Differential properties of dentate gyrus and CA1 neural precursors

Deep brain stimulation mitigates memory deficits in a rodent model of traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a major life-threatening event. In addition to neurological deficits, it can lead to long-term impairments in attention and memory. Deep brain stimulation (DBS) is an established therapy for movement disorders that has been recently investigated for memory improvement in various disorders. In models of TBI, stimulation delivered to different brain targets has been administered to rodents long after the injury with the objective of treating motor deficits, coordination and memory impairment.

OBJECTIVE

To test the hypothesis that DBS administered soon after TBI may prevent the development of memory deficits and exert neuroprotective effects.

METHODS

Male rats were implanted with DBS electrodes in the anterior nucleus of the thalamus (ANT) one week prior to lateral fluid percussion injury (FPI). Immediately after TBI, animals received active or sham stimulation for 6 h. Four days later, they were assessed in a novel object/novel location recognition test (NOR/NLR) and a Barnes maze paradigm. After the experiments, hippocampal cells were counted. Separate groups of animals were sacrificed at different timepoints after TBI to measure cytokines and brain derived neurotrophic factor (BDNF). In a second set of experiments, TBI-exposed animals receiving active or sham stimulation were injected with the tropomyosin receptor kinase B (TrkB) antagonist ANA-12, followed by behavioural testing.

RESULTS

Rats exposed to TBI given DBS had an improvement in several variables of the Barnes maze, but no significant improvements in NOR/NLR compared to Sham DBS TBI animals or non-implanted controls. Animals receiving stimulation had a significant increase in BDNF levels, as well as in hippocampal cell counts in the hilus, CA3 and CA1 regions. DBS failed to normalize the increased levels of TNFα and the proinflammatory cytokine IL1β in the perilesional cortex and the hippocampus of the TBI-exposed animals. Pharmacological experiments revealed that ANA-12 administered alongside DBS did not counter the memory improvement observed in ANT stimulated animals.

CONCLUSIONS

DBS delivered immediately after TBI mitigated memory deficits, increased the expression of BDNF and the number of hippocampal cells in rats. Mechanisms for these effects were not related to an anti-inflammatory effect or mediated via TrkB receptors.

Deep brain stimulation of the anterior nuclei of the thalamus can alleviate seizure severity and induce hippocampal GABAergic neuronal changes in a pilocarpine-induced epileptic mouse brain

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) has been widely used as an effective treatment for refractory temporal lobe epilepsy. Despite its promising clinical outcome, the exact mechanism of how ANT-DBS alleviates seizure severity has not been fully understood, especially at the cellular level. To assess effects of DBS, the present study examined electroencephalography (EEG) signals and locomotor behavior changes and conducted immunohistochemical analyses to examine changes in neuronal activity, number of neurons, and neurogenesis of inhibitory neurons in different hippocampal subregions. ANT-DBS alleviated seizure activity, abnormal locomotor behaviors, reduced theta-band, increased gamma-band EEG power in the interictal state, and increased the number of neurons in the dentate gyrus (DG). The number of parvalbumin- and somatostatin-expressing inhibitory neurons was recovered to the level in DG and CA1 of naïve mice. Notably, BrdU-positive inhibitory neurons were increased. In conclusion, ANT-DBS not only could reduce the number of seizures, but also could induce neuronal changes in the hippocampus, which is a key region involved in chronic epileptogenesis. Importantly, our results suggest that ANT-DBS may lead to hippocampal subregion-specific cellular recovery of GABAergic inhibitory neurons.

A Warburg-like metabolic program coordinates Wnt, AMPK, and mTOR signaling pathways in epileptogenesis

Epilepsy is a complex neurological condition characterized by repeated spontaneous seizures and can be induced by initiating seizures known as status epilepticus (SE). Elaborating the critical molecular mechanisms following SE are central to understanding the establishment of chronic seizures. Here, we identify a transient program of molecular and metabolic signaling in the early epileptogenic period, centered on day five following SE in the pre-clinical kainate or pilocarpine models of temporal lobe epilepsy. Our work now elaborates a new molecular mechanism centered around Wnt signaling and a growing network comprised of metabolic reprogramming and mTOR activation. Biochemical, metabolomic, confocal microscopy and mouse genetics experiments all demonstrate coordinated activation of Wnt signaling, predominantly in neurons, and the ensuing induction of an overall aerobic glycolysis (Warburg-like phenomenon) and an altered TCA cycle in early epileptogenesis. A centerpiece of the mechanism is the regulation of pyruvate dehydrogenase (PDH) through its kinase and Wnt target genes PDK4. Intriguingly, PDH is a central gene in certain genetic epilepsies, underscoring the relevance of our elaborated mechanisms. While sharing some features with cancers, the Warburg-like metabolism in early epileptogenesis is uniquely split between neurons and astrocytes to achieve an overall novel metabolic reprogramming. This split Warburg metabolic reprogramming triggers an inhibition of AMPK and subsequent activation of mTOR, which is a signature event of epileptogenesis. Interrogation of the mechanism with the metabolic inhibitor 2-deoxyglucose surprisingly demonstrated that Wnt signaling and the resulting metabolic reprogramming lies upstream of mTOR activation in epileptogenesis. To augment the pre-clinical pilocarpine and kainate models, aspects of the proposed mechanisms were also investigated and correlated in a genetic model of constitutive Wnt signaling (deletion of the transcriptional repressor and Wnt pathway inhibitor HBP1). The results from the HBP1^-/- mice provide a genetic evidence that Wnt signaling may set the threshold of acquired seizure susceptibility with a similar molecular framework. Using biochemistry and genetics, this paper outlines a new molecular framework of early epileptogenesis and advances a potential molecular platform for refining therapeutic strategies in attenuating recurrent seizures.

Cellular and Molecular Differences Between Area CA1 and the Dentate Gyrus of the Hippocampus

A distinct feature of the hippocampus of the brain is its unidirectional tri-synaptic pathway originating from the entorhinal cortex and projecting to the dentate gyrus (DG) then to area CA3 and subsequently, area CA1 of the Ammon's horn. Each of these areas of the hippocampus has its own cellular structure and distinctive function. The principal neurons in these areas are granule cells in the DG and pyramidal cells in the Ammon's horn's CA1 and CA3 areas with a vast network of interneurons. This review discusses the fundamental differences between the CA1 and DG areas regarding cell morphology, synaptic plasticity, signaling molecules, ability for neurogenesis, vulnerability to various insults and pathologies, and response to pharmacological agents.

Effects of [Nphe1, Arg14, Lys15] N/OFQ-NH2 (UFP-101), a potent NOP receptor antagonist, on molecular, cellular and behavioural alterations associated with chronic mild stress

The present study investigated the effect of [Nphe¹] Arg¹⁴, Lys¹⁵-N/OFQ-NH₂ (UFP-101), a selective NOP receptor antagonist, in chronic mild stress (CMS) in male Wistar rats. NOP receptor antagonists were reported to elicit antidepressant-like effects in rodents. Our aim was to investigate UFP-101 effects on CMS-induced anhedonia and impairment of hippocampal neurogenesis. UFP-101 (10 nmol/rat intracerebroventricularly) did not influence sucrose intake in non-stressed animals, but reinstated basal sucrose consumption in stressed animals from the second week of treatment. UFP-101 also reversed stress effects in forced swimming test and in open field. Fluoxetine (10 mg/kg intraperitoneally) produced similar effects. Moreover, we investigated whether UFP-101 could affect CMS-induced impairment in hippocampal cell proliferation and neurogenesis, and in fibroblast growth factor (FGF-2) expression. Our data confirm that CMS reduced neural stem cell proliferation and neurogenesis in adult rat hippocampus. Chronic UFP-101 treatment did not affect the reduced proliferation (bromodeoxyuridine-positive cells) observed in stressed animals. However, UFP-101 increased the number of doublecortin-positive cells, restoring neurogenesis. Finally, UFP-101 significantly increased FGF-2 expression, reduced by CMS. These findings support the view that blockade of NOP receptors produces antidepressant-like effects in CMS associated with positive effects on neurogenesis and FGF-2 expression. Therefore, NOP receptors may represent a target for innovative antidepressant drugs.

Ozone Therapy in Ethidium Bromide-Induced Demyelination in Rats: Possible Protective Effect

Multiple sclerosis, an autoimmune inflammatory disease of the central nervous system, is characterized by excessive demyelination. The study aimed to investigate the possible protective effect of ozone (O3) therapy in ethidium bromide (EB)-induced demyelination in rats either alone or in combination with corticosteroids in order to decrease the dose of steroid therapy. Rats were divided into Group (1) normal control rats received saline, Group (2) Sham-operated rats received saline, Group (3) Sham-operated rats received vehicle (oxygen), Group (4) EB-treated rats received EB, Group (5) EB-treated rats received O3, Group (6) EB-treated rats received methylprednisolone (MP), and Group (7) EB-treated rats received half the dose of MP concomitant with O3. EB-treated rats showed a significant increase in the number of footfalls in the grid walk test, decreased brain GSH, and paraoxonase-1 enzyme activity, whereas brain MDA, TNF-α, IL-1β, INF-γ, Cox-2 immunoreactivity, and p53 protein levels were increased. A significant decline in brain serotonin, dopamine, norepinephrine, and MBP immunoreactivity was also reported. Significant improvement of the above-mentioned parameters was demonstrated with the administration of either MP or O3, whereas best amelioration was achieved by combining half the dose of MP with ozone.

Effect of intrahippocampal administration of vitamin C and progesterone on learning in a model of multiple sclerosis in rats

PURPOSE

The purpose of this study was to evaluate the effect of intrahippocampal injection of vitamin C and progesterone, alone or in combination, on passive avoidance learning (PAL) in multiple sclerosis.

METHODS

Sixty- three male wistar rats were divided into nine groups (n=7) as following: control (saline), lesion, vitamin C (0.2, 1, 5 mg/kg), progesterone (0.01, 0.1, 1 µg/µl) and combination therapy. Lesion was induced by intrahippocampal injection of ethidium bromide. In combination therapy, animals were treated with vitamin C (5 mg/kg) plus progesterone (0.01 mg/kg). Animals in experimental groups received different treatments for 7 days, and then all groups were tested for step through latency (STL).

RESULTS

Our results showed that intrahippocampal injection of ethidium bromide destroys PAL significantly (p<0.001). Treatment with vitamin C (5mg/kg) significantly (p<0.05) improved PAL. Lower doses of progesterone did not affect latency but dose of 1 µg/µl significantly (p<0.05) increased STL. In combination therapy group STL was significantly (p<0.05) more than in the lesion group, although it was not significantly different from the vitamin C group.

CONCLUSION

Based on our results, we concluded that intrahippocampal injection of vitamin C improves memory for PAL, but progesterone alone or in combination with vitamin C had no improving effects on memory.

A cGMP-applicable expansion method for aggregates of human neural stem and progenitor cells derived from pluripotent stem cells or fetal brain tissue

A cell expansion technique to amass large numbers of cells from a single specimen for research experiments and clinical trials would greatly benefit the stem cell community. Many current expansion methods are laborious and costly, and those involving complete dissociation may cause several stem and progenitor cell types to undergo differentiation or early senescence. To overcome these problems, we have developed an automated mechanical passaging method referred to as "chopping" that is simple and inexpensive. This technique avoids chemical or enzymatic dissociation into single cells and instead allows for the large-scale expansion of suspended, spheroid cultures that maintain constant cell/cell contact. The chopping method has primarily been used for fetal brain-derived neural progenitor cells or neurospheres, and has recently been published for use with neural stem cells derived from embryonic and induced pluripotent stem cells. The procedure involves seeding neurospheres onto a tissue culture Petri dish and subsequently passing a sharp, sterile blade through the cells effectively automating the tedious process of manually mechanically dissociating each sphere. Suspending cells in culture provides a favorable surface area-to-volume ratio; as over 500,000 cells can be grown within a single neurosphere of less than 0.5 mm in diameter. In one T175 flask, over 50 million cells can grow in suspension cultures compared to only 15 million in adherent cultures. Importantly, the chopping procedure has been used under current good manufacturing practice (cGMP), permitting mass quantity production of clinical-grade cell products.

Growth/differentiation factor 15 promotes EGFR signalling, and regulates proliferation and migration in the hippocampus of neonatal and young adult mice

The activation of epidermal growth factor receptor (EGFR) affects multiple aspects of neural precursor behaviour, including proliferation and migration. Telencephalic precursors acquire EGF responsiveness and upregulate EGFR expression at late stages of development. The events regulating this process and its significance are still unclear. We here show that in the developing and postnatal hippocampus (HP), growth/differentiation factor (GDF) 15 and EGFR are co-expressed in primitive precursors as well as in more differentiated cells. We also provide evidence that GDF15 promotes responsiveness to EGF and EGFR expression in hippocampal precursors through a mechanism that requires active CXC chemokine receptor (CXCR) 4. Besides EGFR expression, GDF15 ablation also leads to decreased proliferation and migration. In particular, lack of GDF15 impairs both processes in the cornu ammonis (CA) 1 and only proliferation in the dentate gyrus (DG). Importantly, migration and proliferation in the mutant HP were altered only perinatally, when EGFR expression was also affected. These data suggest that GDF15 regulates migration and proliferation by promoting EGFR signalling in the perinatal HP and represent a first description of a functional role for GDF15 in the developing telencephalon.

Postnatal age governs the extent of differentiation of hippocampal CA1 and CA3 subfield neural stem/progenitor cells into neurons and oligodendrocytes

While neural stem/progenitor cells (NSCs) in the dentate gyrus of the hippocampus have been extensively characterized, the behavior of NSCs in the CA1 and CA3 subfields of the hippocampus is mostly unclear. Therefore, we compared the in vitro behavior of NSCs expanded from the micro-dissected CA1 and CA3 subfields of postnatal day (PND) 4 and 12 Fischer 344 rats. A small fraction (∼1%) of dissociated cells from CA1 and CA3 subfields of both PND 4 and 12 hippocampi formed neurospheres in the presence of EGF and FGF-2. A vast majority of neurosphere cells expressed NSC markers such as nestin, Sox-2 and Musashi-1. Differentiation assays revealed the ability of these NSCs to give rise to neurons, astrocytes, and oligodendrocytes. Interestingly, the overall neuronal differentiation of NSCs from both subfields decreased with age (23-28% at PND4 to 5-10% at PND12) but the extent of oligodendrocyte differentiation from NSCs increased with age (24-32% at PND 4 to 45-55% at PND 12). Differentiation of NSCs into astrocytes was however unchanged (40-48%). Furthermore, NSCs from both subfields gave rise to GABA-ergic neurons including subclasses expressing markers such as calbindin, calretinin, neuropeptide Y and parvalbumin. However, the fraction of neurons that expressed GABA decreased between PND4 (59-67%) and PND 12 (25-38%). Additional analyses revealed the presence of proliferating NSC-like cells (i.e. cells expressing Ki-67 and Sox-2) in different strata of hippocampal CA1 and CA3 subfields of both PND4 and PND 12 animals. Thus, multipotent NSCs persist in both CA1 and CA3 subfields of the hippocampus in the postnatal period. Such NSCs also retain their ability to give rise to both GABA-ergic and non-GABA-ergic neurons. However, their overall neurogenic potential declines considerably in the early postnatal period.

Growth hormone (GH) treatment may cooperate with locally-produced GH in increasing the proliferative response of hippocampal progenitors to kainate-induced injury

PRIMARY OBJECTIVE

This study was designed to investigate the effect of growth hormone treatment on the proliferation of endogenous neural progenitor cells in the dentate gyrus (DG) of the brain stimulated by kainic acid (KA)-induced neurotoxicity.

RESEARCH DESIGN

Neurotoxicity was induced by intraperitoneal injection of KA. GH treatment lasted 4 days, starting either immediately or after 10 days of administration of the neurotoxic insult.

METHODS AND PROCEDURE

Proliferating cells were immunodetected after labelling by in vivo administration of 5-bromodeoxyuridine (BrdU). GH expression was detected by in situ hybridization and immunofluorescence.

MAIN OUTCOMES AND RESULTS

KA administration stimulated the proliferation of hippocampal precursors and this effect was significantly enhanced by GH treatment. Hippocampal GH expression was also up-regulated in response to KA administration.

CONCLUSIONS

The findings support the possibility that the proliferative response observed in the hippocampus of rats treated with KA and GH is a consequence of cooperation between the exogenous and the locally-produced hormone and their synergism with other mitogenic factors generated in response to the neurotoxic damage. Therefore, GH treatment could be used to cooperate with other physiological or pathological stimuli in order to promote cell proliferation.

Developmental profiling of postnatal dentate gyrus progenitors provides evidence for dynamic cell-autonomous regulation

The dentate gyrus of the hippocampus is one of the most prominent regions in the postnatal mammalian brain where neurogenesis continues throughout life. There is tremendous speculation regarding the potential implications of adult hippocampal neurogenesis, though it remains unclear to what extent this ability becomes attenuated during normal aging, and what genetic changes in the progenitor population ensue over time. Using defined elements of the nestin promoter, we developed a transgenic mouse that reliably labels neural stem and early progenitors with green fluorescent protein (GFP). Using a combination of immunohistochemical and flow cytometry techniques, we characterized the progenitor cells within the dentate gyrus and created a developmental profile from postnatal day 7 (P7) until 6 months of age. In addition, we demonstrate that the proliferative potential of these progenitors is controlled at least in part by cell-autonomous cues. Finally, to identify what may underlie these differences, we performed stem cell-specific microarrays on GFP-expressing sorted cells from isolated P7 and postnatal day 28 (P28) dentate gyrus. We identified several differentially expressed genes that may underlie the functional differences that we observe in neurosphere assays from sorted cells and differentiation assays at these different ages. These data suggest that neural progenitors from the dentate gyrus are differentially regulated by cell-autonomous factors that change over time.

GalR2/3 mediates proliferative and trophic effects of galanin on postnatal hippocampal precursors

Understanding how neural activity is functionally linked to the stem cell niche, is assuming ever increasing importance as hippocampal neurogenesis is shown to be important for modulating the behavioural responses to stress and for certain forms of learning and memory. Neuropeptides such as neuropeptide Y and vasoactive intestinal peptide have emerged as important mediators for signalling local interneuron activity to subgranular zone precursors, however, little is known regarding the effects of neuropeptides that are extrinsic modulators of hippocampal information processing. Here, we show that the galanin GalR2/3 agonist Gal2-11 is both trophic and proliferative for postnatal subgranular precursors and proliferating neuroblasts at 10 nM and is purely trophic at doses as low as 100 pM. We found no effect mediated via GalR1. As galanin is co-released from noradrenergic and serotonergic projection neurons to the dentate gyrus, these findings support a direct effect of galanin on hippocampal neurogenesis, which may partly mediate its antidepressant effect via GalR2/3 receptors.

Omega-3 fatty acids reverse age-related decreases in nuclear receptors and increase neurogenesis in old rats

Retinoic acid receptors (RARs), retinoid X receptors (RXRs), and peroxisome proliferator-activated receptors (PPARs) are transcription factors involved in many cellular processes, such as learning and memory. RAR and RXR mRNA levels decrease with ageing, and the decreases can be reversed by retinoic acid treatment, which also alleviates age-related memory deficits. The omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have neuroprotective effects in the aged brain and are endogenous ligands of RXR and PPAR. We investigated whether dietary EPA and DHA supplementation reverses age-related declines in protein levels of these receptors in rat forebrain. Two studies were conducted comparing adult and old rats. In the first, old rats were fed standard or EPA/DHA-enriched (270 mg/kg/day, EPA to DHA ratio 1.5:1) diets for 12 weeks. Analysis by Western blot revealed significant decreases in RARalpha, RXRalpha, RXRbeta, and PPARgamma in the forebrain with ageing, which were reversed by supplementation. Immunohistochemical analysis of the hippocampus showed significant age-related decreases in RARalpha and RXRbeta expression in CA1 and the dentate gyrus, which were restored by supplementation. Decreases in hippocampal doublecortin expression were also partially alleviated, suggesting a positive effect on neurogenesis. We also investigated the effects of DHA supplementation (300 mg/kg/day for 12 weeks) on RARalpha, RXRalpha, and RXRbeta expression in the prefrontal cortex, striatum, and hippocampus. Overall, DHA supplementation appeared to increase receptor expression compared with the untreated old group. These observations illustrate additional mechanisms that might underlie the neuroprotective effects of omega-3 fatty acids in ageing.

Expression and Functions of Fibroblast Growth Factor 2 (FGF-2) in Hippocampal Formation

Among the 23 members of the fibroblast growth factor (FGF) family, FGF-2 is the most abundant one in the central nervous system. Its impact on neural cells has been profoundly investigated by in vitro and in vivo studies as well as by gene knockout analyses during the past 2 decades. Key functions of FGF-2 in the nervous system include roles in neurogenesis, promotion of axonal growth, differentiation in development, and maintenance and plasticity in adulthood. From a clinical perspective, its prominent role for the maintenance of lesioned neurons (e.g., ischemia and following transection of fiber tracts) is of particular relevance. In the unlesioned brain, FGF-2 is involved in synaptic plasticity and processes attributed to learning and memory. The focus of this review is on the expression of FGF-2 and its receptors in the hippocampal formation and the physiological and pathophysiological roles of FGF-2 in this region during development and adulthood.

Vitamins E and D3 attenuate demyelination and potentiate remyelination processes of hippocampal formation of rats following local injection of ethidium bromide

Cognitive deficits have been observed in patients with multiple sclerosis (MS) due to hippocampal insults. Antioxidant vitamins D and E are suggested for patients suffering from neurodegenerative diseases like MS, while their mechanisms of action are not well understood. Here, we have tried to study the effects of these vitamins on demyelination, cell death, and remyelination of rat hippocampus following local ethidium bromide (EB) injection. Animals received 100 mg/kg vitamin E or 5 microg/kg of vitamin D3 for 2, 7, or 28 days. The extent of demyelination, myelin staining intensity, and expression of myelin basic protein and caspase-3 were investigated using histological and immunoblotting verification. Administration of EB alone caused demyelination, cell death, and afterward an endogenous repair. Vitamins E and D3 reduced the EB-induced damage and increased the endogenous remyelination of hippocampus. Although the anti-apoptotic effect of these vitamins and protection against demyelination were predictable based on their antioxidant effect, our results indicated the positive effect of vitamins E and D3 on process of remyelination by endogenous progenitor cells and supported their possible therapeutic effects in the context of demyelinating diseases like MS.

Epigenetic mechanisms underlying human epileptic disorders and the process of epileptogenesis

The rapidly emerging science of epigenetics and epigenomic medicine promises to reveal novel insights into the susceptibility to and the onset and progression of epileptic disorders. Epigenetic regulatory mechanisms are now implicated in orchestrating aspects of neural development (e.g., cell fate specification and maturation), homeostasis and stress responses (e.g., immediate early gene transcription), and neural network function (e.g., excitation-inhibition coupling and activity-dependent plasticity). These same neurobiological processes are responsible for determining the heterogeneous features of complex epileptic disease states. Thus, we highlight recent evidence that is beginning to elucidate the specific roles played by epigenetic mechanisms, including DNA methylation, histone code modifications and chromatin remodeling, noncoding RNAs and RNA editing, in human epilepsy syndromes and in the process of epileptogenesis. The highly integrated layers of the epigenome are responsible for the cell type specific and exquisitely environmentally responsive deployment of genes and functional gene networks that underlie the molecular pathophysiology of epilepsy and its associated comorbidities, including but not limited to neurotransmitter receptors (e.g., GluR2, GLRA2, and GLRA3), growth factors (e.g., BDNF), extracellular matrix proteins (e.g., RELN), and diverse transcriptional regulators (e.g., CREB, c-fos, and c-jun). These important observations suggest that future epigenetic studies are necessary to better understand, classify, prevent, and treat epileptic disorders.

Activin A is essential for neurogenesis following neurodegeneration

It has long been proposed that excitotoxicity contributes to nerve cell death in neurodegenerative diseases. Activin A, a member of the transforming growth factor-β superfamily, is expressed by neurons following excitotoxicity. We show for the first time that this activin A expression is essential for neurogenesis to proceed following neurodegeneration. We found that intraventricular infusion of activin A increased the number of newborn neurons in the dentate gyrus, CA3, and CA1 layers of the normal adult hippocampus and also, following lipopolysaccharide administration, had a potent inhibitory effect on gliosis in vivo and on microglial proliferation in vivo and in vitro. Consistent with the role of activin A in regulating central nervous system inflammation and neurogenesis, intraventricular infusion of follistatin, an activin A antagonist, profoundly impaired neurogenesis and increased the number of microglia and reactive astrocytes following onset of kainic acid-induced neurodegeneration. These results show that inhibiting endogenous activin A is permissive for a potent underlying inflammatory response to neurodegeneration. We demonstrate that the anti-inflammatory actions of activin A account for its neurogenic effects following neurodegeneration because co-administration of nonsteroidal anti-inflammatory drugs reversed follistatin's inhibitory effects on neurogenesis in vivo. Our work indicates that activin A, perhaps working in conjunction with other transforming growth factor-β superfamily molecules, is essential for neurogenesis in the adult central nervous system following excitotoxic neurodegeneration and suggests that neurons can regulate regeneration by suppressing the inflammatory response, a finding with implications for understanding and treating acute and chronic neurodegenerative diseases.

Neural precursor cells and central nervous system radiation sensitivity

The tolerance of normal brain tissues limits the radiation dose that can be delivered safely during cranial radiotherapy, and one of the potential complications that can arise involves cognitive impairment. Extensive laboratory data have appeared recently showing that hippocampal neurogenesis is significantly impacted by irradiation and that such changes are associated with altered cognitive function and involve, in part, changes in the microenvironment (oxidative stress and inflammation). Although there is considerable uncertainty about exactly how these changes evolve, new in vitro and in vivo approaches have provided a means by which new mechanistic insights can be gained relevant to the topic. Together, the data from cell culture and animal-based studies provide complementary information relevant to a potentially serious complication of cranial radiotherapy and should enhance our understanding of the tolerance of normal brain after cranial irradiation.

Localized delivery of fibroblast growth factor-2 and brain-derived neurotrophic factor reduces spontaneous seizures in an epilepsy model

A loss of neurons is observed in the hippocampus of many patients with epilepsies of temporal lobe origin. It has been hypothesized that damage limitation or repair, for example using neurotrophic factors (NTFs), may prevent the transformation of a normal tissue into epileptic (epileptogenesis). Here, we used viral vectors to locally supplement two NTFs, fibroblast growth factor-2 (FGF-2) and brain-derived neurotrophic factor (BDNF), when epileptogenic damage was already in place. These vectors were first characterized in vitro, where they increased proliferation of neural progenitors and favored their differentiation into neurons, and they were then tested in a model of status epilepticus-induced neurodegeneration and epileptogenesis. When injected in a lesioned hippocampus, FGF-2/BDNF expressing vectors increased neuronogenesis, embanked neuronal damage, and reduced epileptogenesis. It is concluded that reduction of damage reduces epileptogenesis and that supplementing specific NTFs in lesion areas represents a new approach to the therapy of neuronal damage and of its consequences.

Region-specific proliferative response of neural progenitors to exogenous stimulation by growth factors following ischemia

The most effective way to augment neural progenitor proliferation after ischemia is still unknown. We administered various agents into the rat cerebral ventricle after transient global ischemia and compared the neural progenitor response in the anterior subventricular zone (aSVZ), dentate gyrus subgranular zone, posterior periventricle, and hypothalamus. We demonstrated that cocktail administration of epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) remarkably increased the numbers of neural progenitors in all four regions examined. The addition of Notch ligand DLL4 to the cocktail elicited the largest progenitor response in the aSVZ and hypothalamus. Our results suggest that EGF and FGF-2, combined with DLL4, represent the universally applicable regimen for the expansion of the neural progenitor pool following ischemia.

CD133 is not present on neurogenic astrocytes in the adult subventricular zone, but on embryonic neural stem cells, ependymal cells, and glioblastoma cells

Human brain tumor stem cells have been enriched using antibodies against the surface protein CD133. An antibody recognizing CD133 also served to isolate normal neural stem cells from fetal human brain, suggesting a possible lineage relationship between normal neural and brain tumor stem cells. Whether CD133-positive brain tumor stem cells can be derived from CD133-positive neural stem or progenitor cells still requires direct experimental evidence, and an important step toward such investigations is the identification and characterization of normal CD133-presenting cells in neurogenic regions of the embryonic and adult brain. Here, we present evidence that CD133 is a marker for embryonic neural stem cells, an intermediate radial glial/ependymal cell type in the early postnatal stage, and for ependymal cells in the adult brain, but not for neurogenic astrocytes in the adult subventricular zone. Our findings suggest two principal possibilities for the origin of brain tumor stem cells: a derivation from CD133-expressing cells, which are normally not present in the adult brain (embryonic neural stem cells and an early postnatal intermediate radial glial/ependymal cell type), or from CD133-positive ependymal cells in the adult brain, which are, however, generally regarded as postmitotic. Alternatively, brain tumor stem cells could be derived from proliferative but CD133-negative neurogenic astrocytes in the adult brain. In the latter case, brain tumor development would involve the production of CD133.

The adult mouse hippocampal progenitor is neurogenic but not a stem cell

The aim of this investigation was to characterize the proliferative precursor cells in the adult mouse hippocampal region. Given that a very large number of new hippocampal cells are generated over the lifetime of an animal, it is predicted that a neural stem cell is ultimately responsible for maintaining this genesis. Although it is generally accepted that a proliferative precursor resides within the hippocampus, contradictory reports exist regarding the classification of this cell. Is it a true stem cell or a more limited progenitor? Using a strict functional definition of a neural stem cell and a number of in vitro assays, we report that the resident hippocampal precursor is a progenitor capable of proliferation and multipotential differentiation but is unable to self-renew and thus proliferate indefinitely. Furthermore, the mitogen FGF-2 stimulates proliferation of these cells to a greater extent than epidermal growth factor (EGF). In addition, we found that BDNF was essential for the production of neurons from the hippocampal progenitor cells, being required during proliferation to trigger neuronal fate. In contrast, a bona fide neural stem cell was identified in the lateral wall of the lateral ventricle surrounding the hippocampus. Interestingly, EGF proved to be the stronger mitogenic factor for this cell, which was clearly a different precursor from the resident hippocampal progenitor. These results suggest that the stem cell ultimately responsible for adult hippocampal neurogenesis resides outside the hippocampus, producing progenitor cells that migrate into the neurogenic zones and proliferate to produce new neurons and glia.

Disruption of the neurogenic potential of the dentate gyrus in a mouse model of temporal lobe epilepsy with focal seizures

Adult hippocampal neurogenesis is enhanced in response to multiple stimuli including seizures. However, the relationship between neurogenesis and the development of temporal lobe epilepsy (TLE) remains unclear. Unilateral intrahippocampal injection of kainate in adult mice models the morphological characteristics (e.g. neuronal loss, gliosis, granule cell dispersion and hypertrophy) and occurrence of chronic, spontaneous recurrent partial seizures observed in human TLE. We investigated the influence of a kainate-induced epileptogenic focus on hippocampal neurogenesis, comparing neural stem cell proliferation following status epilepticus and spontaneous recurrent partial seizures. Cell proliferation in the subgranular zone was transiently increased bilaterally after kainate treatment. As a result, neurogenesis was stimulated in the contralateral dentate gyrus. In contrast, the epileptic hippocampus exhibited a strongly reduced neurogenic potential, even after onset of spontaneous recurrent partial seizures, possibly due to an alteration of the neurogenic niche in the subgranular zone. These results show that neurogenesis does not contribute to the formation of the epileptic focus and may be affected when dispersion of dentate gyrus granule cells occurs. Therefore, in patients with TLE, hippocampal sclerosis and granule cell dispersion may play a significant role in disrupting the potential for hippocampal neurogenesis.

Hippocampal progenitor cells express nestin following cerebral ischemia in rats

This study addresses whether hippocampal progenitor cells express nestin following cerebral ischemia in rats. Cell counts within the hippocampal hilus were significantly greater following severe (eight-vessel occlusion) ischemia than following intermediate (four-vessel occlusion) ischemia (1527+/-87/mm2 vs. 918+/-71/mm2). Bromedeoxyuridine-positive cell counts were significantly higher with severe ischemia than with intermediate ischemia or in sham-operated animals, respectively (368+/-45, 43+/-14 and 7+/-1/mm2). In the eight-vessel occlusion group, 47+/-8/mm2 bromedeoxyuridine-labeled cells expressed nestin, significantly higher than in the four-vessel occlusion group and sham-operated animals (1+/-1 and 1+/-0/mm2, P<0.01 vs. eight-vessel occlusion, respectively). Confocal microscopy verified that a subset of the bromedeoxyuridine-positive cells expressed nestin. In conclusion, severe ischemia elicits nestin expression in hippocampal progenitor cells in rats.

Neuropeptide Y stimulates neuronal precursor proliferation in the post-natal and adult dentate gyrus

Adult dentate neurogenesis is important for certain types of hippocampal-dependent learning and also appears to be important for the maintenance of normal mood and the behavioural effects of antidepressants. Neuropeptide Y (NPY), a peptide neurotransmitter released by interneurons in the dentate gyrus, has important effects on mood, anxiety-related behaviour and learning and memory. We report that adult NPY receptor knock-out mice have significantly reduced cell proliferation and significantly fewer immature doublecortin-positive neurons in the dentate gyrus. We also show that the neuroproliferative effect of NPY is dentate specific, is Y1-receptor mediated and involves extracellular signal-regulated kinase (ERK)1/2 activation. NPY did not exhibit any effect on cell survival in vitro but constitutive loss of the Y1 receptor in vivo resulted in greater survival of newly generated neurons and an unchanged total number of dentate granule cells. These results show that NPY stimulates neuronal precursor proliferation in the dentate gyrus and suggest that NPY-releasing interneurons may modulate dentate neurogenesis.