested to be an important factor in recovering from such behavior. We have previously demonstrated that the hydrophobic dipeptide leucyl-isoleucine (Leu-Ile) induces BDNF in cultured neuronal cells. We therefore investigated possible antidepressant-like effects of Leu-Ile in an animal model using the repeated forced swim test (FST). Mice were forced to swim for 6 min once a day in a cylinder containing water. The mice were treated with Leu-Ile s.c. or p.o. immediately after each FST. Five-day repeated Leu-Ile treatment significantly increased BDNF mRNA levels and activated the BDNF/Akt/mTOR signaling pathway in the hippocampi of the mice. While 2-week repeated FST increased immobility time, Leu-Ile treatment for 2 weeks offset this increase. In C57BL/6J-BDNF heterozygous knockout (BDNF(+/-)) mice, Leu-Ile failed to reduce the immobility time increased by repeated FST. We next investigated the extent of cell proliferation in the hippocampus as 5-bromo-2'-deoxy-uridine (BrdU) uptake into hippocampal cells. Repeated FST significantly reduced the number of BrdU-positive cells in the hippocampal dentate gyrus, while this deficit was prevented by repeated Leu-Ile treatment. These results suggest that Leu-Ile has an antidepressant-like effect, at least in part by supporting cell proliferation through the BDNF signaling pathway.     

Afferent-specific modulation of short-term synaptic plasticity by neurotrophins in dentate gyrus

Neurotrophins modulate synaptic transmission and plasticity in the adult brain. We here show a novel feature of this synaptic modulation, i.e. that two populations of excitatory synaptic connections to granule cells in the dentate gyrus, lateral perforant path (LPP) and medial perforant path (MPP), are differentially influenced by the neurotrophins BDNF and NT-3. Using field recordings and whole-cell patch-clamp recordings in hippocampal slices, we found that paired-pulse (PP) depression at MPP-granule cell synapses was impaired in BDNF knock-out (+/-) mice, but PP facilitation at LPP synapses to the same cells was not impaired. In accordance, scavenging of endogenous BDNF with TrkB-IgG fusion protein also impaired PP depression at MPP-granule cell synapses, but not PP facilitation at LPP-granule cell synapses. Conversely, in NT-3+/- mice, PP facilitation was impaired at LPP-granule cell synapses whilst PP depression at MPP-granule cell synapses was unaffected. These deficits could be reversed by application of exogenous neurotrophins in an afferent-specific manner. Our data suggest that BDNF and NT-3 differentially regulate the synaptic impact of different afferent inputs onto single target neurons in the CNS.     

Enforced physical training promotes neurogenesis in the subgranular zone after focal cerebral ischemia

BACKGROUND: Cerebral ischemia increases neurogenesis in the subventricular zone (SVZ) and in the subgranular zone (SGZ) of the dentate gyrus, and this might be modulated by an enriched environment including voluntary physical activity. We examined whether enforced physical training (EPT) influences neurogenesis in the SVZ and SGZ after cerebral ischemia. METHODS: Adult male Sprague-Dawley rats were subjected to focal cerebral ischemia for 2 h, and divided into an EPT and a non-EPT group. All rats in the EPT group were trained using a rota-rod for 14 days. 5-bromo-2'-deoxyuridine (BrdU) was injected to determine levels of cell proliferation. Functional recovery was assessed using a set of behavioral test batteries. Extents of endogenous neurogenesis in the SVZ and SGZ were quantified by immunofluorescence staining. Although final infarction volumes were not significantly different in the groups, functional recovery was better in the EPT group at 10 and 17 days after ischemia. In the SVZ, BrdU labeling and double labeling of BrdU/Dcx and of BrdU/NeuN were not significantly different in the two groups. However, in the SGZ, EPT significantly increased the number of BrdU-positive cell numbers (EPT vs. non-EPT: 159.1+/-19.9 vs. 101.8+/-7.8, p=0.04), and the number of BrdU/Dcx double-labeled cells (130.6+/-16.9 vs. 73.6+/-7.2, p=0.01). CONCLUSIONS: The results obtained indicate that EPT promotes neurogenesis in the SGZ of the dentate gyrus after ischemia, but not in the SVZ. The biochemical mechanism that determines the differential effects of EPT remains to be clarified.     

Experience‐dependent regulation of adult hippocampal neurogenesis: Effects of long‐term stimulation and stimulus withdrawal

Exposure to an enriched environment has been shown to cause an increase in neurogenesis in the dentate gyrus of adult mice. In this study we examined how this experience‐dependent response in adult hippocampal neurogenesis of C57BL/6 mice is modulated under the conditions of long‐term stimulation and of withdrawal from the enriched environment. We found that a group which experienced withdrawal from the enriched environment 3 months earlier, had more than twice as many proliferating cells in the subgranular zone as controls and mice experiencing long‐term stimulation. We propose that the greater number of proliferating cells after withdrawal reflects a survival‐promoting effect on the dividing neuronal stem and progenitor cells during the earlier period of stimulation. No differences between the groups were observed in the number of surviving progeny or their phenotypes. Therefore, the existence of more dividing cells in the withdrawal group did not translate into a significant net increase in neurogenesis in the absence of continued stimulation. Similarly, the finding in the group experiencing long‐term stimulation showing no clear benefit over controls could be interpreted as a diminished efficiency of continued environmental stimuli to elicit a neurogenic response. Thus, we propose as a working hypothesis that: 1) stimulation early in life may preserve the neurogenic potential in the dentate gyrus, and 2) the novelty of complex stimuli rather than simply continued exposure to complex stimuli elicits the environmental effects on adult hippocampal neurogenesis. Hippocampus 1999;9:321–332. © 1999 Wiley‐Liss, Inc.     

Long‐term effects of autoimmune CNS inflammation on adult hippocampal neurogenesis

Neurogenesis is a well‐characterized phenomenon within the dentate gyrus (DG) of the adult hippocampus. Aging and chronic degenerative disorders have been shown to impair hippocampal neurogenesis, but the consequence of chronic inflammation remains controversial. In this study the chronic experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis was used to investigate the long‐term effects of T cell–mediated central nervous system inflammation on hippocampal neurogenesis. 5‐Bromodeoxyuridine (BrdU)‐labeled subpopulations of hippocampal cells in EAE and control mice (coexpressing GFAP, doublecortin, NeuN, calretinin, and S100) were quantified at the recovery phase, 21 days after BrdU administration, to estimate alterations on the rate and differentiation pattern of the neurogenesis process. The core features of EAE mice DG are (i) elevated number of newborn (BrdU+) cells indicating vigorous proliferation, which in the long term subsided; (ii) enhanced migration of newborn cells into the granule cell layer; (iii) increased level of immature neuronal markers (including calretinin and doublecortin); (iv) trending decrease in the percentage of newborn mature neurons; and (v) augmented gliogenesis and differentiation of newborn neural precursor cells (NPCs) to mature astrocytes (BrdU+/S100+). Although the inflammatory environment in the brain of EAE mice enhances the proliferation of hippocampal NPCs, in the long term neurogenesis is progressively depleted, giving prominence to gliogenesis. The discrepancy between the high number of immature cells and the low number of mature newborn cells could be the result of a caused defect in the maturation pathway. © 2016 Wiley Periodicals, Inc.