Intraventricular administration of BDNF increases the number of newly generated neurons in the adult olfactory bulb

Notch: from neural development to neurological disorders

Notch is an integral membrane protein that functions as receptor for ligands such as jagged and delta that are associated with the surface of neighboring cells. Upon ligand binding, notch is proteolytically cleaved within its transmembrane domain by presenilin-1 (the enzymatic component of the gamma-secretase complex) resulting in the release of a notch intracellular domain which translocates to the nucleus where it regulates gene expression. Notch signaling plays multiple roles in the development of the CNS including regulating neural stem cell (NSC) proliferation, survival, self-renewal and differentiation. Notch is also present in post-mitotic neurons in the adult CNS wherein its activation influences structural and functional plasticity including processes involved in learning and memory. Recent findings suggest that notch signaling in neurons, glia, and NSCs may be involved in pathological changes that occur in disorders such as stroke, Alzheimer's disease and CNS tumors. Studies of animal models suggest the potential of agents that target notch signaling as therapeutic interventions for several different CNS disorders.

Effects of fluoxetine and venlafaxine on serum brain derived neurotrophic factor levels in depressed patients

BACKGROUND

Several studies demonstrated that depressed patients had low serum BDNF levels which correlated with the severity of their depression, and antidepressant treatment increases levels of serum BDNF in depressed patients. It was speculated that agents acting on both noradrenergic and serotonergic transporters might have a greater influence on BDNF levels. The aim of our study was to determine effects of venlafaxine vs. fluoxetine on serum BDNF levels in depressive patients.

METHODS

Forty-three patients diagnosed as major depressive disorder according to DSM-IV are included in the study. Forty-three patients were randomized to take fluoxetine (22 cases) or venlafaxine (21 cases). Serum levels of BDNF were measured by ELISA at baseline and 6 weeks after the start of treatment.

RESULTS

Baseline levels of BDNF were not significantly different between the patient group and the controls. But male patients and the male controls showed statistical differences with respect to baseline BDNF levels. BDNF levels of the patient group did not change with treatment. Yet, the increase of BDNF levels was close to statistically significant in the fluoxetine group, whereas not significant in the venlafaxine group. There were no significant differences in baseline and 6th week BDNF levels between the responders and the non-responders.

CONCLUSION

Further studies controlling for a wide variety of confounding variables are needed, which may help to reach a clear conclusion about the potential of BDNF as a biomarker for depression or as a predictor of antidepressant efficacy.

Brain-derived neurotrophic factor signaling does not stimulate subventricular zone neurogenesis in adult mice and rats

In rodents, the adult subventricular zone (SVZ) generates neuroblasts which migrate to the olfactory bulb (OB) and differentiate into interneurons. Recent work suggests that the neurotrophin Brain-Derived Neurotrophic Factor (BDNF) can enhance adult SVZ neurogenesis, but the mechanism by which it acts is unknown. Here, we analyzed the role of BDNF and its receptor TrkB in adult SVZ neurogenesis. We found that TrkB is the most prominent neurotrophin receptor in the mouse SVZ, but only the truncated, kinase-negative isoform (TrkB-TR) was detected. TrkB-TR is expressed in SVZ astrocytes and ependymal cells, but not in neuroblasts. TrkB mutants have reduced SVZ proliferation and survival and fewer new OB neurons. To test whether this effect is cell-autonomous, we grafted SVZ cells from TrkB knock-out mice (TrkB-KO) into the SVZ of wild-type mice (WT). Grafted progenitors generated neuroblasts that migrated to the OB in the absence of TrkB. The survival and differentiation of granular interneurons and Calbindin(+) periglomerular interneurons seemed unaffected by the loss of TrkB, whereas dopaminergic periglomerular neurons were reduced. Intra-ventricular infusion of BDNF yielded different results depending on the animal species, having no effect on neuron production from mouse SVZ, while decreasing it in rats. Interestingly, mice and rats also differ in their expression of the neurotrophin receptor p75. Our results indicate that TrkB is not essential for adult SVZ neurogenesis and do not support the current view that delivering BDNF to the SVZ can enhance adult neurogenesis.

Sexual dimorphic stages affect both proliferation and serotonergic innervation in the adult rostral migratory stream

One of the sexual dimorphic differences in adult rodents is neural proliferation. Here we demonstrate that physiological hormone stages can modulate this proliferation in the adult forebrain. Female mice, both pregnant and synchronized in oestrus, exhibited higher proliferating cell percentages than males in both the rostral migratory stream (RMS) and the olfactory bulb (OB). Moreover, although the hormonal component also influenced the subventricular zone (SVZ), no differences in proliferation were observed in this region. In addition, both groups of females had higher numbers of serotonergic fibres in these regions. Serotonin may therefore be related to the mechanism of action by which hormones can affect cell proliferation of this brain region. We also evaluated cell death in the SVZ in males and females, finding that this was higher in the former. Taken together, our results support the idea that in female rodents more neuroblasts are able to reach the RMS and then proliferate, apoptosis being an additional mechanism affecting the low proliferation of cells in the RMS and OB in males. Thus, proliferation in the RMS is influenced by sexual dimorphism.

Glucocorticoid signaling and exercise-induced downregulation of the mineralocorticoid receptor in the induction of adult mouse dentate neurogenesis by treadmill running

Physical exercise is known to promote adult neurogenesis, although the underlying mechanisms remain unclear. Glucocorticoid (corticosterone in rodents) is a factor that is known to affect neurogenesis. As physical exercise modulates corticosterone secretion, we hypothesized that corticosterone signaling is involved in exercise-induced adult neurogenesis. We chose treadmill running (TR) to accurately define the intensity and duration of exercise. Our results showed that 5 weeks of TR increased the doublecortin (DCX)-positive neuronal progenitor cells (NPCs) in adult hippocampus and transiently increased the serum corticosterone level at the end of the TR protocol. This protocol reduced the levels of hippocampal mineralocorticoid receptor (MR); however, glucocorticoid receptor levels were unaltered. We then investigated whether reducing corticosterone levels by bilateral adrenalectomy (ADX) attenuated the TR-enhanced adult neurogenesis. Our results showed that ADX not only blocked the TR-induced downregulation of MR, but also reduced the number of TR-enhanced NPCs. In order to examine the role of MR downregulation in TR-induced adult neurogenesis, animals were treated repeatedly with a selective MR antagonist, spironolactone, for 3 weeks. The results revealed that spironolactone increased the number of spontaneously occurring and TR-induced NPC in the dentate area. Further analysis revealed that spironolactone treatment did not alter precursor cell proliferation, but increased the number of DCX-positive NPCs, suggesting that blockage of MR signaling either facilitates the differentiation of progenitor cells towards neurons and/or enhances the survival of NPCs. Taken together, the data indicated that induction of NPCs in the dentate area of adult hippocampus by TR is partly due to the downregulation of glucocorticoid/MR signaling, which subsequently enhances differentiation along a neuronal lineage and/or NPC survival.

Adult hippocampal neurogenesis: regulation, functional implications, and contribution to disease pathology

It is now well established that the mammalian brain has the capacity to produce new neurons into adulthood. One such region that provides the proper milieu to sustain progenitor cells and is permissive to neuronal fate determination is located in the dentate gyrus of the hippocampus. This review will discuss in detail the complex process of adult hippocampal neurogenesis, including proliferation, differentiation, survival, and incorporation into neuronal networks. The regulation of this phenomenon by a number of factors is described, including neurotransmitter systems, growth factors, paracrine signaling molecules, neuropeptides, transcription factors, endogenous psychotropic systems, sex hormones, stress, and others. This review also addresses the functional significance of adult born hippocampal granule cells with regard to hippocampal circuitry dynamics and behavior. Furthermore, the relevance of perturbations in adult hippocampal neurogenesis to the pathophysiology of various disease states, including depression, schizophrenia, epilepsy, and diabetes are examined. Finally, this review discusses the potential of using hippocampal neurogenesis as a therapeutic target for these disorders.

Nerve growth factor and doublecortin expression correlates with improved outcome in children with severe traumatic brain injury

BACKGROUND

In the adult brain, migrating neuroblasts can replace damaged neurons after severe traumatic brain injury (TBI). Little is known about which factors determine the magnitude and amplification of neurogenesis after TBI, but there are some evidences that the nerve growth factor (NGF) and the doublecortin (DCX) can influence neurogenesis and neuronal repair.

METHODS

This study investigates the NGF and DCX levels in the cerebrospinal fluid of 12 children with severe TBI and 12 matched controls, to determine the correlation between the expression of both these factors and the patients outcome. We collected cerebrospinal fluid samples 2 hours (Time T1) and 48 hours (Time T2) after brain injury. NGF levels were measured using a two-site immunoenzymatic assay, whereas the DCX expression by a Western blot analysis.

RESULTS

At time T1 and T2, children with the best outcomes had higher levels of NGF than children with poor outcomes. Evaluating the change of NGF levels from time T1 to time T2, we found that the NGF up-regulation in the early time after injury was significantly associated with good outcomes of patients. Concomitantly, the expression of DCX increased only in patients with NGF up-regulation from time T1 to time T2. In others patients and in controls the expression of DCX remained unchanged.

CONCLUSION

Based on these results, we hypothesize that NGF and DCX contribute to the mechanisms of neuroprotection and neuronal connection reorganization after TBI, playing a key role in the outcome of these patients.

Antidepressant-like behavioral effects of IGF-I produced by enhanced serotonin transmission

Previous research has suggested that mobilization of neurotrophic factors, such as insulin-like growth factor I (IGF-I), can be involved in the effects of antidepressant treatments. The current experiments showed that IGF-I leads to antidepressant-like effects in the modified rat forced swim test when tested 3 days, but not 1 day, after i.c.v. administration. These effects were sustained longer than the antidepressants paroxetine and desipramine. In addition, blockade of the IGF-I receptor with the IGF-I antagonist JB1 30 min before IGF-I administration prevented the antidepressant-like effects of IGF-I. However, when JB1 was administered 3 days after IGF-I administration and 30 min prior to testing, the antidepressant-like effects of IGF-I were still present suggesting that IGF-1 produces a long-term activation of neural systems involved in the antidepressant response. Because the pattern of antidepressant-like effects of IGF-I resembled those of selective serotonin reuptake inhibitors, the role of serotonin in the behavioral effects of IGF-I was studied. Depletion of serotonin, by the tryptophan hydroxylase inhibitor para-chlorophenylalanine, blocked the antidepressant-like effects of IGF-I. Administration of IGF-I increased basal serotonin levels in the ventral hippocampus and altered the effects of acute citalopram. IGF-I administration did not change hippocampal cell proliferation at the 3-day timepoint when behavioral effects were seen. In addition, IGF-I did not alter the expression of mRNA levels of tryptophan hydroxylase or SERT in the brain stem, or [3H] citalopram binding in the hippocampus or cortex. Thus, IGF-I administration initiates a long-lasting cascade of neurochemical effects involving increased serotonin levels that results in antidepressant-like behavioral effects.

Neural progenitor potential in cultured Müller glia: effects of passaging and exogenous growth factor exposure

The Müller radial glial cell is the principal support cell of the adult mammalian retina. Recent reports suggest that these cells retain the capacity to proliferate, express phenotypes reminiscent of retinal progenitor cells (RPC) and generate neuron-like progeny. We isolated rodent Müller cells and generated cultures that could be passaged under conditions used in neural stem/progenitor cell colonies. We demonstrate that during the early period of primary culture, Müller glia proliferate into sphere colonies and express a select regimen of phenotypes normally seen in RPCs. This effect correlates temporally with the loss of retinal neurons post-dissection. When chronically maintained in vitro, Müller cells can be repeatedly passaged, and up-regulate early RPC phenotypes that are suggestive of cellular de-differentiation. Furthermore, exposure of Müller glial cultures to differentiating conditions containing growth factors stimulates Müller glia to up-regulate phenotypes associated with retinal neurons. These data provide further evidence that isolated, adult Müller glia retain functional and phenotypic features of RPCs.

Noninvasive and quantitative monitoring of adult neuronal stem cell migration in mouse brain using bioluminescence imaging

It is now generally accepted that continuous neurogenesis occurs in the adult mammalian brain, including that of humans. Modulation of adult neurogenesis can provide therapeutic benefits for various brain disorders, including stroke and Parkinson's disease. The subventricular zone-olfactory bulb pathway is one of the preferred model systems by which to study neural stem cell proliferation, migration, and differentiation in adult rodent brain. Research on adult neurogenesis would greatly benefit from reliable methods for long-term noninvasive in vivo monitoring. We have used lentiviral vectors encoding firefly luciferase to stably mark endogenous neural stem cells in the mouse subventricular zone. We show that bioluminescence imaging (BLI) allows quantitative follow-up of the migration of adult neural stem cells into the olfactory bulb in time. Moreover, we propose a model to fit the kinetic data that allows estimation of migration and survival times of the neural stem cells using in vivo BLI. Long-term expression of brain-derived neurotrophic factor in the subventricular zone attenuated neurogenesis, as detected by histology and BLI. In vivo monitoring of the impact of drugs or genes on adult neurogenesis is now within reach.

Fluoxetine-induced proliferation and differentiation of neural progenitor cells isolated from rat postnatal cerebellum

Previous studies have shown that the serotonin-reuptake inhibitor (SSRI) fluoxetine affects neural progenitors derived from postnatal cerebellum or adult hippocampus and stimulates their proliferation. In the human cerebellum, the proliferation of cerebellar granule cells (CGC) continues until the 11th postnatal month and could be influenced in infants by breastfeeding-delivered SSRIs. Current information about fluoxetine effects on postnatal cerebellar neural progenitors is limited. Here we report the characterization of fluoxetine actions on rat postnatal cerebellar neural progenitors. RT-PCR and immunostaining revealed the expression of serotonin transporter (SERT), 5HT(1A) receptors, tryptophan hydroxylase (TPH), and serotonin (5HT). Protracted in vitro fluoxetine treatment increased cell proliferation and differentiation. The proliferative effects of fluoxetine, 5HT, and the selective agonist of 5HT(1A) receptors trans-8-hydroxy-2-(N-n-propyl-N-3'-iodo-2'-propenyl)aminotetralin (8-OH-PIPAT) were abolished by the selective antagonist of 5HT(1A) receptors, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY-100635). Furthermore, fluoxetine-induced activation of both the cAMP-response element-binding (CREB) protein and extracellular signal-regulated protein kinases (ERK1/2), which was abolished by the selective inhibitor of MAP kinase kinase (MEK) 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), and increased cyclin D1 expression. All these effects were prevented by WAY-100635. Collectively, our results demonstrate that rat postnatal cerebellum contains neural progenitors capable of proliferating and differentiating in response to fluoxetine exposure, possibly through the activation of 5HT(1A) receptors. The relevance of these findings for possible SSRI effects on the developing postnatal/infant human cerebellum should be explored.

Identification of newborn cells by BrdU labeling and immunocytochemistry in vivo

Bromodeoxyuridine, variously abbreviated as BrdU, BudR, and BrdUrd, is a halogenated thymidine analog that is permanently integrated into the DNA of dividing cells during DNA synthesis in S phase. BrdU can be immunocytochemically detected in vitro and in vivo, allowing the identification of cells that were dividing the period of BrdU exposure. In vivo, it has been used to identify the "birthdate" of cells during development, to examine the fate of postnatally generated cells, and to label cells before transplantation, for subsequent identification.

Variant brain-derived neurotrophic factor (Val66Met) alters adult olfactory bulb neurogenesis and spontaneous olfactory discrimination

Neurogenesis, the division, migration, and differentiation of new neurons, occurs throughout life. Brain derived neurotrophic factor (BDNF) has been identified as a potential signaling molecule regulating neurogenesis in the subventricular zone (SVZ), but its functional consequences in vivo have not been well defined. We report marked and unexpected deficits in survival but not proliferation of newly born cells of adult knock-in mice containing a variant form of BDNF [a valine (Val) to methionine (Met) substitution at position 66 in the prodomain of BDNF (Val66Met)], a genetic mutation shown to lead to a selective impairment in activity-dependent BDNF secretion. Utilizing knock-out mouse lines, we identified BDNF and tyrosine receptor kinase B (TrkB) as the critical molecules for the observed impairments in neurogenesis, with p75 knock-out mice showing no effect on cell proliferation or survival. We then localized the activated form of TrkB to a discrete population of cells, type A migrating neuroblasts, and demonstrate a decrease in TrkB phosphorylation in the SVZ of Val66Met mutant mice. With these findings, we identify TrkB signaling, potentially through activity dependent release of BDNF, as a critical step in the survival of migrating neuroblasts. Utilizing a behavioral task shown to be sensitive to disruptions in olfactory bulb neurogenesis, we identified specific impairments in spontaneous olfactory discrimination, but not general olfactory sensitivity or habituation to olfactory stimuli in BDNF mutant mice. Through these observations, we have identified novel links between genetic variant BDNF and adult neurogenesis in vivo, which may contribute to significant impairments in olfactory function.

Neurogenesis and exercise: past and future directions

Research in humans and animals has shown that exercise improves mood and cognition. Physical activity also causes a robust increase in neurogenesis in the dentate gyrus of the hippocampus, a brain area important for learning and memory. The positive correlation between running and neurogenesis has raised the hypothesis that the new hippocampal neurons may mediate, in part, improved learning associated with exercise. The present review gives an overview of research pertaining to exercise-induced cell genesis, its possible relevance to memory function and the cellular mechanisms that may be involved in this process.

Intraventricular nerve growth factor infusion improves cerebral blood flow and stimulates doublecortin expression in two infants with hypoxic-ischemic brain injury

OBJECTIVE AND IMPORTANCE

Hypoxic-ischemic brain injuries in childhood are associated with poor neurological outcome. Recently, experimental and clinical works show that nerve growth factor (NGF) reduces neurological deficits and promotes endothelial cells proliferation and angiogenesis following hypoxic-ischemic brain injuries. After brain stroke, new neurons express a protein, called doublecortin (DCX), which indicates a new marker for neurogenesis and migrating neuroblasts. This study investigates the effects of intraventricular NGF administration in two infants with severe hypoxic-ischemic brain damage and its role in both the cerebral perfusion and neurogenesis.

CLINICAL PRESENTATION

Two infants, aged 8 and 13 months, with hypoxic-ischemic brain damage, secondary to prolonged cardiorespiratory arrest, were treated with intraventricular NGF administration. Before the therapy, both infants were comatose, aphasic and showed flaccid tetraparesis. After 1 month NGF treatment, their neurological conditions improved, electro-encephalography (EEG) examinations showed increased alpha/theta ratio, and single photon emission computed tomography (SPECT) works demonstrated a better cerebral perfusion. The DCX expression in the cerebrospinal fluid (CSF) increased concomitantly with increasing levels of NGF.

INTERVENTION

The drug utilized was 2.5S NGF purified and lyophilized from male mouse submaxillary glands. The NGF administration was started 4 months after ischemic brain injury. NGF (0.1 mg) was administered via the external drainage catheter into the right cerebral ventricle once a day for 10 consecutive days.

CONCLUSION

Our study shows that the intraventricular NGF administration improves the cerebral perfusion and stimulates the pathway of neurogenesis differentiation with the activation of DCX biosynthesis.

Brain-derived neurotropic factor/TrkB signaling in the pathogenesis and novel pharmacotherapy of schizophrenia

The role of neurotropins, predominantly brain-derived neurotropic factor (BDNF), has been implicated in the pathophysiology as well as treatment outcome of schizophrenia. Both human and rodent studies indicate that the beneficial effects of antipsychotic drugs are mediated, at least in part, through BDNF and its receptor, TrkB. This review will discuss the available data on the levels of BDNF and TrkB in subjects with schizophrenia and in animals with and without conventional antipsychotics. The data concerning the impact of the antipsychotic drugs on BDNF/TrkB signaling will also be discussed. More importantly, this review will provide future perspective on BDNF/TrkB signaling as a novel molecular target to correct the pathogenesis and improve the long-term clinical outcome by treatments with conventional and adjunctive drugs.

Induction of neostriatal neurogenesis slows disease progression in a transgenic murine model of Huntington disease

Ependymal overexpression of brain-derived neurotrophic factor (BDNF) stimulates neuronal addition to the adult striatum, from subependymal progenitor cells. Noggin, by suppressing subependymal gliogenesis and increasing progenitor availability, potentiates this process. We asked whether BDNF/Noggin overexpression might be used to recruit new striatal neurons in R6/2 huntingtin transgenic mice. R6/2 mice injected with adenoviral BDNF and adenoviral Noggin (AdBDNF/AdNoggin) recruited BrdU(+)betaIII-tubulin(+) neurons, which developed as DARPP-32(+) and GABAergic medium spiny neurons that expressed either enkephalin or substance P and extended fibers to the globus pallidus. Only AdBDNF/AdNoggin-treated R6/2 mice harbored migrating doublecortin-defined neuroblasts in their striata, and the new neurons expressed p27 as a marker of mitotic quiescence after parenchymal integration. AdBDNF/AdNoggin-treated R6/2 mice sustained their rotarod performance and open-field activity and survived longer than did AdNull-treated and untreated controls. Neither motor performance nor survival improved in R6/2 mice treated only with AdBDNF, and intraventricular infusion of the mitotic inhibitor Ara-C completely blocked the performance and survival effects of AdBDNF/AdNoggin, suggesting that the benefits of AdBDNF/AdNoggin derived from neuronal addition. Thus, BDNF and Noggin induced striatal neuronal regeneration, delayed motor impairment, and extended survival in R6/2 mice, suggesting a new therapeutic strategy in Huntington disease.

Neural stem cells improve memory in an inducible mouse model of neuronal loss

Neuronal loss is a major pathological outcome of many common neurological disorders, including ischemia, traumatic brain injury, and Alzheimer disease. Stem cell-based approaches have received considerable attention as a potential means of treatment, although it remains to be determined whether stem cells can ameliorate memory dysfunction, a devastating component of these disorders. We generated a transgenic mouse model in which the tetracycline-off system is used to regulate expression of diphtheria toxin A chain. After induction, we find progressive neuronal loss primarily within the hippocampus, leading to specific impairments in memory. We find that neural stem cells transplanted into the brain after neuronal ablation survive, migrate, differentiate and, most significantly, improve memory. These results show that stem cells may have therapeutic value in diseases and conditions that result in memory loss.

The effect of neurodegenerative diseases on the subventricular zone

During brain development, one of the most important structures is the subventricular zone (SVZ), from which most neurons are generated. In adulthood the SVZ maintains a pool of progenitor cells that continuously replace neurons in the olfactory bulb. Neurodegenerative diseases induce a substantial upregulation or downregulation of SVZ progenitor cell proliferation, depending on the type of disorder. Far from being a dormant layer, the SVZ responds to neurodegenerative disease in a way that makes it a potential target for therapeutic intervention.

Fate determinant expression in the lesioned brain: Olig2 induction and its implications for neuronal repair

Although stem cells persist in restricted regions of the adult mammalian central nervous system (CNS), replacement of neurons does not take place in most regions in intact conditions or after injury. In the last years, proliferative multipotent cells have been isolated from the parenchyma of many CNS regions considered constitutively nonneurogenic, suggesting that the nonneurogenic CNS parenchyma is endowed with a latent neurogenic potential that might be exploited for neuronal replacement. However, neurogenic fate determinants acting during development and in the germinative zones are not expressed in the intact brain and after lesion, thus arguing against the presence of neurogenic competence in parenchymal precursors. Conversely, the basic helix-loop-helix transcription factor Olig2 is widely expressed in subsets of glia cells and progenitors, and it is strongly induced at different sites by both acute and chronic injury, albeit with different mechanisms. Antagonizing Olig2 function in cells proliferating after an acute lesion leads to the upregulation of the neurogenic determinant Pax6 and results in a significant number of newly generated immature neurons. Therefore, Olig2 acts as a repressor of neurogenesis in cells reacting to brain injury. Finding the proper way to fully derepress the neurogenic determinants in these cells, together with providing favorable environmental signals, may represent an effective approach towards evoking neuronal repair from parenchymal precursors.

BDNF/ TrkB interaction regulates migration of SVZ precursor cells via PI3-K and MAP-K signalling pathways

Neuroblasts born in the subventricular zone (SVZ) migrate along the rostral migratory stream, reaching the olfactory bulb (OB) where they differentiate into local interneurons. Several extracellular factors have been suggested to control specific steps of this process. The brain-derived neurotrophic factor (BDNF) has been demonstrated to promote morphological differentiation and survival of OB interneurons. Here we show that BDNF and its receptor TrkB are expressed in vivo throughout the migratory pathway, implying that BDNF might also mediate migratory signals. By using in vitro models we demonstrate that BDNF promotes migration of SVZ neuroblasts, acting both as inducer and attractant through TrkB activation. We show that BDNF induces cAMP response element-binding protein (CREB) activation in migrating neuroblasts via phosphatidylinositol 3-kinase (PI3-K) and mitogen-activated protein kinase (MAP-K) signalling. Pharmacological blockade of these pathways on SVZ explants significantly reduces CREB activation and impairs neuronal migration. This study identifies a function of BDNF in the SVZ system, which involves multiple protein kinase pathways leading to neuroblast migration.

Creating a neurogenic environment: The role of BDNF and FGF2

Regional environmental cues present in the adult brain determine the fate of adult neural progenitor cells. To determine whether the growth factors BDNF or FGF2 can create a neurogenic environment outside the SVZ, we used AAV(1/2)-mediated gene transfer to produce ectopic BDNF or FGF2 expression in the normal adult rat striatum and transplanted SVZ-derived progenitor cells into this region. We observed that ectopic expression of BDNF in the striatum promoted neuronal differentiation of transplanted adult neural progenitor cells, while FGF2 expression supported the survival and proliferation of transplanted progenitor cells in the adult striatum. However, region-specific neuronal differentiation of transplanted progenitor cells was not observed in the adult striatum, suggesting ectopic BDNF or FGF2 expression was insufficient for the generation of mature neuronal phenotypes. This study provides direct in vivo evidence that ectopic striatal expression of either BDNF or FGF2 can induce neurogenesis in non-neurogenic regions of the adult brain.

AAV-mediated delivery of BDNF augments neurogenesis in the normal and quinolinic acid-lesioned adult rat brain

Brain-derived neurotrophic factor (BDNF) plays a major role in regulating the survival and fate of progenitor cells in the adult brain. In order to extend previous observations in the normal adult brain and advance our knowledge regarding the effect of BDNF on neurogenesis in the injured brain, this study directly compared the effect of BDNF on basal and injury-induced neurogenesis in relation to progenitor cell distribution and levels of neuronal differentiation and survival. BDNF was overexpressed in the subventricular zone (SVZ) via recombinant adeno-associated virus (AAV(1/2)) delivery, and newly generated cells were identified using bromodeoxyuridine (BrdU) labelling. Selective striatal cell loss was induced in a subgroup of rats by unilateral striatal injection of quinolinic acid (QA) 21 days after AAV(1/2) injection. In the normal brain, BDNF overexpression significantly increased BrdU-positive cell numbers in the rostral migratory stream, indicating enhanced progenitor cell migration. Following QA lesioning, we observed a reduction in BrdU immunoreactivity in the SVZ. Overexpression of BDNF restored BrdU-positive cell numbers in the QA-lesioned SVZ to that observed in the normal brain. Most significantly, BDNF enhanced the recruitment of progenitor cells to the QA-lesioned striatum and promoted neuronal differentiation in both the normal and QA-lesioned striatum. Our findings indicate that BDNF augments the recruitment, neuronal differentiation and survival of progenitor cells in both neurogenic and non-neurogenic regions of the normal or QA-lesioned brain. Enhanced expression of BDNF may therefore be a viable strategy for augmenting neurogenesis from endogenous progenitor cells.

Brain-derived neurotrophic factor and its receptor tropomyosin-related kinase B in the mechanism of action of antidepressant therapies

The focus of this review is to critically examine and review the literature on the role of brain-derived neurotrophic factor (BDNF) and its primary receptor, tropomyosin-related kinase B (TrkB), in the actions of pharmacologically diverse antidepressant treatments for depression. This will include a review of the studies on the regulation of BDNF and TrkB by different types of antidepressant drug treatments and animal in models of depression, as well as altered levels of BDNF and TrkB in the blood and postmortem brain of patients with depression. Results from clinical and basic studies have demonstrated that stress and depression decrease BDNF expression and neurogenesis and antidepressant treatment reverses or blocks these effects, leading to the neurotrophic hypothesis of depression. Clinical studies demonstrate an association between BDNF levels and several disorders, including depression, epilepsy, bipolar disorder, Parkinson's and Alzheimer's diseases. Physical activity and diet exert neurotrophic effects and positively modulate BDNF levels. A common single nucleotide polymorphism (SNP) in the BDNF gene, a methionine substitution for valine, is associated with alterations in brain anatomy and memory, but what role it has in clinical disorders is unclear. Findings suggest that early childhood events and adult stress produce neurodegenerative alterations in the brain that can eventually cause breakdown of information processing in the neuronal networks regulating mood. Antidepressant treatments elevate activity-dependent neuronal plasticity by activating BDNF, thereby gradually restoring network function and ultimately mood.

Progenitor cells and adult neurogenesis in neurodegenerative diseases and injuries of the basal ganglia

1. The subventricular zone (SVZ) of the forebrain that overlies the caudate nucleus is one of the principal brain regions in which neurogenesis occurs in the human brain, throughout life. 2. In response to the degeneration that occurs in the caudate nucleus in Huntington's disease, or in the caudate nucleus or cortex in stroke models, the SVZ increases the production of progenitor cells that migrate towards the site of the damage where they can differentiate into mature neurons and glial cells. The SVZ contains three main cell types and these are progenitor cells, glial cells and migratory neuroblasts; glial cells are the most common cell type and, in response to Huntington's disease, most of the SVZ cell proliferation is glial, but the number of precursor and neuroblasts is also increased. 3. The SVZ is enriched in neuroactive compounds, such as neuropeptide Y and gamma-aminobutyric acid receptor subunits gamma2, which stimulate ongoing neurogenesis. Interestingly, these stimulating cues are upregulated in the SVZ in response to Huntington's disease. Thus, the SVZ comprises heterogeneous cell types that are maintained in an environment that is permissive to neurogenesis and gliogenesis, and responds to neurodegenerative changes in adjacent brain regions by increasing progenitor cell proliferation and neurogenesis in an attempt to replace the cells that die as a result of neurodegeneration.

Changes in neurogenesis in dementia and Alzheimer mouse models: are they functionally relevant?

Alzheimer's disease and related dementias are devastating disorders that lead to the progressive decline of cognitive functions. Characteristic features are severe brain atrophy, paralleled by accumulation of beta amyloid and neurofibrillary tangles. With the discovery of neurogenesis in the adult brain, the hopes have risen that these neurodegenerative conditions could be overcome, or at least ameliorated, by the generation of new neurons. The location of the adult neurogenic zones in the hippocampus and the lateral ventricle wall, close to corpus callosum and neocortex, indicates strategic positions for potential repair processes. However, we also need to consider that the generation of new neurons is possibly involved in cognitive functions and could, therefore, be influenced by disease pathology. Moreover, aberrant neurogenic mechanisms could even be a part of the pathological events of neurodegenerative diseases. It is the scope of this review to summarize and analyze the recent data from neurogenesis research with respect to Alzheimer's disease and its animal models.

Estrogen and adult neurogenesis in the amygdala and hypothalamus

In mammals, adult neurogenesis has been extensively studied in the dentate gyrus of the hippocampus and subventricular zone. However, newly proliferated neurons have also been documented in other brain regions, including the amygdala and hypothalamus. In this review, we will examine the evidence for new neurons in the adult amygdala and hypothalamus and then discuss how environmental influences can alter cell proliferation. As some of these environmental effects may be attributed to changes in the levels of circulating hormones, we will provide evidence for estrogen-mediated cell proliferation among different species and between sexes. Finally, we will review recent data suggesting that new neurons may become functionally significant in adulthood.

p75 neurotrophin receptor expression defines a population of BDNF-responsive neurogenic precursor cells

Although our understanding of adult neurogenesis has increased dramatically over the last decade, confusion still exists regarding both the identity of the stem cell responsible for neuron production and the mechanisms that regulate its activity. Here we show, using flow cytometry, that a small population of cells (0.3%) within the stem cell niche of the rat subventricular zone (SVZ) expresses the p75 neurotrophin receptor (p75(NTR)) and that these cells are responsible for neuron production in both newborn and adult animals. In the adult, the p75(NTR)-positive population contains all of the neurosphere-producing precursor cells, whereas in the newborn many of the precursor cells are p75(NTR) negative. However, at both ages, only the neurospheres derived from p75(NTR)-positive cells are neurogenic. We also show that neuron production from p75(NTR)-positive but not p75(NTR)-negative precursors is greatly enhanced after treatment with brain-derived neurotrophic factor (BDNF) or nerve growth factor. This effect appears to be mediated specifically by p75(NTR), because precursor cells from p75(NTR)-deficient mice show a 70% reduction in their neurogenic potential in vitro and fail to respond to BDNF treatment. Furthermore, adult p75(NTR)-deficient mice have significantly reduced numbers of PSA-NCAM (polysialylated neural cell adhesion molecule)-positive SVZ neuroblasts in vivo and a lower olfactory bulb weight. Thus, p75(NTR) defines a discrete population of highly proliferative SVZ precursor cells that are able to respond to neurotrophin activation by increasing neuroblast generation, making this pathway the most likely mechanism for the increased neurogenesis that accompanies raised BDNF levels in a variety of disease and behavioral situations.

Different networks, common growth factors: shared growth factors and receptors of the vascular and the nervous system

Growth factors and their respective receptors are key regulators during development and for homeostasis of the nervous system. In addition, changes in growth factor function, availability or downstream signaling is involved in many neuropathological disorders like Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke and brain tumours. Research of the recent years revealed that some growth factors, initially discovered as neural growth factors are also affecting blood vessels [e.g. nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF)]. Likewise, vascular growth factors, such as vascular endothelial growth factor (VEGF), which was previously described as an endothelial cell specific mitogen, also affect neural cells. The discovery of shared growth factors affecting the vascular and the nervous system is of relevance for potential therapies of vascular and neurological diseases. This review aims to give an overview about the growing field of common growth factors and receptors within the two different networks.

Intravenous brain-derived neurotrophic factor enhances poststroke sensorimotor recovery and stimulates neurogenesis

BACKGROUND AND PURPOSE

The discovery of spontaneous neuronal replacement in the adult brain has shifted experimental stroke therapies toward a combined approach of preventing neuronal cell death and inducing neuronal plasticity. Brain-derived neurotrophic factor (BDNF) was shown to induce antiapoptotic mechanisms after stroke and to reduce infarct size and secondary neuronal cell death. Moreover, in intact animals, BDNF is a potent stimulator of adult neurogenesis.

METHODS

The current study analyzed the effects of BDNF on induction of neuronal progenitor cell migration and sensorimotor recovery after cortical photothrombotic stroke.

RESULTS

Daily intravenous bolus applications of BDNF during the first 5 days after stroke resulted in significantly improved sensorimotor scores up to 6 weeks. At the structural level, BDNF significantly increased neurogenesis in the dentate gyrus and enhanced migration of subventricular zone progenitor cells to the nearby striatum of the ischemic hemisphere. BDNF treatment could not, however, further stimulate progenitor cell recruitment to the cortex.

CONCLUSIONS

These findings consolidate the role of BDNF as a modulator of neurogenesis in the brain and as an enhancer of long-term functional neurological outcome after cerebral ischemia.

Differential response to ischemia in adjacent hippocampalsectors: neuronal death in CA1versus neurogenesis in dentate gyrus

Two hippocampal sectors show distinct responses to transient ischemia: the cornu Ammonis (CA)1 sector undergoes a delayed neuronal death followed by a lack of neuronal generation, while the dentate gyrus (DG) shows slight postischemic damage followed by an increased neurogenesis. Using the monkey experimental paradigm of transient whole brain global ischemia, the 'calpain-cathepsin hypothesis' was formulated in 1998. This hypothesis proposes that following ischemia calpain compromises the integrity of lysosomal membrane, causing a leakage of degrading hydrolytic enzymes--cathepsins--into the cytoplasm. Ischemia induces Ca(2+) mobilization, calpain activation, lysosomal membrane disruption, and cathepsin release, which all occur specifically in the CA1 sector and cause neuronal death. In the postischemic DG, a vascular niche has been implicated in adult neurogenesis, in that adventitial cells of the DG microvascular environment provoke postischemic up-reguation of neurogenesis with the aid of brain-derived neurotrophic factor and polysialylated form of the neural cell adhesion molecule. In parallel, Down's syndrome cell adhesion molecule has recently been shown to be expressed specifically in the neural progenitor cells of DG. In this review, we focus on the monkey experimental paradigm to reveal the remarkable contrasts between CA1 and DG in response to the ischemic insult.

Adult neurogenesis and cellular brain repair with neural progenitors, precursors and stem cells

Recent work in neuroscience has shown that the adult central nervous system (CNS) contains neural progenitors, precursors and stem cells that are capable of generating new neurons, astrocytes and oligodendrocytes. While challenging the previous dogma that no new neurons are born in the adult mammalian CNS, these findings bring with them the future possibilities for development of novel neural repair strategies. The purpose of this review is to present the current knowledge about constitutively occurring adult mammalian neurogenesis, highlight the critical differences between 'neurogenic' and 'non-neurogenic' regions in the adult brain, and describe the cardinal features of two well-described neurogenic regions-the subventricular zone/olfactory bulb system and the dentate gyrus of the hippocampus. We also provide an overview of presently used models for studying neural precursors in vitro, mention some precursor transplantation models and emphasize that, in this rapidly growing field of neuroscience, one must be cautious with respect to a variety of methodological considerations for studying neural precursor cells both in vitro and in vivo. The possibility of repairing neural circuitry by manipulating neurogenesis is an intriguing one, and, therefore, we also review recent efforts to understand the conditions under which neurogenesis can be induced in non-neurogenic regions of the adult CNS. This work aims towards molecular and cellular manipulation of endogenous neural precursors in situ, without transplantation. We conclude this review with a discussion of what might be the function of newly generated neurons in the adult brain, and provide a summary of present thinking about the consequences of disturbed adult neurogenesis and the reaction of neurogenic regions to disease.

Exposure in fetus of methylazoxymethanol in the rat alters brain neurotrophins' levels and brain cells' proliferation

Changes during gestation have been shown to induce brain maldevelopment associated with changes in neurotrophins as nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and neuropsychiatric disorders in humans. A rat model of altered prenatal brain development resembling the onset of schizophrenia has been obtained by administering in fetus methylazoxymethanol (MAM) at gestational day 12 which impairs the growth of limbic pathways between the entorhinal cortex and the hippocampus. Using the MAM model we studied in young rats the brain levels of both NGF/BDNF and their main receptors, TrkA/TrkB, to investigate whether or not changes in neurotrophins could affect the presence of brain BrdU positive cells. We found increased NGF and BDNF protein levels, associated with elevated TrkA and TrkB expression, in the hippocampus, entorhinal cortex, olfactory lobes and subventricular zone (SVZ), brain areas playing a key role in the production and migration of new dividing cells. We also found higher levels of BrdU positive cells in the SVZ and hippocampus but not a significant potentiation in the entorhinal cortex and olfactory lobes. All together the findings indicate that prenatal MAM exposure in young rats may elicit both neurotrophins' elevation and cell proliferation in limbic brain areas.

Repeated electroconvulsive stimuli have long-lasting effects on hippocampal BDNF and decrease immobility time in the rat forced swim test

Electroconvulsive therapy is considered an effective treatment for severe depression. However, the mechanisms for its long-lasting antidepressant efficacy are poorly understood. In the present study, we investigated changes of the immobility time in the forced swim test and brain-derived neurotrophic factor (BDNF) protein after withdrawal from 14-day repeated electroconvulsive stimuli (ECS, 50 mA, 0.2 s) in rats. Immobility time in the forced swim test was markedly decreased 6 h after withdrawal following 14-day ECS treatment. Thereafter, prolongation of the withdrawal period gradually diminished the decreasing effect of immobility time, but significant effects persisted for up to 3 days after the withdrawal. Locomotor activity in the open-field test increased 6 h after withdrawal from the ECS treatment, and the enhanced effect persisted for at least 7 days. The BDNF protein level in the hippocampus was markedly increased 6 h after the withdrawal, and remained high for at least 7 days. These findings provide further evidence that repeated ECS has long-lasting effect on increase in BDNF and locomotor activity and decrease in immobility time in the forced swim test.

Generation of GABAergic and dopaminergic interneurons from endogenous embryonic olfactory bulb precursor cells

During the embryonic period, many olfactory bulb (OB) interneurons arise in the lateral ganglionic eminence (LGE) from precursor cells expressing Dlx2, Gsh2 and Er81 transcription factors. Whether GABAergic and dopaminergic interneurons are also generated within the embryonic OB has not been studied thoroughly. In contrast to abundant Dlx2 and Gsh2 expression in ganglionic eminences (GE), Dlx2 and Gsh2 proteins are not expressed in the E12.5-13.5 mouse OB, whereas the telencephalic pallial domain marker Pax6 is abundant. We found GABAergic and dopaminergic neurons originating from dividing precursor cells in E13.5 OB and in short-term dissociated cultures prepared from the rostral half of E13.5 OB. In OB cultures, 22% of neurons were GAD+, of which 53% were Dlx2+, whereas none expressed Gsh2. By contrast, 70% of GAD+ cells in GE cultures were Dlx2+ and 16% expressed Gsh2. In E13.5 OB slices transplanted with EGFP-labeled E13.5 OB precursor cells, 31.7% of EGFP+ cells differentiated to GABAergic neurons. OB and LGE precursors transplanted into early postnatal OB migrated and differentiated in distinct patterns. Transplanted OB precursors gave rise to interneurons with dendritic spines in close proximity to synaptophysin-positive boutons. Interneurons were also abundant in differentiating OB neural stem cell cultures; the neurons responded to the neurotrophin Bdnf and expressed presynaptic proteins. In vivo, the Bdnf receptor TrkB colocalized with synaptic proteins at the glomeruli. These findings suggest that, in addition to receiving interneurons from the LGE, the embryonic OB contains molecularly distinct local precursor cells that generate mature GABAergic and dopaminergic neurons.

PSA-NCAM in postnatally generated immature neurons of the olfactory bulb: a crucial role in regulating p75 expression and cell survival

In the mammalian brain, ongoing neurogenesis via the rostral migratory stream (RMS) maintains neuronal replacement in the olfactory bulb throughout life. Mechanisms that regulate the final number of new neurons in this system include proliferation, migration and apoptosis. Here we show that the polysialylated isoforms of the neural cell adhesion molecule (PSA-NCAM) act as a pro-survival molecule in immature newborn neurons. Confocal microscopic analysis revealed a threefold increase in TUNEL-positive cells in the subventricular zone (SVZ) and the RMS of transgenic animals lacking the gene encoding NCAM (NCAM(-/-)), as compared with wild types. The enhanced apoptotic cell death occurred specifically in the population of mCD24-positive newborn neurons, but not in GFAP-positive astrocytes. Using in vitro cultures of purified SVZ-derived neurons, we demonstrate that the loss or inactivation of PSA on NCAM, as well as the deletion of NCAM, lead to reduced survival in response to neurotrophins including BDNF and NGF. These changes in cell survival are accompanied by an upregulation of p75 neurotrophin receptor expression in vitro as well as in vivo. Furthermore, the negative effects of PSA-NCAM inactivation on cell survival could be prevented by the pharmacological blockade of the p75 receptor-signaling pathway. We propose that PSA-NCAM may promote survival by controlling the expression of the p75 receptor in developing neurons.

Identification of Proteomic Changes during Differentiation of Adult Mouse Subventricular Zone Progenitor Cells

The use of neural precursor cells (NPCs) represents a promising repair strategy for many neurological disorders. However, the molecular events and biological features that control NPC proliferation and their differentiation into neurons, astrocytes, and oligodendrocytes are unclear. In the present study, we used a comparative proteomics approach to identify proteins that were differentially regulated in NPCs after short-term differentiation. We also used a subcellular fractionation technique for enrichment of nuclei and other dense organelles to identify proteins that were not readily detected in whole cell extracts. In total, 115 distinct proteins underwent expression changes during NPC differentiation. Forty one of these were only identified following subcellular fractionation. These included transcription factors, RNA-processing factors, cell cycle proteins, and proteins that translocate between the nucleus and cytoplasm. Biological network analysis showed that the differentiation of NPCs was associated with significant changes in cell cycle and protein synthesis machinery. Further characterization of these proteins could provide greater insight into the mechanisms involved in regulation of neurogenesis in the adult central nervous system (CNS) and potentially identify points of therapeutic intervention.

Ischemia-Induced Neurogenesis: Role of Growth Factors

The neurogenic response in ischemic brain to growth factors is the net result of cell division and cell survival in specific regions of the brain. To increase the cell number, these physiologic processes should be active. Hence, when growth factors are infused into the brain, they might stimulate survival, cell division, or both to enhance neurogenesis. The end result is the interplay of all the endogenous factors with the infused exogenous factors. It is essential to understand the growth factors and their regulators that are expressed after ischemia if one is to pharmacologically enhance neurogenesis. It seems that a combinational therapy of factors or their inhibitors may provide powerful therapeutic potential for enhancing stroke-induced neurogenesis and restoring the damaged tissue to function.

Neurotrophins in the dentate gyrus

Since the discovery of nerve growth factor (NGF) in the 1950s and brain-derived neurotrophic factor (BDNF) in the 1980s, a great deal of evidence has mounted for the roles of neurotrophins (NGF; BDNF; neurotrophin-3, NT-3; and neurotrophin-4/5, NT-4/5) in development, physiology, and pathology. BDNF in particular has important roles in neural development and cell survival, as well as appearing essential to molecular mechanisms of synaptic plasticity and larger scale structural rearrangements of axons and dendrites. Basic activity-related changes in the central nervous system (CNS) are thought to depend on BDNF modulation of synaptic transmission. Pathologic levels of BDNF-dependent synaptic plasticity may contribute to conditions such as epilepsy and chronic pain sensitization, whereas application of the trophic properties of BDNF may lead to novel therapeutic options in neurodegenerative diseases and perhaps even in neuropsychiatric disorders. In this chapter, I review neurotrophin structure, signal transduction mechanisms, localization and regulation within the nervous system, and various potential roles in disease. Modulation of neurotrophin action holds significant potential for novel therapies for a variety of neurological and psychiatric disorders.

Role of the cholinergic system in regulating survival of newborn neurons in the adult mouse dentate gyrus and olfactory bulb

Neurogenesis in the subgranular zone of the hippocampal dentate gyrus and olfactory bulbs continues into adulthood and has been implicated in the cognitive function of the adult brain. The basal forebrain cholinergic system has been suggested to play a role in regulating neurogenesis as well as learning and memory in these regions. Herein, we report that highly polysialylated neural cell adhesion molecule (PSA-NCAM)-positive immature cells as well as neuronal nuclei (NeuN)-positive mature neurons in the dentate gyrus and olfactory bulb express multiple acetylcholine receptor subunits and make contact with cholinergic fibers. To examine the function of acetylcholine in neurogenesis, we used donepezil (Aricept), a potent and selective acetylcholinesterase inhibitor that improves cognitive impairment in Alzheimer's disease. Intraperitoneal administrations of donepezil significantly enhanced the survival of newborn neurons, but not proliferation of neural progenitor cells in the subgranular zone or the subventricular zone of normal mice. Moreover, donepezil treatment reversed the chronic stress-induced decrease in neurogenesis. Taken together, these results suggest that activation of the cholinergic system promotes survival of newborn neurons in the adult dentate gyrus and olfactory bulb under both normal and stressed conditions.

A progressive and cell non-autonomous increase in striatal neural stem cells in the Huntington's disease R6/2 mouse

Neural stem and progenitor cells are located in the subependyma of the adult forebrain. An increase in adult subependymal cell proliferation is reported after various kinds of brain injury. We demonstrate an expansion of neural precursor cells in the postnatal subependyma in a murine genetic disease model of Huntington's disease (HD), the R6/2 mouse. We used the in vitro neurosphere assay as an index of the number of neural stem cells in vivo and to assess proliferation kinetics in vitro and in vivo bromodeoxyuridine labeling to assess the progenitor cell population and their fates. Disease progression in this model leads to an increase in the numbers of neural stem cells in the adult striatal subependyma. This increase is produced cell non-autonomously by events in the R6/2 brains as the mice become increasingly symptomatic. Once the neural stem cell increase is induced in vivo, it is maintained during in vitro passaging of neural stem cells, but the neural stem cell increase is not reproduced during in vitro passaging of neural stem cells from presymptomatic R6/2 mice. In addition, we show that some of the R6/2 neural progenitor cells show a change from their normal migration destiny toward the olfactory bulb. Instead, some of these cells migrate into the striatum, one of the main affected areas in HD. Our findings demonstrate that HD damage recruits precursor cells in two ways: expansion of neural stem cells and altered migration of progenitor cells.

Environmental enrichment stimulates neurogenesis in apolipoprotein E3 and neuronal apoptosis in apolipoprotein E4 transgenic mice

Neurodegeneration in Alzheimer's disease (AD) is associated with the activation of neurogenesis. The mechanisms underlying this crosstalk between neuronal death and birth and the extent to which it is affected by genetic risk factors of AD are not known. We employed transgenic mice expressing human apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for AD, or expressing human apoE3 (an AD-benign allele), in order to examine the hypothesis that apoE4 tilts the balance between neurogenesis and neuronal cell death in favor of the latter. The results showed an isoform-specific increase in neurogenesis in the hippocampal dentate gyrus (DG) under standard conditions in apoE4-transgenic mice. Environmental stimulation, which increases neurogenesis in the DG of apoE3-transgenic and wild-type mice, had the opposite effect on the apoE4 mice, where it triggered apoptosis while decreasing hippocampal neurogenesis. These effects were specific to the DG and were not observed in the subventricular zone, where neurogenesis was unaffected by either the apoE genotype or the environmental conditions. These in vivo findings demonstrate a linkage between neuronal apoptosis and the impaired neuronal plasticity and cognition of apoE4-transgenic mice, and suggest that similar interactions between apoE4 and environmental factors might occur in AD.

Region specific hypothalamic neuronal activation and endothelial cell proliferation in response to electroconvulsive seizures

BACKGROUND

Major depression is often associated with disturbances in basal biological functions regulated by the hypothalamus. Electroconvulsive therapy (ECT), an efficient anti-depressant treatment, alters the activity of hypothalamic neurons. We have previously shown an increased proliferation of endothelial cells in specific areas of the rat hippocampus in response to electroconvulsive seizure (ECS) treatment, an animal model for ECT. Here we examine the effect of ECS treatment on neuronal activation and endothelial cell proliferation in mid-hypothalamus.

METHODS

Rats received one daily ECS treatment for 5 days and cell proliferation was detected by bromodeoxyuridine (BrdU). The number of cells double-labeled for BrdU and the endothelial cell marker rat endothelial cell antigen-1 was determined. Neuronal activation in response to acute ECS treatment was detected as c-Fos immunoreactivity in an additional experiment.

RESULTS

We demonstrate a correlating pattern of increases in neuronal activation and increased endothelial cell proliferation in the paraventricular nucleus, the supraoptic nucleus, and the ventromedial nucleus of the hypothalamus after ECS treatment.

CONCLUSIONS

Hypothalamic areas with the largest increase in neuronal activation after ECS treatment exhibit increased endothelial cell proliferation. We suggest that similar angiogenic responses to ECT might counteract hypothalamic dysfunction in depressive disorder.

Insulin-like growth factor-I enhances the biological activity of brain-derived neurotrophic factor on cerebrocortical neurons

Insulin-like growth factor (IGF)-I and brain-derived neurotrophic factor (BDNF) act within the brain to enhance neuronal survival and plasticity. We extend these findings by showing that the presence of both neurotrophins is required to depress the rise in intracellular Ca2+ caused by glutamate in primary cultures of cerebrocortical neurons. IGF-I enhanced expression of BDNF receptors (Trk-B) and increased the ability of BDNF to induce ERK1/2 phosphorylation. This IGF-I-induced increase in BDNF responsiveness describes a new interaction between these peptides in the brain.