Long-term stress degenerates, but imipramine regenerates, noradrenergic axons in the rat cerebral cortex

Altered expression of vesicular glutamate transporter-2 and cleaved caspase-3 in the locus coeruleus of nerve-injured rats

Neuropathic pain is a debilitating chronic condition provoked by a lesion in the nervous system and it induces functional alterations to the noradrenergic locus coeruleus (LC), affecting distinct dimensions of pain, like sensorial hypersensitivity, pain-induced depression, and anxiety. However, the neurobiological changes induced by nerve damage in the LC remain unclear. Here, we analyzed excitatory and inhibitory inputs to the LC, as well as the possible damage that noradrenergic neurons suffer after the induction of neuropathic pain through chronic constriction injury (CCI). Neuropathic pain was induced in male Sprague-Dawley rats, and the expression of the vesicular glutamate transporter 1 or 2 (VGLUT1 or VGLUT2), vesicular GABA transporter (VGAT), and cleaved caspase-3 (CC3) was analyzed by immunofluorescence 7 (CCI7d) or 28 days after the original lesion (CCI28d). While no significant differences in the density of VGLUT1 puncta were evident, CCI7d induced a significant increase in the perisomatic VGLUT2/VGAT ratio relative to Sham-operated and CCI28d animals. By contrast, when the entire region of LC is evaluated, there was a significant reduction in the density of VGLUT2 puncta in CCI28d animals, without changes in VGLUT2/VGAT ratio relative to the CCI7d animals. Additionally, changes in the noradrenergic soma size, and a lower density of mitochondria and lysosomes were evident in CCI28d animals. Interestingly, enhanced expression of the apoptotic marker CC3 was also evident in the CCI28d rats, mainly co-localizing with glial fibrillary acidic protein but not with any neuronal or noradrenergic marker. Overall, short-term pain appears to lead to an increase of markers of excitatory synapses in the perisomatic region of noradrenergic cells in the LC, an effect that is lost after long-term pain, which appears to activate apoptosis.

Neuroplasticity and the Biological Role of Brain Derived Neurotrophic Factor in the Pathophysiology and Management of Depression

Depression is a mental illness that can have serious implications if left untreated. Studies involving a neurotrophic factor called brain derived neurotrophic factor (BDNF) and its associated signaling pathways have solidified our understanding of the pathophysiology of depression. The objective of this literature review is to gain a better understanding of the mechanism by which reduced levels of BDNF are implicated in depression and how antidepressants facilitate the treatment of depression by increasing BDNF levels. The specific approach is to learn about the key involvements of BDNF and its receptor TrkB (tropomyosin receptor kinase B) and how their interactions and subsequent intracellular signaling cascades bring about enhanced neuroplastic changes. In this literature review, we searched for past review articles focusing on BDNF. We collected data using PubMed and created a summary of our findings. The results showed that stress and depression through the reduction of BDNF levels contribute to neuroplastic changes while antidepressants through enhanced BDNF levels are able to generate positive neuroplastic outcomes and thereby help resolve depressive symptoms. In this paper, we will delve into how a better understanding of the neural circuitry involving BDNF will enable us to both understand how current antidepressants work in the limbic regions of the brain as well as search for novel rapid-acting antidepressants to use in clinical practice.

Stress-Induced Microstructural Alterations Correlate With the Cognitive Performance of Rats: A Longitudinal in vivo Diffusion Tensor Imaging Study

Background: Stress-induced cellular changes in limbic brain structures contribute to the development of various psychopathologies. In vivo detection of these microstructural changes may help us to develop objective biomarkers for psychiatric disorders. Diffusion tensor imaging (DTI) is an advanced neuroimaging technique that enables the non-invasive examination of white matter integrity and provides insights into the microstructure of pathways connecting brain areas.

Objective: Our aim was to examine the temporal dynamics of stress-induced structural changes with repeated in vivo DTI scans and correlate them with behavioral alterations.

Methods: Out of 32 young adult male rats, 16 were exposed to daily immobilization stress for 3 weeks. Four DTI measurements were done: one before the stress exposure (baseline), two scans during the stress (acute and chronic phases), and a last one 2 weeks after the end of the stress protocol (recovery). We used a 4.7T small-animal MRI system and examined 18 gray and white matter structures calculating the following parameters: fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). T2-weighted images were used for volumetry. Cognitive performance and anxiety levels of the animals were assessed in the Morris water maze, novel object recognition, open field, and elevated plus maze tests.

Results: Reduced FA and increased MD and RD values were found in the corpus callosum and external capsule of stressed rats. Stress increased RD in the anterior commissure and reduced MD and RD in the amygdala. We observed time-dependent changes in several DTI parameters as the rats matured, but we found no evidence of stress-induced volumetric alterations in the brains. Stressed rats displayed cognitive impairments and we found numerous correlations between the cognitive performance of the animals and between various DTI metrics of the inferior colliculus, corpus callosum, anterior commissure, and amygdala.

Conclusions: Our data provide further support to the translational value of DTI studies and suggest that chronic stress exposure results in similar white matter microstructural alterations that have been documented in stress-related psychiatric disorders. These DTI findings imply microstructural abnormalities in the brain, which may underlie the cognitive deficits that are often present in stress-related mental disorders.

Poor Diet, Stress, and Inactivity Converge to Form a "Perfect Storm" That Drives Alzheimer's Disease Pathogenesis

North American incidence of Alzheimer's disease (AD) is expected to more than double over the coming generation. Although genetic factors surrounding the production and clearance of amyloid-β and phosphorylated tau proteins are known to be responsible for a subset of early-onset AD cases, they do not explain the pathogenesis of the far more prevalent sporadic late-onset variant of the disease. It is thus likely that lifestyle and environmental factors contribute to neurodegenerative processes implicated in the pathogenesis of AD. Herein, we review evidence that (1) excess sucrose consumption induces AD-associated liver pathologies and brain insulin resistance, (2) chronic stress overdrives activity of locus coeruleus neurons, leading to loss of function (a common event in neurodegeneration), (3) high-sugar diets and stress promote the loss of neuroprotective sex hormones in men and women, and (4) Western dietary trends set the stage for a lithium-deficient state. We propose that these factors may intersect as part of a "perfect storm" to contribute to the widespread prevalence of neurodegeneration and AD. In addition, we put forth the argument that exercise and supplementation with trace lithium can counteract many of the deleterious consequences associated with excessive caloric intake and perpetual stress. We conclude that lifestyle and environmental factors likely contribute to AD pathogenesis and that simple lifestyle and dietary changes can help counteract their effects.

Mirtazapine for chronic breathlessness? A review of mechanistic insights and therapeutic potential

INTRODUCTION

Chronic breathlessness is a common and distressing symptom of advanced disease with few effective treatments. Central nervous system mechanisms are important in respiratory sensation and control. Consequently, drugs which may modify processing and perception of afferent information in the brain may have a role. Antidepressants have been proposed; however, current evidence is limited. Of potentially suitable antidepressants, mirtazapine is an attractive option given its tolerability profile, low cost, and wide availability, along with additional potential benefits. Areas covered: The paper provides an overview of the physiology of breathlessness, with an emphasis on central mechanisms, particularly the role of fear circuits and the associated neurotransmitters. It provides a potential rationale for how mirtazapine may improve chronic breathlessness and quality of life in patients with advanced disease. The evidence was identified by a literature search performed in PubMed through to October 2018. Expert opinion: Currently, there is insufficient evidence to support the routine use of antidepressants for chronic breathlessness in advanced disease. Mirtazapine is a promising candidate to pursue, with definitive randomized controlled trials required to determine its efficacy and safety in this setting.

Clinical implications of mechanisms of action of antidepressants

The purpose of this review is briefly to consider the biological basis of depression and to attempt to illustrate how antidepressants produce their beneficial effects by correcting these abnormalities.

Structural Integrity in the Genu of Corpus Callosum Predicts Conflict-induced Functional Connectivity Between Medial Frontal Cortex and Right Posterior Parietal Cortex

Studies using the flanker task have reported that response conflict is detected by the medial frontal cortex (MFC). As a conflict alert system, the MFC shows enhanced functional communication with task-related regions. Previous studies have revealed individual differences in functional connectivity during cognitive task performance. However, the mechanisms underlying these individual differences remain unclear. In the current study, electroencephalography (EEG) was recorded while 30 subjects performed a flanker task that was modified to exclude feature integration and contingency learning. The diffusion tensor imaging (DTI) data were collected the day before the EEG session. FCz-P3/4 theta phase synchronization was used to measure functional connectivity between the MFC and posterior parietal cortex (PPC). Hierarchical regression analyses were used to assess the relationship between MFC-PPC conflict-induced theta phase synchronization and white matter integrity in significant regions derived from tract-based spatial statistics (TBSS) analysis. As expected, MFC-PPC theta phase synchronization was significantly enhanced during conflict, suggesting a conflict-induced functional connectivity. However, these findings were only found in the right hemisphere, which may be related to the asymmetrical role of the bilateral PPC in response conflict processing. Furthermore, hierarchical regression analyses revealed that 44% of individual variability in FCz-P4 conflict-induced theta phase synchronization could be explained by variations in axial diffusivity (AD) in the genu of the corpus callosum (gCC). These results demonstrated that structural integrity in the gCC predicts conflict-induced functional connectivity between the MFC and right PPC.

Pain exacerbates chronic mild stress-induced changes in noradrenergic transmission in rats

Depression can influence pain and vice versa, yet the biological mechanisms underlying how one influences the pathophysiology of the other remains unclear. Dysregulation of locus coeruleus-noradrenergic transmission is implicated in both conditions, although it is not known whether this effect is exacerbated in cases of co-morbid depression and chronic pain. We studied locus coeruleus activity using immunofluorescence and electrophysiological approaches in rats subjected to unpredictable chronic mild stress (CMS, an experimental model of depression) and/or chronic constriction injury (CCI, a model of chronic neuropathic pain) for 2 weeks. CCI alone had no effect on any of the locus coeruleus parameters studied, while CMS led to a slight reduction in the electrophysiological activity of the locus coeruleus. Furthermore, CMS was associated with an increase in the number of tyrosine hydroxylase-positive cells in the locus coeruleus, although they were smaller in size. Interestingly, these effects of CMS were exacerbated when combined with CCI, even though no changes in the α2-adrenoreceptors or the noradrenaline transporter were observed in any group. Together, these findings suggest that CMS triggers several modifications in locus coeruleus-noradrenergic transmission that are exacerbated by co-morbid chronic pain.

Modulation of early stress-induced neurobiological changes: a review of behavioural and pharmacological interventions in animal models

Childhood adversity alters the predisposition to psychiatric disorders later in life. Those with psychiatric conditions and a history of early adversity exhibit a higher incidence of treatment resistance compared with individuals with no such history. Modulation of the influence early stress exerts over neurobiology may help to prevent the development of psychiatric disorders in some cases, while attenuating the extent of treatment resistance in those with established psychiatric disorders. This review aims to critically evaluate the ability of behavioural, environmental and pharmacologic interventions to modulate neurobiological changes induced by early stress in animal models. Databases were systematically searched to locate literature relevant to this review. Early adversity was defined as stress that resulted from manipulation of the mother-infant relationship. Analysis was restricted to animal models to enable characterisation of how a given intervention altered specific neurobiological changes induced by early stress. A wide variety of changes in neurobiology due to early stress are amenable to intervention. Behavioural interventions in childhood, exercise in adolescence and administration of epigenetic-modifying drugs throughout life appear to best modulate cellar and behavioural alterations induced by childhood adversity. Other pharmacotherapies, such as endocannabinoid system modulators, anti-inflammatories and antidepressants can also influence these neurobiological and behavioural changes that result from early stress, although findings are less consistent at present and require further investigation. Further work is required to examine the influence that behavioural interventions, exercise and epigenetic-modifying drugs exert over alterations that occur following childhood stress in human studies, before possible translational into clinical practice is possible.

Synaptic regulation of affective behaviors; role of BDNF

Brain derived neurotrophic factor (BDNF), a neurotrophin essential for nervous system development and synaptic plasticity, has been found to have a significant influence on affective behaviors. The notion that an impairment in BDNF signaling might be involved in affective disorders is originated primarily from the opposing effects of antidepressants and stress on BDNF signaling. Antidepressants enhance BDNF signaling and synaptic plasticity. On the other hand, negative environmental factors such as severe stress suppress BDNF signaling, impair synaptic activity and increase susceptibility to affective disorders. Postmortem studies provided strong support for decreased BDNF signaling in depressive disorders. Remarkably, studies in humans with a single nucleotide polymorphism in the BDNF gene, the BDNF Val66Met which affects regulated release of BDNF, showed profound deficits in hippocampal and prefrontal cortical (PFC) plasticity and cognitive behaviors. BDNF regulates synaptic mechanisms responsible for various cognitive processes including attenuation of aversive memories, a key process in the regulation of affective behaviors. The unique role of BDNF in cognitive and affective behaviors suggests that cognitive deficits due to altered BDNF signaling might underlie affective disorders. Understanding how BDNF modulates synapses in neural circuits relevant to affective behaviors, particularly the medial prefrontal cortical (mPFC)-hippocampus-amygdala pathway, and its interaction with development, sex, and environmental risk factors might shed light on potential therapeutic targets for affective disorders. This article is part of the Special Issue entitled 'BDNF Regulation of Synaptic Structure, Function, and Plasticity'.

Mechanisms of white matter changes induced by meditation

Using diffusion tensor imaging, several recent studies have shown that training results in changes in white matter efficiency as measured by fractional anisotropy (FA). In our work, we found that a form of mindfulness meditation, integrative body-mind training (IBMT), improved FA in areas surrounding the anterior cingulate cortex after 4-wk training more than controls given relaxation training. Reductions in radial diffusivity (RD) have been interpreted as improved myelin but reductions in axial diffusivity (AD) involve other mechanisms, such as axonal density. We now report that after 4-wk training with IBMT, both RD and AD decrease accompanied by increased FA, indicating improved efficiency of white matter involves increased myelin as well as other axonal changes. However, 2-wk IBMT reduced AD, but not RD or FA, and improved moods. Our results demonstrate the time-course of white matter neuroplasticity in short-term meditation. This dynamic pattern of white matter change involving the anterior cingulate cortex, a part of the brain network related to self-regulation, could provide a means for intervention to improve or prevent mental disorders.

The circadian clock, reward, and memory

During our daily activities, we experience variations in our cognitive performance, which is often accompanied by cravings for small rewards, such as consuming coffee or chocolate. This indicates that the time of day, cognitive performance, and reward may be related to one another. This review will summarize data that describe the influence of the circadian clock on addiction and mood-related behavior and put the data into perspective in relation to memory processes.

Altered expression of tyrosine hydroxylase in the locus coeruleus noradrenergic system in citalopram neonatally exposed rats and monoamine oxidase a knock out mice

In rodents, noradrenergic (NE) locus coeruleus (LC) neurons are well known to express tyrosine hydroxylase (TH) immunoreactivity. However, due to its very low enzyme activity, NE cortical fibers do not typically express TH immunoreactivity, thus dopamine-β-hydroxylase (DBH) immunoreactivity is commonly utilized as a marker for NE cortical fibers. In this study, we performed double and/or triple immunofluorescent staining using antibodies against TH, DBH, and/or norepinephrine transporter (NET) to investigate the altered NE TH expression of cortical fibers in citalopram (CTM)-exposed rats and monoamine oxidase (MAO) A knock out (KO) mice. We have noted the following novel findings: (1) neonatal exposure to the selective serotonin reuptake inhibitor (SSRI) CTM enhanced NE TH immunoreactive fibers throughout the entire neocortex, and a few of them appeared to be hypertrophic; (2) slightly enhanced NE cortical TH immunoreactive fibers were also noted in MAO A KO mice, and many of them revealed varicosities compared with the rather smooth NE cortical TH immunoreactive fibers in wild-type (WT) mice; (3) LC dendrites of MAO A KO mice exhibited beaded morphology compared with the smooth LC dendrites in WT mice. Our findings suggest that both genetic and environmental factors during early development may play a critical role in the regulation and proper function of NE TH expression in the neocortex.

Constant darkness induces IL-6-dependent depression-like behavior through the NF-κB signaling pathway

Substantial experimental evidence indicates a major role for the circadian system in mood disorders. Additionally, proinflammatory cytokines have been proposed to be involved in the pathogenesis of depression. However, the molecular elements determining the functional interplay between these two systems in depression have not been described as yet. Here we investigate whether long-term light deprivation in the constant darkness (DD) paradigm affects depression-like behavior in mice and concomitantly modulates the levels of proinflammatory cytokines. We find that after 4 weeks of DD, mice display depression-like behavior, which is paralleled by reduced hippocampal cell proliferation. This chronobiologically induced depressive state is associated with elevated levels of plasma IL-6 (interleukin-6) and IL-6 and Il1-R1 (interleukin 1 receptor, type I) protein levels in the hippocampus and also alters hippocampal protein levels of the clock genes per2 and npas2. Using pharmacological blockers of the NF-κB pathway, we provide evidence that the effects of DD on depression-like behavior, on hippocampal cell proliferation, on altered expressional levels of brain and plasma IL-6, and on the modulation of clock gene expression are mediated through NF-κB signaling. Moreover, NF-κB activity is enhanced in hippocampal tissue of DD mice. Mice with a deletion of IL-6, one of the target genes of NF-κB, are resistant to DD-induced depression-like behavior, which suggests a pivotal role for this cytokine in the constant darkness mouse model of depression. We here first describe some of the molecular elements bridging chronobiological and inflammatory processes in the constant darkness mouse model of depression.

Exposure to 1-bromopropane causes degeneration of noradrenergic axons in the rat brain

1-Bromopropane (1-BP) has been used as an alternative to ozone-depleting solvents. Previous studies showed that 1-BP is neurotoxic in animals and humans. In humans, exposure to 1-BP caused various neurological and neurobehavioral symptoms or signs including depressive or irritated mood. However, the neurobiological changes underlying the depressive symptoms induced by 1-BP remain to be determined. The depressive symptoms are thought to be associated with degeneration of axons containing noradrenaline and serotonin. Based on this hypothesis, the present study examined the effects of repeated exposure to 1-BP on serotonergic and noradrenergic axons. Exposure to 1-BP induced dose-dependent decreases in the density of noradrenergic axons in the rat prefrontal cortex, but no apparent change in the density of serotonergic axons. The results suggest that depressive symptoms in workers exposed to 1-BP are due, at least in part, to the degeneration of noradrenergic axons in the brain.

Current perspectives of the roles of the central norepinephrine system in anxiety and depression

Norepinephrine (NE) is a major monoamine neurotransmitter that has widespread effects across multiple brain areas to regulate arousal and stress responses. The underlying function of the NE cortical system is to balance vigilance/scanning behavior with focused attention on novel environmental stimuli and the state of arousal. The central NE system is involved intrinsically with the stress response system, and dysregulation within the NE system has been implicated in the pathogenesis of anxiety and depressive disorders. Central NE activity paradoxically has either anxiogenic or anxiolytic effects, depending on whether the time course of the stress is acute or chronic, whether the stress is predictable or unpredictable, and which underlying brain regions are affected. Under conditions of chronic stress, NE system activity dysregulation of the hypothalamic-pituitary-adrenal system may turn a homeostatic stress response into a pathological stress response. Data suggest that the NE interplay with the serotonin system may exert neurobiological normalization of the pathophysiological state of anxious depression. Accordingly, pharmacological interventions targeting the NE system can result in anxiolytic, rather than anxiogenic, outcomes when used to treat patients with anxiety and depression.

Effects of postnatal isolation rearing and antidepressant treatment on the density of serotonergic and noradrenergic axons and depressive behavior in rats

The development of monoaminergic axons is affected by pharmacological and environmental manipulations during early periods of brain development. In addition, it has been proposed that changes in the density of monoaminergic axons are involved in the pathophysiology of depression. The present experiments examined the effects of neonatal treatment with antidepressants on the density of monoaminergic axons containing 5-HT or noradrenaline (NA) and depressive behavior in rats. In this study, clomipramine (CL) was used as an antidepressant, because a large amount of data has been accumulated on the effects of neonatal CL treatment on monoaminergic neurons and depressive behavior. It was also examined whether the effects of neonatal CL treatment could be further modified by environmental conditions. In the present experiments, postweaning isolation rearing (Iso) was examined as an environmental condition, because postweaning Iso is reported to change the density of 5-HT axons in the rat brain. Unexpectedly, neonatal CL treatment alone had no effect on the density of 5-HT or NA axons or depressive behavior. Postweaning social Iso rearing reduced the density of 5-HT axons in the central nucleus and basolateral nucleus of the amygdala and CA3 of the hippocampus. In the prelimbic area and infralimbic area of medial prefrontal cortex and the dentate gyrus of the hippocampus, the density of 5-HT axons was not affected by social Iso alone, but was reduced when animals were socially isolated after neonatal CL treatment. Postweaning Iso, but not neonatal CL treatment, increased immobility in the forced swim test in adolescence/early adulthood. These findings suggest that postweaning social Iso alters the density of monoaminergic axons, particularly 5-HT axons, and induces a possible model of depression, while neonatal CL treatment alone has no effect on the density of NA or 5-HT axons or depressive behavior in adolescence/early adulthood.

Tyrosine hydroxylase immunoreactivity in the locus coeruleus is elevated in violent suicidal depressive patients

Our postmortem study aimed to determine the impact of suicide on the number of noradrenergic neurons of the locus coeruleus (LC) in suicidal depressive patients. Noradrenergic neurons were shown by immunostaining tyrosine hydroxylase in the LC of 22 non-elderly patients with mood disorders compared to 21 age- and sex-matched normal controls. Eleven patients were suicide victims and the other eleven died of natural causes. Seven violent suicide victims revealed an increased number of tyrosine hydroxylase immunoreactive (TH-ir) neurons compared with non-violent suicide victims and controls. No difference was found between the number of TH-ir neurons in all suicidal patients and controls and between non-suicidal patients and controls. The differences of TH-immunoreactivity could neither be attributed to medication nor to the polarity of depressive disorder (unipolar/bipolar). The numbers of TH-ir neurons in suicidal patients correlated negatively with the mean doses of antidepressants. The study suggested a presynaptic noradrenergic dysregulation in the LC related to the level of self-aggression. Traditional antidepressants may, therefore, regulate noradrenergic activity of the LC in suicide patients, however, without demonstrating the suicide-preventing effect.

Morphology of pyramidal neurons in the rat prefrontal cortex: lateralized dendritic remodeling by chronic stress

The prefrontal cortex (PFC) plays an important role in the stress response. We filled pyramidal neurons in PFC layer III with neurobiotin and analyzed dendrites in rats submitted to chronic restraint stress and in controls. In the right prelimbic cortex (PL) of controls, apical and distal dendrites were longer than in the left PL. Stress reduced the total length of apical dendrites in right PL and abolished the hemispheric difference. In right infralimbic cortex (IL) of controls, proximal apical dendrites were longer than in left IL, and stress eliminated this hemispheric difference. No hemispheric difference was detected in anterior cingulate cortex (ACx) of controls, but stress reduced apical dendritic length in left ACx. These data demonstrate interhemispheric differences in the morphology of pyramidal neurons in PL and IL of control rats and selective effects of stress on the right hemisphere. In contrast, stress reduced dendritic length in the left ACx.

Light deprivation damages monoamine neurons and produces a depressive behavioral phenotype in rats

Light is an important environmental factor for regulation of mood. There is a high frequency of seasonal affective disorder in high latitudes where light exposure is limited, and bright light therapy is a successful antidepressant treatment. We recently showed that rats kept for 6 weeks in constant darkness (DD) have anatomical and behavioral features similar to depressed patients, including dysregulation of circadian sleep-waking rhythms and impairment of the noradrenergic (NA)-locus coeruleus (LC) system. Here, we analyzed the cell viability of neural systems related to the pathophysiology of depression after DD, including NA-LC, serotoninergic-raphe nuclei and dopaminergic-ventral tegmental area neurons, and evaluated the depressive behavioral profile of light-deprived rats. We found increased apoptosis in the three aminergic systems analyzed when compared with animals maintained for 6 weeks in 12:12 light-dark conditions. The most apoptosis was observed in NA-LC neurons, associated with a significant decrease in the number of cortical NA boutons. Behaviorally, DD induced a depression-like condition as measured by increased immobility in a forced swim test (FST). DD did not appear to be stressful (no effect on adrenal or body weights) but may have sensitized responses to subsequent stressors (increased fecal number during the FST). We also found that the antidepressant desipramine decreases these neural and behavioral effects of light deprivation. These findings indicate that DD induces neural damage in monoamine brain systems and this damage is associated with a depressive behavioral phenotype. Our results suggest a mechanism whereby prolonged limited light intensity could negatively impact mood.

Stress and ageing interactions: A paradox in the context of shared etiological and physiopathological processes

Gerontology has made considerable progress in the understanding of the mechanisms underlying the ageing process and age-related neurodegenerative disorders. However, ways to improve quality of life in the elderly remain to be elucidated. It is now clear that stress and the ageing process share a number of underlying mechanisms bound in a very close, if not indissociable, relationship. The ageing process is regulated by the factors underlying the ability to adjust to stress, whilst stress has an influence on the life span and the quality of ageing. In addition, the ability to cope with stress in adulthood predicts life expectancy and quality of life at senescence. The ageing process and stress also share several common mechanisms, particularly in relation to the energy factor. Stress consumes energy and ageing may be considered as a cost of the energy expended to deal with the stressors to which the body is exposed throughout its lifetime. This suggests that the ageing process is associated with and/or a consequence of a long-lasting activation of the major stress responsive systems. However, despite common features, the interaction between stress and the ageing process gives rise to some paradoxes. Stress can either diminish or exacerbate the ageing process just as the ageing process can worsen or counter the effects of stress. There has been little attempt to understand how ageing and stress might interact to promote "successful" or pathological ageing. A key factor in this respect is the individual's ability to adapt to stress. Viewed from this angle, the quality of life of aged subjects may be improved through therapy designed to improve the tolerance to stress.

Interferon-α reduces the density of monoaminergic axons in the rat brain

Interferon-alpha commonly induces depressive symptoms in clinical populations; however, the mechanism by which this occurs is unclear. Recent studies suggest that the degeneration of axons containing serotonin and noradrenaline is involved in the pathophysiology of depression. The present immunohistochemical study shows that the density of serotonergic axons decreased in the ventral medial prefrontal cortex and amygdala in the interferon-alpha-treated animals. Additionally, interferon-alpha induced decreases in the density of noradrenergic axons in the dorsal medial prefrontal cortex, ventral medial prefrontal cortex, and dentate gyrus. These results support the hypothesis that long-term administration of interferon-alpha causes the degeneration of monoaminergic axons in specific brain regions, which might be associated with depressive symptoms occurring in interferon-alpha-treated patients.

Central alpha1-adrenergic system in behavioral activity and depression

Central alpha(1)-adrenoceptors are activated by norepinephrine (NE), epinephrine (EPI) and possibly dopamine (DA), and function in two fundamental and opposed types of behavior: (1) positively motivated exploratory and approach activities, and (2) stress reactions and behavioral inhibition. Brain microinjection studies have revealed that the positive-linked receptors are located in eight to nine brain regions spanning the neuraxis including the secondary motor cortex, piriform cortex, nucleus accumbens, preoptic area, lateral hypothalamic area, vermis cerebellum, locus coeruleus, dorsal raphe and possibly the C1 nucleus of the ventrolateral medulla, whereas the stress-linked receptors are present in at least three areas including the paraventricular nucleus of the hypothalamus, central nucleus of the amygdala and bed nucleus of the stria terminalis. Recent studies utilizing c-fos expression and mitogen-activated protein kinase activation have shown that various diverse models of depression in mice produce decreases in positive region-neural activity elicited by motivating stimuli along with increases in neural activity of stress areas. Both types of change are attenuated by various antidepressant agents. This has suggested that the balance of the two networks determines whether an animal displays depressive behavior. A central unresolved question concerns how the alpha(1)-receptors in the positive-activity and stress systems are differentially activated during the appropriate behavioral conditions and to what extent this is related to differences in endogenous ligands or receptor subtype distributions.

Chronic stress increases the plasmalemmal distribution of the norepinephrine transporter and the coexpression of tyrosine hydroxylase in norepinephrine axons in the prefrontal cortex

Norepinephrine (NE) potently modulates the cognitive and affective functions of the prefrontal cortex (PFC). Deficits in NE transmission are implicated in psychiatric disorders, and antidepressant drugs that block the NE transporter (NET) effectively treat these conditions. Our initial ultrastructural studies of the rat PFC revealed that most NE axons (85-90%) express NET primarily within the cytoplasm and lack detectable levels of the synthetic enzyme tyrosine hydroxylase (TH). In contrast, the remaining 10-15% of PFC NE axons exhibit predominantly plasmalemmal NET and evident TH immunoreactivity. These unusual characteristics suggest that most PFC NE axons have an unrecognized, latent capacity to enhance the synthesis and recovery of transmitter. In the present study, we used dual-labeling immunocytochemistry and electron microscopy to examine whether chronic cold stress, a paradigm that persistently increases NE activity, would trigger cellular changes consistent with this hypothesis. After chronic stress, neither the number of profiles exhibiting NET labeling nor their size was changed. However, the proportion of plasmalemmal NET nearly doubled from 29% in control animals to 51% in stressed rats. Moreover, the expression of detectable TH in NET-labeled axons increased from only 13% of profiles in control rats to 32% of profiles in stressed animals. Despite the consistency of these findings, the magnitude of the changes varied across individual rats. These data represent the first demonstration of activity-dependent trafficking of NET and expression of TH under physiological conditions and have important implications for understanding the pathophysiology and treatment of stress-related affective disorders.

Age-dependent interactive changes in serotonergic and noradrenergic cortical axon terminals in F344 rats

In the frontal cortex of aging rats, we found an increase in sprouting of the noradrenergic (NA) axons originated from the locus coeruleus (LC). The serotonergic (5-HT) axons originating from the dorsal raphe (DR) share the same cortical area and their age-dependent changes and interactions with NA axons were still unclear. To compare quantitatively the extent of axonal sprouting of DR and LC neurons in the frontal cortex, we extracellularly recorded from both DR and LC neurons in the same animals and antidromically stimulated 32 cortical sites (a pair of stimulating electrodes was moved at 100-mum intervals from 500 to 2000 microm in depth). In addition, to examine the effects of degeneration of 5-HT axons on NA axons, and vice versa, we used specific neurotoxins for 5-HT (PCA) or NA (DSP-4) axons. We also used noradrenaline uptake inhibitor (maprotiline) to verify the effects of NA on degeneration of 5-HT axons. Results suggested that 5-HT axons sprouted between 15 and 17 months of age and noradrenaline accelerated the age-dependent change of 5-HT axons.

Antidepressants and prolonged stress in rats modulate CAM-L1, laminin, and pCREB, implicated in neuronal plasticity

Previously, we reported an ability of NE to promote processes of plasticity in neuroblastoma cells, as observed by morphological changes such as an elongated granule-rich cell body and neuritegenesis, in addition to a progressive decrease in the pluripotent marker Oct4 and an increase in the growth cone marker GAP-43. This was accompanied by the induction of three plasticity genes forming a functional cluster, the cell adhesion molecule L1 (CAM-L1), laminin, and CREB, all involved in neuronal plasticity and neurite outgrowth. In the present study, we hypothesized that the regulation of CAM-L1, laminin, and CREB/pCREB by NE could mediate processes of plasticity in the mode of action of antidepressants, as well as in the long-term effects of stress, in rats, given the association of both with NE alterations and neuronal plasticity. In the first experiment, rats were chronically administered with antidepressants (21 days). In the second experiment, rats were exposed to chronic stress and examined 4 months later, a model shown to exhibit behavioral indices of stress. We found brain region-specific alterations in mRNA and protein levels of CAM-L1, laminin, and pCREB in rats chronically treated with the noradrenergic antidepressant desipramine and, to a lesser extent, in those treated with fluoxetine. Stressed rats presented a decrease in CAM-L1, laminin, and pCREB, specifically in brain areas implicated in stress. Our findings suggest that noradrenergic-regulated plasticity genes such as CAM-L1, laminin, and CREB play an important role both in stress and in the treatment of depression.

Nitric oxide synthesis is required for exercise-induced increases in hippocampal BDNF and phosphatidylinositol 3' kinase expression

Previous studies have shown that running exercise, either alone or in combination with antidepressant treatment, results in increased hippocampal BDNF levels. Nitric oxide (NO) is an important signaling molecule that has neuronal survival-promoting properties and has been shown to play an important role in plasticity associated with activating interventions. Herein, we administered the NO synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), in conjunction with the monoamine oxidase inhibitor (MAOI) antidepressant, tranylcypromine, and voluntary wheel-running exercise to determine whether the enhancement in full-length BDNF mRNA occurring with these interventions is dependent upon NO synthesis. Our results demonstrate that both chronic exercise and chronic exercise-plus-tranylcypromine lead to enhanced hippocampal BDNF mRNA and protein expression. NOS inhibition prevents this effect of chronic exercise, but only partly prevents the effects of the exercise/antidepressant combination. Thus, the robust enhancement in BDNF mRNA occurring with exercise appears to be NO synthesis-dependent, but the intervention including antidepressant may enhance BDNF expression through alternative intracellular mechanisms. In addition, because exercise and antidepressants have both been shown to activate survival-promoting genes, we evaluated the levels of hippocampal phosphatidylinositol 3' kinase (PI-3K), an important signaling molecule within a principal neuronal survival-promoting intracellular pathway. Like BDNF mRNA and protein, exercise increases the expression of PI-3K, whereas concomitant NOS inhibition prevents this increase in PI-3K immunoreactivity above control levels. Our results are discussed in light of possible overlapping, but distinct intracellular pathways activated by exercise and antidepressant treatment to bring about enhancements in BDNF expression and other survival-promoting effects. These findings further demonstrate the potential therapeutic potential of chronic exercise to supplement pharmacotherapeutic treatment of mood disorders.

Contribution of the stress-induced degeneration of the locus coeruleus noradrenergic neurons to the pathophysiology of depression: a study on an animal model

A novel theory on the pathophysiology of depression would be expected to resolve a contradiction between therapeutic time lag and monoamine hypothesis. On the basis of the fact that a subgroup of depression appears during or after stress, we exposed rats to a long-term (2 weeks) forced walking stress and produced depression-model rats in one group and spontaneous recovery rats in another. The density of axon terminals of the locus coeruleus (LC) neurons in the frontal cortex stained by dopamine β-hydroxylase antiserum was lower in the depression-model rats than in the spontaneous recovery rats and in the control rats without stress. The density was higher in the model rats daily treated with imipramine than in those treated with saline. Morphological projection (MP) index (a percentage of horseradish peroxidase-positive LC cells in total number of LC cells) and electrophysiological projection index (a percentage of LC neurons activated antidromically by electrical stimulation of the cerebral cortex) were lower in the depression-model rats than in the recovery and control rats. MP index was higher in the imipramine-treated rats than that in the saline-treated rats. Electron microscopic examination of the LC disclosed such degenerative changes as low-dense areas without structure, aggregation of intracellular organs, destroyed membranes around the rough endoplasmic reticulum (rER), a decreased number of deformed subsurface cisterns, glia invaginated into the LC neurons and prominent appearance of microglia containing increased number of lipofustin or lysosome in the model rats, but not in the spontaneous recovery rats. These findings suggest that the terminals and cell bodies of the LC noradrenergic neurons degenerate in the stress-induced depression-model rats and regenerate in the imipramine-treated model rats. This degenerative change may possibly contribute to the decrease in synthesis and metabolism of noradrenaline (NA), the slowing of axonal flow, the accumulation of NA in the neurons, the decrease in discharge rate of LC neurons without stress and the increase in release of NA in response to an additional stress. It may also explain the therapeutic time lag that is required to repair the noradrenergic neurons.

Opposite morphological responses of partially denervated cortical serotonergic and noradrenergic axons to repeated stress in adult rats

We examined plastic changes in serotonin (5-HT) axons following repeated stress in the adult rat brain, and compared stress-induced changes between 5-HT and noradrenaline (NA) axons. We locally injected the specific neurotoxin to 5-HT axons or to NA axons into the frontal cortex to cause partial denervation. The animals were mildly restrained from 1 day after the neurotoxin injection and this stress was repeated daily for 20 min during the first 2 days and for 40 min during the next 11 days. On the fourteenth day after injection, the brains were removed to visualize 5-HT and NA axons by immunohistochemistry. Repeated stress did not significantly alter the denervation area of 5-HT or NA axons, but the density of 5-HT axons was increased whereas that of NA axons was decreased in cortical regions outside the denervation site. In addition, the expression of brain-derived neurotrophic factor (BDNF) was increased in cortical regions where the 5-HT axon density was increased in response to stress. These results suggest that repeated stress causes opposite changes in the morphology of partially denervated 5-HT and NA axons in the cerebral cortex. The stress-induced increase in BDNF expression may contribute to 5-HT axon sprouting following repeated stress.

New insights into the mechanisms of antidepressant therapy

Depressive disorders are among the most frequent psychiatric diseases in the Western world with prevalence numbers between 9% and 18%. They are characterized by depressed mood, a diminished interest in pleasurable activities, feelings of worthlessness or inappropriate guilt, decrease in appetite and libido, insomnia, and recurrent thoughts of death or suicide. Among other findings, reduced activity of monoaminergic neurotransmission has been postulated to play a role in the pathogenesis of depression. Consistent with this hypothesis, most antidepressive drugs exert their action by elevating the concentration of monoamines in the synaptic cleft. However, it is not the enhancement of monoaminergic signaling per se, but rather long-term, adaptive changes that may underlie the therapeutic effect. These include functional and structural changes that are discussed later. In addition, in the last years, evidence has emerged that remissions induced in patients using lithium or electroconvulsive therapy are accompanied by structural changes in neuronal networks thereby affecting synaptic plasticity in various regions of the brain.

Interaction between serotonergic and noradrenergic axons during axonal regeneration

The present experiments focused on the morphological interaction between serotonergic (5-HT) and noradrenergic (NA) axons during regeneration following partial axonal denervation in the cerebral cortex in adult rats. The denervation paradigm used employed two neurotoxins, one for 5-HT and one for NA axons, infused together at one cortical site while a single neurotoxin to either 5-HT or NA was infused at the symmetrical cortical site in the other hemisphere. This treatment enabled us to assess the role of 5-HT or NA axons in the regeneration of the other monoaminergic axon. 5-HT axon regeneration became apparent as early as 28 days after the toxin injection, whereas the regeneration of NA axons was not evident even at 60 days after the toxin injection. Since NA axons revealed marked regeneration in the cortical site with denervation of 5-HT axons, intact 5-HT axons may be inhibitory on the regeneration of NA axons. In contrast, since the regeneration of 5-HT axons was suppressed in the absence of NA axons, NA axons appear to exert a facilitatory effect on 5-HT axon regeneration. These results suggest that the role of 5-HT axons in the regeneration of NA axons is opposite to that of NA axons in the regeneration of 5-HT axons. In addition, the regeneration of 5-HT axons occurred much faster than that of NA axons in response to axonal damage. The differential roles of 5-HT and NA axons in axonal regeneration may play a role in a variety of physiological functions related to these monoamines and possibly in the pathophysiology of clinical depression.

Chronic treatment with imipramine inhibits cell growth and enhances serotonin 2C receptor mRNA expression in NG 108-15 cells

We previously reported that NG108-15 cells contain intrinsic serotonin 2C receptor (5-HT2CR). The effects of imipramine, a 5-HT2CR antagonist, on cell growth, cell viability, and the 5-HT2CR mRNA level were investigated in this study. Repeated treatment with imipramine at concentrations of 1 - 10 microM for 5 days inhibited cell growth in a concentration-dependent manner without affecting cell viability. In addition, the level of 5-HT2CR mRNA was elevated. At 30 microM, imipramine significantly reduced cell viability. Our findings suggest that the effect of imipramine on neuronal growth may be related to its effects on 5-HT2CR.

Increased expression of corticotropin-releasing factor receptor mRNA in the locus coeruleus of stress-induced rat model of depression

Hypersecretion of corticotropin-releasing factor (CRF) has been hypothesized to occur in depression. To investigate CRF receptor (CRFR) response to the increased production of CRF in chronically stressed rats, we measured by in situ hybridization the expression of CRFR mRNA in the locus coeruleus (LC) concomitant with measuring plasma adrenocorticotropin (ACTH). The expression of both CRFR mRNA in the LC and the plasma level of ACTH increased significantly in "depression-model rats" which exhibit reduced activity following exposure to 14 days forced walking stress (FWS), but not in "spontaneous recovery rats" whose activity was restored after the long-term stress. These results suggest that the LC neurons continue to be stimulated by CRF, and that the hypothalamic-pituitary-adrenal (HPA) axis is hyperfunctioning in the depression-model rats.

[Neurobiological principles of bipolar affective disorders]

The neurobiology of bipolar affective illness can be described in a model with structural and functional components, which also address the role of stressors, coping mechanisms, and psychophysical disposition. More data exist on depressive than on manic patients or on patients switching from one clinical pole to the other. Structural and functional chronobiological alterations appear to play a major role in the pathophysiology of bipolar illness. From an anatomical view, neurobiological abnormalities are primarily confined to limbic-striatal-pallidal-thalamocortical circuits. The whole cascade of neural signaling is changed starting from neurotransmitters and neuromodulators to receptor-mediated intracellular signal transduction targeting nuclear gene expression. Transnosological factors such as suicidal tendency appear to essentially modulate those changes. Replicated data on decisive neurobiological differences between bipolar and unipolar affective disorders are currently not yet available.

Norepinephrine alters the expression of genes involved in neuronal sprouting and differentiation: relevance for major depression and antidepressant mechanisms

Recent research into depression has focused on the involvement of long-term intracellular processes, leading to abnormal neuronal plasticity in brains of depressed patients, and reversed by antidepressant treatment. Given a suggested decrease in noradrenergic transmission in depression, and an antidepressant induced increase in norepinephrine (NE) level, a possible role for NE in mediating alterations in neuronal morphology and plasticity was examined. Human neuroblastoma SH-SY5Y cells treated with 10-5 m NE presented an elongated granule-rich cell-body and increased number of neurites, when compared with non-treated cells. Moreover, cell survival was enhanced in the presence of NE, while proliferation was inhibited. The above effects suggest a role for NE in cell differentiation. Indeed similar effects on cell survival and neurite outgrowth were induced in SH-SY5Y cells by retinoic acid (RA), an established differentiating agent. Finally, NE treatment resulted in a progressive decrease in the pluripotent marker Oct4 and an increase in the neuronal growth cone marker, growth-associated-protein 43 (GAP-43). Alongside these effects, NE-treated cells presented alterations in the expression of 44 genes as observed in a neurobiology cDNA microarray. Among the altered genes, an increase in the expression level of two neurite-outgrowth promoting genes, neural cell adhesion molecule L1 and laminin, was confirmed by RT-PCR. Taken together, the results support a role for NE in processes of synaptic connectivity, and may point to a role for this neurotransmitter in mediating the suggested neuronal plasticity in depression and in antidepressant treatment.

Morphological brain changes in depression: can antidepressants reverse them?

Structural neuroimaging and postmortem histopathological studies of the brain have revealed morphological changes in cortical and subcortical regions in individuals diagnosed with depression. Moreover, these regions are known to be functionally altered in mood disorders. This indicates that the morphological changes might be directly involved in the pathophysiology of depression, and implies that antidepressants may be able to regulate or reverse the detected structural abnormalities. Work with animal models has shown that antidepressants are capable of inducing structural alterations in dendrites and axons and changes in the numbers of neural cells. However, there have been no studies in the human brain that have directly addressed whether antidepressant treatment can reverse or regulate the depression-related structural changes. Nevertheless, experience with lithium in bipolar disorder and antipsychotics in schizophrenia suggests that treatment with psychotropic drugs can result in structural changes that are consistent with reversion towards normal values. Clearly, ascertaining the role of the reversal of structural changes in the therapeutic actions of antidepressants will require further longitudinal studies and careful comparisons between those patients with mood disorder who are treated with antidepressants and those who are not.

Decreased serum brain-derived neurotrophic factor levels in major depressed patients

Recent findings with animal models have suggested a possible role for brain-derived neurotrophic factor (BDNF) in depression. We have therefore hypothesized that depression could be characterized by low levels of serum BDNF. Major depressed patients (15F + 15M) diagnosed according to DSM-IV criteria and healthy controls (15F + 15M) participated in the study. Serum BDNF was assayed with the ELISA method and the severity of depression was evaluated with Montgomery-Asberg-Depression Rating Scale (MADRS). BDNF levels were significantly lower in patients than in controls: 22.6 +/- 3 and 26.5 +/- 7 ng/ml (t-test = 2.7; d.f. = 58; P < 0.01). They were negatively correlated to the MADRS scores (r = -0.55; P < 0.02). Female patients were more depressed and released less BDNF than men. Analysis of covariance (MADRS and gender as independent variable vs. BDNF as dependent variable) indicated that depression severity mainly accounted for the negative correlation. These results suggest that major depression is characterized by low serum BDNF levels and support the hypothesis of neurotrophic factor involvement in affective disorders.

Role of serotonergic and noradrenergic systems in the pathophysiology of depression and anxiety disorders

There is abundant evidence for abnormalities of the norepinephrine (NE) and serotonin (5HT) neurotransmitter systems in depression and anxiety disorders. The majority of evidence supports underactivation of serotonergic function and complex dysregulation of noradrenergic function, most consistent with overactivation of this system. Treatment for these disorders requires perturbation of these systems. Reproducible increases in serotonergic function and decreases in noradrenergic function accompany treatment with antidepressants, and these alterations may be necessary for antidepressant efficacy. Dysregulation of these systems clearly mediates many symptoms of depression and anxiety. The underlying causes of these disorders, however, are less likely to be found within the NE and 5HT systems, per se. Rather their dysfunction is likely due to their role in modulating, and being modulated by, other neurobiologic systems that together mediate the symptoms of affective illness. Clarification of noradrenergic and serotonergic modulation of various brain regions may yield a greater understanding of specific symptomatology, as well as the underlying circuitry involved in euthymic and abnormal mood and anxiety states. Disrupted cortical regulation may mediate impaired concentration and memory, together with uncontrollable worry. Hypothalamic abnormalities likely contribute to altered appetite, libido, and autonomic symptoms. Thalamic and brainstem dysregulation contributes to altered sleep and arousal states. Finally, abnormal modulation of cortical-hippocampal-amygdala pathways may contribute to chronically hypersensitive stress and fear responses, possibly mediating features of anxiety, anhedonia, aggression, and affective dyscontrol. The continued appreciation of the neural circuitry mediating affective states and their modulation by neurotransmitter systems should further the understanding of the pathophysiology of affective and anxiety disorders.

Role of norepinephrine in the pathophysiology of neuropsychiatric disorders

The concatenation of convergent lines of evidence from basic to clinical research continues to reveal that norepinephrine (NE) is a crucial regulator of a myriad of behaviors ranging from stress response to memory formation. Furthermore, many neuropsychiatric disorders involve neurocircuitry that is directly modulated by NE. This report summarizes the physiological roles of NE, as well as the main findings implicating a role for NE system dysfunction in mood and anxiety disorders, posttraumatic stress disorder, attention-deficit/hyperactivity disorder, and Alzheimer's disease. In each of these disorders, there appears to be a complex dysregulation of NE function, with changes in locus ceruleus firing, NE availability, and both pre- and postsynaptic receptor regulation. Many symptoms of these disorders are attributable to abnormalities within distributed neural circuits regulated by NE. Appreciation of NE's role in modulating the neural circuitry mediating cognition and affect should help elucidate the pathophysiology of a variety of neuropsychiatric disorders and the development of novel treatments.

An in-vivo magnetic resonance imaging study of the olfactory bulbectomized rat model of depression

The olfactory bulbectomized (OB) rat is a well-accepted animal model of depression. The present magnetic resonance imaging (MRI) investigation demonstrates alterations in signal intensities in cortical, hippocampal, caudate and amygdaloid regions in OB animals, but not in sham operated controls. Ventricular enlargement was also evident in OB animals. These alterations have implications with regard to the face and construct validity of this model.

Prolonged c-Jun expression in the basolateral amygdala following bulbectomy: possible implications for antidepressant activity and time of onset

Olfactory bulbectomy is a well established animal model of depression. Neurochemical and behavioral alterations observed following olfactory bulbectomy, are due, in part, to the neurodegeneration of specific brain structures. Amygdaloid dysfunction in particular, is known to play a substantial role in the syndrome of the olfactory bulbectomized rat. The present study examined both short- and long-term alterations in immediate early gene expression, tyrosine hydroxylase and serotonin immunoreactivity, and classical silver staining, following olfactory bulbectomy in the basolateral amygdala. The results indicated no consistent change in Fos expression observed over the experimental period. Following bulbectomy, long term (up to 64 days post-lesion) Jun expression, not coincident with silver staining, was observed in the basolateral nucleus. The basolateral nucleus was also intensely immunoreactive for serotonin at this timepoint post-bulbectomy. Thus, following bulbectomy long term alterations in Jun expression occurs in the serotonin rich basolateral amygdala. As a site of action for antidepressant compounds, alterations at the immediate early gene level in this region may have implications both for the model, and antidepressant drug action therein.

The neuropathological effects of antipsychotic drugs

In addition to their neurochemical effects, antipsychotic (neuroleptic) drugs produce structural brain changes. This property is relevant not only for understanding the drugs' mode of action, but because it complicates morphological studies of schizophrenia. Here the histological neuropathological effects of antipsychotics are reviewed, together with brief mention of those produced by other treatments sometimes used in schizophrenia (electroconvulsive shock, lithium and antidepressants). Most data come from drug-treated rats, though there are also some human post-mortem studies with broadly congruent findings. The main alteration associated with antipsychotic medication concerns the ultrastructure and proportion of synaptic subpopulations in the caudate nucleus. In rats, synapses and dendrites in lamina VI of the prefrontal cortex are also affected. The changes are indicative of a drug-induced synaptic plasticity, although the underlying mechanisms are poorly understood. Similarly, it is unclear whether the neuropathological features relate primarily to the therapeutic action of antipsychotics or, more likely, to their predisposition to cause tardive dyskinesia and other motor side-effects. Clozapine seems to cause lesser and somewhat different alterations than do typical antipsychotics, albeit based on few data. There is no good evidence that antipsychotics cause neuronal loss or gliosis, nor that they promote neurofibrillary tangle formation or other features of Alzheimer's disease.

Role of norepinephrine in the pathophysiology and treatment of mood disorders

For four decades, norepinephrine (NE) has been postulated to play an important, possibly primary, role in the pathophysiology and subsequent treatment of mood disorders. The long-held hypothesis was that depression and pathological elation are direct functions of low and high activity of norepinephrine-containing neurons, respectively. Decades of research in this field have been devoted to further clarifying this relationship. However, there continues to be inconsistencies in the data, with different studies finding significant differences in NE metabolites and changes in receptor populations. Furthermore, antidepressants that do not act directly on the NE system appear to be quite effective in the treatment of depression. Although differential NE activity and treatment response may be partially due to different subtypes of depression, this clearly does not explain all the data. This review attempts to consolidate the relevant physiology of the NE system with the pathological changes found in depression. Norepinephrine clearly has an important role in this disease, but absolute changes in its activity are less likely to be the primary cause of the disorder. Evidence for dysregulation of the locus ceruleus-NE system in depression is quite apparent, however, contributing to disrupted attention, concentration, memory, arousal, and sleep. Homeostatic changes likely occur after chronic treatment with antidepressants, allowing a new regulatory state to occur in which NE modulation is once again effective. The availability of new tools such as selective ligands for the NE transporter that can be utilized with positron emission tomography imaging will undoubtedly advance the field.

The noradrenergic system in pathological anxiety: a focus on panic with relevance to generalized anxiety and phobias

Over the past three decades of psychiatric research, abnormalities in the noradrenergic system have been identified in particular anxiety disorders such as panic disorder. Simultaneously, neuroscience research on fear pathways and the stress response have delineated central functions for the noradrenergic system. This review focuses on the noradrenergic system in anxiety spectrum disorders such as panic disorder, generalized anxiety disorder, and phobias for the purpose of elucidating current conceptualizations of the pathophysiologies. Neuroanatomic pathways that are theoretically relevant in anxiogenesis are discussed and the implications for treatment reviewed.

Castration differentially alters [3H]nisoxetine binding to norepinephrine uptake sites in olfactory bulb and frontal cortex of male rats

In the present study, [3H]nisoxetine binding to norepinephrine (NE) uptake sites and [3H]norepinephrine uptake were investigated within olfactory bulb (OB) and frontal cortex homogenates from intact and castrated male rats. Statistically significant reductions in the number of [3H]nisoxetine binding sites (Bmax) were found in OB from the castrates, while significantly increased Bmax values were obtained in the frontal cortex. Castration also significantly altered the affinity (Kd) of [3H]nisoxetine binding in the frontal cortex, but not in the OB. Assessment of [3H]norepinephrine uptake showed that in neither brain regions were there any statistically significant differences in Km nor Vmax between the castrated and intact male rats, indicating that the basal uptake process is not changed following castration in either of these brain areas. These results demonstrate the differential effects of castration upon [3H]nisoxetine binding sites between the OB and frontal cortex. Such findings provide new evidence for one of the mechanisms by which androgens may modulate central noradrenergic activity.

Neurotrophins and depression

Exogenous delivery of the neurotrophic factors, brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3), promotes the function, sprouting and regrowth of 5-HT-containing neurones in the brains of adult rats. Similar infusions of BDNF into the dorsal raphe nucleus produce an antidepressant effect, as evaluated by several 'learned helplessness' paradigms. Environmental stressors such as immobilization induce depression and decrease BDNF mRNA. Antidepressants increase BDNF mRNA in the brain, via 5-HT2A and beta-adrenoceptor subtypes and prevent the stress-induced decreases in BDNF mRNA. In this article, Tony Altar discusses how existing treatments of depression might work by increasing endogenous brain levels of BDNF or NT-3, which in turn could promote monoamine-containing neurone growth and function. Drugs that selectively stimulate the production of neurotrophins could represent a new generation of antidepressants.

Increased expression of magnocellular arginine vasopressin mRNA in paraventricular nucleus of stress-induced depression-model rats

Exposure of rats to long-term intermittent walking stress results in a persistent inactive behavior in the subsequent two weeks in about 50% of rats (depression-model rats) while the activity returns gradually toward baseline in other rats (spontaneous recovery rats). To explore the role of hypothalamic-pituitary-adrenal (HPA) axis in these depression-model rats, we examined changes in the gene expression of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) in the paraventricular nucleus (PVN) of the hypothalamus using in situ hybridization histochemistry. We imposed the intermittent walking stress for two weeks in male Wistar rats, then compared the response of the depression-model rats and spontaneous recovery rats. The expression of CRF mRNA in PVN increased significantly by 60% and 80% compared to controls, in the model and the recovery rats, respectively. The magnocellular AVP mRNA in PVN increased significantly in the model rats by 60% compared to controls. The concentration of plasma ACTH increased in the model rats, but no significant change in plasma corticosterone or AVP level was noted in all three groups. Our results suggest that increased magnocellular AVP in PVN plays an important role in the regulation of HPA axis of the depression-model rats induced by long-term walking stress.