A novel DCX missense mutation in a family with X-linked lissencephaly and subcortical band heterotopia syndrome inherited from a low-level somatic mosaic mother: Genetic and functional studies

PURPOSE

To study the genetics and functional alteration of a family with X-linked lissencephaly and subcortical band heterotopia.

METHODS

Five affected patients (one male with lissencephaly, four female with subcortical band heterotopia) and their relatives were studied. Sanger sequencing of DCX gene, allele specific PCR and molecular inversion probe technique were performed. Mutant and wild type of the gene products, namely doublecortin, were expressed in cells followed by immunostaining to explore the localization of doublecortin and microtubules in cells. In vitro microtubule-binding protein spin-down assay was performed to quantify the binding ability of doublecortin to microtubules.

KEY FINDINGS

We identified a novel DCX mutation c.785A > G, p.Asp262Gly that segregated with the affected members of the family. Allele specific PCR and molecular inversion probe technique demonstrated that the asymptomatic female carrier had an 8% mutant allele fraction in DNA derived from peripheral leukocytes. This mother had 7 children, 4 of whom were affected and all four affected siblings carried the mutation. Functional study showed that the mutant doublecortin protein had a significant reduction of its ability to bind microtubules.

SIGNIFICANCE

Low level mosaicism could be a cause of inherited risk from asymptomatic parents for DCX related lissencephaly-subcortical band heterotopia spectrum. This is particularly important in terms of genetic counselling for recurrent risk of future pregnancies. The reduced binding affinity of mutant doublecortin may contribute to developmental malformation of the cerebral cortex.

Acute deep brain stimulation in the thalamic reticular nucleus protects against acute stress and modulates initial events of adult hippocampal neurogenesis

Deep brain stimulation (DBS) is used as an alternative therapeutic procedure for pharmacoresistant psychiatric disorders. Recently the thalamic reticular nucleus (TRN) gained attention due to the description of a novel pathway from the amygdala to this nucleus suggesting that may be differentially disrupted in mood disorders. The limbic system is implicated in the regulation of these disorders that are accompanied by neuroplastic changes. The hippocampus is highly plastic and shows the generation of new neurons, process affected by stress but positively regulated by antidepressant drugs. We explored the impact of applying acute DBS to the TRN (DBS-TRN) in male Wistar rats exposed to acute stress caused by the forced-swim Porsolt's test (FST) and on initial events of hippocampal neurogenesis. After the first session of forced-swim, rats were randomly subdivided in a DBS-TRN and a Sham group. Stimulated rats received 10min of DBS, thus the depressant-like behavior reflected as immobility was evaluated in the second session of forced-swim. Locomotricity was evaluated in the open field test. Cell proliferation and doublecortin-associated cells were quantified in the hippocampus of other cohorts of rats. No effects of electrode implantation were found in locomotricity. Acute DBS-TRN reduced immobility in comparison to the Sham group (p<0.001). DBS-TRN increased cell proliferation (Ki67 or BrdU-positive cells; p=0.02, p=0.02) and the number of doublecortin-cells compared to the Sham group (p<0.02). Similar effects were found in rats previously exposed to the first session of forced-swim. Our data could suggest that TRN brain region may be a promising target for DBS to treat intractable depression.

Caloric restriction in young rats disturbs hippocampal neurogenesis and spatial learning

It is widely known that caloric restriction (CR) has benefits on several organic systems, including the central nervous system. However, the majority of the CR studies was performed in adult animals and the information about the consequences on young populations is limited. In this study, we analyzed the effects of young-onset CR, started at 4weeks of age, in the number of neuropeptide Y (NPY)-containing neurons and in neurogenesis of the hippocampal formation, using doublecortin (DCX) and Ki67 as markers. Knowing that CR treatment could interfere with exploratory activity, anxiety, learning and memory we have analyzed the performance of the rats in the open-field, elevated plus-maze and Morris water maze tests. Animals aged 4weeks were randomly assigned to control or CR groups. Controls were maintained in the ad libitum regimen during 2months. The adolescent CR rats were fed, during 2months, with 60% of the amount of food consumed by controls. We have found that young-onset CR treatment did not affect the total number of NPY-immunopositive neurons in dentate hilus, CA3 and CA1 hippocampal subfields and did not change the exploratory activity and anxiety levels. Interestingly, we have found that young-onset CR might affect spatial learning process since those animals showed worse performance during the acquisition phase of Morris water maze. Furthermore, young-onset CR induced alterations of neurogenesis in the dentate subgranular layer that seems to underlie the impairment of spatial learning. Our data suggest that adolescent animals are vulnerable to CR treatment and that this diet is not suitable to be applied in this age phase.

Pbx1 is required for adult subventricular zone neurogenesis

TALE-homeodomain proteins function as components of heteromeric complexes that contain one member each of the PBC and MEIS/PREP subclasses. We recently showed that MEIS2 cooperates with the neurogenic transcription factor PAX6 in the control of adult subventricular zone (SVZ) neurogenesis in rodents. Expression of the PBC protein PBX1 in the SVZ has been reported, but its functional role(s) has not been investigated. Using a genetic loss-of-function mouse model, we now show that Pbx1 is an early regulator of SVZ neurogenesis. Targeted deletion of Pbx1 by retroviral transduction of Cre recombinase into Pbx2-deficient SVZ stem and progenitor cells carrying floxed alleles of Pbx1 significantly reduced the production of neurons and increased the generation of oligodendrocytes. Loss of Pbx1 expression in neuronally committed neuroblasts in the rostral migratory stream in a Pbx2 null background, by contrast, severely compromised cell survival. By chromatin immunoprecipitation from endogenous tissues or isolated cells, we further detected PBX1 binding to known regulatory regions of the neuron-specific genes Dcx and Th days or even weeks before the respective genes are expressed during the normal program of SVZ neurogenesis, suggesting that PBX1 might act as a priming factor to mark these genes for subsequent activation. Collectively, our results establish that PBX1 regulates adult neural cell fate determination in a manner beyond that of its heterodimerization partner MEIS2.

Migration of bone marrow progenitor cells in the adult brain of rats and rabbits

Neurogenesis takes place in the adult mammalian brain in three areas: Subgranular zone of the dentate gyrus (DG); subventricular zone of the lateral ventricle; olfactory bulb. Different molecular markers can be used to characterize the cells involved in adult neurogenesis. It has been recently suggested that a population of bone marrow (BM) progenitor cells may migrate to the brain and differentiate into neuronal lineage. To explore this hypothesis, we injected recombinant SV40-derived vectors into the BM and followed the potential migration of the transduced cells. Long-term BM-directed gene transfer using recombinant SV40-derived vectors leads to expression of the genes delivered to the BM firstly in circulating cells, then after several months in mature neurons and microglial cells, and thus without central nervous system (CNS) lesion. Most of transgene-expressing cells expressed NeuN, a marker of mature neurons. Thus, BM-derived cells may function as progenitors of CNS cells in adult animals. The mechanism by which the cells from the BM come to be neurons remains to be determined. Although the observed gradual increase in transgene-expressing neurons over 16 mo suggests that the pathway involved differentiation of BM-resident cells into neurons, cell fusion as the principal route cannot be totally ruled out. Additional studies using similar viral vectors showed that BM-derived progenitor cells migrating in the CNS express markers of neuronal precursors or immature neurons. Transgene-positive cells were found in the subgranular zone of the DG of the hippocampus 16 mo after intramarrow injection of the vector. In addition to cells expressing markers of mature neurons, transgene-positive cells were also positive for nestin and doublecortin, molecules expressed by developing neuronal cells. These cells were actively proliferating, as shown by short term BrdU incorporation studies. Inducing seizures by using kainic acid increased the number of BM progenitor cells transduced by SV40 vectors migrating to the hippocampus, and these cells were seen at earlier time points in the DG. We show that the cell membrane chemokine receptor, CCR5, and its ligands, enhance CNS inflammation and seizure activity in a model of neuronal excitotoxicity. SV40-based gene delivery of RNAi targeting CCR5 to the BM results in downregulating CCR5 in circulating cells, suggesting that CCR5 plays an important role in regulating traffic of BM-derived cells into the CNS, both in the basal state and in response to injury. Furthermore, reduction in CCR5 expression in circulating cells provides profound neuroprotection from excitotoxic neuronal injury, reduces neuroinflammation, and increases neuronal regeneration following this type of insult. These results suggest that BM-derived, transgene-expressing, cells can migrate to the brain and that they become neurons, at least in part, by differentiating into neuron precursors and subsequently developing into mature neurons.

Endocrine and social regulation of adult neurogenesis in songbirds

The identification of pronounced seasonal changes in the volume of avian song control nuclei stimulated the discovery of adult neurogenesis in songbirds as well as renewed studies in mammals including humans. Neurogenesis in songbirds is modulated by testosterone and other factors such as photoperiod, singing activity and social environment. Adult neurogenesis has been widely studied by labeling, with tritiated thymidine or its analog BrdU, cells duplicating their DNA in anticipation of their last mitotic division and following their fate as new neurons. New methods based on endogenous markers of cell cycling or of various stages of neuronal life have allowed for additional progress. In particular immunocytochemical visualization of the microtubule-associated protein doublecortin has provided an integrated view of neuronal replacement in the song control nucleus HVC. Multiple questions remain however concerning the specific steps in the neuronal life cycle that are modulated by various factors and the underlying cellular mechanisms.

Low intensity, long term exposure to tobacco smoke inhibits hippocampal neurogenesis in adult mice

Previous data have shown that high dose of nicotine administration or tobacco smoke exposure can reduce cell formation and the survival rate of adult-born neurons in the dentate gyrus. Here, we subjected adult mice to low intensity cigarette smoke exposure over long time periods. We did a 2×30min/day smoke exposure with two cigarettes per occasion over 1- or 2-months. Subsequently, we carried out a systematic quantitative histopathological analysis to assess the number of newborn neurons in the dentate gyrus. To investigate cell proliferation, the exogenous marker 5-bromo-2'-deoxyuridine (BrdU) was administered on the last experimental day and animals were sacrificed 2h later. To investigate the effect of tobacco smoke on the population of immature neurons, we quantified the number of doublecortin-positive (DCX+) neurons in the same animals. We found that exposing animals to cigarette smoke for 1- or 2-months had no influence on cell proliferation rate, but significantly reduced the number of DCX-positive immature neurons. Our tobacco smoke exposure regimen caused no substantial changes in respiratory functions, but histopathological analysis of the pulmonary tissue revealed a marked perivascular/peribronchial edema formation after 1-month and signs of chronic pulmonary inflammation after 2-months of cigarette smoke exposure. These data demonstrate that even mild exposure to cigarette smoke, without significantly affecting respiratory functions, can have a negative effect on adult-born neurons in the dentate gyrus, when applied over longer time periods. Our data indicate that besides nicotine other factors, such as inflammatory mediators, may also contribute to this effect.

The neurogenic effects of an enriched environment and its protection against the behavioral consequences of chronic mild stress persistent after enrichment cessation in six-month-old female Balb/C mice

Because stress may underlie the presence of depressive episodes, strategies to produce protection against or to reverse the effects of stress on neuroplasticity and behavior are relevant. Preclinical studies showed that exposure to stimuli, such as physical activity and environmental enrichment (ENR), produce beneficial effects against stress causing antidepressant-like effects in rodents. Additionally, ENR induces positive effects on neuroplasticity, neurochemistry and behavior at any age of rodents tested. Here, we analyzed whether ENR exposure prevents the development of depressive-like behavior produced by unpredictable, chronic mild stress (CMS) exposure as well as changes in hippocampal neurogenesis in a six-month-old female Balb/C mice, strain that shows low baseline levels of hippocampal neurogenesis. Mice were assigned to one of four groups: (1) normal housing-normal housing (NH-NH), (2) NH-CMS, (3) ENR-NH, or (4) ENR-CMS. The animals were exposed over 46 days to ENR or NH and subsequently to NH or CMS for 4 weeks. ENR induces long-term effects protecting against CMS induction of anhedonia and hopelessness behaviors. Independent of housing conditions, ENR increased the number of proliferative cells (Ki67), and CMS decreased the number of proliferative cells. ENR increased the newborn cells (BrdU) and mature phenotypes of neurons; these effects were not changed by CMS exposure. Similarly, the number of doublecortin-positive cells was not affected by CMS in ENR mice, which showed more cells with complex dendrite arborizations. Our study suggests that ENR induces protection against the effects of CMS on behavior and neuroplasticity in six-month-old Balb/C mice.

Chronic administration of a melatonin membrane receptor antagonist, luzindole, affects hippocampal neurogenesis without changes in hopelessness-like behavior in adult mice

Melatonin is involved in the regulation of hippocampal neuronal development during adulthood. Emerging evidence indicates that exogenous melatonin acts during different events of the neurogenic process and exerts antidepressant-like behavior in rodents. Thus, melatonin might act through different mechanism, including acting as an antioxidant, interacting with intracellular proteins and/or activating membrane receptors. The melatonin membrane receptors (MMRs; Mt1/Mt2) are distributed throughout the hippocampus with an interesting localization in the hippocampal neurogenic microenvironment (niche), suggesting the involvement of these receptors in the beneficial effects of melatonin on hippocampal neurogenesis and behavior. In this study, we analyzed the participation of MMRs in the baseline neurogenesis in C57BL/6 mice. To this end, we used a pharmacological approach, administering luzindole (10 mg/kg) for 14 days. We observed a decrease in the absolute number of doublecortin-positive cells (49%) without changes in either the dendrite complexity of mature doublecortin-cells or the number of apoptotic cells (TUNEL). However, after the chronic administration of luzindole, cell proliferation (Ki67) significantly decreased (36%) with increasing (>100%) number of neural stem cells (NSCs; GFAP(+)/Sox2(+)) in the subgranular zone of the dentate gyrus of the hippocampus. In addition, luzindole did not affect hopelessness-like behavior in the forced swim test (FST) or changes in the novelty suppressed feeding test (NST) after 14 days of treatment either neuronal activation in the dentate gyrus after FST. These results suggest that the MMRs are involved in the effects of endogenous melatonin to mediate the transition from NSCs and proliferative cells to the following developmental stages implicated in the hippocampal neurogenic process of adult female C57BL/6 mice.

The prebiotics 3'Sialyllactose and 6'Sialyllactose diminish stressor-induced anxiety-like behavior and colonic microbiota alterations: Evidence for effects on the gut-brain axis

There are extensive bidirectional interactions between the gut microbiota and the central nervous system (CNS), and studies demonstrate that stressor exposure significantly alters gut microbiota community structure. We tested whether oligosaccharides naturally found in high levels in human milk, which have been reported to impact brain development and enhance the growth of beneficial commensal microbes, would prevent stressor-induced alterations in gut microbial community composition and attenuate stressor-induced anxiety-like behavior. Mice were fed standard laboratory diet, or laboratory diet containing the human milk oligosaccharides 3'Sialyllactose (3'SL) or 6'Sialyllactose (6'SL) for 2 weeks prior to being exposed to either a social disruption stressor or a non-stressed control condition. Stressor exposure significantly changed the structure of the colonic mucosa-associated microbiota in control mice, as indicated by changes in beta diversity. The stressor resulted in anxiety-like behavior in both the light/dark preference and open field tests in control mice. This effect was associated with a reduction in immature neurons in the dentate gyrus as indicated by doublecortin (DCX) immunostaining. These effects were not evident in mice fed milk oligosaccharides; stressor exposure did not significantly change microbial community structure in mice fed 3'SL or 6'SL. In addition, 3'SL and 6'SL helped maintain normal behavior on tests of anxiety-like behavior and normal numbers of DCX+ immature neurons. These studies indicate that milk oligosaccharides support normal microbial communities and behavioral responses during stressor exposure, potentially through effects on the gut microbiota-brain axis.

Effect of sub-optimal doses of fluoxetine plus estradiol on antidepressant-like behavior and hippocampal neurogenesis in ovariectomized rats

Estrogens and antidepressants synergize to reduce depressive symptoms and stimulate neurogenesis and neuroplastic events. The aim of this study was to explore whether the antidepressant-like effect induced by the combination of low doses of estradiol (E2) and fluoxetine (FLX) involves changes in cell proliferation, early survival, morphology and dendrite complexity of hippocampal new-immature neurons. The antidepressant-like effects of E2 and/or FLX were evaluated by the forced swimming test (FST), cell proliferation was determined with the endogenous marker Ki67, survival of newborn cells was established with bromo-deoxiuridine (BrdU) and immature neurons were ascertained by doublecortin (DCX) labeling while their dendrite complexity was evaluated with Sholl analysis. Ovariectomized Wistar rats were randomly assigned to one of the following groups: Vehicle (saline/14 days+Oil/-8h before FST); E2 (saline/14 days + E2 2.5 or 10 μg/rat; -8 h before FST); FLX (1.25 or 10 mg/kg for 14 days + oil -8h before FST), and FLX plus E2 (FLX 1.25 mg/kg for 14 days + E2 2.5 μg/rat -8 h before FST). The combination of sub-threshold doses of FLX plus E2 produced antidepressant-like actions similar to those induced by FLX or E2 given independently at optimal doses. Only FLX at an optimal dose and the combination of FLX plus E2 increased cell proliferation, the number of DCX-labeled immature neurons and the complexity of their dendritic tree, suggesting that these events may be responsible for their antidepressant-like effect.

Alcohol and pregnancy: Effects on maternal care, HPA axis function, and hippocampal neurogenesis in adult females

Chronic alcohol consumption negatively affects health, and has additional consequences if consumption occurs during pregnancy as prenatal alcohol exposure adversely affects offspring development. While much is known on the effects of prenatal alcohol exposure in offspring less is known about effects of alcohol in dams. Here, we examine whether chronic alcohol consumption during gestation alters maternal behavior, hippocampal neurogenesis and HPA axis activity in late postpartum female rats compared with nulliparous rats. Rats were assigned to alcohol, pair-fed or ad libitum control treatment groups for 21 days (for pregnant rats, this occurred gestation days 1-21). Maternal behavior was assessed throughout the postpartum period. Twenty-one days after alcohol exposure, we assessed doublecortin (DCX) (an endogenous protein expressed in immature neurons) expression in the dorsal and ventral hippocampus and HPA axis activity. Alcohol consumption during pregnancy reduced nursing and increased self-directed and negative behaviors, but spared licking and grooming behavior. Alcohol consumption increased corticosterone and adrenal mass only in nulliparous females. Surprisingly, alcohol consumption did not alter DCX-expressing cell density. However, postpartum females had fewer DCX-expressing cells (and of these cells more immature proliferating cells but fewer postmitotic cells) than nulliparous females. Collectively, these data suggest that alcohol consumption during pregnancy disrupts maternal care without affecting HPA function or neurogenesis in dams. Conversely, alcohol altered HPA function in nulliparous females only, suggesting that reproductive experience buffers the long-term effects of alcohol on the HPA axis.

Impaired adult hippocampal neurogenesis and cognitive ability in a mouse model of intrastriatal hemorrhage

Thrombin released by hematoma is an important mediator of the secondary injury of intracerebral hemorrhage (ICH), however, the effect of thrombin on adult neurogenesis and cognitive ability remains elusive. In this study, intrastriatal injection of 0.05 U thrombin didn't affect the neurogenesis at the subgranular zone (SGZ), which was distal to the injection site. 0.1 U thrombin increased the 5-bromo-2-deoxyuridine(+) (BrdU(+), S-phase proliferating cells)/doublecortin(+) (DCX(+), immature neurons) double labelled neurons, but decreased BrdU(+)/NeuN(+) double labelled mature neurons. Higher doses of thrombin (1 U, 2 U, and 5 U) significantly decreased the BrdU(+)/DCX(+) and BrdU(+)/NeuN(+) double labelled cells. After 1 U thrombin injection, cell apoptosis was found at the dentate gyrus of hippocampus at 3-24 h, but not 5 d post-injury. Thrombin infusion (1 U) induced spatial memory deficits in Morris water maze test; whereas, hirudin, the thrombin antagonist, significantly reversed both neurogenesis loss and spatial learning and memory impairment. In conclusion, at least at short term (5 days) after striatum ICH, the effect of high dose of thrombin on neurogenesis of SGZ, and the spatial learning and memory ability, is detrimental.

Chronic P7C3 treatment restores hippocampal neurogenesis in the Ts65Dn mouse model of Down Syndrome [Corrected]

Down syndrome (DS) is the most common genetic cause of intellectual disability and developmental delay. In addition to cognitive dysfunction, DS patients are marked by diminished neurogenesis, a neuropathological feature also found in the Ts65Dn mouse model of DS. Interestingly, manipulations that enhance neurogenesis - like environmental enrichment or pharmacological agents - improve cognition in Ts65Dn mice. P7C3 is a proneurogenic compound that enhances hippocampal neurogenesis, cell survival, and promotes cognition in aged animals. However, this compound has not been tested in the Ts65Dn mouse model of DS. We hypothesized that P7C3 treatment would reverse or ameliorate the neurogenic deficits in Ts65Dn mice. To test this, adult Ts65Dn and age-matched wild-type (WT) mice were administered vehicle or P7C3 twice daily for 3 months. After 3 months, brains were examined for indices of neurogenesis, including quantification of Ki67, DCX, activated caspase-3 (AC3), and surviving BrdU-immunoreactive(+) cells in the granule cell layer (GCL) of the hippocampal dentate gyrus. P7C3 had no effect on total Ki67+, DCX+, AC3+, or surviving BrdU+ cells in WT mice relative to vehicle. GCL volume was also not changed. In keeping with our hypothesis, however, P7C3-treated Ts65Dn mice had a significant increase in total Ki67+, DCX+, and surviving BrdU+ cells relative to vehicle. P7C3 treatment also decreased AC3+ cell number but had no effect on total GCL volume in Ts65Dn mice. Our findings show 3 months of P7C3 is sufficient to restore the neurogenic deficits observed in the Ts65Dn mouse model of DS.

Single episode of mild murine malaria induces neuroinflammation, alters microglial profile, impairs adult neurogenesis, and causes deficits in social and anxiety-like behavior

Cerebral malaria is associated with cerebrovascular damage and neurological sequelae. However, the neurological consequences of uncomplicated malaria, the most prevalent form of the disease, remain uninvestigated. Here, using a mild malaria model, we show that a single Plasmodium chabaudi adami infection in adult mice induces neuroinflammation, neurogenic, and behavioral changes in the absence of a blood-brain barrier breach. Using cytokine arrays we show that the infection induces differential serum and brain cytokine profiles, both at peak parasitemia and 15days post-parasite clearance. At the peak of infection, along with the serum, the brain also exhibited a definitive pro-inflammatory cytokine profile, and gene expression analysis revealed that pro-inflammatory cytokines were also produced locally in the hippocampus, an adult neurogenic niche. Hippocampal microglia numbers were enhanced, and we noted a shift to an activated profile at this time point, accompanied by a striking redistribution of the microglia to the subgranular zone adjacent to hippocampal neuronal progenitors. In the hippocampus, a distinct decline in progenitor turnover and survival was observed at peak parasitemia, accompanied by a shift from neuronal to glial fate specification. Studies in transgenic Nestin-GFP reporter mice demonstrated a decline in the Nestin-GFP(+)/GFAP(+) quiescent neural stem cell pool at peak parasitemia. Although these cellular changes reverted to normal 15days post-parasite clearance, specific brain cytokines continued to exhibit dysregulation. Behavioral analysis revealed selective deficits in social and anxiety-like behaviors, with no change observed in locomotor, cognitive, and depression-like behaviors, with a return to baseline at recovery. Collectively, these findings indicate that even a single episode of mild malaria results in alterations of the brain cytokine profile, causes specific behavioral dysfunction, is accompanied by hippocampal microglial activation and redistribution, and a definitive, but transient, suppression of adult hippocampal neurogenesis.

Cdk5 and its substrates, Dcx and p27kip1, regulate cytoplasmic dilation formation and nuclear elongation in migrating neurons

Neuronal migration is crucial for development of the mammalian-specific six-layered cerebral cortex. Migrating neurons are known to exhibit distinct features; they form a cytoplasmic dilation, a structure specific to migrating neurons, at the proximal region of the leading process, followed by nuclear elongation and forward movement. However, the molecular mechanisms of dilation formation and nuclear elongation remain unclear. Using ex vivo chemical inhibitor experiments, we show here that rottlerin, which is widely used as a specific inhibitor for PKCδ, suppresses the formation of a cytoplasmic dilation and nuclear elongation in cortical migrating neurons. Although our previous study showed that cortical neuronal migration depends on Jnk, another downstream target of rottlerin, Jnk inhibition disturbs only the nuclear elongation and forward movement, but not the dilation formation. We found that an unconventional cyclin-dependent kinase, Cdk5, is a novel downstream target of rottlerin, and that pharmacological or knockdown-mediated inhibition of Cdk5 suppresses both the dilation formation and nuclear elongation. We also show that Cdk5 inhibition perturbs endocytic trafficking as well as microtubule organization, both of which have been shown to be required for dilation formation. Furthermore, knockdown of Dcx, a Cdk5 substrate involved in microtubule organization and membrane trafficking, or p27(kip1), another Cdk5 substrate involved in actin and microtubule organization, disturbs the dilation formation and nuclear elongation. These data suggest that Cdk5 and its substrates, Dcx and p27(kip1), characterize migrating neuron-specific features, cytoplasmic dilation formation and nuclear elongation in the mouse cerebral cortex, possibly through the regulation of microtubule organization and an endocytic pathway.

Sex steroid-independent effects of photostimulation on the song-control system of white-throated sparrows (Zonotrichia albicollis)

Brain nuclei within the song-control system of songbirds are seasonally plastic during adulthood. These nuclei are larger in birds exposed to long, spring-like days than short, winter-like days. There is overwhelming evidence that this effect is mediated by testosterone (T). However, castration studies have also demonstrated that photostimulation has gonad-independent effects on song-control system plasticity, but these studies rarely control for extra-gonadal sources of T. In this study, we used anti-androgen and anti-estrogen treatments in combination with castration to determine the sex steroid-independent effects of photostimulation on HVC size and doublecortin immunoreactivity in white-throated sparrows (Zonotrichia albicollis). Birds were kept on short days or photostimulated for 1 month. Photostimulated birds were intact, castrated and treated with anti-androgens and anti-estrogens, or castrated and treated with T. HVC volumes of photostimulated birds were significantly larger than short-day birds. HVC volume of castrated birds given anti-androgens/-estrogens was significantly larger than short-day birds, indicating a sex steroid-independent effect of photostimulation. Similar results were observed for RA. The number of migrating neurons (immunoreactive for doublecortin) in HVC did not differ between treatment groups. Our data support the view that photostimulation alone can drive song-control system nuclei growth, and that concurrent exposure to T potentiates this growth. Moreover, these effects do not appear dependent on modulation of neuron migration.

Changes in hippocampal neurogenesis throughout early development

Adult hippocampal neurogenesis drastically diminishes with age but the underlying mechanisms remain unclear. Here, age-related influences on the hippocampal early neuroprogenitor cell (NPC) pool was examined by quantifying changes in Sox1-expressing cells in the dentate gyrus subgranular zone from early adulthood (3 months) to middle age (12 months). Proliferation of distinct NPC subpopulations (Sox1+, Nestin+, and Doublecortin+) and newborn cell survival were also investigated. Examination of total 5-bromodeoxyuridine (BrdU)+ and Doublecortin (DCX)± cells revealed an early and dramatic age-dependent decline of hippocampal neurogenesis. Increasing age from 3 to 12 months was primarily associated with reduced total proliferation, in vivo (-79% of BrdU+ cells) but not in vitro, and DCX+ cell numbers (-89%). When proliferative rates of individual NPC subpopulations were examined, a different picture emerged as proliferating Nestin+ neuroprogenitors (-95% at 9 months) and BrdU+/DCX+ neuroblasts and/or immature neurons (-83% at 12 months) declined the most, whereas proliferating Sox1+ NPCs only dropped by 53%. Remarkably, despite greatly reduced proliferative rates and recent reports of Nestin+ neuroprogenitor loss, total numbers of early Sox1+ NPCs were unaffected by age (at least up to middle age), and newborn cell survival within the dentate gyrus was increased. Neuronal differentiation was concomitantly reduced; however, thus suggesting age-associated changes in fate-choice determination.

Chronic Treatment with the 5-HT1A Receptor Partial Agonist Tandospirone Increases Hippocampal Neurogenesis

INTRODUCTION

A large-scale clinical trial, the Sequence Trial Alternatives to Relieve Depression (STAR*D) study, concluded that about one-third of the studied patients with major depressive disorder remitted during the initial treatment with selective serotonin reuptake inhibitors and that approximately half of the remitted subjects relapsed over a 1-year follow-up. The development of new therapeutic approaches with potent efficacy and good tolerability for the treatment of depressive disorders is of great importance. Adult hippocampal neurogenesis has been proposed to be important for understanding and treating depression and anxiety. The present study aimed to elucidate whether or not 5-hydroxytryptamine 1A (5-HT1A) receptor partial agonists have a potential therapeutic effect for the treatment of depressive and anxiety disorders, from the standpoint of neurogenesis.

METHODS

Male Sprague-Dawley rats were subcutaneously administered a vehicle or tandospirone (TDS) (1 or 10 mg/kg) once daily for 14 days. The effects of chronic TDS treatment on neurogenesis were evaluated on the day after the last injection. The quantification of hippocampal neurogenesis was estimated using immunostaining with doublecortin (DCX), a marker protein of newborn neurons.

RESULTS

Chronic TDS treatment resulted in a significant increase in the number of DCX-positive cells per volume of dentate gyrus in a dose-dependent manner.

CONCLUSION

The results strongly suggest that 5-HT1A receptor partial agonists would be useful and beneficial in the treatment of depressive and anxiety disorders through increased hippocampal neurogenesis.

Fluorescence-based assays for microtubule architecture

In vitro fluorescence-based assays have enabled the direct observation of single microtubule-associated proteins (MAPs) alongside the measurement of microtubule growth and shrinkage. Fluorescence-based assays have not, however, been able to address questions of "microtubule architecture." Tubulin can form diverse polymer structures in vitro. Importantly, microtubules nucleated spontaneously have different numbers of protofilaments (pfs), ranging from 11-pf to 16-pf, as well as sheet-like structures, indicating flexibility in tubulin-tubulin bonds. This structural diversity influences microtubule dynamics and the binding of MAPs to microtubules. Observation of microtubule architecture has required the imaging of microtubules by electron microscopy (EM). Because EM requires chemical fixation or freezing, it has not been possible to observe, in real time, how microtubule dynamics might influence structure and vice versa; it also remains technically challenging to directly observe some MAPs, especially small ones, by EM. It is therefore imperative to develop fluorescence-based assays that enable the direct, real-time observation of microtubule architecture alongside growth, shrinkage, and MAP binding. In this chapter, we describe our efforts to control microtubule architecture for fluorescence-based assays. We also describe how microtubule structure can be probed with the help of GFP-tagged doublecortin, a MAP that binds preferentially to 13-pf microtubules.

Effects of the angiotensin-(1-7) receptor Mas on cell proliferation and on the population of doublecortin positive cells within the dentate gyrus and the piriform cortex

Aside from the well-known biologically active angiotensin II, other biologically active angiotensins have been discovered, including angiotensin IV and angiotensin-(1-7). Some years ago, we and others discovered that the Mas proto-oncogene encodes a G protein-coupled receptor being essential for angiotensin-(1-7) signaling. Mas is not only expressed in the periphery but also within the brain, e.g. in the dentate gyrus (DG) and the piriform cortex (PC). Since the DG is capable of adult neurogenesis, we examined the impact of a deletion of Mas upon adult neurogenesis. Deletion of Mas did not alter cell proliferation in the adult DG (as monitored with phosphohistone H3) and did not alter cell death (as monitored with activated Caspase 3). However, Mas deficiency resulted in an increase in the number of doublecortin (DCX) positive cells, indicating that lack of Mas increases the number of this cell population. Concerning the PC, it is discussed whether adult neurogenesis occurs under physiological conditions in this area. We could demonstrate that Mas deficiency has an impact on cell division and on the population of DCX-positive cells within the PC. Since Mas is not expressed before birth within the brain, our data may suggest that adult hippocampal neurogenesis and neurogenesis occurring during prenatal development share several common mechanisms, but are, at least in part, differentially regulated. Moreover, since deficiency for Mas increases the numbers of DCX-positive young neurons, blockage of Mas might be beneficial in stimulating neurogenesis in adults.

Ionizing radiation induced long-term alterations in the adult rat rostral migratory stream

Ionizing radiation can induce significant injury to normal brain structures. To assess radiation-induced late effects, adult male Wistar rats received whole-body exposure with fractionated doses of gamma rays (a total dose of 4Gy) and were investigated thirty, sixty and ninety days later. Immunohistochemistry and confocal microscopy were used to determine the density of neuroblasts derived from the anterior subventricular zone (SVZa) and brain resident microglia distributed along and/or adjacent to subventricular zone-olfactory bulb axis (SVZ-OB axis). Cell counting was performed in four anatomical parts along the well defined pathway, known as the rostral migratory stream (RMS) represented by the SVZa, vertical arm, elbow and horizontal arm of the RMS. Strong overdistribution of neuroblasts was seen in the SVZa thirty and sixty days after irradiation replaced by a steep decline in the following parts of the RMS and the highest decrease ninety days after radiation treatment along the entire SVZ-OB axis. Radiation treatment led to a decline or loss of microglia in almost all counted parts through the entire experiment. Results showed that ultimate decline of the SVZa descendants and loss of microglia suggests a contributory role of reduced neurogenesis in the development of radiation-induced late effects.

Cognitive deficits and disruption of neurogenesis in a mouse model of apolipoprotein E4 domain interaction

Apolipoprotein E4 (apoE4) allele is the major genetic risk factor for sporadic Alzheimer disease (AD) due to the higher prevalence and earlier onset of AD in apoE4 carriers. Accumulating data suggest that the interaction between the N- and the C-terminal domains in the protein may be the main pathologic feature of apoE4. To test this hypothesis, we used Arg-61 mice, a model of apoE4 domain interaction, by introducing the domain interaction feature of human apoE4 into native mouse apoE. We carried out hippocampus-dependent learning and memory tests and related cellular and molecular assays on 12- and 3-month-old Arg-61 and age-matched background C57BL/6J mice. Learning and memory task performance were impaired in Arg-61 mice at both old and young ages compared with C57BL/6J mice. Surprisingly, young Arg-61 mice had more mitotic doublecortin-positive cells in the subgranular zone; mRNA levels of brain-derived neurotrophic factor (BDNF) and TrkB were also higher in 3-month-old Arg-61 hippocampus compared with C57BL/6J mice. These early-age neurotrophic and neurogenic (proliferative) effects in the Arg-61 mouse may be an inadequate compensatory but eventually detrimental attempt by the system to "repair" itself. This is supported by the higher cleaved caspase-3 levels in the young animals that not only persisted, but increased in old age, and the lower levels of doublecortin at old age in the hippocampus of Arg-61 mice. These results are consistent with human apoE4-dependent cognitive and neuro-pathologic changes, supporting the principal role of domain interaction in the pathologic effect of apoE4. Domain interaction is, therefore, a viable therapeutic/prophylactic target for cognitive impairment and AD in apoE4 subjects.

Maternal choline supplementation improves spatial learning and adult hippocampal neurogenesis in the Ts65Dn mouse model of Down syndrome

In addition to intellectual disability, individuals with Down syndrome (DS) exhibit dementia by the third or fourth decade of life, due to the early onset of neuropathological changes typical of Alzheimer's disease (AD). Deficient ontogenetic neurogenesis contributes to the brain hypoplasia and hypocellularity evident in fetuses and children with DS. A murine model of DS and AD (the Ts65Dn mouse) exhibits key features of these disorders, notably deficient ontogenetic neurogenesis, degeneration of basal forebrain cholinergic neurons (BFCNs), and cognitive deficits. Adult hippocampal (HP) neurogenesis is also deficient in Ts65Dn mice and may contribute to the observed cognitive dysfunction. Herein, we demonstrate that supplementing the maternal diet with additional choline (approximately 4.5 times the amount in normal rodent chow) dramatically improved the performance of the adult trisomic offspring in a radial arm water maze task. Ts65Dn offspring of choline-supplemented dams performed significantly better than unsupplemented Ts65Dn mice. Furthermore, adult hippocampal neurogenesis was partially normalized in the maternal choline supplemented (MCS) trisomic offspring relative to their unsupplemented counterparts. A significant correlation was observed between adult hippocampal neurogenesis and performance in the water maze, suggesting that the increased neurogenesis seen in the supplemented trisomic mice contributed functionally to their improved spatial cognition. These findings suggest that supplementing the maternal diet with additional choline has significant translational potential for DS.

Chroman-like cyclic prenylflavonoids promote neuronal differentiation and neurite outgrowth and are neuroprotective

Flavonoids target a variety of pathophysiological mechanisms and are therefore increasingly considered as compounds encompassed with therapeutic potentials in diseases such as cancer, diabetes, arteriosclerosis, and neurodegenerative diseases and mood disorders. Hops (Humulus lupulus L.) is rich in flavonoids such as the flavanone 8-prenylnaringenin, which is the most potent phytoestrogen identified so far, and the prenylchalcone xanthohumol, which has potent tumor-preventive, anti-inflammatory and antiviral activities. In the present study, we questioned whether hops-derived prenylflavonoids and synthetic derivatives thereof act on neuronal precursor cells and neuronal cell lines to induce neuronal differentiation, neurite outgrowth and neuroprotection. Therefore, mouse embryonic forebrain-derived neural precursors and Neuro2a neuroblastoma-derived cells were stimulated with the prenylflavonoids of interest, and their potential to activate the promoter of the neuronal fate-specific doublecortin gene and to stimulate neuronal differentiation and neurite outgrowth was analyzed. In this screening, we identified highly "neuroactive" compounds, which we termed "enhancement of neuronal differentiation factors" (ENDFs). The most potent molecule, ENDF1, was demonstrated to promote neuronal differentiation of neural stem cells and neurite outgrowth of cultured dorsal root ganglion neurons and protected neuronal PC12 cells from cobalt chloride-induced as well as cholinergic neurons of the nucleus basalis of Meynert from deafferentation-induced cell death. The results indicate that hops-derived prenylflavonoids such as ENDFs might be powerful molecules to promote neurogenesis, neuroregeneration and neuroprotection in cases of chronic neurodegenerative diseases, acute brain and spinal cord lesion and age-associated cognitive impairments.

Treadmill exercise alleviates post-traumatic stress disorder-induced impairment of spatial learning memory in rats

Post-traumatic stress disorder (PTSD) is a condition which occurs after a person has experienced unusual stress. The neurons in the hippocampus are especially vulnerable to the PTSD. In the present study, the effect of treadmill exercise on spatial learning memory and cell proliferation in the hippocampus of rats with PTSD. Radial 8-arm maze test and immunohistochemistr for 5-bromo-2'-deoxyridine (BrdU) and double-cortin (DCX) were conducted for this experiment. For the inducing PTSD, the rats were exposure to 0.2 mA electric foot shock for 7 consecutive days. Electric foot shock continued 6 seconds, repeated 10 times with a 30 sec interval per one trial, and repeated 3 trials per day. The rats in the exercise groups were forced to run on a motorized treadmill for 30 min once a day for 4 weeks, stating one day after finishing last electric food shock. Presently, the PTSD rats showed longer time of successful performance, higher error number, and lower correct number in the radial-8-arm maze test. Cell proliferation and DCX expression in the hippocampal dentate gyrus were suppressed in the PTSD rats. In contrast, treadmill exercise alleviated PTSD-induced impairment of spatial learning memory. The rats performed treadmill exercise showed longer time of successful performance, higher error number, and lower correct number in the radial-8-arm maze test. Treadmill exercise also enhanced cell proliferation and DCX expression in the hippocampal dentate gyrus of PTSD rats. The present study demonstrated that treadmill exercise ameliorated PTSD-induced memory impairment through enhancing cell proliferation in the hippocampus.

Resveratrol improves postnatal hippocampal neurogenesis and brain derived neurotrophic factor in prenatally stressed rats

Prenatal stress induced neuronal dysfunction is multifactorial, including suppressed neurogenesis in developing brain. Resveratrol is known to exert its neuroprotective potential by enhancing neurogenesis. But the efficacy of resveratrol against prenatal stress was not addressed in detail. Hence in the present study we evaluated the neuroprotective action of resveratrol on prenatal stress-induced impaired neurogenesis. Pregnant rats were subjected to restraint stress during early or late gestational period. Another sets of rats received resveratrol during entire gestational period along with early or late gestational stress. The study parameters included neuronal assay of doublecortin positive neurons (DCX +ve) and brain derived neurotrophic factor (BDNF) estimations in 40th postnatal day rat brain. Both early and late gestational stress resulted in significant decrease in generation of new born neurons and BDNF expression in hippocampus. The decrease in number of DCX +ve neurons and hippocampal BDNF expression was more profound in the offspring who received late gestational stress compared to early gestational stress. Resveratrol treatment has improved the expression of DCX +ve neurons and BDNF expression. These data suggest the neuroprotective efficacy of resveratrol against prenatal stress induced impaired neurogenesis.

Neuroglobin: neuroprotection and neurogenesis

Globins, such as hemoglobin, serve as oxygen sensors. Neuroglobin is the globin in brain. It is induced by ischemia and is protective in modeled stroke. Here, Haines et al. describe an additional property of neuroglobin, its expression in progenitor cell populations in brain during development. A physiologic role is offered but other data show progenitor cells response to injury and their neurotropic properties in ischemic brain.

Effects of hypothyroidism on cell proliferation and neuroblasts in the hippocampal dentate gyrus in a rat model of type 2 diabetes

We observed how the hypothyroid state affects diabetic states and modifies cell proliferation and neuroblast differentiation in the hippocampal dentate gyrus (DG). For this, 0.03% methimazole, an anti-thyroid drug, was administered to 7-week-old, pre-diabetic Zucker diabetic fatty (ZDF) rats by drinking water for 5 weeks, and the animals were sacrificed at 12 weeks of age. At this age, corticosterone levels were significantly increased in the ZDF rats compared to those in the control (Zucker lean control, ZLC) rats. Methimazole (methi) treatment in the ZDF rats (ZDF-methi rats) significantly decreased corticosterone levels and diabetes-induced hypertrophy of adrenal glands. In the DG, Ki67 (a marker for cell proliferation)- and doublecortin (DCX, a marker for neuronal progenitors)-immunoreactive cells were much lower in the ZDF rats than those in the ZLC rats. However, in ZDF-methi rats, numbers of Ki67- and DCX-immunoreactive cells were similar to those in the ZLC rats. These suggest that methi significantly reduces diabetes-induced hypertrophy of the adrenal gland and alleviates the diabetes-induced reduction of cell proliferation and neuronal progenitors in the DG.