Structural plasticity of the adult brain: how animal models help us understand brain changes in depression and systemic disorders related to depression

Mechanisms of stress-attributed breast cancer incidence and progression

Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer deaths in women, with psychosocial stress commonly cited by patients as one of its causes. While there is conflicting epidemiological evidence investigating the association between psychosocial stress and breast cancer incidence and progression, there is reason to believe that interventions aimed at reducing stress pharmacologically or psychologically may improve breast cancer outcomes. The aim of this review is to discuss the molecular and biological mechanisms of stress-attributed breast cancer incidence and progression, including the induction of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS), as well as decreased immune function and stress hormone-induced resistance to chemotherapy. Moreover, these mechanisms have been cited as potential therapeutic targets of pharmacologic and psychological interventions that may improve the care, well-being and survival of breast cancer patients. Further research is recommended to investigate whether interventions in the primary care setting for women with risk factors for breast cancer development may lead to a decreased incidence of invasive breast tumors.

Changes in structural plasticity of hippocampal neurons in an animal model of multiple sclerosis

Structural plasticity is critical for the functional diversity of neurons in the brain. Experimental autoimmune encephalomyelitis (EAE) is the most commonly used model for multiple sclerosis (MS), successfully mimicking its key pathological features (inflammation, demyelination, axonal loss, and gliosis) and clinical symptoms (motor and non-motor dysfunctions). Recent studies have demonstrated the importance of synaptic plasticity in EAE pathogenesis. In the present study, we investigated the features of behavioral alteration and hippocampal structural plasticity in EAE-affected mice in the early phase (11 days post-immunization, DPI) and chronic phase (28 DPI). EAE-affected mice exhibited hippocampus-related behavioral dysfunction in the open field test during both early and chronic phases. Dendritic complexity was largely affected in the cornu ammonis 1 (CA1) and CA3 apical and dentate gyrus (DG) subregions of the hippocampus during the chronic phase, while this effect was only noted in the CA1 apical subregion in the early phase. Moreover, dendritic spine density was reduced in the hippocampal CA1 and CA3 apical/basal and DG subregions in the early phase of EAE, but only reduced in the DG subregion during the chronic phase. Furthermore, mRNA levels of proinflammatory cytokines ( Il1β, Tnfα, and Ifnγ) and glial cell markers ( Gfap and Cd68) were significantly increased, whereas the expression of activity-regulated cytoskeleton-associated protein (ARC) was reduced during the chronic phase. Similarly, exposure to the aforementioned cytokines in primary cultures of hippocampal neurons reduced dendritic complexity and ARC expression. Primary cultures of hippocampal neurons also showed significantly reduced extracellular signal-regulated kinase (ERK) phosphorylation upon treatment with proinflammatory cytokines. Collectively, these results suggest that autoimmune neuroinflammation alters structural plasticity in the hippocampus, possibly through the ERK-ARC pathway, indicating that this alteration may be associated with hippocampal dysfunctions in EAE.

Association Between Taurine Level in the Hippocampus and Major Depressive Disorder in Young Women: A Proton Magnetic Resonance Spectroscopy Study at 7T

BACKGROUND

Major depressive disorder (MDD) is characterized by depressed mood or loss of interest or pleasure. Generally, women are twice as likely as men to have depression. Taurine, a type of amino acid, plays critical roles in neuronal generation, differentiation, arborization, and formation of synaptic connections. Importantly, it enhances proliferation and synaptogenesis in the hippocampus. When injected into animals, taurine has an antidepressant effect. However, there is no in vivo evidence to show an association between taurine concentration in the human brain and the development of MDD.

METHODS

Forty-one unmedicated young women with MDD (ages 18-29) and 43 healthy control participants matched for gender and age were recruited in South Korea. Taurine concentration was measured in the hippocampus, anterior cingulate cortex, and occipital cortex of the MDD and healthy control groups using proton magnetic resonance spectroscopy at 7T. Analysis of covariance was used to examine differences in taurine concentration, adjusting for age as a covariate.

RESULTS

Taurine concentration in the hippocampus was lower (F1,75 = 5.729, p = .019, Δη2 = 0.073) for the MDD group (mean [SEM] = 0.91 [0.06] mM) than for the healthy control group (1.13 [0.06] mM). There was no significant difference in taurine concentration in the anterior cingulate cortex or occipital cortex between the two groups.

CONCLUSIONS

This study demonstrates that a lower level of taurine concentration in the hippocampus may be a novel characteristic of MDD.

Subcortical Brain Development in Autism and Fragile X Syndrome: Evidence for Dynamic, Age- and Disorder-Specific Trajectories in Infancy

OBJECTIVE

Previous research has demonstrated that the amygdala is enlarged in children with autism spectrum disorder (ASD). However, the precise onset of this enlargement during infancy, how it relates to later diagnostic behaviors, whether the timing of enlargement in infancy is specific to the amygdala, and whether it is specific to ASD (or present in other neurodevelopmental disorders, such as fragile X syndrome) are all unknown.

METHODS

Longitudinal MRIs were acquired at 6-24 months of age in 29 infants with fragile X syndrome, 58 infants at high likelihood for ASD who were later diagnosed with ASD, 212 high-likelihood infants not diagnosed with ASD, and 109 control infants (1,099 total scans).

RESULTS

Infants who developed ASD had typically sized amygdala volumes at 6 months, but exhibited significantly faster amygdala growth between 6 and 24 months, such that by 12 months the ASD group had significantly larger amygdala volume (Cohen's d=0.56) compared with all other groups. Amygdala growth rate between 6 and 12 months was significantly associated with greater social deficits at 24 months when the infants were diagnosed with ASD. Infants with fragile X syndrome had a persistent and significantly enlarged caudate volume at all ages between 6 and 24 months (d=2.12), compared with all other groups, which was significantly associated with greater repetitive behaviors.

CONCLUSIONS

This is the first MRI study comparing fragile X syndrome and ASD in infancy, demonstrating strikingly different patterns of brain and behavior development. Fragile X syndrome-related changes were present from 6 months of age, whereas ASD-related changes unfolded over the first 2 years of life, starting with no detectable group differences at 6 months. Increased amygdala growth rate between 6 and 12 months occurs prior to social deficits and well before diagnosis. This gradual onset of brain and behavior changes in ASD, but not fragile X syndrome, suggests an age- and disorder-specific pattern of cascading brain changes preceding autism diagnosis.

Sex differences in the association between basal serum cortisol concentrations and cortical thickness

Background

Basal cortisol concentrations vary between men and women. Likewise, previous findings suggest stress-related cortical thickness alterations. Thus, we aimed at elucidating sex differences in the association between serum cortisol concentrations and cortical thickness.

Methods

Data of 2594 participants (55.55% male; mean age = 53.55 years ± 13.17 years) of the general population were used to investigate sex differences in basal serum cortisol concentrations and associations of serum cortisol concentrations with global and regional cortical thickness. The validity of the results was tested by including sex hormone concentrations as a biological and childhood maltreatment and depressive symptoms as a psychological confounder.

Results

Basal serum cortisol concentrations were higher in men than in women (β = -0.158, t₍₂₅₇₅₎ = -6.852, p = 9.056e-12). Sex differences in serum cortisol concentrations were diminished by including serum concentrations of testosterone, estrone, or estradiol in the models. In men but not in women, serum cortisol concentrations were inversely associated with the global cortical thickness (men: β = -0.064, t₍₁₄₁₂₎ = -3.010, p = .003; women: β = -0.016, t₍₁₁₃₁₎ = -0.607, p = .544). Additionally, these effects were observed in eleven cortical regions after adjusting for multiple testing. The associations were independent of childhood maltreatment and depressive symptoms.

Conclusion

Sex differences in serum cortisol concentrations and the association between serum cortisol concentrations and cortical thickness suggest important sex-specific effects of stress on the brain. Future studies should integrate the interaction between the hypothalamic-pituitary-adrenal (HPA) axis and hypothalamic-pituitary-gonadal (HPG) axis in sex-stratified analyses.

Mechanisms of neuroplasticity linking early adversity to depression: developmental considerations

Early exposure to psychosocial adversity is among the most potent predictors of depression. Because depression commonly emerges prior to adulthood, we must consider the fundamental principles of developmental neuroscience when examining how experiences of childhood adversity, including abuse and neglect, can lead to depression. Considering that both the environment and the brain are highly dynamic across the period spanning gestation through adolescence, the purpose of this review is to discuss and integrate stress-based models of depression that center developmental processes. We offer a general framework for understanding how psychosocial adversity in early life disrupts or calibrates the biobehavioral systems implicated in depression. Specifically, we propose that the sources and nature of the environmental input shaping the brain, and the mechanisms of neuroplasticity involved, change across development. We contend that the effects of adversity largely depend on the developmental stage of the organism. First, we summarize leading neurobiological models that focus on the effects of adversity on risk for mental disorders, including depression. In particular, we highlight models of allostatic load, acceleration maturation, dimensions of adversity, and sensitive or critical periods. Second, we expound on and review evidence for the formulation that distinct mechanisms of neuroplasticity are implicated depending on the timing of adverse experiences, and that inherent within certain windows of development are constraints on the sources and nature of these experiences. Finally, we consider other important facets of adverse experiences (e.g., environmental unpredictability, perceptions of one's experiences) before discussing promising research directions for the future of the field.

Enhanced neurogenesis is involved in neuroprotection provided by rottlerin against trimethyltin-induced delayed apoptotic neuronal damage

AIMS

We here investigated the effect of late- and post-ictal treatment with rottlerin, a polyphenol compound isolated from Mallotus philippinensis, on delayed apoptotic neuronal death induced by trimethyltin (TMT) in mice.

MAIN METHODS

Male C57BL/6N mice received a single injection of TMT (2.4 mg/kg, i.p.), and mice were treated with rottlerin after a peak time (i.e., 2 d post-TMT) of convulsive behaviors and apoptotic cell death (5.0 mg/kg, i.p. at 3 and 4 d after TMT injection). Object location test and tail suspension test were performed at 5 d after TMT injection. In addition, changes in the expression of apoptotic and neurogenic markers in the dentate gyrus were examined.

KEY FINDINGS

Late- and post-ictal treatment with rottlerin suppressed delayed neuronal apoptosis in the dentate gyrus, and attenuated memory impairments (as evaluated by object location test) and depression-like behaviors (as evaluated by tail suspension test) at 5 days after TMT injection in mice. In addition, rottlerin enhanced the expression of Sox2 and DCX, and facilitated p-ERK expression in BrdU-incorporated cells in the dentate gyrus of TMT-treated mice. Rottlerin also increased p-Akt expression, and attenuated the increase in the ratio of pro-apoptotic factors/anti-apoptotic factors, and consequent cytosolic cytochrome c release and caspase-3 cleavage. Rottlerin-mediated action was significantly reversed by SL327, an ERK inhibitor.

SIGNIFICANCE

Our results suggest that late- and post-ictal treatment with rottlerin attenuates TMT-induced delayed neuronal apoptosis in the dentate gyrus of mice via promotion of neurogenesis and inhibition of an on-going apoptotic process through up-regulation of p-ERK.

Association of obesity with cognitive function and brain structure in patients with major depressive disorder

BACKGROUND

Obesity has been implicated in the pathophysiology of major depressive disorder (MDD), which prompted us to examine the possible association of obesity with cognitive function and brain structure in patients with MDD.

METHODS

Three hundred and seven patients with MDD and 294 healthy participants, matched for age, sex, ethnicity (Japanese), and handedness (right) were recruited for the study. Cognitive function was assessed using the Brief Assessment of Cognition in Schizophrenia (BACS). Gray and white matter structures were analyzed using voxel-based morphometry and diffusion tensor imaging in a subsample of patients (n = 114) whose magnetic resonance imaging (MRI) data were obtained using a 1.5 T MRI system.

RESULTS

Verbal memory, working memory, motor speed, attention, executive function, and BACS composite scores were lower for the MDD patients than for the healthy participants (p < 0.05). Among the patient group, working memory, motor speed, executive function, and BACS composite scores were lower in obese patients (body mass index ≥ 30, n = 17) than in non-obese patients (n = 290, p < 0.05, corrected). MRI determined frontal, temporal, thalamic, and hippocampal volumes, and white matter fractional anisotropy values in the internal capsule and left optic radiation were reduced in obese patients (n = 7) compared with non-obese patients (n = 107, p < 0.05, corrected).

LIMITATIONS

Sample size for obese population was not very large.

CONCLUSIONS

Obesity is associated with decreased cognitive function, reduced gray matter volume, and impaired white matter integrity in cognition-related brain areas in patients with MDD.

Pathogenesis of depression- and anxiety-like behavior in an animal model of hypertrophic cardiomyopathy

Cardiovascular dysfunction is highly comorbid with mood disorders, such as anxiety and depression. However, the mechanisms linking cardiovascular dysfunction with the core behavioral features of mood disorder remain poorly understood. In this study, we used mice bearing a knock-in sarcomeric mutation, which is exhibited in human hypertrophic cardiomyopathy (HCM), to investigate the influence of HCM over the development of anxiety and depression. We employed behavioral, MRI, and biochemical techniques in young (3-4 mo) and aged adult (7-8 mo) female mice to examine the effects of HCM on the development of anxiety- and depression-like behaviors. We focused on females because in both humans and rodents, they experience a 2-fold increase in mood disorder prevalence vs. males. Our results showed that young and aged HCM mice displayed echocardiographic characteristics of the heart disease condition, yet only aged HCM females displayed anxiety- and depression-like behaviors. Electrocardiographic parameters of sympathetic nervous system activation were increased in aged HCM females vs. controls and correlated with mood disorder-related symptoms. In addition, when compared with controls, aged HCM females exhibited adrenal gland hypertrophy, reduced volume in mood-related brain regions, and reduced hippocampal signaling proteins, such as brain-derived neurotrophic factor and its downstream targets vs. controls. In conclusion, prolonged systemic HCM stress can lead to development of mood disorders, possibly through inducing structural and functional brain changes, and thus, mood disorders in patients with heart disease should not be considered solely a psychologic or situational condition.-Dossat, A. M., Sanchez-Gonzalez, M. A., Koutnik, A. P., Leitner, S., Ruiz, E. L., Griffin, B., Rosenberg, J. T., Grant, S. C., Fincham, F. D., Pinto, J. R. Kabbaj, M. Pathogenesis of depression- and anxiety-like behavior in an animal model of hypertrophic cardiomyopathy.

Bacopa monniera (CDRI-08) Upregulates the Expression of Neuronal and Glial Plasticity Markers in the Brain of Scopolamine Induced Amnesic Mice

Preclinical studies on animal models have discerned the antiamnesic and memory-enhancing potential of Bacopa monniera (Brahmi) crude extract and standardized extracts. These studies primarily focus on behavioral consequences. However, lack of information on molecular underpinnings has limited the clinical trials of the potent herb in human subjects. In recent years, researchers highlight plasticity markers as molecular correlates of amnesia and being crucial to design therapeutic targets. In the present report, we have investigated the effect of a special extract of B. monniera (CDRI-08) on the expression of key neuronal (BDNF and Arc) and glial (GFAP) plasticity markers in the cerebrum of scopolamine induced amnesic mice. Pre- and postadministration of CDRI-08 ameliorated amnesic effect of scopolamine by decreasing acetyl cholinesterase activity and drastically upregulating the mRNA and protein expression of BDNF, Arc, and GFAP in mouse cerebrum. Interestingly, the plant extract per se elevated BDNF and Arc expression as compared to control but GFAP was unaltered. In conclusion, our findings provide the first molecular evidence for antiamnesic potential of CDRI-08 via enhancement of both neuronal and glial plasticity markers. Further investigations on detailed molecular pathways would encourage therapeutic application of the extract in memory disorders.

Allostasis as a conceptual framework linking bipolar disorder and addiction

Bipolar disorders (BDs) and addictions constitute reciprocal risk factors and are best considered under a unitary perspective. The concepts of allostasis and allostatic load (AL) may contribute to the understanding of the complex relationships between BD and addictive behaviors. Allostasis entails the safeguarding of reward function stability by recruitment of changes in the reward and stress system neurocircuitry and it may help to elucidate neurobiological underpinnings of vulnerability to addiction in BD patients. Conceptualizing BD as an illness involving the cumulative build-up of allostatic states, we hypothesize a progressive dysregulation of reward circuits clinically expressed as negative affective states (i.e., anhedonia). Such negative affective states may render BD patients more vulnerable to drug addiction, fostering a very rapid transition from occasional drug use to addiction, through mechanisms of negative reinforcement. The resulting addictive behavior-related ALs, in turn, may contribute to illness progression. This framework could have a heuristic value to enhance research on pathophysiology and treatment of BD and addiction comorbidity.

Effect of selective serotonin reuptake inhibitors and immunomodulator on cytokines levels: an alternative therapy for patients with major depressive disorder

Major depressive disorder (MDD) is a psychiatric illness that presents as a deficit of serotonergic neurotransmission in the central nervous system. MDD patients also experience alterations in cortisol and cytokines levels. Treatment with selective serotonin reuptake inhibitors (SSRIs) is the first-line antidepressant regimen for MDD. The aim of this study was to determine the effect of a combination of SSRIs and an immunomodulator-human dialyzable leukocyte extract (hDLE)-on cortisol and cytokines levels. Patients received SSRIs or SSRIs plus hDLE. The proinflammatory cytokines IL-1 β , IL-2, and IFN- γ ; anti-inflammatory cytokines IL-13 and IL-10; and 24-h urine cortisol were measured at weeks (W) 0, 5, 20, 36, and 52 of treatment. The reduction in cortisol levels in the SSRI-treated group was 30% until W52, in contrast, the combined treatment induced a 54% decrease at W36. The decline in cortisol in patients who were treated with SSRI plus hDLE correlated with reduction of anti-inflammatory cytokines and increases levels of proinflammatory cytokines at the study conclusion. These results suggest that the immune-stimulating activity of hDLE, in combination with SSRIs, restored the pro- and anti-inflammatory cytokine balance and cortisol levels in depressed patients versus those who were given SSRIs alone.

Neuroplasticity in mood disorders

Neuroimaging and neuropathological studies of major depressive disorder (MDD) and bipolar disorder (BD) have identified abnormalities of brain structure in areas of the prefrontal cortex, amygdala, striatum, hippocampus, parahippocampal gyrus, and raphe nucleus. These structural imaging abnormalities persist across illness episodes, and preliminary evidence suggests they may in some cases arise prior to the onset of depressive episodes in subjects at high familial risk for MDD. In other cases, the magnitude of abnormality is reportedly correlated with time spent depressed. Postmortem histopathological studies of these regions have shown abnormal reductions of synaptic markers and glial cells, and, in rare cases, reductions in neurons in MDD and BD. Many of the regions affected by these structural abnormalities show increased glucose metabolism during depressive episodes. Because the glucose metabolic signal is dominated by glutamatergic transmission, these data support other evidence that excitatory amino acid transmission is elevated in limbic-cortical-striatal-pallidal-thalamic circuits during depression. Some of the subject samples in which these metabolic abnormalities have been demonstrated were also shown to manifest abnormally elevated stressed plasma cortisol levels. The co-occurrence of increased glutamatergic transmission and Cortisol hypersecretion raises the possibility that the gray matter volumetric reductions in these depressed subjects are partly accounted for by processes homologous to the dendritic atrophy induced by chronic stress in adult rodents, which depends upon interactions between elevated glucocorticoid secretion and N-meihyl-D-aspartate (NMDA)-glutamate receptor stimulation. Some mood-stabilizing and antidepressant drugs that exert neurotrophic effects in rodents appear to reverse or attenuate the gray matter volume abnormalities in humans with mood disorders. These neurotrophic effects may be integrally related to the therapeutic effects of such agents, because the regions affected by structural abnormalities in mood disorders are known to play major roles in modulating the endocrine, autonomic, behavioral, and emotional experiential responses to stressors.

Sleep deprivation as a neurobiologic and physiologic stressor: Allostasis and allostatic load

Sleep has important homeostatic functions, and sleep deprivation is a stressor that has consequences for the brain, as well as many body systems. Whether sleep deprivation is due to anxiety, depression, or a hectic lifestyle, there are consequences of chronic sleep deprivation that impair brain functions and contribute to allostatic load throughout the body. Allostatic load refers to the cumulative wear and tear on body systems caused by too much stress and/or inefficient management of the systems that promote adaptation through allostasis. Chronic sleep deprivation in young healthy volunteers has been reported to increase appetite and energy expenditure, increase levels of proinflammatory cytokines, decrease parasympathetic and increase sympathetic tone, increase blood pressure, increase evening cortisol levels, as well as elevate insulin and blood glucose. Repeated stress in animal models causes brain regions involved in memory and emotions, such as hippocampus, amygdala, and prefrontal cortex, to undergo structural remodeling with the result that memory is impaired and anxiety and aggression are increased. Structural and functional magnetic resonance imaging studies in depression and Cushing's disease, as well as anxiety disorders, provide evidence that the human brain may be similarly affected. Moreover, brain regions such as the hippocampus are sensitive to glucose and insulin, and both type 1 and type 2 diabetes mellitus are associated with cognitive impairment and (for type 2 diabetes mellitus) increased risk for Alzheimer's disease. Animal models of chronic sleep deprivation indicate that memory is impaired along with depletion of glycogen stores and increases in oxidative stress and free radical production. Taken together, these changes in brain and body are further evidence that sleep deprivation is a chronic stressor and that the resulting allostatic load can contribute to cognitive problems, which can, in turn, further exacerbate pathways that lead to disease.

Stress and depression-induced immune dysfunction: implications for the development and progression of cancer

The persistent activation of the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenal-medullary axes in chronic stress response and in depression impairs the immune response and contributes to the development and progression of some types of cancer. This overview presents results from experimental animal models, human studies, and clinical evidence that various cellular and molecular immunological parameters are compromised in chronic stress and depression. At the cellular level, stressed and depressed patients had overall leukocytosis, high concentrations of circulating neutrophils, reduced mitogen-stimulated lymphocyte proliferation and neutrophil phagocytosis. At the molecular level, high levels of serum basal cortisol, acute phase proteins, specific antibodies against herpes simplex virus type 1 and Epstein Barr virus, plasma concentration of interleukins IL-1, IL-6, and TNF-alpha, and a shift in the balance of Th1 and Th2 immune response were observed. Both stress and depression were associated with the decreased cytotoxic T-cell and natural killer cell activities affecting the processes of the immune surveillance of tumours, and the events that modulate the development and the accumulation of somatic mutations and genomic instability. DNA damage, growth and angiogenic factors, proteases, matrix metalloproteinases, and reactive oxygen species were also related to the chronic stress response and depression. Behavioural strategies, psychological, and psychopharmacotherapeutic interventions that enhance effective coping and reduce affective distress showed beneficial effects in cancer patients. A better understanding of the bidirectional communication between the neuroendocrine and immune systems could contribute to novel clinical and treatment strategies in oncology.

Stressed or stressed out: what is the difference?

The term "allostasis" has been coined to clarify ambiguities associated with the word "stress". Allostasis refers to the adaptive processes that maintain homeostasis through the production of mediators such as adrenalin, cortisol and other chemical messengers. These mediators of the stress response promote adaptation in the aftermath of acute stress, but they also contribute to allostatic overload, the wear and tear on the body and brain that result from being "stressed out". This conceptual framework has created a need to know how to improve the efficiency of the adaptive response to stressors while minimizing overactivity of the same systems, since such overactivity results in many of the common diseases of modern life. This framework has also helped to demystify the biology of stress by emphasizing the protective as well as the damaging effects of the body's attempts to cope with the challenges known as stressors.

Glucocorticoids, depression, and mood disorders: structural remodeling in the brain

The hippocampal formation expresses high levels of adrenal steroid receptors and is a malleable brain structure that is important for certain types of learning and memory. It is also vulnerable to the effects of stress and trauma. The amygdala is an important target of stress and mediates physiological and behavioral responses associated with fear and strong emotions. The prefrontal cortex plays an important role in working memory and executive function and is also involved in extinction of learning. All 3 regions are targets of stress hormones, and stress is known to precipitate and exacerbate mood disorders. In long-term depressive illness, the hippocampus and prefrontal cortex undergo atrophy, whereas the amygdala is hyperactive in anxiety and mood disorders and may undergo a biphasic change in structure--increasing in size in acute depression and shrinking on long-term depression. In animal models of acute and chronic stress, neurons in the hippocampus and prefrontal cortex respond to repeated stress by showing atrophy that leads to memory impairment, whereas neurons in amygdala show a growth response that leads to increased anxiety and aggression. Yet, these are not necessarily "damaged" and may be treatable with the right medications. The mechanisms that distinguish between protection and damage of brain cells from stress are discussed in this context.

Neuroplasticity in mood disorders

Neuroimaging and neuropathological studies of major depressive disorder (MDD) and bipolar disorder (BD) have identified abnormalities of brain structure in areas of the prefrontal cortex, amygdala, striatum, hippocampus, parahippocampal gyrus, and raphe nucleus. These structural imaging abnormalities persist across illness episodes, and preliminary evidence suggests they may in some cases arise prior to the onset of depressive episodes in subjects at high familial risk for MDD. In other cases, the magnitude of abnormality is reportedly correlated with time spent depressed. Postmortem histopathological studies of these regions have shown abnormal reductions of synaptic markers and glial cells, and, in rare cases, reductions in neurons in MDD and BD. Many of the regions affected by these structural abnormalities show increased glucose metabolism during depressive episodes. Because the glucose metabolic signal is dominated by glutamatergic transmission, these data support other evidence that excitatory amino acid transmission is elevated in limbic-cortical-striatal-pallidal-thalamic circuits during depression. Some of the subject samples in which these metabolic abnormalities have been demonstrated were also shown to manifest abnormally elevated stressed plasma cortisol levels. The co-occurrence of increased glutamatergic transmission and Cortisol hypersecretion raises the possibility that the gray matter volumetric reductions in these depressed subjects are partly accounted for by processes homologous to the dendritic atrophy induced by chronic stress in adult rodents, which depends upon interactions between elevated glucocorticoid secretion and N-meihyl-D-aspartate (NMDA)-glutamate receptor stimulation. Some mood-stabilizing and antidepressant drugs that exert neurotrophic effects in rodents appear to reverse or attenuate the gray matter volume abnormalities in humans with mood disorders. These neurotrophic effects may be integrally related to the therapeutic effects of such agents, because the regions affected by structural abnormalities in mood disorders are known to play major roles in modulating the endocrine, autonomic, behavioral, and emotional experiential responses to stressors.