Electroconvulsive seizures increase hippocampal neurogenesis after chronic corticosterone treatment

Neurogenesis in neurological and psychiatric diseases and brain injury: from bench to bedside

Researchers who have uncovered the presence of stem cells in an adult's central nervous system have not only challenged the dogma that new neurons cannot be generated during adulthood, but also shed light on the etiology and disease mechanisms underlying many neurological and psychiatric disorders. Brain trauma, neurodegenerative diseases, and psychiatric disorders pose enormous burdens at both personal and societal levels. Although medications for these disorders are widely used, the treatment mechanisms underlying the illnesses remain largely elusive. In the past decade, an increasing amount of evidence indicate that adult neurogenesis (i.e. generating new CNS neurons during adulthood) may be involved in the pathology of different CNS disorders, and thus neurogenesis may be a potential target area for treatments. Although new neurons were shown to be a major player in mediating treatment efficacy of neurological and psychotropic drugs on cognitive functions, it is still debatable if the altered production of new neurons can cause the disorders. This review hence seeks to discuss pre and current clinical studies that demonstrate the functional impact adult neurogenesis have on neurological and psychiatric illnesses while examining the related underlying disease mechanisms.

Statins prevent adverse effects of postnatal glucocorticoid therapy on the developing brain in rats

BACKGROUND

Postnatal glucocorticoid therapy in the treatment of chronic lung disease benefits lung function, however it adversely affects brain development. We hypothesized that combined postnatal glucocorticoid and statin therapy diminishes adverse effects of glucocorticoids on the developing brain.

METHODS

On postnatal days (P) 1-3, one male pup per litter received i.p. injections of saline control (C), n = 13) or dexamethasone (0.5, 0.3, 0.1 µg/g; D, n = 13), ± pravastatin (10 mg/kg i.p.; CP, n = 12; DP, n = 15). Statins or saline continued from P4-6. At P21, brains were perfusion fixed for histological and stereological analyses.

RESULTS

Relative to controls, dexamethasone reduced total (837 ± 23 vs. 723 ± 37), cortical (378 ± 12 vs. 329 ± 15), and deep gray matter (329 ± 12 vs. 284 ± 15) volume (mm(3)), cortical neuronal number (23 ± 1 vs. 19 ± 1 × 10(6)), and hippocampal neuronal soma volume (CA1: 1,206 ± 32 vs. 999 ± 32; dentate gyrus: 679 ± 28 vs. 542 ± 24 µm(3); all P < 0.05). Dexamethasone increased the glial fibrillary acidic protein-positive astrocyte density in the white matter (96 ± 2 vs. 110 ± 4/0.1 mm(2)); P < 0.05. These effects no longer occurred in brains from pups treated with combined dexamethasone and pravastatin. Pravastatin alone had no effect on these variables.

CONCLUSION

Concomitant dexamethasone with statins in premature infants may be safer for the developing brain than dexamethasone alone in the treatment of chronic lung disease.

Genetic fate mapping of type-1 stem cell-dependent increase in newborn hippocampal neurons after electroconvulsive seizures

Electroconvulsive therapy (ECT) is a uniquely effective treatment for major depressive disorder. An increase in hippocampal neurogenesis is implicated in the recovery from depression. We used an inducible genetic mouse model in which only GFAP-expressing stem-like cells (type-1 cells) and their progeny are selectively labeled with the reporter protein β-galactosidase to track the process of neurogenesis in the dentate gyrus over 3 months following electroconvulsive seizures (ECS), the mouse equivalent of ECT. All ECS protocols tested induced a transient increase in type-1 cell divisions. While this led to an expansion of the type-1 cell pool after high-frequency ECS sessions for 5 consecutive days (5-ECS), asymmetric divisions drove neurogenesis by giving rise to Doublecortin (DCX)-expressing neuroblasts that matured into NeuN+ neurons. Significantly, the increase in newly generated DCX+ and NeuN+ cells after 5-ECS could be traced back to proliferating type-1 cells. Low-frequency continuation ECS (c-ECS) consisting of five single ECS sessions administered every 2 weeks resulted in a similar increase in newborn neurons as the high-frequency 5-ECS protocol. Moreover, the combination of 5-ECS and c-ECS led to a further significant increase in newborn neurons, suggesting a cellular mechanism responsible for the propitious effects of high-frequency ECT followed by continuation ECT in severely depressed patients. The ability of high- and low-frequency ECS to induce normally quiescent type-1 cells to proliferate and generate new neurons sets it apart from other antidepressant treatments and may underlie the superior clinical efficacy of ECT.

The neural plasticity theory of depression: assessing the roles of adult neurogenesis and PSA-NCAM within the hippocampus

Depression is a devastating and prevalent disease, with profound effects on neural structure and function; however the etiology and neuropathology of depression remain poorly understood. Though antidepressant drugs exist, they are not ideal, as only a segment of patients are effectively treated, therapeutic onset is delayed, and the exact mechanism of these drugs remains to be elucidated. Several theories of depression do exist, including modulation of monoaminergic neurotransmission, alterations in neurotrophic factors, and the upregulation of adult hippocampal neurogenesis, and are briefly mentioned in the review. However none of these theories sufficiently explains the pathology and treatment of depression unto itself. Recently, neural plasticity theories of depression have postulated that multiple aspects of brain plasticity, beyond neurogenesis, may bridge the prevailing theories. The term “neural plasticity” encompasses an array of mechanisms, from the birth, survival, migration, and integration of new neurons to neurite outgrowth, synaptogenesis, and the modulation of mature synapses. This review critically assesses the role of adult hippocampal neurogenesis and the cell adhesion molecule, PSA-NCAM (which is known to be involved in many facets of neural plasticity), in depression and antidepressant treatment.

Corticosterone combined with intramedial prefrontal cortex infusion of SCH 23390 impairs the strong fear response in high-fear-reactivity rats

Accumulating evidence suggests that stress-dose corticosteroids impair fear memory in animals and humans. Corticosteroid treatment after critical illness is seen as a potential psychotropic medication by which to prevent posttraumatic stress disorder. However, individual difference in the responsiveness to stress (i.e., stress reactivity) is a factor that modulates the efficacy of corticosteroids. To understand the contribution of fear reactivity to the effect of post-stress corticosterone, male Sprague-Dawley rats were subjected to classical tone-cued fear conditioning and separated into high and low reactivity (HR and LR, respectively) responder groups based on their levels of freezing during conditioning. The HR rats showed significantly higher fear responses than the LR rats during conditioning as assessed by freezing behavior. At two intervals, 30 min and 48 hr later, the HR rats still displayed more pronounced conditioned responses to cued stimuli compared with the LR rats. Moreover, in contrast to the LR rats, the enhanced fear response in the HR rats was difficult to attenuate by post-training high-dose corticosterone. These results suggest that fear reactivity results in stronger fear memory, and that it is difficult to disrupt this strong fear memory in the HR phenotype using monotherapy. However, the strong fear memory in the HR rats was impaired by concurrent intramedial prefrontal cortex infusion of a high dose of the dopamine D1 receptor antagonist SCH 23390 and systemic administration of corticosterone. SCH 23390 and corticosterone alone did not decrease freezing levels in the HR rats. The fear impairment induced by SCH 23390 combined with corticosterone was not attributable to the effect of these drugs on locomotor activity. This effect was not found with administration of the D2 antagonist eticlopride combined with corticosterone. Our findings demonstrate that the conditioned fear memory in individuals with high stress reactivity is difficult to disrupt using monotherapy, but that combined pharmacotherapy may be useful for treating intervention-resistant fear.

Synaptic Plasticity, But not Hippocampal Neurogenesis, Mediated the Counteractive Effect of Wolfberry on Depression in Rats

Depression is a life-threatening psychiatric disorder characterized with a long-term hypercortisolemia in depressed patients. Based on this clinical feature, hypercortisolemia was mimicked in experimental animals to understand the neuropathogy of depression and to explore new therapeutic strategies. Wolfberry, also known as Lycium barbarum, is a type of common fruit produced in mainland China. Accumulated evidence has shown that the extracts from Lycium barbarum (LBP) had a wide range of neuroprotective effects in various neurogenerative models. However, the antidepressant effect of LBP on depression and its mechanism has not yet been explored. In the present study, we investigated the effects of LBP on counteracting depression using an animal model injected with moderate dose (40 mg/kg) or severe dose (50 mg/kg) of corticosterone (CORT) treatments for 14 days. The results showed that CORT significantly increased immobility time and decreased hippocampal cell proliferation. LBP treatment significantly decreased the immobility time in forced swimming test, a test for the intensity of depressive behaviors, both in 40 and 50 mg/kg CORT stressed rats. Moreover, LBP treatment restored the reduced proliferation of neuroprogentior cells in the hippocampus in 40 mg/kg CORT stressed rats and the neuronal differentiation but not the proliferation in 50 mg/kg CORT stressed rats. After ablation of adult neurogenesis with Ara-c infusion, the beneficial effect of LBP treatment in reducing immobility time was not affected in 40 and 50 mg/kg CORT stressed rats. Golgi staining and Western blotting detection showed that LBP treatment restored the reduced spine density and the decreased level of PSD-95 in the hippocampus caused by 40 and 50 mg/kg CORT, respectively, indicating enhanced synaptic plasticity in the hippocampus. The data showed a novel effect of LBP on reducing depression-like behavior and its antidepressant effect may be mediated by enhanced synaptic plasticity, but not hippocampal neurogenesis.

Effects of chronic treatment with corticosterone and imipramine on fos immunoreactivity and adult hippocampal neurogenesis

In a previous study we showed that rats chronically treated with corticosterone (CORT) display anxiogenic behavior, evidenced by facilitation of avoidance responses in the elevated T-maze (ETM) model of anxiety. Treatment with the tricyclic antidepressant imipramine significantly reversed the anxiogenic effects of CORT, while inhibiting ETM escape, a response related to panic disorder. To better understand the neurobiological mechanisms underlying these behavioral effects, analysis of c-fos protein immunoreactivity (fos-ir) was used here to map areas activated by chronic CORT (200 mg pellets, 21-day release) and imipramine (15 mg/kg, IP) administration. We also evaluated the number of cells expressing the neurogenesis marker doublecortin (DCX) in the hippocampus and measured plasma CORT levels on the 21st day of treatment. Results showed that CORT increased fos-ir in the ventrolateral septum, medial amygdala and paraventricular hypothalamic nucleus and decreased fos-ir in the lateral periaqueductal gray. Imipramine, on the other hand, increased fos-ir in the medial amygdala and decreased fos-ir in the anterior hypothalamus. CORT also decreased the number of DCX-positive cells in the ventral and dorsal hippocampus, an effect antagonized by imipramine. CORT levels were significantly higher after treatment. These data suggest that the behavioral effects of CORT and imipramine are mediated through specific, at times overlapping, neuronal circuits, which might be of relevance to a better understanding of the physiopathology of generalized anxiety and panic disorder.

A comparison of brief pulse and ultrabrief pulse electroconvulsive stimulation on rodent brain and behaviour

Brief pulse electroconvulsive therapy (BP ECT; pulse width 0.5-1.5ms) is a very effective treatment for severe depression but is associated with cognitive side-effects. It has been proposed that ultrabrief pulse (UBP; pulse width 0.25-0.30ms) ECT may be as effective as BP ECT but have less cognitive effects because it is a more physiological form of neuronal stimulation. To investigate this further, we treated normal rats with a 10 session course of either BP (0.5ms), UBP (0.3ms), or sham electroconvulsive stimulation (ECS) and measured antidepressant-related changes in dentate gyrus cell proliferation and hippocampal BDNF protein levels as well as hippocampal-dependant spatial reference memory using the water plus maze and immobility time on the forced swim test. Both BP and UBP ECS induced very similar types of motor seizures. However, BP ECS but not UBP ECS treatment led to a significant, near 3-fold, increase in cell proliferation (p=0.026) and BDNF levels (p=0.01). In the forced swim test, only BP ECS treated animals had a significantly lower immobility time (p=0.046). There was a trend for similarly reduced hippocampal-dependent memory function in both BP and UBP groups but overall there was not a significant difference between treatment and control animals when tested 10 days after completing allocated treatment. These findings show that, even though both forms of ECS elicited similar motor seizures, UBP ECS was less efficient than BP ECS in inducing antidepressant-related molecular, cellular and behavioural changes.

Quantitative hippocampal structural changes following electroconvulsive seizure treatment in a rat model of depression

OBJECTIVE

The pathophysiology of depression and the effects of antidepressant treatment are hypothesized to be related to hippocampal structural changes. This study aims to investigate the effect of electroconvulsive seizures on behavior and hippocampal structure in a rat model of depression.

METHODS

Flinders Sensitive Line (FSL) and Flinders Resistant Line (FRL) rats were treated daily for 10 days with either electroconvulsive seizures or sham treatment. The behavior was evaluated using the forced swim test. Design-based stereological methods were used to quantify the hippocampal volume and the numbers of neurons and glial cells in specific hippocampal subregions.

RESULTS

The basal level of hippocampal volume and neuron number differed significantly between the two rat strains, and a trend toward the FSL strain having more glial cells was found. The structural differences found between the sham-treated animals were counteracted by electroconvulsive seizure (ECS) treatment, which also normalized the behavior. ECS treatment increased the number of glial cells in hilus significantly in the FRL rats and with the same tendency for the FSL rats.

CONCLUSION

Our results indicate that along with hippocampal neurogenesis, gliogenesis may also be involved in the pathophysiology of depression and in the effect of antidepressant treatment. The underlying mechanisms remain unknown, and further investigations are required to clarify whether the structural changes are necessary to induce a therapeutic effect of antidepressant treatment or if they rather represent an epiphenomenon.

Roles of NG2 glial cells in diseases of the central nervous system

NG2 cells are a novel distinct class of central nervous system (CNS) glial cells, characterized by the expression of the chondroitin sulfate proteoglycan NG2. They have been detected in a variety of human CNS diseases. As morphological, physiological and biomolecular studies of NG2 cells have been conducted, their roles have been gradually revealed. Research on cellular and molecular mechanisms in the pathophysiological state was built on the preliminary findings of their physiological functions; and in turn, this helps to clarify their physiological roles and leads to the identification of novel therapeutic targets. This review summarizes recent findings regarding the potential roles of NG2 cells in traumatic brain injury, multiple sclerosis, glioma, epilepsy, Alzheimer's disease and electroconvulsive therapy for depression.

Major depression: a role for hippocampal neurogenesis?

Since its discovery in mammals, adult neurogenesis, the process of generating functional neurons from neural progenitor cells in the adult brain, has inspired numerous animal studies. These have revealed that adult neurogenesis is a highly regulated phenomenon. Enriched environment, exercise and learning for instance, are positive regulators while stress and age are major negative regulators. Stressful life events are not only shown to reduce adult neurogenesis levels but are also discussed to be a key element in the development of various neuropsychiatric disorders such as depression. Interestingly, altered monoaminergic brain levels resulting from antidepressant treatment are shown to have a strong reinforcing effect on adult neurogenesis. Additionally, disturbed adult neurogenesis, possibly resulting in a malfunctioning hippocampus, may contribute to the cognitive deficits and reduced hippocampal volumes observed in depressed patients. Hence, the question arises as to whether disturbed adult neurogenesis and the etiopathogenesis of depression are causally linked. In this chapter, we discuss the possible causal interrelation of disturbed adult neurogenesis and the etiopathogenesis of depression as well as the possibility that adult neurogenesis is not exclusively linked to depression but is also linked to other psychiatric disorders including schizophrenia and neurodegenerative diseases like Alzheimer's disease. Additionally, we look at the functional relevance of adult neurogenesis in different species, upon which we base our discussion as to whether adult neurogenesis could be causally linked to the development of certain brain disorders in humans, or whether it is only an epiphenomenon.

Depression, antidepressants, and neurogenesis: a critical reappraisal

The neurogenesis hypothesis of depression posits (1) that neurogenesis in the subgranular zone of the dentate gyrus is regulated negatively by stressful experiences and positively by treatment with antidepressant drugs and (2) that alterations in the rate of neurogenesis play a fundamental role in the pathology and treatment of major depression. This hypothesis is supported by important experimental observations, but is challenged by equally compelling contradictory reports. This review summarizes the phenomenon of adult hippocampal neurogenesis, the initial and continued evidence leading to the development of the neurogenesis hypothesis of depression, and the recent studies that have disputed and/or qualified those findings, to conclude that it can be affected by stress and antidepressants under certain conditions, but that these effects do not appear in all cases of psychological stress, depression, and antidepressant treatment.

Hippocampal neurogenesis and dendritic plasticity support running-improved spatial learning and depression-like behaviour in stressed rats

Exercise promotes hippocampal neurogenesis and dendritic plasticity while stress shows the opposite effects, suggesting a possible mechanism for exercise to counteract stress. Changes in hippocampal neurogenesis and dendritic modification occur simultaneously in rats with stress or exercise; however, it is unclear whether neurogenesis or dendritic remodeling has a greater impact on mediating the effect of exercise on stress since they have been separately examined. Here we examined hippocampal cell proliferation in runners treated with different doses (low: 30 mg/kg; moderate: 40 mg/kg; high: 50 mg/kg) of corticosterone (CORT) for 14 days. Water maze task and forced swim tests were applied to assess hippocampal-dependent learning and depression-like behaviour respectively the day after the treatment. Repeated CORT treatment resulted in a graded increase in depression-like behaviour and impaired spatial learning that is associated with decreased hippocampal cell proliferation and BDNF levels. Running reversed these effects in rats treated with low or moderate, but not high doses of CORT. Using 40 mg/kg CORT-treated rats, we further studied the role of neurogenesis and dendritic remodeling in mediating the effects of exercise on stress. Co-labelling with BrdU (thymidine analog) /doublecortin (immature neuronal marker) showed that running increased neuronal differentiation in vehicle- and CORT-treated rats. Running also increased dendritic length and spine density in CA3 pyramidal neurons in 40 mg/kg CORT-treated rats. Ablation of neurogenesis with Ara-c infusion diminished the effect of running on restoring spatial learning and decreasing depression-like behaviour in 40 mg/kg CORT-treated animals in spite of dendritic and spine enhancement. but not normal runners with enhanced dendritic length. The results indicate that both restored hippocampal neurogenesis and dendritic remodelling within the hippocampus are essential for running to counteract stress.

Effects of repeated electroconvulsive seizure on cell proliferation in the rat hippocampus

Electroconvulsive therapy (ECT) is known as a successful treatment for severe depression. Despite great efforts, the biological mechanisms underlying the beneficial effects of ECT remain largely unclear. In this study, animals received a single, 10, or 20 applications of electroconvulsive seizure (ECS), and then cell proliferation and apoptosis were investigated in the subgranular zone (SGZ) of the dentate gyrus. We analyzed whether a series of ECSs could induce changes in the dentate gyrus in a dose-response fashion. A single-ECS seizure significantly increased cell proliferation in the SGZ by ∼2.3-fold compared to sham treatment. After 10 ECSs, a significant increase in cell proliferation was observed in the SGZ by ∼2.4-fold compared to sham treatment. Moreover, 10 ECSs induced a significant increase in cell proliferation by 1.3-fold compared to a single-ECS group. However, cell proliferation did not differ between the group with 20 ECSs and sham group. In addition, a significant increase in the number of apoptotic cells was found in the group with 10 ECSs, whereas no significant change in it was found in either a single ECS or 20 ECSs group compared to sham treatment. These findings indicate that the optimal number of treatments and duration of stimulation requires investigation. Further studies are needed to elucidate the intracellular mechanisms underlying both effective and excessive ECT.

How does electroconvulsive therapy work? Theories on its mechanism

This article reviews 3 current theories of electroconvulsive therapy (ECT). One theory points to generalized seizures as essential for the therapeutic efficacy of ECT. Another theory highlights the normalization of neuroendocrine dysfunction in melancholic depression as a result of ECT. A third theory is based on recent findings of increased hippocampal neurogenesis and synaptogenesis in experimental animals given electroconvulsive seizures. Presently, the endocrine theory has the strongest foundation to explain the working mechanism of ECT.

Effect of corticosterone and paroxetine on masculine mating behavior: possible involvement of neurogenesis

INTRODUCTION

Corticosterone inhibits male rodent sexual behavior while the mechanism remains obscured. Recent studies have disclosed that neurogenesis in the subventricular zone (SVZ) can be increased by pheromone exposure from the opposite sex, and neurogenesis is essential for normal mating behavior of female mice. Together with the neurogenesis-inhibiting effect of corticosterone, we hypothesize that cell proliferation in the olfactory system is essential for male rodent sexual functioning.

AIM

The current study explored the relationship between cell proliferation in the olfactory system and male sexual behavior.

MAIN OUTCOME MEASURES

Sexual behavior performance, proliferative cell counts, and c-fos-expressing cell counts.

METHODS

Adult male rats were treated with corticosterone and/or paroxetine, an antidepressant, for 2 weeks. These two drugs were shown to suppress and enhance hippocampus and SVZ cell proliferation, respectively. Mating behavior was assessed after the treatment, and proliferation of new cells and c-fos-expressing cells, activated neurons in the mating-related regions in the brain, were analyzed. To further confirm the necessity of cell proliferation in mating, inhibition of cell proliferation was performed by intracerebroventricular infusion of cytostatic cytosine arabinose (Ara-c).

RESULTS

Corticosterone treatment, which inhibited cell proliferation in both the SVZ and olfactory epithelium, led to inhibited male sexual performance. In contrast, paroxetine increased cell proliferation and improved the performance in corticosterone-treated animals. When cell proliferation in the brain was inhibited by Ara-c, a suppressed sexual performance was found. However, cell proliferation in olfactory epithelium was not inhibited by Ara-c and thus the sexual inhibition is unlikely to be linked to this region. Furthermore, a decrease in c-fos expression in the mating-related regions upon female pheromone stimulation was found.

CONCLUSIONS

These results suggest that cell proliferation in the SVZ and hippocampus may be involved in the reproduction of the male rodents, and pharmacological treatments may affect sexual functioning through alteration of neurogenesis.

How antidepressant drugs act: A primer on neuroplasticity as the eventual mediator of antidepressant efficacy

Depression is conventionally viewed as a state of chemical imbalance, and antidepressants are suggested to act through increasing monoaminergic neurotransmission. These views are currently considered simplistic. This article examines the animal and human literature on the neurohistological mechanisms underlying stress, depression and antidepressant treatment. Pathological stress and depression are associated with changes such as loss of dendritic spines, shrinkage of the dendritic tree and loss of synapses in the hippocampus and prefrontal cortex. There is also a decrease in glia. Apoptosis may occur under extreme circumstances. In contrast, there is increased dendritic arborization and synaptogenesis in the amygdala. Antidepressant treatment protects against and even reverses some but not all of these stress-induced neurohistological changes. Pathological stress results in an aberrant neuroplasticity response characterized by abnormally increased activity in the amygdala and by impaired functioning of the hippocampus, prefrontal cortex and downstream structures. This aberrant neuroplasticity response directly explains most of the clinical symptoms of depression. Antidepressant treatment protects against stress-induced pathoplastic neurohistological and neurocognitive changes. Antidepressant treatment also restores functional neuroplasticity in stressed organisms and, thereby, presumably, facilitates re-adaptation through learning and memory mechanisms. Thus, the stress-depression syndrome and the therapeutic and prophylactic efficacy of antidepressant treatments can be explained through a hardwiring analogy. In this context, glutamate is an important neurotransmitter.

The antidepressant effects of running and escitalopram are associated with levels of hippocampal NPY and Y1 receptor but not cell proliferation in a rat model of depression

One hypothesis of depression is that it is caused by reduced neuronal plasticity including hippocampal neurogenesis. In this study, we compared the effects of three long-term antidepressant treatments: escitalopram, voluntary running, and their combination on hippocampal cell proliferation, NPY and the NPY-Y1 receptor mRNAs, targets assumed to be important for hippocampal plasticity and mood disorders. An animal model of depression, the Flinders Sensitive Line (FSL) rat, was used and female rats were chosen because the majority of the depressed population is females. We investigated if these treatments were correlated to immobility, swimming, and climbing behaviors, which are associated with an overall, serotonergic-like and noradrenergic-like antidepressant response, in the Porsolt swim test (PST). Interestingly, while escitalopram, running and their combination increased the number of hippocampal BrdU immunoreactive cells, the antidepressant-like effect was only detected in the running group and the group with access both to running wheel and escitalopram. Hippocampal NPY mRNA and the NPY-Y1 receptor mRNA were elevated by running and the combined treatment. Moreover, correlations were detected between NPY mRNA levels and climbing and cell proliferation and NPY-Y1 receptor mRNA levels and swimming. Our results suggest that increased cell proliferation is not necessarily associated with an antidepressant effect. However, treatments that were associated with an antidepressant-like effect did regulate hippocampal levels of mRNAs encoding NPY and/or the NPY-Y1 receptor and support the notion that NPY can stimulate cell proliferation and induce an antidepressant-like response.

Behavioral and neurobiological consequences of prolonged glucocorticoid exposure in rats: relevance to depression

Stress is a critical environmental trigger for the development of clinical depression, yet little is known about the specific neurobiological mechanisms by which stress influences the development of depressive symptomatology. Animal models provide an efficient way to study the etiology of human disorders such as depression, and a number of preclinical models have been developed to assess the link between stress, glucocorticoids, and depressive behavior. These mode ls typically make use of repeated exposure to physical or psychological stressors in rodents or other small laboratory animals. This review focuses primarily on a recently developed preclinical model of depression that uses exogenous administration of the stress hormone corticosterone (CORT) in rodents instead of exposure to physical or psychological stressors. Repeated CORT administration in rats or mice produces reliable behavioral and neurobiological alterations that parallel many of the core symptoms and neurobiological changes associated with human depression. This provides an opportunity to study behavior and neurobiology in the same animal, so that the neurobiological factors that underlie specific symptoms can be identified. Taken together, these findings suggest that exogenous CORT administration is a useful method for studying the relationship between stress, glucocorticoids, and depression. Further study with this model may provide important new data regarding the neurobiological bases of depression.

Increase in hippocampal volume after electroconvulsive therapy in patients with depression: a volumetric magnetic resonance imaging study

BACKGROUND

Major depression has traditionally been regarded as a neurochemical disease, but findings of a decreased hippocampal volume in patients with depression have turned the pathophysiological focus toward impairments in structural plasticity. The mechanisms of action of the most effective antidepressive treatment, electroconvulsive therapy (ECT), still remains elusive, but recent animal research has provided evidence for a cell proliferative effect in the hippocampus. The aim of this prospective study was to determine if hippocampal volume changes after ECT in patients with depression.

METHODS

Twelve patients with depression and ongoing antidepressive pharmacological treatment were investigated with clinical ratings and 3 T magnetic resonance imaging within 1 week before and after the ECT series. Each hippocampus was manually outlined on coronal slices, and the volume was calculated.

RESULTS

The left as well as the right hippocampal volume increased significantly after ECT.

CONCLUSIONS

The hippocampal volume increases after ECT, supporting the hypothesis that hippocampus may play a central role in the treatment of depression.

Electroconvulsive therapy: Part I. A perspective on the evolution and current practice of ECT

The concept of inducing convulsions, mainly through chemical means, to promote mental wellness has existed since the 16th century. In 1938, Italian scientists first applied electrically induced therapeutic seizures. Although electroconvulsive therapy (ECT) is employed in the treatment of several psychiatric disorders, it is most frequently used today to treat severe depressive episodes and remains the most effective treatment available for those disorders. Despite this, ECT continues to be the most stigmatized treatment available in psychiatry, resulting in restrictions on and reduced accessibility to a helpful and potentially life-saving treatment. The psychiatric and psychosocial ramifications of this stigmatization may include the exacerbation of the increasingly serious, global health problem of major depressive disorders as well as serious consequences for individual patients who may not be offered, or may refuse, a potentially beneficial treatment. The goal of this first article in this two-part series is to provide an overview of ECT's historical development and discuss the current state of knowledge about ECT, including technical aspects of delivery, patient selection, its side-effect profile, and factors that may contribute to underuse of ECT.

Intracerebroventricular infusion of cytosine-arabinoside causes prepulse inhibition disruption

Adult neurogenesis in hippocampus is associated with behaviors such as learning. Hippocampus is involved in the regulation of prepulse inhibition (PPI), but the relationship between neurogenesis and PPI is unexplored. We conducted four experiments to determine the role of neural progenitor cell proliferation in PPI. Intracerebroventricular infusion of cytostatic cytosine arabinoside caused PPI disruption but repeated exposure to PPI sessions prevented the PPI disruption. Corticosterone treatment, which decreases hippocampal cell proliferation, caused PPI disruption, whereas antidepressant and exercise, which increased cell proliferation, did not affect PPI. These results suggest that cell proliferation is involved in the first encounter with PPI test while its importance may decrease upon repeated exposures to the tests.

Target identification for CNS diseases by transcriptional profiling

Gene expression changes in neuropsychiatric and neurodegenerative disorders, and gene responses to therapeutic drugs, provide new ways to identify central nervous system (CNS) targets for drug discovery. This review summarizes gene and pathway targets replicated in expression profiling of human postmortem brain, animal models, and cell culture studies. Analysis of isolated human neurons implicates targets for Alzheimer's disease and the cognitive decline associated with normal aging and mild cognitive impairment. In addition to tau, amyloid-beta precursor protein, and amyloid-beta peptides (Abeta), these targets include all three high-affinity neurotrophin receptors and the fibroblast growth factor (FGF) system, synapse markers, glutamate receptors (GluRs) and transporters, and dopamine (DA) receptors, particularly the D2 subtype. Gene-based candidates for Parkinson's disease (PD) include the ubiquitin-proteosome system, scavengers of reactive oxygen species, brain-derived neurotrophic factor (BDNF), its receptor, TrkB, and downstream target early growth response 1, Nurr-1, and signaling through protein kinase C and RAS pathways. Increasing variability and decreases in brain mRNA production from middle age to old age suggest that cognitive impairments during normal aging may be addressed by drugs that restore antioxidant, DNA repair, and synaptic functions including those of DA to levels of younger adults. Studies in schizophrenia identify robust decreases in genes for GABA function, including glutamic acid decarboxylase, HINT1, glutamate transport and GluRs, BDNF and TrkB, numerous 14-3-3 protein family members, and decreases in genes for CNS synaptic and metabolic functions, particularly glycolysis and ATP generation. Many of these metabolic genes are increased by insulin and muscarinic agonism, both of which are therapeutic in psychosis. Differential genomic signals are relatively sparse in bipolar disorder, but include deficiencies in the expression of 14-3-3 protein members, implicating these chaperone proteins and the neurotransmitter pathways they support as possible drug targets. Brains from persons with major depressive disorder reveal decreased expression for genes in glutamate transport and metabolism, neurotrophic signaling (eg, FGF, BDNF and VGF), and MAP kinase pathways. Increases in these pathways in the brains of animals exposed to electroconvulsive shock and antidepressant treatments identify neurotrophic and angiogenic growth factors and second messenger stimulation as therapeutic approaches for the treatment of depression.

Repeated electroconvulsive seizure induces c-Myc down-regulation and Bad inactivation in the rat frontal cortex

Repeated electroconvulsive seizure (ECS), a model for electroconvulsive therapy (ECT), exerts neuroprotective and proliferative effects in the brain. This trophic action of ECS requires inhibition of apoptotic activity, in addition to activation of survival signals. c-Myc plays an important role in apoptosis of neurons, in cooperation with the Bcl-2 family proteins, and its activity and stability are regulated by phosphorylation and ubiquitination. We examined c-Myc and related proteins responsible for apoptosis after repeated ECS. In the rat frontal cortex, repeated ECS for 10 days reduced the total amount of c-Myc, while increasing phosphorylation of c-Myc at Thr58, which reportedly induces degradation of c-Myc. As expected, ubiquitination of both phosphorylated and total c-Myc increased after 10 days ECS, suggesting that ECS may reduce c-Myc protein level via ubiquitination-proteasomal degradation. Bcl-2 family proteins, caspase, and poly(ADP-ribose) polymerase (PARP) were investigated to determine the consequence of down-regulating c-Myc. Protein levels of Bcl-2, Bcl-X(L), Bax, and Bad showed no change, and cleavage of caspase-3 and PARP were not induced. However, phosphorylation of Bad at Ser-155 and binding of Bad to 14-3-3 increased without binding to Bcl-X(L) after repeated ECS, implying that repeated ECS sequesters apoptotic Bad and frees pro-survival Bcl-XL. Taken together, c-Myc down-regulation via ubiquitination-proteasomal degradation and Bad inactivation by binding to 14-3-3 may be anti-apoptotic mechanisms elicited by repeated ECS in the rat frontal cortex. This finding further supports the trophic effect of ECS blocking apoptosis as a possible therapeutic effect of ECT.

Brain-derived neurotropic factor and neurogenesis in the adult rat dentate gyrus: interactions with corticosterone

Flattening the diurnal corticosterone rhythm prevented the stimulating action of L-NAME (a nitric oxide synthase, NOS, inhibitor) on progenitor cell proliferation in the dentate gyrus in Lister-Hooded adult male rats. The increased expression of brain-derived neurotrophic factor (BDNF) and trkB mRNA in the dentate gyrus which otherwise occurred after L-NAME was also prevented by clamping the corticoid rhythm in adrenalectomized rats, but was restored by daily additional injections of corticosterone (which replicates the diurnal rhythm). Unilateral infusions of BDNF into the lateral ventricle increased proliferation in the dentate gyrus on the side of the infusion, but this was not observed following implantation of subcutaneous corticosterone, which flattened the diurnal corticosterone rhythm. 5HT1A mRNA in the dentate gyrus was increased on both sides of the brain by unilateral BDNF infusions, but this was also prevented by subcutaneous corticosterone pellets. These results show that the diurnal rhythm of corticosterone regulates the stimulating action of NOS inhibitors on BDNF as well as on neurogenesis in the dentate gyrus, and that BDNF becomes ineffective on both proliferation rates and 5HT1A expression in the absence of a rhythm in corticosterone. This, together with our previous findings, suggests that corticoid rhythms permit both serotonin and NO access to BDNF, and the latter to regulate progenitor cell activity.

Differential inhibition of neurogenesis and angiogenesis by corticosterone in rats stimulated with electroconvulsive seizures

Antidepressant drugs and electroconvulsive seizure (ECS)-treatment, an animal model of electroconvulsive therapy, induce neurogenesis in adult rats. Stress and high levels of corticosterone (CORT) on the contrary inhibit neurogenesis. Hippocampal neurogenesis has been described to occur in an angiogenic niche where proliferation of neural progenitors takes place in an environment with active vascular growth. Here we investigate the effect of ECS-treatment on the proliferation of endothelial cells and neuronal precursors in hippocampus of CORT-treated rats. Bromodeoxyuridine (BrdU) was used to identify dividing cells. The number of newborn neuronal precursors and endothelial cells was quantified in the subgranular zone (SGZ) and the molecular layer (ML) of the dentate gyrus. The increase in neuronal precursor proliferation in the SGZ following ECS-treatment was not inhibited by elevated levels of CORT despite CORT strongly inhibiting ECS-induced endothelial cell proliferation. Also in the ML CORT-treatment inhibited the ECS-induced angiogenic response. We conclude that despite common factors regulating neurogenesis and angiogenesis, ECS-induced proliferation of neuronal precursors can take place even if the angiogenic response is blunted. Whether inhibition of angiogenesis affects other steps in the chain of events leading to the formation of fully integrated granule neurons remains to be elucidated.

Oxidative stress parameters in different rat brain structures after electroconvulsive shock-induced seizures

Electroconvulsive therapy has been used in the treatment of psychiatric disorders since the 1930s, but little progress has been made in understanding the cellular mechanisms underlying its therapeutic and adverse effects. Electroconvulsive shock (ECS) in animals provides a common experimental model for studying the effects of electroconvulsive therapy in humans. In order to examine the changes of the brain oxidative stress parameters in several brain structures in the early time period after ECS-induced seizures, the levels of lipid peroxidation as well as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities in the rat hippocampus, cerebellum, frontal cortex and the pons/medulla region were determined at different time points during the first 24 h after single ECS-induced seizures. In the hippocampus and cerebellum the levels of lipid peroxidation were unchanged, while the SOD and GSH-Px activities were significantly increased. Levels of lipid peroxidation and the activities of SOD and GSH-Px were not statistically changed in the pons/medulla region. Levels of lipid peroxidation in the frontal cortex were significantly higher in comparison to the control group at all time points examined while the SOD and GSH-Px activities were not statistically changed. In conclusion, the results of the present study indicate that single ECS causes the rat brain structure-specific alterations in the levels of lipid peroxidation as well as in the SOD and GSH-Px activities at different time points within the first 24 h after the seizures induction. Oxidative lipid damage was evident only in the frontal cortex, while the hippocampus, cerebellum and the pons/medulla region remained oxidatively unaffected in our experimental conditions.

Biological studies on alcohol-induced neuronal damage

Alcohol is a well-known cytotoxic agent which causes various kinds of neuronal damage. In spite of thousands of published studies, the true mechanism of alcohol-induced neuronal damage remains unclear. Neurogenesis is the generation of neurons from neural stem cells (NSCs) and occurs in predominantly two regions of the brain, the subventricular zone and the dentate gyrus of the hippocampus. NSCs are the self-renewing, multipotent precursor cells of neurons, astrocytes, and oligodendrocytes in the central nervous system. Recent studies have begun to illuminate the role of neurogenesis in the biological and cellular basis of psychiatric disorders and several clinical symptoms seen in alcoholism such as depression, cognitive impairment, underlying stress and brain atrophy have been linked to impaired neurogenesis. Heavy alcohol consumption decreases neurogenesis in animals, while in vitro studies have shown decreased generation of new neurons after alcohol exposure. These findings suggest that decreased neurogenesis is important in the pathophysiology of alcoholism. Neurogenesis can be divided into four stages; proliferation, migration, differentiation and survival. Our in vitro studies on NSCs showed that alcohol decreased neuronal differentiation at doses lower than those that affected cell survival and suggested that neuron-restrictive silencer factor, or repressor element-1 silencing transcription factor (NRSF/REST) could be involved in alcohol-induced inhibition of neuronal differentiation. In an animal model of fetal alcohol effects behavioral symptoms improved after NSC transplantation. Neurogenesis could be the target for new strategies to treat alcohol related disorders.

Chronic low dose corticosterone exposure decreased hippocampal cell proliferation, volume and induced anxiety and depression like behaviours in mice

A dysregulated hypothalamic-pituitary-adrenal axis (HPA) has been implicated in major depressive disorder and most commonly used animal models of depression have been shown to elevate circulating levels of plasma corticosterone. We have compared the effects of chronic and acute corticosterone administration on hippocampal cell proliferation (as measured by BrdU immunohistochemistry), hippocampal volume and the appearance of anxiety (light dark box) and depression (forced swim test) like behaviours in CD1 mice. We have also examined the effects of chronic administration of fluoxetine and imipramine on these parameters. Chronic (14 days) but not acute treatment with corticosterone resulted in reduced hippocampal cell proliferation and granule cell layer volume, these changes were prevented by co-administration of imipramine and fluoxetine. In contrast, acute and 7 day but not 14 or 21 day treatment with corticosterone gave rise to a "depressed" phenotype in the forced swim test. Mice treated for 14 days with corticosterone also developed an anxious phenotype in the light dark box but only upon repeated testing. The results presented here demonstrate that moderately elevated corticosterone for a prolonged period is sufficient to induce cellular changes in the hippocampus that are prevented by chronic administration of antidepressants.

Repeated paroxetine treatment reverses anhedonia induced in rats by chronic mild stress or dexamethasone

The present study was designed to assess the effect of dexamethasone, a synthetic glucocorticoid receptor agonist, in the sucrose preference test in rats. Rats treated acutely with dexamethasone (5-10 mg/kg) showed a significant decrease in sucrose preference (anhedonia) in comparison to vehicle treated rats, although 1 mg/kg dexamethasone did not alter the sucrose preference. Daily paroxetine treatment (10 g/kg, i.p., 14 days) reversed the anhedonic effect of acute dexamethasone (5 mg/kg), while causing no increased sucrose preference in rats that received dexamethasone vehicle. The paroxetine vehicle treated rats showed anhedonia even 14 days after acute dexamethasone administration. Paroxetine (10 mk/kg, i.p. for 28 days) also reversed anhedonia induced by chronic mild stress (8 weeks). In conclusion, acute dexamethasone induced an enduring anhedonic state that was reversed by repeated paroxetine treatment. Thus, the present study adds new data to the evidence supporting an important role for glucocorticoid in depression.

The role of neurotrophic factors in adult hippocampal neurogenesis, antidepressant treatments and animal models of depressive-like behavior

Major depressive disorder (MDD) is characterized by structural and neurochemical changes in limbic structures, including the hippocampus, that regulate mood and cognitive functions. Hippocampal atrophy is observed in patients with depression and this effect is blocked or reversed by antidepressant treatments. Brain-derived neurotrophic factor and other neurotrophic/growth factors are decreased in postmortem hippocampal tissue from suicide victims, which suggests that altered trophic support could contribute to the pathophysiology of MDD. Preclinical studies demonstrate that exposure to stress leads to atrophy and cell loss in the hippocampus as well as decreased expression of neurotrophic/growth factors, and that antidepressant administration reverses or blocks the effects of stress. Accumulating evidence suggests that altered neurogenesis in the adult hippocampus mediates the action of antidepressants. Chronic antidepressant administration upregulates neurogenesis in the adult hippocampus and this cellular response is required for the effects of antidepressants in certain animal models of depression. Here, we review cellular (e.g. adult neurogenesis) and behavioral studies that support the neurotrophic/neurogenic hypothesis of depression and antidepressant action. Aberrant regulation of neuronal plasticity, including neurogenesis, in the hippocampus and other limbic nuclei may result in maladaptive changes in neural networks that underlie the pathophysiology of MDD.

Modulation of the suppressive effect of corticosterone on adult rat hippocampal cell proliferation by paroxetine

OBJECTIVE

The literature has shown that cognitive and emotional changes may occur after chronic treatment with glucocorticoids. This might be caused by the suppressive effect of glucocorticoids on hippocampal neurogenesis and cell proliferation. Paroxetine, a selective serotonin reuptake transporter, is a commonly used antidepressant for alleviation of signs and symptoms of clinical depression. It was discovered to promote hippocampal neurogenesis in the past few years and we wanted to investigate its interaction with glucocorticoid in this study.

METHODS

Adult rats were given vehicle, corticosterone, paroxetine, or both corticosterone and paroxetine for 14 d. Cell proliferation in the dentate gyrus was quantified using 5-bromo-2-deoxyuridine (BrdU) immunohistochemistry.

RESULTS

The corticosterone treatment suppressed while paroxetine treatment increased hippocampal cell proliferation. More importantly, paroxetine treatment could reverse the suppressive effect of corticosterone on hippocampal cell proliferation.

CONCLUSION

This may have clinic application in preventing hippocampal damage after glucocorticoid treatment.

Electroconvulsive seizures stimulate glial proliferation and reduce expression of Sprouty2 within the prefrontal cortex of rats

BACKGROUND

Reductions in cell number are found within the medial prefrontal cortex (PFC) in major depression and bipolar disorder, conditions for which electroconvulsive therapy (ECT) is a highly effective treatment. We investigated whether electroconvulsive seizure (ECS) in rats stimulates cellular proliferation in the PFC immediately and four weeks after the treatments. In parallel, we examined if ECS also alters the expression of Sprouty2 (SPRY2), an inhibitor of cell proliferation.

METHODS

Sprague-Dawley rats received 10 days of ECS treatments and bromodeoxyuridine (BrdU) injections. After a four week survival period, we estimated the density and number of BrdU-, proliferating cell nuclear antigen (PCNA)-, and SPRY2-immunoreactive cells in the medial (infralimbic) PFC (ILPFC). We also determined the percentage of BrdU-labeled cells that were immunoreactive for markers specific to oligodendrocytes, astrocytes, endothelial cells and neurons.

RESULTS

ECS dramatically enhanced the proliferation of new cells in the infralimbic PFC, and this effect persisted four weeks following the treatments. The percentage of new cells expressing oligodendrocyte precursor cell markers increased slightly following ECS. In contrast, ECS dramatically reduced the number of cells expressing SPRY2.

CONCLUSIONS

ECS stimulates long-lasting increases in glial proliferation within the ILPFC. ECS also decreases SPRY2 expression in the same region, an effect that might contribute to increased glial proliferation.

Chronic stress: implications for neuronal morphology, function and neurogenesis

In normal life, organisms are repeatedly exposed to brief periods of stress, most of which can be controlled and adequately dealt with. The presently available data indicate that such brief periods of stress have little influence on the shape of neurons or adult neurogenesis, yet change the physiological function of cells in two time-domains. Shortly after stress excitability in limbic areas is rapidly enhanced, but also in brainstem neurons which produce catecholamines; collectively, during this phase the stress hormones promote focused attention, alertness, vigilance and the initial steps in encoding of information linked to the event. Later on, when the hormone concentrations are back to their pre-stress level, gene-mediated actions by corticosteroids reverse and normalize the enhanced excitability, an adaptive response meant to curtail defense reactions against stressors and to enable further storage of relevant information. When stress is experienced repetitively in an uncontrollable and unpredictable manner, a cascade of processes in brain is started which eventually leads to profound, region-specific alterations in dendrite and spine morphology, to suppression of adult neurogenesis and to inappropriate functional responses to a brief stress exposure including a sensitized activation phase and inadequate normalization of brain activity. Although various compounds can effectively prevent these cellular changes by chronic stress, the exact mechanism by which the effects are accomplished is poorly understood. One of the challenges for future research is to link the cellular changes seen in animal models for chronic stress to behavioral effects and to understand the risks they can impose on humans for the precipitation of stress-related disorders.

Hippocampal Bcl-2 expression is selectively increased following chronic but not acute treatment with antidepressants, 5-HT1A or 5-HT2C/2B receptor antagonists

Expression of the anti-apoptotic protein Bcl-2 has been shown to increase in the hippocampus and cortex following chronic administration of mood stabilizers such as lithium and valproate, but the effects of long-term antidepressant administration have not been demonstrated. CD1 mice were dosed either acutely or chronically with either antidepressants or 5-HT receptor subtype selective antagonists. Cortex, hippocampus and hypothalamus from these mice were analysed by Western blot for changes in expression of Bcl-2 and Bax protein. Fourteen day but not acute treatment with citalopram (20 mg/kg), imipramine (10 mg/kg) and amitriptyline (10 mg/kg) in mice significantly elevated hippocampal Bcl-2 protein expression as compared to vehicle treated animals (59, 48 and 42% respectively). Similarly, fourteen day but not acute treatment with the 5-HT(1A) and 5-HT(2C/2B) receptor antagonists WAY100635 (0.3 mg/kg) and SB221284 (1 mg/kg) also markedly and significantly increased hippocampal Bcl-2 expression (95 and 52% respectively). Bcl-2 expression was unaffected in cortex by any treatment. There was a smaller increase of hippocampal Bax protein levels following treatment with imipramine after 1 or 14 days, and following citalopram and amitriptyline after 14 but not 1 day. These data present the first substantive evidence that clinically used antidepressants increase the expression of hippocampal Bcl-2 as did chronic blockade of 5-HT(1A) and 5-HT(2C/2B) receptors, which may be involved in the mechanism of action of antidepressants. The induction of hippocampal Bcl-2 expression by long-term antidepressant treatment may contribute to the clinical efficacy of such compounds via its well described neurotrophic and/or anti-apoptotic effects on neuronal function.

Antidepressant-induced neurogenesis in the hippocampus of adult nonhuman primates

New neurons are generated in the adult hippocampus of many species including rodents, monkeys, and humans. Conditions associated with major depression, such as social stress, suppress hippocampal neurogenesis in rodents and primates. In contrast, all classes of antidepressants stimulate neuronal generation, and the behavioral effects of these medications are abolished when neurogenesis is blocked. These findings generated the hypothesis that induction of neurogenesis is a necessary component in the mechanism of action of antidepressant treatments. To date, the effects of antidepressants on newborn neurons have been reported only in rodents and tree shrews. This study examines whether neurogenesis is increased in nonhuman primates after antidepressant treatment. Adult monkeys received repeated electroconvulsive shock (ECS), which is the animal analog of electroconvulsive therapy (ECT), the most effective short-term antidepressant. Compared with control conditions, ECS robustly increased precursor cell proliferation in the subgranular zone (SGZ) of the dentate gyrus in the monkey hippocampus. A majority of these precursors differentiated into neurons or endothelial cells, while a few matured into glial cells. The ECS-mediated induction of cell proliferation and neurogenesis was accompanied by increased immunoreactivity for the neuroprotective gene product BCL2 (B cell chronic lymphocytic lymphoma 2) in the SGZ. The ECS interventions were not accompanied by increased hippocampal cell death or injury. This study demonstrates that ECS is capable of inducing neurogenesis in the nonhuman primate hippocampus and supports the possibility that antidepressant interventions produce similar alterations in the human brain.

Region-specific transcriptional changes following the three antidepressant treatments electro convulsive therapy, sleep deprivation and fluoxetine

The significant proportion of depressed patients that are resistant to monoaminergic drug therapy and the slow onset of therapeutic effects of the selective serotonin reuptake inhibitors (SSRIs)/serotonin/noradrenaline reuptake inhibitors (SNRIs) are two major reasons for the sustained search for new antidepressants. In an attempt to identify common underlying mechanisms for fast- and slow-acting antidepressant modalities, we have examined the transcriptional changes in seven different brain regions of the rat brain induced by three clinically effective antidepressant treatments: electro convulsive therapy (ECT), sleep deprivation (SD), and fluoxetine (FLX), the most commonly used slow-onset antidepressant. Each of these antidepressant treatments was applied with the same regimen known to have clinical efficacy: 2 days of ECT (four sessions per day), 24 h of SD, and 14 days of daily treatment of FLX, respectively. Transcriptional changes were evaluated on RNA extracted from seven different brain regions using the Affymetrix rat genome microarray 230 2.0. The gene chip data were validated using in situ hybridization or autoradiography for selected genes. The major findings of the study are: 1. The transcriptional changes induced by SD, ECT and SSRI display a regionally specific distribution distinct to each treatment. 2. The fast-onset, short-lived antidepressant treatments ECT and SD evoked transcriptional changes primarily in the catecholaminergic system, whereas the slow-onset antidepressant FLX treatment evoked transcriptional changes in the serotonergic system. 3. ECT and SD affect in a similar manner the same brain regions, primarily the locus coeruleus, whereas the effects of FLX were primarily in the dorsal raphe and hypothalamus, suggesting that both different regions and pathways account for fast onset but short lasting effects as compared to slow-onset but long-lasting effects. However, the similarity between effects of ECT and SD is somewhat confounded by the fact that the two treatments appear to regulate a number of transcripts in an opposite manner. 4. Multiple transcripts (e.g. brain-derived neurotrophic factor (BDNF), serum/glucocorticoid-regulated kinase (Sgk1)), whose level was reported to be affected by antidepressants or behavioral manipulations, were also found to be regulated by the treatments used in the present study. Several novel findings of transcriptional regulation upon one, two or all three treatments were made, for the latter we highlight homer, erg2, HSP27, the proto oncogene ret, sulfotransferase family 1A (Sult1a1), glycerol 3-phosphate dehydrogenase (GPD3), the orphan receptor G protein-coupled receptor 88 (GPR88) and a large number of expressed sequence tags (ESTs). 5. Transcripts encoding proteins involved in synaptic plasticity in the hippocampus were strongly affected by ECT and SD, but not by FLX. The novel transcripts, concomitantly regulated by several antidepressant treatments, may represent novel targets for fast onset, long-duration antidepressants.

Electroconvulsive therapy in melancholia: the role of hippocampal neurogenesis

OBJECTIVE

To elucidate the relationship between the effects of electroconvulsive therapy (ECT) on hippocampal anatomy and function in the therapy of melancholic depression and preclinical observations of increased neurogenesis in the hippocampus of experimental animals receiving electroconvulsive seizures (ECS). We emphasize the role of hypercortisolaemia in melancholic depression and in experimental hippocampal neurogenesis.

METHOD

Our statements are based on a variety of studies pointing to i) ECT being superior to all other treatment modalities in the therapy of melancholia, ii) melancholia being associated with hypercortisolaemia and iii) evidence of hippocampal neurogenesis being relevant for understanding both melancholia and ECT.

RESULTS

The increased neurogenesis found in animal studies shows stronger effect of seizures than of antidepressant drugs. The onset of effect is not only faster but is also sustained. Newborn cells are found to be functional. Suppression of neurogenesis by chronic treatment with corticosterone is associated with depression-like biology and behaviour making comparison with human depression and its response to ECT relevant.

CONCLUSION

We hypothesize that the superior antimelancholic effect of induced seizures may be understood in the light of the powerful control of neural plasticity exerted by the regulation of the hypothalamic-pituitary-adrenal axis and, perhaps, other regulatory factors.

Dentate gyrus neurogenesis and depression

Major depressive disorder (MDD) is a debilitating and complex psychiatric disorder that involves multiple neural circuits and genetic and non-genetic risk factors. In the quest for elucidating the neurobiological basis of MDD, hippocampal neurogenesis has emerged as a candidate substrate, both for the etiology as well as treatment of MDD. This chapter critiques the advances made in the study of hippocampal neurogenesis as they relate to the neurogenic hypothesis of MDD. While an involvement of neurogenesis in the etiology of depression remains highly speculative, preclinical studies have revealed a novel and previously unrecognized role for hippocampal neurogenesis in mediating some of the behavioral effects of antidepressants. The implications of these findings are discussed to reevaluate the role of hippocampal neurogenesis in MDD.

Panic comorbidity with bipolar disorder: what is the manic-panic connection?

CONTEXT

Bipolar/panic comorbidity has been observed in clinical, community and familial samples. As both are episodic disorders of affect regulation, the common pathophysiological mechanism is likely to involve deficits in amygdala-mediated, plasticity-dependent emotional conditioning.

EVIDENCE

Neuronal genesis and synaptic remodeling occur in the amygdala; bipolar and panic disorders have both been associated with abnormality in the amygdala and related structures, as well as in molecules that modulate plasticity, such as serotonin, norepinephrine, brain-derived neurotrophic factor (BDNF) and corticotrophin releasing factor (CRF). These biological elements are involved in behavioral conditioning to threat and reward.

MODEL

Panic attacks resemble the normal acute fear response, but are abnormally dissociated from any relevant threat. Abnormal reward-seeking behavior is central to both manic and depressive syndromes. Appetites can be elevated or depressed; satisfaction of a drive may fail to condition future behavior. These dissociations may be the result of deficits in plasticity-dependent processes of conditioning within different amygdala subregions.

CONCLUSIONS

This speculative model may be a useful framework with which to connect molecular, cellular, anatomic and behavioral processes in panic and bipolar disorders. The primary clinical implication is that behavioral treatment may be critical to restore function in some bipolar patients who respond only partially to medications.

Endothelial proliferation and increased blood-brain barrier permeability in the basal ganglia in a rat model of 3,4-dihydroxyphenyl-L-alanine-induced dyskinesia

3,4-Dihydroxyphenyl-L-alanine (L-DOPA)-induced dyskinesia is associated with molecular and synaptic plasticity in the basal ganglia, but the occurrence of structural remodeling through cell genesis has not been explored. In this study, rats with 6-hydroxydopamine lesions received injections of the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) concomitantly with L-DOPA for 2 weeks. A large number of BrdU-positive cells were found in the striatum and its output structures (globus pallidus, entopeduncular nucleus, and substantia nigra pars reticulata) in L-DOPA-treated rats that had developed dyskinesia. The vast majority (60-80%) of the newborn cells stained positively for endothelial markers. This endothelial proliferation was associated with an upregulation of immature endothelial markers (nestin) and a downregulation of endothelial barrier antigen on blood vessel walls. In addition, dyskinetic rats exhibited a significant increase in total blood vessel length and a visible extravasation of serum albumin in the two structures in which endothelial proliferation was most pronounced (substantia nigra pars reticulata and entopeduncular nucleus). The present study provides the first evidence of angiogenesis and blood-brain barrier dysfunction in an experimental model of L-DOPA-induced dyskinesia. These microvascular changes are likely to affect the kinetics of L-DOPA entry into the brain, favoring the occurrence of motor complications.

High post-partum levels of corticosterone given to dams influence postnatal hippocampal cell proliferation and behavior of offspring: A model of post-partum stress and possible depression

Post-partum stress and depression (PPD) have a significant effect on child development and behavior. Depression is associated with hypercortisolism in humans, and the fluctuating levels of hormones, including corticosterone, during pregnancy and the post-partum, may contribute to PPD. The present study was developed to investigate the effects of high-level corticosterone (CORT) post-partum in the mother on postnatal neurogenesis and behavior in the offspring. Sprague-Dawley dams were treated with either CORT (40 mg/kg) or sesame oil injections daily for 26 days beginning the day after giving birth. Dams were tested in the forced swim test (FST) and in the open field test (OFT) on days 24-26 post-partum. Results showed that the dams exposed to CORT expressed "depressive-like" behavior compared to controls, with decreased struggling behavior and increased immobility in the FST. To investigate the effects of treatment on hippocampal postnatal cell proliferation and survival in the offspring, males and females from treated dams were injected with BrdU (50 mg/kg) on postnatal day 21 and perfused either 24 h (cell proliferation) or 21 days (cell survival) later. Furthermore, male and female offspring from each litter were tested in adulthood on various behavioral tests, including the forced swim test, open field test, resistance to capture test and elevated plus maze. Intriguingly, male, but not female, offspring of CORT-treated dams exhibited decreased postnatal cell proliferation in the dentate gyrus. Both male and female offspring of CORT-treated dams showed higher resistance to capture and greater locomotor activity as assessed in the open field test. As high levels of CORT may be a characteristic of stress and/or depression, these findings support a model of 'CORT-induced' post-partum stress and possibly depression and demonstrate that the offspring of affected dams can exhibit changes in postnatal neurogenesis and behavior in adulthood.