Depression: a case of neuronal life and death?

Retinoic acid signaling and function in the adult hippocampus

Retinoic acid (RA) is an essential growth factor, derived from vitamin A, which controls growth by activating specific receptors that are members of the nuclear receptor family of transcriptional regulators. Its function in control of growth and differentiation in the embryonic CNS has been extensively investigated, but a role for RA in the mature brain has only recently become apparent. Although the adult CNS has much less capacity for change compared to the embryonic CNS, a limited amount of flexibility, referred to as neural plasticity, still exists. It is these processes that RA influences in the adult brain, including long-term potentiation and neurogenesis. The hippocampus is a brain region dependent upon neural plasticity for its function in learning and memory, and this review focuses on the roles that RA may play in regulating these processes in the adult.

Hippocampal neurogenesis: Opposing effects of stress and antidepressant treatment

The hippocampus is one of several limbic brain structures implicated in the pathophysiology and treatment of mood disorders. Preclinical and clinical studies demonstrate that stress and depression lead to reductions of the total volume of this structure and atrophy and loss of neurons in the adult hippocampus. One of the cellular mechanisms that could account for alterations of hippocampal structure as well as function is the regulation of adult neurogenesis. Stress exerts a profound effect on neurogenesis, leading to a rapid and prolonged decrease in the rate of cell proliferation in the adult hippocampus. In contrast, chronic antidepressant treatment up-regulates hippocampal neurogenesis, and could thereby block or reverse the atrophy and damage caused by stress. Recent studies also demonstrate that neurogenesis is required for the actions of antidepressants in behavioral models of depression. This review discusses the literature that has lead to a neurogenic hypothesis of depression and antidepressant action, as well as the molecular and cellular mechanisms that underlie the regulation of adult neurogenesis by stress and antidepressant treatment.

Impaired fear memory and decreased hippocampal neurogenesis following olfactory bulbectomy in rats

It has been proposed that a decrease in adult hippocampal neurogenesis provides a biological and cellular basis for major depression. The olfactory bulbectomy (OB) in rats is widely accepted as an animal model of depression. In the present study, we investigated the effect of OB on memory formation in the memory tasks related to the hippocampal function and adult hippocampal neurogenesis. OB induced a behavioural syndrome, which was characterized by an increased activity in the open-field test and impairment in passive avoidance behaviour and contextual fear conditioning. The behavioural changes, following OB, were accompanied by a decrease in the number of proliferating cells in the dentate gyrus. Furthermore, the differentiation of the newly born cells, into mature calbindin-positive neurons, was also retarded. Stereological analysis revealed a decrease in the total granule neuron numbers within the granule cell layer of the dentate gyrus, without a significant decrease in volume of the dentate gyrus. Although a relationship between altered neurogenesis and behavioural syndrome, induced by OB, is not established yet, our results suggest that decreased neurogenesis might at least partly contribute for behavioural deficits following OB.

Cytokines sing the blues: inflammation and the pathogenesis of depression

Increasing amounts of data suggest that inflammatory responses have an important role in the pathophysiology of depression. Depressed patients have been found to have higher levels of proinflammatory cytokines, acute phase proteins, chemokines and cellular adhesion molecules. In addition, therapeutic administration of the cytokine interferon-alpha leads to depression in up to 50% of patients. Moreover, proinflammatory cytokines have been found to interact with many of the pathophysiological domains that characterize depression, including neurotransmitter metabolism, neuroendocrine function, synaptic plasticity and behavior. Stress, which can precipitate depression, can also promote inflammatory responses through effects on sympathetic and parasympathetic nervous system pathways. Finally, depression might be a behavioral byproduct of early adaptive advantages conferred by genes that promote inflammation. These findings suggest that targeting proinflammatory cytokines and their signaling pathways might represent a novel strategy to treat depression.

Raised circulating corticosterone inhibits neuronal differentiation of progenitor cells in the adult hippocampus

Neurons are added throughout life to the dentate gyrus of the hippocampus of the mammalian brain. Progenitors residing in the dentate gyrus progress through three distinct stages of adult neurogenesis: proliferation, survival and differentiation. One of the most potent factors which regulates adult neurogenesis is adrenal-derived glucocorticoids. Raised levels of glucocorticoids suppress progenitor division, while removal of glucocorticoids by adrenalectomy stimulates proliferation of these cells in the dentate gyrus. We have recently reported that both pre- and post-mitotic corticoid environments powerfully regulate survival of progenitor cells in a time-dependent manner. However, it is unknown if glucocorticoids alter the process of neuronal differentiation, since not all of the newly-formed cells acquire a neuronal fate during development. Here we employ triple immuno-fluorescence staining techniques to phenotype surviving progenitor cells 28 days after labeling. Results show that high levels of corticosterone (the major glucocorticoid in rodents) either before or after progenitor labeling discouraged the acquisition of neuronal fate. Similar to its effect on survival, post-mitotic corticosterone also regulates neuronal differentiation in a time-dependent fashion, but this action is most prominent from around 19–27 days after the cells were born. In contrast, a corticoid-free environment either before or after progenitor proliferation did not affect neuronal differentiation. Combining these data with previous survival data obtained from the same animals allowed us to estimate the total number of neurons formed resulting from different corticoid treatments. Raised corticosterone significantly reduced neuronal production while adrenalectomy resulted in significantly higher number of neurons in the adult male rat hippocampus.

Psychiatry as a clinical neuroscience discipline

One of the fundamental insights emerging from contemporary neuroscience is that mental illnesses are brain disorders. In contrast to classic neurological illnesses that involve discrete brain lesions, mental disorders need to be addressed as disorders of distributed brain systems with symptoms forged by developmental and social experiences. While genomics will be important for revealing risk, and cellular neuroscience should provide targets for novel treatments for these disorders, it is most likely that the tools of systems neuroscience will yield the biomarkers needed to revolutionize psychiatric diagnosis and treatment. This essay considers the discoveries that will be necessary over the next two decades to translate the promise of modern neuroscience into strategies for prevention and cures of mental disorders. To deliver on this spectacular new potential, clinical neuroscience must be integrated into the discipline of psychiatry, thereby transforming current psychiatric training, tools, and practices.

From clinical research to clinical practice: a 4-year review of ziprasidone

Ziprasidone is a second-generation antipsychotic that received Food and Drug Administration approval in February 2001. It has a unique receptor profile that includes high-affinity antagonist activity at dopamine D2 receptors, inverse agonist activity at serotonin (5-HT)2A receptors, agonist activity at 5-HTlA receptors, and a relatively high affinity for the serotonin and norepinephrine transporters. The 5-HTIA affinity, together with the inhibitory effect on mono-amine reuptake, may underlie the hypothesized beneficial effects on comorbid affective and cognitive abnormalities in schizophrenia and schizoaffective disorder. The short-term efficacy of ziprasidone for core positive symptoms of schizophrenia appears to be comparable to other conventional and atypical antipsychotics. The short-term efficacy of ziprasidone in acute mania has been established based on two 3-week, double-blind, placebo-controlled trials.Open-label treatment for up to 52 weeks confirms the sustained efficacy and safety of ziprasidone in bipolar disorder. Maintenance studies in schizophrenia and schizoaffective disorder indicate that long-term ziprasidone therapy is effective in preventing relapse, while maintaining cognitive and psychosocial benefits. The safety database suggests that the overall cardiovascular and cerebrovascular risk associated with ziprasidone is lower than with other atypicals, with notably lower risk of drug-related increases in weight, glucose, or lipids. The data also suggest a modestly increased risk of QTc prolongation that is not dose related or linked to torsades de pointes. Switching to ziprasidone from other atypicals appears to improve both clinical symptoms and metabolic parameters, though more studies are needed to fully characterize these benefits. This monograph summarizes the efficacy, tolerability, and safety of oral ziprasidone in the treatment of schizophrenia, schizoaffective disorder, and bipolar mania.

The Cingulate as a Catalyst Region for Global Dysfunction: a Dynamical Modelling Paradigm

The anterior cingulate (AC) often exhibits both structural and functional abnormalities in affective disorders. Neither the cause for this vulnerability nor its effect on behaviour is known. Due to its extensive connectivity, minor output changes from the AC may exert widespread consequences. A causal model describing coupling coefficients (effective connectivity) among several brain regions in healthy subjects performing a memory task inspired our work. This stationary causal analysis provides a theoretical framework for our nonlinear dynamical models. We tested the effects of global and local perturbations upon stability of a systems-level neural network of interconnected brain regions. Interactions between regions, represented by path coefficients, were modelled using connectivity matrices. We found that both characteristic behaviour and response to perturbation differed in networks representing perceptual matching and long-delay conditions. Owing to the highly interconnected character of the networks, activation of a few areas was sufficient to trigger characteristic patterns of behaviour. However, only perturbation of key regions resulted in global dysfunction. Likewise, recovery of function was possible by increasing output from some, but not all, regions. We suggest for this recovery to be context specific, conditional on the task, integrity of other regions and global properties such as neuronal excitability.

Neurotrophic factors and regulation of mood: role of exercise, diet and metabolism

Results from basic and clinical studies demonstrate that stress and depression decrease neurotrophic factor expression and neurogenesis in brain, and that antidepressant treatment blocks or reverses these effects, leading to a neurotrophic hypothesis of depression. Neurotrophic factor expression and neurogenesis are also decreased during aging and could be risk factors for depression. In contrast, exercise and enriched environment increase neurotrophic support and neurogenesis, which could contribute to the blockade of the effects of stress and aging and produce antidepressant effects. A brief overview of this work and the specific neurotrophic factors involved are discussed in this review.

The Role of Glial Adenosine Receptors in Neural Resilience and the Neurobiology of Mood Disorders

Adenosine receptors were classified into A1- and A2-receptors in the laboratory of Bernd Hamprecht more than 25 years ago. Adenosine receptors are instrumental to the neurotrophic effects of glia cells. Both microglia and astrocytes release after stimulation via adenosine receptors factors that are important for neuronal survival and growth. Neuronal resilience is now considered as of pivotal importance in the neurobiology of mood disorders and their treatment. Both sleep deprivation and electroconvulsive therapy, two effective therapeutic measures in mood disorders, are associated with an increase of adenosine and upregulation of adenosine A1-receptors in the brain. Parameters closely related to adenosine receptor activation such as cerebral metabolic rate and delta power in the sleep EEG provide indirect evidence that adenosinergic signaling may be associated with the therapeutic response to these measures. Thus, neurotrophic effects evoked by adenosine receptors might be important in the mechanism of action of ECT and perhaps also sleep deprivation.

Intermittent individual housing increases survival of newly proliferated cells

In this study, we analyzed how intermittent individual housing with or without a running wheel influenced corticosterone levels and survival of newly proliferated cells in the dentate gyrus of the hippocampus. Female Balb/c mice, in standard or enhanced housing, were divided into groups that were individually housed with or without running wheels on every second day. Intermittent individual housing without, but not with, running wheels increased survival of proliferated cells in the dentate gyrus as compared with continuous group housing in standard or enhanced conditions. Thus, changes in housing conditions on every second day can, under certain circumstances, have an impact on the survival of newly proliferated cells in the dentate gyrus.

Dépression et neuroplasticité : implication des systèmes sérotoninergiques

Neuroplasticity contributes to both normal and pathological brain function. A recent hypothesis links depression to lack of adaptive responses to stress or other aversive stimuli, and effects of antidepressant treatments on adult neurogenesis are more and more extensively studied because of the structural changes involved in the pathophysiology of depression. Indeed, neuronal remodelling in hippocampal formation is associated with chronic stress and is reversed by antidepressant treatments in animals. Decrease in hippocampal volume has also been associated to cognitive deficits in patients with major depression. Interestingly, serotonergic (5-HT) systems play a major role both as antidepressants and by increasing hippocampal neurogenesis through various receptor subtypes. Recently, we have also demonstrated that agomelatine, a new antidepressant drug having serotonergic and melatonergic properties, can increase proliferation and survival of newly formed hippocampal cells. Although the mechanisms underlying such effects are still unknown, these data reinforce the view that changes in hippocampal neurogenesis might belong to the cellular correlates of mood disorders.

Social threat and novel cage stress-induced sustained extracellular-regulated kinase1/2 (ERK1/2) phosphorylation but differential modulation of brain-derived neurotrophic factor (BDNF) expression in the hippocampus of NMRI mice

The extracellular signal-regulated kinase1/2 (ERK1/2) pathway has a key role in cell survival and brain plasticity, processes that are impaired following exposure to stressful situations. We have recently validated two repeated intermittent stress procedures in male NMRI mice, social threat and repeated exposure to a novel cage, which result in clear behavioral effects following 4 weeks of application. The present results demonstrate that both repeated intermittent stress procedures alter the activity of the ERK1/2 pathway in the brain, as shown by changes in phosphorylated ERK1/2 (phospho-ERK1/2) protein expression and in the expression of downstream proteins: phosphorylated cAMP response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF), in the hippocampus, the frontal cortex and the hypothalamus. The hippocampus showed greater responsiveness to stress as the two stressors increased phospho-ERK1/2 and BDNF expression under acute condition. Following repeated stress, hyperphosphorylation of ERK1/2 was associated with up-regulation of hippocampal BDNF expression in the social threat group but not in mice exposed to novel cage. This lack of a pro-survival effect of ERK1/2 with repeated novel cage exposure may constitute an early event in stress-mediated brain pathology. The sustained BDNF up-regulation in the hippocampi of mice subjected to repeated social threat could be related to rewarding aspects of aggressive interactions, suggested by our previous studies.

The role of 5-HT1A receptors in the proliferation and survival of progenitor cells in the dentate gyrus of the adult hippocampus and their regulation by corticoids

These experiments explore the role of 5-HT1A receptors in the regulation of cell proliferation in the dentate gyrus of the intact and adrenalectomized adult rat. Depleting 5-HT with p-chlorophenylalanine (300 mg/kg initially followed by 100 mg/kg/day) or stimulating 5-HT1A receptors with 8-OH-DPAT (1 mg/kg or 2 mg/kg, s.c. injections twice daily) for 14 days had no effect on cell proliferation as measured by Ki-67 or BrdU (5-bromo-3-deoxyuridine) immunocytochemistry in the dentate gyrus. However, combined treatment with p-chlorophenylalanine followed by 8-OH-DPAT significantly increased cell proliferation compared with p-chlorophenylalanine alone. Micro-injection of the 5-HT neurotoxin 5,7-dihydroxytryptamine into the fimbria-fornix (3.0 microg/side) and the cingulate bundle (1.8 microg/side) depleted hippocampal 5-HT locally but did not change cell proliferation 3 weeks after the surgery. However, 8-OH-DPAT (1 mg/kg, twice daily) stimulated cell proliferation in the dentate gyrus of hippocampal 5-HT-depleted rats compared with controls. These results suggest that 5-HT(1A) modulates cell proliferation in the hippocampus by a direct post-synaptic effect. Previous studies demonstrate that adrenalectomy increases hippocampal 5-HT1A receptor expression and binding, and thus we investigated whether the effect of adrenalectomy on cell proliferation and survival was dependent on the activity of the 5-HT1A receptors. In contrast to the null effect following twice-daily s.c. injection, 8-OH-DPAT (2.0 mg/kg/day) delivered by s.c. osmotic pumps increased proliferation in intact rats. The 5-HT1A antagonist WAY-100635 (1.5 mg/kg/day also delivered by osmotic pump) by itself did not alter cell proliferation, confirming that reduced serotonin activity does not change proliferation, but blocked the effect of 8-OH-DPAT. However, WAY-100635 could not block the stimulating action of adrenalectomy cell proliferation. 5-HT1A mRNA expression was not altered in the hippocampus by adrenalectomy. Thus, the effect of adrenalectomy on cell proliferation and survival is not 5-HT1A dependent, despite the interaction between 5-HT1A and corticosterone.

Retrospective birth dating of cells in humans

The generation of cells in the human body has been difficult to study, and our understanding of cell turnover is limited. Testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope 14C in the atmosphere, followed by an exponential decrease after 1963. We show that the level of 14C in genomic DNA closely parallels atmospheric levels and can be used to establish the time point when the DNA was synthesized and cells were born. We use this strategy to determine the age of cells in the cortex of the adult human brain and show that whereas nonneuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region. Retrospective birth dating is a generally applicable strategy that can be used to measure cell turnover in man under physiological and pathological conditions.

Suicide brain is associated with decreased expression of neurotrophins

BACKGROUND

Neurotrophins mediate diverse biological responses, including maintenance and growth of neurons and synaptic plasticity in adult brain. This study examined whether suicide brain is associated with changes in the expression of neurotrophins.

METHODS

Messenger ribonucleic acid (mRNA) levels of nerve growth factor (NGF), neurotrophin (NT)-3, NT-4/5, and of cyclophilin and neuron-specific enolase (NSE) were measured by quantitative reverse transcriptase polymerase chain reaction, whereas protein levels of neurotrophins were determined by enzyme-linked immunosorbent assay, in prefrontal cortex (PFC) and hippocampus from 28 suicide victims and 21 control subjects.

RESULTS

In hippocampus of suicide subjects compared with control subjects mRNA levels of NGF (p < .001), NT-3 (p < .001), and NT-4/5 (p < .001) were decreased, whether or not they were expressed as a ratio to cyclophilin or NSE. This was accompanied by a decrease in their respective protein levels (NGF [p < .001], NT-3 [p < .001], and NT-4/5 [p < .001]). In PFC, however, mRNA (p = .001) and protein (p < .001) levels of NT-4/5 and only protein level of NGF (p < .001) were decreased; NT-3 levels were unchanged.

CONCLUSIONS

Given the role of neurotrophins in synaptic plasticity and maintenance of adult neurons, our findings of altered expression of neurotrophins in postmortem brain of suicide victims suggest that these molecules might play a vital role in the pathophysiology of suicide.

Examining SLV-323, a novel NK1 receptor antagonist, in a chronic psychosocial stress model for depression

RATIONALE

Substance P antagonists have been proposed as candidates for a new class of antidepressant compounds.

OBJECTIVES

We examined the effects of SLV-323, a novel neurokinin 1 receptor (NK1R) antagonist, in the chronic psychosocial stress paradigm of adult male tree shrews.

METHODS

Animals were subjected to a 7 day period of psychosocial stress before being treated daily with SLV-323 (20 mg kg(-1) day(-1)). The psychosocial stress continued throughout the treatment period of 28 days. Brain metabolite concentrations were determined in vivo by proton magnetic resonance spectroscopy. Norepinephrine excretion was monitored from daily urine samples, and serum testosterone concentrations were measured at the end of the experiment. All animals were videotaped daily to analyze scent-marking behavior and locomotor activity. Cell proliferation in the dentate gyrus and hippocampal volume were measured postmortem.

RESULTS

Stress significantly decreased cerebral concentrations of N-acetyl-aspartate, total creatine, and choline-containing compounds in vivo and resulted in an increase of urinary norepinephrine and decrease of serum testosterone concentrations. Moreover, stressed animals displayed decreased scent-marking behavior and locomotor activity. The proliferation rate of the granule precursor cells in the dentate gyrus was reduced, and hippocampal volume was mildly decreased. The stress-induced alterations in the central nervous system were partially prevented by concomitant administration of SLV-323, while drug treatment had only a minor effect on the stress-induced behavioral changes.

CONCLUSIONS

The novel NK1R antagonist SLV-323 has certain antidepressant-like effects in a valid animal model of depression.

Thyroid hormone regulates hippocampal neurogenesis in the adult rat brain

We have examined the influence of thyroid hormone on adult hippocampal neurogenesis, which encompasses the proliferation, survival and differentiation of dentate granule cell progenitors. Using bromodeoxyuridine (BrdU), we demonstrate that adult-onset hypothyroidism significantly decreases hippocampal neurogenesis. This decline is predominantly the consequence of a significant decrease in the survival and neuronal differentiation of BrdU-positive cells. Both the decreased survival and neuronal differentiation of hippocampal progenitors could be rescued by restored euthyroid status. Adult-onset hyperthyroidism did not influence hippocampal neurogenesis, suggesting that the effects of thyroid hormone may be optimally permissive at euthyroid levels. Our in vivo and in vitro results revealed that adult hippocampal progenitors express thyroid receptor isoforms. The in vitro studies demonstrate that adult hippocampal progenitors exhibit enhanced proliferation, survival and glial differentiation in response to thyroid hormone. These results support a role for thyroid hormone in the regulation of adult hippocampal neurogenesis and raise the possibility that altered neurogenesis may contribute to the cognitive and behavioral deficits associated with adult-onset hypothyroidism.

Mechanisms of action of antidepressants: from neurotransmitter systems to signaling pathways

Antidepressants are commonly used in the treatment of anxiety and depression, medical conditions that affect approximately 17-20% of the population. The clinical effects of antidepressants take several weeks to manifest, suggesting that these drugs induce adaptive changes in brain structures affected by anxiety and depression. In order to develop shorter-acting and more effective drugs for the treatment of anxiety and depression, it is important to understand how antidepressants bring about their beneficial effects. Recent reports suggest that antidepressants can induce neurogenesis in the adult brain, although the mechanisms involved are not clearly understood. In this review, we describe the different neurotransmitter systems that are affected by anxiety and depression and how they are modulated by antidepressant treatment with a focus on signaling molecules and pathways that are activated during neurotransmitter receptor induced neurogenesis.

Selective neuron loss in the paraventricular nucleus of hypothalamus in patients suffering from major depression and bipolar disorder

The structural basis for depressive disorders remains unknown. Studies using neuroimaging and postmortem brain tissue indicate that anatomic substrates may contribute to major depression disorder (MDD) and bipolar disorder (BD). The present study used design-based stereology to assess neuron loss in 2 well-defined hypothalamic structures, the paraventricular nucleus (PVN) and supraoptic nucleus (SON), in clinically well-studied cases with severe depression. The left or right diencephalon was blocked from 26 brains removed at autopsy from age-matched controls (5 male/3 female) and patients with MDD (6 male/5 female) and BD (5 male/2 female). Serial sections were cut at an instrument setting of 60 microm through the entire PVN and SON from left hypothalamus and 8 to 10 sections per brain were systematic-random sampled and stained with cresyl violet. A trained operator blind to clinical diagnosis used computerized stereology to estimate total neuron numbers in PVN and SON. The results revealed a selective, robust reduction of approximately 50% in total neuron number in the PVN for major depression and bipolar cases compared with age-matched controls, with no differences in neuron numbers in the SON. This selective neuronal loss in the PVN appears to identify an important neurobiologic substrate for the behavioral manifestations of depression.

Antidepressant-like effects of uridine and omega-3 fatty acids are potentiated by combined treatment in rats

BACKGROUND

Brain phospholipid metabolism and membrane fluidity may be involved in the pathophysiology of mood disorders. We showed previously that cytidine, which increases phospholipid synthesis, has antidepressant-like effects in the forced swim test (FST) in rats, a model used in depression research. Because cytidine and uridine both stimulate synthesis of cytidine 5'-diphosphocholine (CDP-choline, a critical substrate for phospholipid synthesis), we examined whether uridine would also produce antidepressant-like effects in rats. We also examined the effects of omega-3 fatty acids (OMG), which increase membrane fluidity and reportedly have antidepressant effects in humans, alone and in combination with uridine.

METHODS

We first examined the effects of uridine injections alone and dietary supplementation with OMG alone in the FST. We then combined sub-effective treatment regimens of uridine and OMG to determine whether these agents would be more effective if administered together.

RESULTS

Uridine dose-dependently reduced immobility in the FST, an antidepressant-like effect. Dietary supplementation with OMG reduced immobility when given for 30 days, but not for 3 or 10 days. A sub-effective dose of uridine reduced immobility in rats given sub-effective dietary supplementation with OMG.

CONCLUSIONS

Uridine and OMG each have antidepressant-like effects in rats. Less of each agent is required for effectiveness when the treatments are administered together.

Lithium: Potential Therapeutics Against Acute Brain Injuries and Chronic Neurodegenerative Diseases

In addition to the well-documented mood-stabilizing effects of lithium in manic-depressive illness patients, recent in vitro and in vivo studies in rodents and humans have increasingly implicated that lithium can be used in the treatment of acute brain injuries (e.g., ischemia) and chronic neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, tauopathies, and Huntington's disease). Consistent with this novel view, substantial evidences suggest that depressive illness is not a mere neurochemical disease, but is linked to gray matter atrophy due to the reduced number/size of neurons and glia in brain. Importantly, neurogenesis, that is, birth/maturation of functional new neurons, continues to occur throughout the lifetime in human adult brains (e.g., hippocampus); the neurogenesis is impaired by multiple not-fully defined factors (e.g., aging, chronic stress-induced increase of glucocorticoids, and excitotoxicity), accounting for brain atrophy in patients with depressive illness and neurodegenerative diseases. Chronic treatment of lithium, in agreement with the delayed-onset of mood-stabilizing effects of lithium, up-regulates cell survival molecules (e.g., Bcl-2, cyclic AMP-responsive element binding protein, brain-derived neurotrophic factor, Grp78, Hsp70, and beta-catenin), while down-regulating pro-apoptotic activities (e.g., excitotoxicity, p53, Bax, caspase, cytochrome c release, beta-amyloid peptide production, and tau hyperphosphorylation), thus preventing or even reversing neuronal cell death and neurogenesis retardation.

New neurons in old brains

The brain was traditionally viewed as a static organ, without turnover of neurons or significant capacity for self-repair after insults. Research in the last years has established that neurons are renewed in certain areas throughout life. The prospect of stimulation of endogenous neurogenesis as well as cell transplantation has raised hope for new therapies for neurological diseases.

Chronic olanzapine or fluoxetine administration increases cell proliferation in hippocampus and prefrontal cortex of adult rat

BACKGROUND

There has been increasing evidence that atypical antipsychotics are effective in the treatment of mood disorders or for augmenting 5-hydroxytryptamine selective reuptake inhibitors for treatment-resistant depression.

METHODS

Upregulation of neurogenesis in the adult hippocampus is a marker of antidepressant activity, and the present study investigated the influence of the atypical antipsychotic drug olanzapine on cell proliferation in the hippocampus of adult rat. The regulation of cell proliferation in the prelimbic cortex of adult rat was also examined.

RESULTS

Chronic (21 days) olanzapine administration increased the number of newborn cells in the dentate gyrus of the hippocampus to the same extent as fluoxetine. Olanzapine or fluoxetine treatment also increased the number of proliferating cells in the prelimbic cortex. In contrast, there was no effect of either drug in the subventricular zone or primary motor cortex, and there was a trend for an increase in the striatum. Subchronic (7 days) administration of olanzapine had no effect on cell proliferation in hippocampus or prelimbic cortex, consistent with the time course for the effect of fluoxetine and the therapeutic actions of antidepressant treatment. The combination of olanzapine plus fluoxetine did not result in a greater induction of cell proliferation in either brain region. Analysis of the cell phenotype demonstrated that approximately 20% of the newborn cells in the prelimbic cortex differentiated into endothelial cells but not neurons, in contrast to the dentate gyrus, where most newborn cells differentiated into neurons.

CONCLUSIONS

The results demonstrate that antidepressant or atypical antipsychotic medications can increase the proliferation of glia in limbic brain structures, an effect that could reverse the loss of glia that has been observed in depressed patients.