Cell proliferation in adult hippocampus is decreased by inescapable stress: reversal by fluoxetine treatment

Adult neurogenesis: integrating theories and separating functions

The continuous incorporation of new neurons in the dentate gyrus of the adult hippocampus raises exciting questions about memory and learning, and has inspired new computational models to understand the function of adult neurogenesis. These theoretical approaches suggest distinct roles for new neurons as they slowly integrate into the existing dentate gyrus network: immature adult-born neurons seem to function as pattern integrators of temporally adjacent events, thereby enhancing pattern separation for events separated in time; whereas maturing adult-born neurons possibly contribute to pattern separation by being more amenable to learning new information, leading to dedicated groups of granule cells that respond to experienced environments. We review these hypothesized functions and supporting empirical research and point to new directions for future theoretical efforts.

Region- and phase-dependent effects of 5-HT(1A) and 5-HT(2C) receptor activation on adult neurogenesis

Adult neurogenesis and serotoninergic transmission are associated to mood disorders and their treatments. The present study focused on the effects of chronic activation of 5-HT(1A) and 5-HT(2C) receptors on newborn cell survival in the dentate gyrus (DG) and olfactory bulb (OB), and examined whether potential neurogenic zones as the prefrontal cortex (PFC) and striatum (ST) are reactive to these treatments. Administration of 8-OH-DPAT, but not RO600,175 increases neurogenesis and survival of late differentiating cells (15-21days) in the DG. Both 8-OH-DPAT and RO600,175 increase neurogenesis in the OB, but only 8-OH-DPAT affected cell survival, inducing a parallel decrease in the number of BrdU cells in the OB and increase in the SVZ, which suggests an impaired migration. In the PFC and ST, 8-OH-DPAT and R0600,175 increase gliogenesis (NG2-labeled cells). This study provides new insights on the serotonergic regulation of critical phases of neurogenesis helpful to understand the neurogenic and gliogenic effects of antidepressant treatments in different brain regions.

Impact of cocaine on adult hippocampal neurogenesis in an animal model of differential propensity to drug abuse

Hippocampal plasticity (e.g. neurogenesis) likely plays an important role in maintaining addictive behavior and/or relapse. This study assessed whether rats with differential propensity to drug-seeking behavior, bred Low-Responders (bLR) and bred High-Responders (bHR) to novelty, show differential neurogenesis regulation after cocaine exposure. Using specific immunological markers, we labeled distinct populations of adult stem cells in the dentate gyrus at different time-points of the cocaine sensitization process; Ki-67 for newly born cells, NeuroD for cells born partway, and 5-bromo-2'-deoxyuridine for older cells born prior to sensitization. Results show that: (i) bHRs exhibited greater psychomotor response to cocaine than bLRs; (ii) acute cocaine did not alter cell proliferation in bLR/bHR rats; (iii) chronic cocaine decreased cell proliferation in bLRs only, which became amplified through the course of abstinence; (iv) neither chronic cocaine nor cocaine abstinence affected the survival of immature neurons in either phenotype; (v) cocaine abstinence decreased survival of mature neurons in bHRs only, an effect that paralleled the greater psychomotor response to cocaine; and (vi) cocaine treatment did not affect the ratio of neurons to glia in bLR/bHR rats as most cells differentiated into neurons in both lines. Thus, cocaine exerts distinct effects on neurogenesis in bLR vs. bHR rats, with a decrease in the birth of new progenitor cells in bLRs and a suppression of the survival of new neurons in bHRs, which likely leads to an earlier decrease in formation of new connections. This latter effect in bHRs could contribute to their enhanced degree of cocaine-induced psychomotor behavioral sensitization.

Duration of untreated psychosis and duration of untreated illness: new vistas

The duration of untreated illness (DUI), defined as the interval between the onset of a psychiatric disorder and the administration of the first pharmacological treatment, has been increasingly investigated in the last decade as a predictor of outcome across different psychiatric conditions including schizophrenia and psychotic disorders (duration of untreated psychosis), and mood and anxiety disorders. Converging evidence indicates that a prolonged DUI may be viewed as a negative prognostic factor in schizophrenia and increasing data point toward a similar conclusion in mood and anxiety disorders. Through a Medline search, the present article highlights the role of the DUI in this group of psychiatric disorders, focusing on social and psychopathological determinants of the DUI, as well as the clinical consequences related to a longer DUI in terms of outcome. Hypotheses on neurobiological mechanisms underpinning outcome differences in relation to a prolonged DUI are provided and methodological limitations related to the assessment of the DUI in published studies and clinical practice discussed. Finally, given that DUI is supposed to be a potentially modifiable prognostic factor, intervention programs aimed to reduce this variable are briefly considered and discussed.

Norepinephrine directly activates adult hippocampal precursors via beta3-adrenergic receptors

Adult hippocampal neurogenesis is a critical form of cellular plasticity that is greatly influenced by neural activity. Among the neurotransmitters that are widely implicated in regulating this process are serotonin and norepinephrine, levels of which are modulated by stress, depression and clinical antidepressants. However, studies to date have failed to address a direct role for either neurotransmitter in regulating hippocampal precursor activity. Here we show that norepinephrine but not serotonin directly activates self-renewing and multipotent neural precursors, including stem cells, from the hippocampus of adult mice. Mechanistically, we provide evidence that beta(3)-adrenergic receptors, which are preferentially expressed on a Hes5-expressing precursor population in the subgranular zone (SGZ), mediate this norepinephrine-dependent activation. Moreover, intrahippocampal injection of a selective beta(3)-adrenergic receptor agonist in vivo increases the number of proliferating cells in the SGZ. Similarly, systemic injection of the beta-adrenergic receptor agonist isoproterenol not only results in enhancement of proliferation in the SGZ but also leads to an increase in the percentage of nestin/glial fibrillary acidic protein double-positive neural precursors in vivo. Finally, using a novel ex vivo "slice-sphere" assay that maintains an intact neurogenic niche, we demonstrate that antidepressants that selectively block the reuptake of norepinephrine, but not serotonin, robustly increase hippocampal precursor activity via beta-adrenergic receptors. These findings suggest that the activation of neurogenic precursors and stem cells via beta(3)-adrenergic receptors could be a potent mechanism to increase neuronal production, providing a putative target for the development of novel antidepressants.

Lesions of the basolateral amygdala reverse the long-lasting interference with shuttle box escape produced by uncontrollable stress

Exposure to an uncontrollable, but not a controllable, stressor produces a constellation of behaviors called learned helplessness. In rodents, uncontrollable stress interferes with the ability to learn to escape from escapable shocks delivered in a shuttle box. The stress-induced shuttle box escape deficit is a common screening tool for potential antidepressant strategies. Inconsistencies in the literature exist regarding the time-course of, and mechanisms underlying, stress-induced escape deficits. When no common cues are shared between the stressor and testing environment, the escape deficit is short lived and independent of conditioned freezing. In contrast, when stress and testing occur in the same or similar environments, the escape deficit is very long lasting. The current studies address the hypothesis that the long-lived escape deficit produced by uncontrollable stress is dependent upon conditioned fear and the basolateral amygdala (BLA). Rats received bilateral excitotoxic lesions of the BLA 2 weeks following uncontrollable foot shocks. One week after surgery, rats were tested for conditioned freezing and escape behavior in the same shuttle boxes in which prior foot shocks were delivered. Stressed rats with sham lesions displayed robust conditioned freezing and failed to escape during shuttle box testing. Lesions of the BLA eliminated conditioned freezing and completely restored stressed rats' ability to perform the escape contingency. These data indicate that the long-lived stress-induced escape deficit produced under conditions in which the stressor and testing environments share common cues is dependent upon conditioned freezing elicited by the BLA. Results have important implications for the mechanisms underlying learned helplessness phenomena.

Anti-glucocorticoid gene therapy reverses the impairing effects of elevated corticosterone on spatial memory, hippocampal neuronal excitability, and synaptic plasticity

Moderate release of the major stress hormones, glucocorticoids (GCs), improves hippocampal function and memory. In contrast, excessive or prolonged elevations produce impairments. Enzymatic degradation and reformation of GCs help to maintain optimal levels within target tissues, including the brain. We hypothesized that expressing a GC-degrading enzyme in hippocampal neurons would attenuate the negative impact of an excessive elevation in GC levels on synaptic physiology and spatial memory. We tested this by expressing 11-beta-hydroxysteroid dehydrogenase (type II) in dentate gyrus granule cells during a 3 d GC treatment followed by examination of synaptic responses in hippocampal slices or spatial performance in the Morris water maze. In adrenalectomized rats with basal GC replacement, additional GC treatments for 3 d reduced synaptic strength and promoted the expression of long-term depression at medial perforant path synapses, increased granule cell and CA1 pyramidal cell excitability, and impaired spatial reference memory (without influencing learning). Expression of 11-beta-hydroxysteroid dehydrogenase (type II), mostly in mature dentate gyrus granule cells, reversed the effects of high GC levels on granule cell and pyramidal cell excitability, perforant path synaptic plasticity, and spatial memory. These data demonstrate the ability of neuroprotective gene expression limited to a specific cell population to both locally and trans-synaptically offset neurophysiological disruptions produced by prolonged increases in circulating stress hormones. This report supplies the first physiological explanation for previously demonstrated cognitive sparing by anti-stress gene therapy approaches and lends additional insight into the hippocampal processes that are important for memory.

A reduced number of hippocampal granule cells does not associate with an anhedonia-like phenotype in a rat chronic mild stress model of depression

Several clinical and preclinical studies have indicated that hippocampal shrinkage and decreased neurogenesis are implicated in the pathology of depression. Recent animal studies have shown, however, that the development of depression-related symptoms may take place through neurogenesis-independent pathways. To evaluate whether the stress-induced morphological changes in the hippocampal formation are causally related to the development of anhedonia-like symptoms, we combined the chronic mild stress (CMS) rat model of depression with stereological estimations of the number of proliferating progenitors, the total number of granule cells, and the volume of the ventral hippocampal formation (VHF). First, we found that stress-susceptible and stress-resilient animals, as categorized according to the behavioral read-out, both have a decrease in hippocampal cell proliferation. Our results also indicated that the anhedonia-like state in CMS rats develops prior to maximal suppression of cell proliferation, but correlates with a reduction in the total number of granule cells in the VHF. Furthermore, recovery from depression-related symptoms correlated with re-establishment of proliferation rates, but not with the total number of granule cells. Notably, decreases in the number of granule cells occurred independently of the induction of an anhedonia-like phenotype. There were no stress-induced changes in the volume of the VHF. We conclude that cell proliferation and a reduction in the total number of granule cells in the VHF are triggered by chronic stress, but do not associate with development of an anhedonia-like state in rats.

Adult hippocampal neurogenesis is functionally important for stress-induced social avoidance

The long-term response to chronic stress is variable, with some individuals developing maladaptive functioning, although other "resilient" individuals do not. Stress reduces neurogenesis in the dentate gyrus subgranular zone (SGZ), but it is unknown if stress-induced changes in neurogenesis contribute to individual vulnerability. Using a chronic social defeat stress model, we explored whether the susceptibility to stress-induced social avoidance was related to changes in SGZ proliferation and neurogenesis. Immediately after social defeat, stress-exposed mice (irrespective of whether they displayed social avoidance) had fewer proliferating SGZ cells labeled with the S-phase marker BrdU. The decrease was transient, because BrdU cell numbers were normalized 24 h later. The survival of BrdU cells labeled before defeat stress was also not altered. However, 4 weeks later, mice that displayed social avoidance had more surviving dentate gyrus neurons. Thus, dentate gyrus neurogenesis is increased after social defeat stress selectively in mice that display persistent social avoidance. Supporting a functional role for adult-generated dentate gyrus neurons, ablation of neurogenesis via cranial ray irradiation robustly inhibited social avoidance. These data show that the time window after cessation of stress is a critical period for the establishment of persistent cellular and behavioral responses to stress and that a compensatory enhancement in neurogenesis is related to the long-term individual differences in maladaptive responses to stress.

Structural plasticity and hippocampal function

The hippocampus is a region of the mammalian brain that shows an impressive capacity for structural reorganization. Preexisting neural circuits undergo modifications in dendritic complexity and synapse number, and entirely novel neural connections are formed through the process of neurogenesis. These types of structural change were once thought to be restricted to development. However, it is now generally accepted that the hippocampus remains structurally plastic throughout life. This article reviews structural plasticity in the hippocampus over the lifespan, including how it is investigated experimentally. The modulation of structural plasticity by various experiential factors as well as the possible role it may have in hippocampal functions such as learning and memory, anxiety, and stress regulation are also considered. Although significant progress has been made in many of these areas, we highlight some of the outstanding issues that remain.

Destruction of dopaminergic neurons in the midbrain by 6-hydroxydopamine decreases hippocampal cell proliferation in rats: reversal by fluoxetine

Background

Non-motor symptoms (e.g., depression, anxiety, and cognitive deficits) in patients with Parkinson disease (PD) precede the onset of the motor symptoms. Although these symptoms do not respond to pharmacological dopamine replacement therapy, their precise pathological mechanisms are currently unclear. The present study was undertaken to examine whether the unilateral 6-hydroxydopamine (6-OHDA) lesion to the substantia nigra pars compacta (SNc), which represents a model of long-term dopaminergic neurotoxicity, could affect cell proliferation in the adult rat brain. Furthermore, we examined the effects of the selective serotonin reuptake inhibitor (SSRI) fluoxetine and the selective noradrenaline reuptake inhibitor maprotiline on the reduction in cell proliferation in the subgranular zone (SGZ) by the unilateral 6-OHDA lesion.

Methodology/Principal Findings

A single unilateral injection of 6-OHDA into the rat SNc resulted in an almost complete loss of tyrosine hydroxylase (TH) immunoreactivity in the striatum and SNc, as well as in reductions of TH-positive cells and fibers in the ventral tegmental area (VTA). On the other hand, an injection of vehicle alone showed no overt change in TH immunoreactivity. A unilateral 6-OHDA lesion to SNc significantly decreased cell proliferation in the SGZ ipsilateral to the 6-OHDA lesion, but not in the contralateral SGZ or the subventricular zone (SVZ), of rats. Furthermore, subchronic (14 days) administration of fluoxetine (5 mg/kg/day), but not maprotiline significantly attenuated the reduction in cell proliferation in the SGZ by unilateral 6-OHDA lesion.

Conclusions/Significance

The present study suggests that cell proliferation in the SGZ of the dentate gyrus might be, in part, under dopaminergic control by SNc and VTA, and that subchronic administration of fluoxetine reversed the reduction in cell proliferation in the SGZ by 6-OHDA. Therefore, SSRIs such as fluoxetine might be potential therapeutic drugs for non-motor symptoms as well as motor symptoms in patients with PD, which might be associated with the reduction in cell proliferation in the SGZ.

The chemotherapy agent, thioTEPA, yields long-term impairment of hippocampal cell proliferation and memory deficits but not depression-related behaviors in mice

ThioTEPA is a chemotherapeutic agent used in the treatment of cancers, and more recently has been proposed as a component of high-dose therapy for young patients with recurrent malignant brain tumors. We previously demonstrated a significant dose-dependent reduction of cell proliferation in the dentate gyrus of the hippocampus in mice immediately following a 3-day regiment of thioTEPA. The aim of this study was to evaluate the long-term effects of thioTEPA treatment on hippocampal cell proliferation and potential effects on memory deficit or depression-related behavior in C57BL/6J mice. A 3-day regimen of thioTEPA (10mg/kg/d, i.p.) yielded a significant reduction in cell proliferation immediately after treatment as assessed by BrdU incorporation, and none of the labeled progeny that initially survived the treatment were detectable one week later. Following a 3-week rebound in proliferation following treatment, a significant deficit in proliferation reappeared and persisted for at least 21 weeks following treatment. ThioTEPA-treated mice subjected to an object recognition test 1, 2, 3, 4, 8, 12, 20 or 30 weeks following treatment demonstrated significant memory deficits at 12 and 20 weeks. Mice demonstrated a similar deficit in an object placement test when tested 20 weeks following thioTEPA treatment. However, no observable effects on performance in the Porsolt forced swim test or the tail suspension test were observed in thioTEPA-treated mice. Together, these studies suggest that cumulative long-term negative effects of thioTEPA treatment on proliferation of new cells in the dentate gyrus may contribute to cognitive impairments associated with its use in the treatment of cancer.

Glucocorticoids and lithium in adult hippocampal neurogenesis

Adult hippocampal neurogenesis is decreased in rodent models for stress-related disorders partly through an elevated level of glucocorticoids (GCs). On the other hand, lithium (Li), a mood stabilizer and an inhibitor of GSK-3beta, increases adult hippocampal neurogenesis. However, it remains unclear whether GCs-induced decrease can be recovered by Li or not. Recently we established the culture system of adult rat dentate gyrus-derived neural precursor cell (ADP) and examined GCs and Li actions on ADP proliferation. GCs decreased ADP proliferation and Li recovered it. Both cyclin Dl expression and nuclear beta-catenin are also reciprocally regulated by GCs and Li. In addition, GCs activated GSK-3beta. Therefore, GSK-3beta/beta-catenin pathway may be important in the reciprocal actions of GCs and Li on ADP proliferation. In this manuscript, we review the past literature and our study and summarize what is currently known about the effects of GCs and Li on adult hippocampal neurogenesis.

Knockdown of brain-derived neurotrophic factor in specific brain sites precipitates behaviors associated with depression and reduces neurogenesis

Depression has been associated with reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus. In addition, animal studies suggest an association between reduced hippocampal neurogenesis and depressive-like behavior. These associations were predominantly established based on responses to antidepressant drugs and alterations in BDNF levels and neurogenesis in depressive patients or animal models for depressive behavior. Nevertheless, there is no direct evidence that the actual reduction of the BDNF protein in specific brain sites can induce depressive-like behaviors or affect neurogenesis in vivo. Using BDNF knockdown by RNA interference and lentiviral vectors injected into specific subregions of the hippocampus we show that a reduction in BDNF expression in the dentate gyrus, but not the CA3, reduces neurogenesis and affects behaviors associated with depression. Moreover, we show that BDNF has a critical function in neuronal differentiation, but not proliferation in vivo. Finally, we found that a specific BDNF knockdown in the ventral subiculum induces anhedonic-like behavior. These findings provide substantial support for the neurotrophic hypothesis of depression and specify anatomical and neurochemical targets for potential antidepressant interventions. Moreover, the specific effect of BDNF reduction on neuronal differentiation has broader implications for the study of neurodevelopment and neurodegenerative diseases.

The effects of exercise and stress on the survival and maturation of adult-generated granule cells

Stress strongly inhibits proliferation of granule cell precursors in the adult dentate gyrus, whereas voluntary running has the opposite effect. Few studies, however, have examined the possible effects of these environmental manipulations on the maturation and survival of young granule cells. We examined the number of surviving granule cells and the proportion of young neurons that were functionally mature, as defined by seizure-induced immediate-early gene (IEG) expression, in 14- and 21-day-old granule cells in mice that were given access to a running wheel, restrained daily for 2 h, or given no treatment during this period. Treatments began 2 days after BrdU injection, to isolate effects on survival from those on cell proliferation. We found a large increase in granule cell survival in running mice when compared with controls at both time points. In addition, running increased the proportion of granule cells expressing the IEG Arc in response to seizures, suggesting that it speeds incorporation into circuits, i.e., functional maturation. Stressed mice showed no change in Arc expression, compared with control animals, but, surprisingly, showed a transient increase in survival of 14-day-old granule cells, which was gone 7 days later. Examination of cell proliferation, using the endogenous mitotic marker PCNA showed an increase in cell proliferation after 12 days of running but not after 19 days of running. The number of proliferating cells was unchanged 24 h after the 12th or 19th episode of daily restraint stress. These findings demonstrate that running has strong effects on survival and maturation of young granule cells as well as their birth and that stress can have positive but short-lived effects on granule cell survival. Published 2009 Wiley-Liss, Inc.

Thymidine analog methods for studies of adult neurogenesis are not equally sensitive

Adult neurogenesis is often studied by labeling new cells with the thymidine analog bromodeoxyuridine (BrdU) and using immunohistochemical methods for their visualization. Using this approach, considerable variability has been reported in the number of new cells produced in the dentate gyrus of adult rodents. We examined whether immunohistochemical methods, including BrdU antibodies from different vendors (Vector, BD, Roche, Dako, Novocastra, and Accurate) and DNA denaturation pretreatments alter the quantitative and qualitative patterns of BrdU labeling. We also compared the sensitivity and specificity of BrdU with two other thymidine analogs, iododeoxyuridine (IdU) and chlorodeoxyuridine (CldU). We found that the number of BrdU-labeled cells in the dentate gyrus of adult rats was dependent on the BrdU antibody used but was unrelated to differences in antibody penetration. Even at a higher concentration, some antibodies (Vector and Novocastra) stained fewer cells. A sensitive BrdU antibody (BD) was specific for dividing cells; all BrdU-labeled cells stained for Ki67, an endogenous marker of cell proliferation. We also observed that DNA denaturation pretreatments affected the number of BrdU-labeled cells and staining intensity for a marker of neuronal differentiation, NeuN. Finally, we found that IdU and CldU, when used at molarities comparable to those that label the maximal number of cells with BrdU, are less sensitive. These data suggest that antibody and thymidine analog selection, as well as the staining procedure employed, can affect the number of newly generated neurons detected in the adult brain, thus providing a potential explanation for some of the variability in the adult neurogenesis literature.

Adverse stress, hippocampal networks, and Alzheimer's disease

Recent clinical data have implicated chronic adverse stress as a potential risk factor in the development of Alzheimer's disease (AD) and data also suggest that normal, physiological stress responses may be impaired in AD. It is possible that pathology associated with AD causes aberrant responses to chronic stress, due to potential alterations in the hypothalamic-pituitary-adrenal (HPA) axis. Recent study in rodent models of AD suggests that chronic adverse stress exacerbates the cognitive deficits and hippocampal pathology that are present in the AD brain. This review summarizes recent findings obtained in experimental AD models regarding the influence of chronic adverse stress on the underlying cellular and molecular disease processes including the potential role of glucocorticoids. Emerging findings suggest that both AD and chronic adverse stress affect hippocampal neural networks in a similar fashion. We describe alterations in hippocampal plasticity, which occur in both chronic stress and AD including dendritic remodeling, neurogenesis, and long-term potentiation. Finally, we outline potential roles for oxidative stress and neurotrophic factor signaling as the key determinants of the impact of chronic stress on the plasticity of neural networks and AD pathogenesis.

The neurotrophic and neuroprotective effects of psychotropic agents

Accumulating evidence suggests that psychotropic agents such as mood stabilizers, antidepressants, and antipsychotics realize their neurotrophic/neuroprotective effects by activating the mitogen activated protein kinaselextracellular signal-related kinase, PI3-kinase, and winglesslglycogen synthase kinase (GSK) 3 signaling pathways. These agents also upregulate the expression of trophic/protective molecules such as brain-derived neurotrophic factor, nerve growth factor, B-cell lymphoma 2, serine-threonine kinase, and Bcl-2 associated athanogene 1, and inactivate proapoptotic molecules such as GSK-3, They also promote neurogenesis and are protective in models of neurodegenerative diseases and ischemia. Most if not all, of this evidence was collected from animal studies that used clinically relevant treatment regimens. Furthermore, human imaging studies have found that these agents increase the volume and density of brain tissue, as well as levels of N-acetyl aspartate and glutamate in selected brain regions. Taken together, these data suggest that the neurotrophic/neuroprotective effects of these agents have broad therapeutic potential in the treatment, not only of mood disorders and schizophrenia, but also neurodegenerative diseases and ischemia.

Social Isolation Selectively Increases Anxiety in Mice without Affecting Depression-like Behavior

It is hypothesized that a number of environmental factors affect animals' behavior. Without controlling these variables, it is very hard for researchers to get not only reliable, but replicable data from various behavioral experiments testing animals' cognitive as well as emotional functions. For example, laboratory mice which had restricted environment showed different synaptic potentiation properties with wild mice (Zhao MG et al., 2009). While performing behavioral experiments, however, it is sometimes inevitable that the researcher changes the animals' environments, as by switching the cages in which experimental animals are housed and separating animals raised together into small experimental groups. In this study, we investigated the effect of environmental changes on mice's emotional behaviors by socially isolating them or reducing the size of their cage. We found that social isolation selectively increases the animals' levels of anxiety, while leaving depression-like behaviors unchanged. On the other hand, alteration of the housing dimensions affected neither their anxiety levels nor their depression-like behaviors. These results suggest that environmental variables may have a prominent impact on experimental animals' emotional behaviors and possibly their psychological states, leading to bias in the behavioral data produced from experiments.

A population-based study of risk of epilepsy after hospitalization for traumatic brain injury

PURPOSE

This study was undertaken to determine the risk of developing posttraumatic epilepsy (PTE) within 3 years after discharge among a population-based sample of older adolescents and adults hospitalized with traumatic brain injury (TBI) in South Carolina. It also identifies characteristics related to development of PTE within this population.

METHODS

A stratified random sample of persons aged 15 and older with TBI was selected from the South Carolina nonfederal hospital discharge dataset for four consecutive years. Medical records of recruits were reviewed, and they participated in up to three yearly follow-up telephone interviews.

RESULTS

The cumulative incidence of PTE in the first 3 years after discharge, after adjusting for loss to follow-up, was 4.4 per 100 persons over 3 years for hospitalized mild TBI, 7.6 for moderate, and 13.6 for severe. Those with severe TBI, posttraumatic seizures prior to discharge, and a history of depression were most at risk for PTE. This higher risk group also included persons with three or more chronic medical conditions at discharge.

DISCUSSION

These results raise the possibility that although some of the characteristics related to development of PTE are nonmodifiable, other factors, such as depression, might be altered with intervention. Further research into factors associated with developing PTE could lead to risk-reducing treatments.

Sub-chronic administration of rimonabant causes loss of antidepressive activity and decreases doublecortin immunoreactivity in the mouse hippocampus

Rimonabant is a cannabinoid receptor 1 antagonist, and is used to treat anorexia and obesity. However, it has been suggested that rimonabant may act as a depressant. In the present study, we investigated the depressive effects of rimonabant using behavioral and biochemical methods. A single treatment with rimonabant (10mg/kg, p.o.) reduced immobility duration in the forced swimming test (FST) to a level similar to that observed for the tricyclic antidepressant, imipramine (15mg/kg, i.p.). However, mice treated with rimonabant for 2 weeks did not show any significant reductions in immobility duration versus vehicle-treated controls. To investigate why the antidepressant effect of rimonabant disappeared after extended treatment, we carried out 5-bromo-2-deoxyuridine (BrdU) and doublecortin (DCX) immunohistochemistry assay. Numbers of BrdU-immunoreactive cells were not significantly changed after administering rimonabant (10mg/kg, p.o.) for 2 weeks in the hippocampal dentate gyrus (DG), but interestingly, numbers of DCX-immunopositive cells in the DG were significantly reduced after 2 weeks of rimonabant treatment at doses of 1 or 10mg/(kgday) compared with vehicle-treated controls (P<0.05). These results suggest that sub-chronic treatments with rimonabant inhibit cell proliferation in DG, and that a lack of antidepressive activity may be related to a reduction in cell proliferation in this region.

Cognitive effects of second-generation antipsychotics: current insights into neurochemical mechanisms

Historically, pharmacotherapy for schizophrenia was mainly focused on finding drugs to treat psychotic symptoms only, without addressing other crucial domains of the disorder such as cognitive impairments. As a result, these domains have remained undertreated. In this review, we discuss recent preclinical research efforts, including investigation of synaptic mechanisms as well as intracellular signalling pathways and mechanisms involved in neuroplasticity and cell resilience, that may represent new mechanisms participating in the pathogenesis of schizophrenia, particularly at the level of the prefrontal cortex and hippocampus, and that might lead to the development of drugs that can counteract, at least partially, the cognitive impairments typical of schizophrenia.

Ageing abolishes the effects of fluoxetine on neurogenesis

Depression constitutes a widespread condition observed in elderly patients. Recently, it was found that several drugs employed in therapies against depression stimulate hippocampal neurogenesis in young rodents and nonhuman primates. As the rate of neurogenesis is dramatically reduced during ageing, we examined the influences of ageing on neurogenic actions of antidepressants. We tested the impact of fluoxetine, a broadly used antidepressant, on hippocampal neurogenesis in mice of three different age groups (100, 200 and over 400 days of age). Proliferation and survival rate of newly generated cells, as well as the percentage of cells that acquired a neuronal phenotype were analyzed in the hippocampus of mice that received fluoxetine daily in a chronic manner. Surprisingly, the action of fluoxetine on neurogenesis was decreasing as a function of age and was only significant in young animals. Hence, fluoxetine increased survival and the frequency of neuronal marker expression in newly generated cells of the hippocampus in the young adult group (that is 100 days of age) only. No significant effects on neurogenesis could be detected in fluoxetine-treated adult and elderly mice (200 and over 400 days of age). The data indicate that the action of fluoxetine on neurogenesis is highly dependent on the age of the treated individual. Although the function of neurogenesis in the clinical manifestation of depression is currently a matter of speculation, this study clearly shows that the therapeutic effects of antidepressants in elderly patients are not mediated by neurogenesis modulation.

Antidepressants and dementia

BACKGROUND

It has been suggested that antidepressants may have neuroprotective abilities but it has newer been investigated lately whether treatment with antidepressants reduces the risk of dementia.

METHOD

Linkage of registers of all prescribed antidepressants and diagnoses of dementia in Denmark during a period from 1995 to 2005.

RESULTS

Persons who purchased antidepressants once (N=687,552) had an increased rate of dementia compared to persons unexposed to antidepressants (N=779,831). Nevertheless, the rate of dementia changed over time; thus during the initial prescription periods the rate increased with the number of prescriptions but continued long-term antidepressants treatment was associated with a reduction in the rate of dementia, however, not to the same level as the rate for the general population. This pattern was found for all classes of antidepressants (SSRIs, newer non-SSRI antidepressants and older antidepressants). All findings were replicated in sub-analyses with Alzheimer's disease as outcome.

LIMITATIONS

Methodological reasons for the findings cannot be excluded due to the non-randomized nature of data.

CONCLUSIONS

Continued long-term antidepressant treatment was associated with a reduced rate of dementia, however, not to the same level as the rate for the general population.

Treatment with escitalopram but not desipramine decreases escape latency times in a learned helplessness model using juvenile rats

RATIONALE

The pharmacological treatment of depression in children and adolescents is different from that of adults due to the lack of efficacy of certain antidepressants in the pediatric age group. Our current understanding of why these differences occur is very limited.

OBJECTIVES

To develop more effective treatments, a juvenile animal model of depression was tested to validate it as a possible model to specifically study pediatric depression.

MATERIALS AND METHODS

Procedures for use with juvenile rats at postnatal day (PND) 21 and 28 were adapted from the adult learned helplessness model in which, 24 h after exposure to inescapable stress, animals are unable to remove themselves from an easily escapable stressor. Rats were treated for 7 days with either the selective serotonin reuptake inhibitor escitalopram at 10 mg/kg or the tricyclic antidepressant desipramine at 3, 10, or 15 mg/kg to determine if treatment could decrease escape latency times.

RESULTS

Escitalopram treatment was effective at decreasing escape latency times in all ages tested. Desipramine treatment did not decrease escape latency times for PND 21 rats, but did decrease times for PND 28 and adult animals.

CONCLUSIONS

The learned helplessness model with PND 21 rats predicts the efficacy of escitalopram and the lack of efficacy of desipramine seen in the treatment of pediatric depression. These findings suggest that the use of PND 21 rats in a modified learned helplessness procedure may be a valuable model of human pediatric depression that can predict pediatric antidepressant efficacy and be used to study antidepressant mechanisms involved in pediatric depression.

Decreased cell proliferation in the dentate gyrus does not associate with development of anhedonic-like symptoms in rats

Depressive disorders have been proposed to be caused by stress-induced down-regulation of hippocampal neurogenesis. Nevertheless, several reports have recently pointed out that, in rodent models of depression, suppression of generation of new hippocampal neurons is not by itself sufficient to induce the development of depression-related symptoms. In the present study, we used the cell proliferation blocker methylazoxymethanol (MAM) and the rat chronic mild stress (CMS) model of depression to challenge the neurogenic theory of depression. In order to achieve a comparable reduction in hippocampal cytogenesis, rats were either chronically treated with MAM for 2 weeks, or subjected to an 8 week regime of chronic mild stress. Consumption of a palatable sucrose solution was monitored once a week to assess the development of anhedonic behavior. Prior to terminal perfusion, the animals were injected with bromodeoxyuridine, a marker of proliferating cells. The number of proliferating cells and total cell number and volume were estimated for the granule cell layer of the ventral hippocampal formation. Unlike CMS, chronic injections with MAM did not induce anhedonia-like symptoms in rats. Both MAM-treated and CMS-exposed groups of rats showed a comparable significant reduction in cell proliferation in the granular cell layer of the ventral hippocampal formation. However, the total cell number was reduced for CMS-exposed rats only while the granule cell layer volume was conserved for both groups. Our results show that suppression of cell proliferation in the hippocampal formation is not an absolute factor for induction of an anhedonia-like state in rats. However, it may still represent an important causal factor for vulnerable subjects.

Age-dependent effect of prenatal stress on hippocampal cell proliferation in female rats

Stressors occurring during pregnancy can alter the developmental trajectory of offspring and lead to, among other deleterious effects, cognitive deficits and hyperactivity of the hypothalamo-pituitary-adrenal axis. A recent feature of the prenatal stress (PS) model is its reported influence on structural plasticity in hippocampal formation, which sustains both cognitive functions and stress responsiveness. Indeed, we and others have previously reported that males exposed to stress in utero are characterized by a decrease in hippocampal cell proliferation, and consequently neurogenesis, from adolescence to senescence. Recent studies in females submitted to PS have reported conflicting results, ranging from no effect to a decrease in cell proliferation. We hypothesized that changes in cell proliferation in PS female rats are age dependent. To address this issue, we examined the impact of PS on hippocampal cell proliferation in juvenile, young, middle-aged and old females. As hypothesized, we found an age-dependent effect of PS in female rats as cell proliferation was significantly decreased only when animals reached senescence, a time when adrenal gland weight also increased. These data suggest that the deleterious effects of PS on hippocampal cell proliferation in females are either specific to senescence or masked during adulthood by protective factors.

Suppression of hippocampal cell proliferation by short-term stimulant drug administration in adult rats

Sleep loss is known to potently suppress adult hippocampal cell proliferation and neurogenesis. Whether sleep suppression following acute administration of stimulant drugs also decreases hippocampal cell proliferation is not known. The present study examined the effect of three mechanistically distinct stimulants (caffeine, methamphetamine and modafinil) on cell proliferation. To maximize sleep suppression, these drugs were administered to rats (three i.p. injections, once every 4 h) during their sleep period (i.e. 12-h light phase). At the end of the light phase, 5-bromo-2'-deoxyuridine (200 mg/kg, i.p.) was injected and animals were killed 2 h later. Polygraphic recordings and locomotor activity measurements confirmed the wake-promoting and sleep-suppressing actions of each treatment. Results indicate that caffeine (20 mg/kg), methamphetamine (1.5 mg/kg) and modafinil (300 mg/kg) differentially suppressed sleep (45-91%) and selectively reduced cell proliferation in the hilus (12-44%), these results being significant for both caffeine and modafinil. When the same experiment was repeated in the dark (active) phase, the suppressant effect on hippocampal cell proliferation was either absent or greatly attenuated. In a further experiment, the effect of acute modafinil treatment in the light phase was shown to persist for 3 weeks after BrdU administration. We hypothesize that the differential effect of the stimulant drugs in the light vs. dark phase is attributable primarily to sleep suppression in the light. As abuse of stimulant drugs invariably leads to disrupted sleep in humans, our results suggest that they may, at least in part, decrease hippocampal neurogenesis via sleep loss and thereby adversely affect hippocampal-dependent processes.

Maternal postpartum learned helplessness (LH) affects maternal care by dams and responses to the LH test in adolescent offspring

It is known that the early environment affects the mental development of rodent and human offspring. However, it is not known specifically whether a postpartum depressive state influences the depressive state in offspring. Using learned helplessness (LH) in rats as an animal model of depression, we examined the influence of maternal postpartum LH on responses to the LH test of offspring. Dam rats were judged as LH or non-helpless (nLH) on postnatal days (PN) 2-3, and maternal behavior was recorded during PN2-14. On PN 45-46, offspring were subjected to the LH test. Plasma corticosterone (CORT) levels, hippocampal levels of glucocorticoid receptor (GR) and brain-derived neurotrophic factor (BDNF) mRNA were measured before and after the LH test in offspring. Active nursing in LH dams was significantly lower than that in nLH dams. Susceptibility to LH in the offspring of LH dams was significantly higher than in those of nLH dams, and was negatively correlated with active nursing by LH dams. The GR mRNA levels before and after the LH test were lower in the offspring of LH dams than in those of nLH dams, and the reduced basal GR mRNA and protein might have resulted in the higher CORT response after the LH test. There was no significant difference in BDNF mRNA in the offspring of LH and nLH dams. These findings suggest that early postpartum LH decreased active nursing and increased depression-like behavior in the adolescent offspring via dysfunction of the hypothalamic-pituitary-adrenal axis.

T-817MA, a neurotrophic agent, ameliorates the deficits in adult neurogenesis and spatial memory in rats infused i.c.v. with amyloid-beta peptide

BACKGROUND AND PURPOSE

Adult neurogenesis occurs throughout life in the subgranular zone and the dentate gyrus of the hippocampus. Deficient neurogenesis may be responsible for deficient hippocampal functions in neurodegenerative disorders such as Alzheimer's disease (AD). T-817MA [1-{3-[2-(1-Benzothiophen-5-yl)ethoxy] propyl}-3-azetidinol maleate] is a newly synthesized agent for AD treatment with neuroprotective effects against toxicity from amyloid-beta peptide (Abeta) and actions promoting neurite outgrowth in vitro. Furthermore, systemic administration of T-817MA ameliorated cognitive dysfunctions caused by neurodegeneration in a rat model of AD, induced by intracerebroventricular (i.c.v.) infusion of Abeta. The present study investigated quantitative relationships between spatial memory performance in Abeta-infused rats and hippocampal neurogenesis, and the effects of T-817MA on neuronal proliferation in vivo.

EXPERIMENTAL APPROACH

Seven weeks after infusion of Abeta (peptide 1-40; 300 pmol.day(-1); i.c.v.), rats were tested in a place learning task in which they were required to alternately visit two reward places in an open field to obtain intracranial self-stimulation as rewards.

KEY RESULTS

Rats given Abeta infusions for 10 weeks displayed spatial memory impairments and a decrease in neurogenesis compared with those infused with vehicle. Treatment of the Abeta-infused rats with T-817MA (8.4 mg.kg(-1).day(-1), p.o.) significantly increased hippocampal neurogenesis and ameliorated spatial learning impairments. Furthermore, spatial learning in the task was significantly correlated with neurogenesis.

CONCLUSIONS AND IMPLICATIONS

These results suggest that defective hippocampal neurogenesis is a new target for AD treatment. The neurotrophic compound T-817MA increased hippocampal neurogenesis in an AD model and might be useful for treatment of AD patients.

A new role for FGF2 as an endogenous inhibitor of anxiety

Human postmortem studies have demonstrated that fibroblast growth factor-2 (FGF2) expression is decreased in the brain of depressed individuals. It remained unclear, however, whether this is a consequence of the illness or whether FGF2 plays a primary role in the control of mood and emotions. In this series of studies, we first ask whether endogenous FGF2 expression correlates with spontaneous anxiety, a trait associated with vulnerability to severe mood disorders in humans. This is tested in two genetically distinct groups of rats selectively bred to differ dramatically in their response to novelty and anxiety-provoking conditions (HRs = low anxiety/high response to novelty vs LRs = high anxiety/low response to novelty). We demonstrate that high-anxiety LRs have significantly lower levels of hippocampal FGF2 mRNA relative to low-anxiety HRs. We then demonstrate that FGF2 expression is modifiable by environmental factors that alter anxiety--thus, environmental complexity reduces anxiety behavior and induces FGF2 expression in hippocampus, particularly in high-anxiety LRs. Finally, we directly test the role of FGF2 as an anxiolytic and show that a 3 week treatment regimen of peripherally administered FGF2 is highly effective at blunting anxiety behavior, specifically in high-anxiety LRs. This treatment is accompanied by an increase in survival of adult-born hippocampal cells, both neurons and astrocytes, most clearly in LRs. These findings implicate hippocampal FGF2 as a central integrator of genetic and environmental factors that modify anxiety, point to hippocampal neurogenesis and gliogenesis as key in this modulation, and underscore FGF2's potential as a new target for treatment of depression and anxiety disorders.

5HTTLPR predicts left fusiform gyrus activation to positive emotional stimuli

This study was designed to replicate and extend past research examining the impact of the serotonin transporter gene-linked polymorphic region (5HTTLPR) on neural activation during emotional processing. Six women with at least one short allele were compared to six age-matched women with long/long alleles of the 5HTTLPR. Participants were shown 36 positive and 36 negative slides from the International Affective Picture Set, while functional images were acquired using a 4-T magnetic resonance imaging scanner. Although we were unable to replicate past research demonstrating relatively increased amygdala activation among individuals with an "s" allele to negative stimuli, women with an s allele evidenced decreased left fusiform gyrus activation to positive emotional stimuli (as expected). We suggest that women with a short allele may be either less attentive or less "expert" with regard to positive emotional stimuli, and ideas for future research are presented.

Enriched environment restores hippocampal cell proliferation and ameliorates cognitive deficits in chronically stressed rats

Adult neurogenesis, particularly in the subgranular zone, is thought to be linked with learning and memory. Chronic stress inhibits adult hippocampal neurogenesis and also impairs learning and memory. On the other hand, exposure to enriched environment (EE) is reported to enhance the survival of new neurons and improve cognition. Accordingly, in the present study, we examined whether short-term EE after stress could ameliorate the stress-induced decrease in hippocampal cell proliferation and impairment in radial arm maze learning. After restraint stress (6 hr/day, 21 days) adult rats were exposed to EE (6 hr/day, 10 days). We observed that chronic restraint stress severely affected formation of new cells and learning. Stressed rats showed a significant decrease (70%) in the number of BrdU (5-bromo-2'-deoxyuridine)-immunoreactive cells and impairment in the performance of the partially baited radial arm maze task. Interestingly, EE after stress completely restored the hippocampal cell proliferation. On par with the restoration of hippocampal cytogenesis, short-term EE after stress resulted in a significant increase in percentage correct choices and a decrease in the number of reference memory errors compared with the stressed animals. Also, EE per se significantly increased the cell proliferation compared with controls. Furthermore, stress significantly reduced the hippocampal volume that was reversed after EE. Our observations demonstrate that short-term EE completely ameliorates the stress-induced decrease in cell proliferation and learning deficit, thus demonstrating the efficiency of rehabilitation in reversal of stress-induced deficits and suggesting a probable role of newly formed cells in the effects of EE.

Abstinence following alcohol drinking produces depression-like behavior and reduced hippocampal neurogenesis in mice

Alcoholism and depression show high degrees of comorbidity. Clinical evidence also indicates that depression that emerges during abstinence from chronic alcohol use has a greater negative impact on relapse than pre-existing depression. Although no single neurobiological mechanism can account for the behavioral pathologies associated with these devastating disorders, converging evidence suggests that aspects of both alcoholism and depression are linked to reductions in hippocampal neurogenesis. Here, we report results from a novel preclinical behavioral model showing that abstinence from voluntary alcohol drinking leads to the emergence of depression-like behavior and reductions in neurogenesis. C57BL/6J mice were allowed to self-administer ethanol (10% v/v) vs H(2)O in the home cage for 28 days. Alcohol was then removed for 1 or 14 days, and mice were tested in the forced swim test to measure depression-like behavior. After 14 days, but not 1 day of abstinence from alcohol drinking, mice showed a significant increase in depression-like behavior. The significant increase in depression-like behavior during abstinence was associated with a reduction in proliferating cell nuclear antigen (PCNA) and doublecortin (DCX) immunoreactivity in the dentate gyrus of the hippocampus indicating that both the number of proliferating neural progenitor cells (NPC) and immature neurons were reduced, respectively. The number of NPCs that were labeled with bromo-deoxyuridine (BrdU) at the beginning of alcohol exposure was not altered indicating that survival of NPCs is not linked to abstinence-induced depression. Chronic treatment (14 days) with the antidepressant desipramine during abstinence prevented both the emergence of depression-like behavior and the reduction in hippocampal neurogenesis indicating that abstinence-induced depression is associated with structural plasticity in the hippocampus. Overall, the results of this study support the conclusion that profound functional (i.e. behavioral) and structural changes occur during abstinence from alcohol use and suggest that antidepressant treatment may alleviate some of these pathological neurobehavioral adaptations.

Requirement of AQP4 for antidepressive efficiency of fluoxetine: implication in adult hippocampal neurogenesis

Aquaporin-4 (AQP4), a key molecule for maintaining water homeostasis in the central nervous system, is expressed in adult neural stem cells (ANSCs) as well as astrocytes. Neural stem cells give rise to new hippocampal neurons throughout adulthood, and defects in neurogenesis may predispose an individual to depression. Nevertheless, the role of AQP4 in adult hippocampal neurogenesis and chronic mild stress (CMS)-induced depression remains unknown. We herein report that AQP4 knockout disrupted 4-week fluoxetine (10 mg/kg per day i.p) treatment-induced enhancement of adult mouse hippocampal neurogenesis as well as behavioral improvement under both basal condition and CMS-evoked depressive state. Meanwhile, AQP4 knockout abolished fluoxetine-induced enhancement of hippocampal cyclic AMP-responsive element binding protein (CREB) phosphorylation. The CMS procedure inhibited hippocampal protein kinase A (PKA) activity, extracellular signal-regulated kinases (ERK1/2), and calcium/calmodulin-dependent protein kinase IV (CaMKIV) phosphorylation in AQP4(+/+) and AQP4(-/-) mice. Fluoxetine treatment could reverse CMS-induced inhibition of PKA activity and ERK1/2 phosphorylation in both genotypes. However, fluoxetine restored CMS-induced inhibition of hippocampal CaMKIV phosphorylation in AQP4(+/+) mice but failed in AQP4(-/-) mice. Notably, CMS procedure significantly increased the hippocampal AQP4 expression, which was reversed by 4-week fluoxetine treatment. Further investigation showed AQP4 knockout inhibited the proliferation of cultured ANSCs and eliminated the pro-proliferative effect of fluoxetine in vitro. Collectively, these findings suggest that AQP4 is required for the antidepressive action of fluoxetine via regulating adult hippocampal neurogenesis.

Remodeling of hippocampal spine synapses in the rat learned helplessness model of depression

BACKGROUND

Although it has been postulated for many years that depression is associated with loss of synapses, primarily in the hippocampus, and that antidepressants facilitate synapse growth, we still lack ultrastructural evidence that changes in depressive behavior are indeed correlated with structural synaptic modifications.

METHODS

We analyzed hippocampal spine synapses of male rats (n=127) with electron microscopic stereology in association with performance in the learned helplessness paradigm.

RESULTS

Inescapable footshock (IES) caused an acute and persistent loss of spine synapses in each of CA1, CA3, and dentate gyrus, which was associated with a severe escape deficit in learned helplessness. On the other hand, IES elicited no significant synaptic alterations in motor cortex. A single injection of corticosterone reproduced both the hippocampal synaptic changes and the behavioral responses induced by IES. Treatment of IES-exposed animals for 6 days with desipramine reversed both the hippocampal spine synapse loss and the escape deficit in learned helplessness. We noted, however, that desipramine failed to restore the number of CA1 spine synapses to nonstressed levels, which was associated with a minor escape deficit compared with nonstressed control rats. Shorter, 1-day or 3-day desipramine treatments, however, had neither synaptic nor behavioral effects.

CONCLUSIONS

These results indicate that changes in depressive behavior are associated with remarkable remodeling of hippocampal spine synapses at the ultrastructural level. Because spine synapse loss contributes to hippocampal dysfunction, this cellular mechanism may be an important component in the neurobiology of stress-related disorders such as depression.

Monoaminergic regulation of Sonic hedgehog signaling cascade expression in the adult rat hippocampus

Monoamines are implicated in the modulation of adult hippocampal neurogenesis in depression models and following chronic antidepressant treatment. Given the key role of Sonic hedgehog (Shh) in adult neurogenesis, we examined whether monoaminergic perturbations regulate the expression of Shh or its co-receptors Smoothened (Smo) and Patched (Ptc). Combined depletion of both serotonin and norepinephrine with para-chlorophenylalanine (PCPA) resulted in a significant decrease in Smo and Ptc mRNA within the dentate gyrus subfield of the hippocampus. However, selective depletion of serotonin, using the serotonergic neurotoxin 5,7-dihyrdroxytryptamine (5,7-DHT), or norepinephrine, using the noradrenergic neurotoxin DSP-4, did not alter expression of Shh and its co-receptors, Smo and Ptc. Acute treatment with the monoamine releasing agent, para-chloroamphetamine (PCA) significantly upregulated Smo mRNA within the dentate gyrus. However, acute or chronic treatment with pharmacological antidepressants that modulate monoaminergic neurotransmission did not regulate Shh cascade expression. These results indicate that robust changes in monoamine levels can regulate the expression of the Shh signaling cascade in the adult rodent brain.

5-HT(1A) receptor function in major depressive disorder

Dysfunction of the serotonin 1A receptor (5-HT(1A)) may play a role in the genesis of major depressive disorder (MDD). Here we review the pharmacological, post-mortem, positron emission tomography (PET), and genetic evidence in support of this statement. We also touch briefly on two MDD-associated phenotypes, cognitive impairment and somatic pain. The results of pharmacological challenge studies with 5-HT(1A) receptor agonists are indicative of blunted endocrine responses in depressed patients. Lithium, valproate, selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs), and other treatment, such as electroconvulsive shock therapy (ECT), all increase post-synaptic 5-HT(1A) receptor signaling through either direct or indirect effects. Reduced somatodendritic and postsynaptic 5-HT(1A) receptor numbers or affinity have been reported in some post-mortem studies of suicide victims, a result consistent with well-replicated PET analyses demonstrating reduced 5-HT(1A) receptor binding potential in diverse regions such as the dorsal raphe, medial prefrontal cortex (mPFC), amygdala and hippocampus. 5-HT(1A) receptor knockout (KO) mice display increased anxiety-related behavior, which, unlike in their wild-type counterparts, cannot be rescued with antidepressant drug (AD) treatment. In humans, the G allele of a single nucleotide polymorphism (SNP) in the 5-HT(1A) receptor gene (HTR1A; rs6295), which abrogates a transcription factor binding site for deformed epidermal autoregulatory factor-1 (Deaf-1) and Hes5, has been reported to be over-represented in MDD cases. Conversely, the C allele has been associated with better response to AD drugs. We raise the possibility that 5-HT(1A) receptor dysfunction represents one potential mechanism underpinning MDD and other stress-related disorders.

PUFA induce antidepressant-like effects in parallel to structural and molecular changes in the hippocampus

Epidemiological data suggest that omega-3 polyunsaturated fatty acids (PUFA) consumption may be inversely correlated to the prevalence and severity of depression but little is known about the underlying mechanisms. In this study, we experimentally investigated whether a chronic supplementation with PUFA may induce antidepressant-like effects in mice in parallel to brain structural and molecular changes. Six weeks feeding with a PUFA-enriched diet induced behavioral changes in the Forced Swim Test (FST), the Tail Suspension Test and the Novelty-Suppressed Feeding Test. Moreover, more than 5 weeks supplementation with a PUFA blend containing 70% alpha-linolenic acid induced antidepressant-like effects in the FST with an increase in both swimming and climbing behaviors. The combination of a shorter duration of PUFA supplementation with a low dose of imipramine also induced an additive effect in the FST. Finally, PUFA supplementation was associated with an increase in the hippocampal volume, an over-expression of both synaptophysin and BDNF, and a raise in the number of newborn cells. Besides the possible modulation of brain plasticity, present results highlight the effectiveness of PUFA given alone or in combination with antidepressant drug as potential treatment of depressive disorders.

Glucocorticoids and lithium reciprocally regulate the proliferation of adult dentate gyrus-derived neural precursor cells through GSK-3beta and beta-catenin/TCF pathway

Adult hippocampal neurogenesis is decreased in rodent models for stress-related disorders at least partly through an elevated level of glucocorticoids. On the other hand, the mood stabilizer lithium (Li) commonly used for their treatment increases it. This effect is thought to be one of the therapeutic actions of Li, but the molecular mechanism has been poorly understood. Here we established the culture system of adult rat dentate gyrus-derived neural precursor cells (ADPs) and examined the effects of dexamethasone (DEX), an agonist of glucocorticoids receptor, and Li on ADP proliferation. It is possible for ADP to be a type 2a cell, which corresponds to the second stage in a model of four differentiation stages in adult hippocampal neural precursor cells. DEX decreased ADP proliferation, but Li did not have any effect on it. However, Li recovered ADP proliferation decreased by DEX. The recovery effect of Li was abolished by quercetin, an inhibitor of beta-catenin/TCF pathway. The intranuclear translocation of beta-catenin and expression of cyclin D1 are reciprocally regulated by DEX and Li in a way similar to proliferation. In addition, DEX increased the phosphorylation of Tyr(216), which renders glycogen synthase kinase-3beta (GSK-3beta) active on it. These results suggest that GSK-3beta and beta-catenin/TCF pathway might be important in the reciprocal effects between DEX and Li on ADP proliferation and are new targets of therapeutic agents for stress-related disorders.

Opposite effects of early maternal deprivation on neurogenesis in male versus female rats

Background

Major depression is more prevalent in women than in men. The underlying neurobiological mechanisms are not well understood, but recent data shows that hippocampal volume reductions in depressed women occur only when depression is preceded by an early life stressor. This underlines the potential importance of early life stress, at least in women, for the vulnerability to develop depression. Perinatal stress exposure in rodents affects critical periods of brain development that persistently alter structural, emotional and neuroendocrine parameters in adult offspring. Moreover, stress inhibits adult hippocampal neurogenesis, a form of structural plasticity that has been implicated a.o. in antidepressant action and is highly abundant early postnatally. We here tested the hypothesis that early life stress differentially affects hippocampal structural plasticity in female versus male offspring.

Principal Findings

We show that 24 h of maternal deprivation (MD) at PND3 affects hippocampal structural plasticity at PND21 in a sex-dependent manner. Neurogenesis was significantly increased in male but decreased in female offspring after MD. Since no other structural changes were found in granule cell layer volume, newborn cell survival or proliferation rate, astrocyte number or gliogenesis, this indicates that MD elicits specific changes in subsets of differentiating cells and differentially affects immature neurons. The MD induced sex-specific effects on neurogenesis cannot be explained by differences in maternal care.

Conclusions

Our data shows that early environment has a critical influence on establishing sex differences in neural plasticity and supports the concept that the setpoint for neurogenesis may be determined during perinatal life. It is tempting to speculate that a reduced level of neurogenesis, secondary to early stress exposure, may contribute to maladaptation of the HPA axis and possibly to the increased vulnerability of women to stress-related disorders.

Depression-like behaviour in neural cell adhesion molecule (NCAM)-deficient mice and its reversal by an NCAM-derived peptide, FGL

The neural cell adhesion molecule (NCAM) plays a pivotal role in brain plasticity. Brain plasticity itself has a crucial role in the development of depression. The aim of this study was to analyze whether NCAM-deficient (NCAM(-/-)) mice exhibit depression-like behaviour and whether a peptide termed FGL, derived from the NCAM binding site for the fibroblast growth factor (FGF) receptor, is able to reverse the depression-like signs in NCAM(-/-) mice. Our study showed that NCAM(-/-) mice demonstrated increased freezing time in the tail-suspension test and reduced preference for sucrose consumption in the sucrose preference test, reduced adult neurogenesis in the dentate gyrus and reduced levels of the phosphorylated cAMP response element-binding protein (pCREB) in the hippocampus. FGL administered acutely or repeatedly reduced depression-like behaviour in NCAM(-/-) mice without having an effect on their wild-type littermates. Repeated administration of FGL enhanced survival of the newly born neurons in NCAM(-/-) mice and increased the levels of pCREB in both NCAM(+/+) and NCAM(-/-) mice. In conclusion, our data demonstrate that NCAM deficiency in mice results in a depression-like phenotype which can be reversed by the acute or repeated administration of FGL. The results also suggest a role of the deficit in NCAM signalling through the FGF receptor in depression.