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Duman RS, Aghajanian GK, Sanacora G, Krystal JH. Synaptic plasticity and depression: new insights from stress and rapid-acting antidepressants. Nat Med 2016; 22:238-49. [PMID: 26937618 PMCID: PMC5405628 DOI: 10.1038/nm.4050] [Citation(s) in RCA: 1020] [Impact Index Per Article: 127.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Accepted: 01/21/2016] [Indexed: 02/06/2023]
Abstract
Depression is a common, devastating illness. Current pharmacotherapies help many patients, but high rates of a partial response or no response, and the delayed onset of the effects of antidepressant therapies, leave many patients inadequately treated. However, new insights into the neurobiology of stress and human mood disorders have shed light on mechanisms underlying the vulnerability of individuals to depression and have pointed to novel antidepressants. Environmental events and other risk factors contribute to depression through converging molecular and cellular mechanisms that disrupt neuronal function and morphology, resulting in dysfunction of the circuitry that is essential for mood regulation and cognitive function. Although current antidepressants, such as serotonin-reuptake inhibitors, produce subtle changes that take effect in weeks or months, it has recently been shown that treatment with new agents results in an improvement in mood ratings within hours of dosing patients who are resistant to typical antidepressants. Within a similar time scale, these new agents have also been shown to reverse the synaptic deficits caused by stress.
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Affiliation(s)
- Ronald S Duman
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - George K Aghajanian
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Gerard Sanacora
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - John H Krystal
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, USA
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102
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Abnormality in glutamine-glutamate cycle in the cerebrospinal fluid of cognitively intact elderly individuals with major depressive disorder: a 3-year follow-up study. Transl Psychiatry 2016; 6:e744. [PMID: 26926880 PMCID: PMC4872461 DOI: 10.1038/tp.2016.8] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 01/07/2016] [Accepted: 01/14/2016] [Indexed: 12/17/2022] Open
Abstract
Major depressive disorder (MDD), common in the elderly, is a risk factor for dementia. Abnormalities in glutamatergic neurotransmission via the N-methyl-D-aspartate receptor (NMDA-R) have a key role in the pathophysiology of depression. This study examined whether depression was associated with cerebrospinal fluid (CSF) levels of NMDA-R neurotransmission-associated amino acids in cognitively intact elderly individuals with MDD and age- and gender-matched healthy controls. CSF was obtained from 47 volunteers (MDD group, N=28; age- and gender-matched comparison group, N=19) at baseline and 3-year follow-up (MDD group, N=19; comparison group, N=17). CSF levels of glutamine, glutamate, glycine, L-serine and D-serine were measured by high-performance liquid chromatography. CSF levels of amino acids did not differ across MDD and comparison groups. However, the ratio of glutamine to glutamate was significantly higher at baseline in subjects with MDD than in controls. The ratio decreased in individuals with MDD over the 3-year follow-up, and this decrease correlated with a decrease in the severity of depression. No correlations between absolute amino-acid levels and clinical variables were observed, nor were correlations between amino acids and other biomarkers (for example, amyloid-β42, amyloid-β40, and total and phosphorylated tau protein) detected. These results suggest that abnormalities in the glutamine-glutamate cycle in the communication between glia and neurons may have a role in the pathophysiology of depression in the elderly. Furthermore, the glutamine/glutamate ratio in CSF may be a state biomarker for depression.
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103
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Anterior cingulate Glutamate-Glutamine cycle metabolites are altered in euthymic bipolar I disorder. Eur Neuropsychopharmacol 2015; 25:2221-9. [PMID: 26476706 DOI: 10.1016/j.euroneuro.2015.09.020] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Revised: 07/27/2015] [Accepted: 09/28/2015] [Indexed: 12/12/2022]
Abstract
Bipolar disorder (BD) has been consistently associated with abnormalities in the Glutamate/GABA-Glutamine cycle. Magnetic resonance spectroscopy (MRS) studies have reported increased brain Glutamate (Glu) and Glx (Glu+Glutamine) in subjects with BD. However, data on separate measures of GABA and Glutamine (Gln) in BD are sparse due to overlapping resonant signals. The development of new sequence methods in the quantification of these metabolites has allowed a better understanding of the Glu/GABA-Gln cycle but data on this field of research remains sparse in BD. Eighty-eight subjects (50 euthymic BD and 38 HC) underwent 3T proton magnetic resonance spectroscopy (1H MRS) in the anterior cingulate cortex (ACC; 2×2×4.5cm(3)) using a two-dimensional JPRESS sequence. GABA, Glutamine (Gln) and Glutamate (Glu) were quantified with the ProFit program. Using image segmentation and known creatine (Cre) concentrations for white and grey matter, metabolite concentrations were calculated for the excited MRS voxel. GABA levels did not differ between groups. Gln level was higher in euthymic BD patients than in healthy controls. The Glu level and Glu/Gln ratio were lower in BD patients than in controls. The use of anticonvulsants was associated with Gln increase but did not affect Glu or Glu/Gln. Neither lithium nor antipsychotic use influenced metabolite levels. The ACC MRS findings indicate that the glutamatergic function in euthymic medicated BD patients is altered relative to controls. Whether this feature is a metabolic signature of euthymic BD subjects should be the focus of future studies.
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104
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Iorio R. Treatment-Resistant Depression and Aquaporin-4 Autoantibodies: Is There a Link? Biol Psychiatry 2015; 78:e1-e2. [PMID: 25442791 DOI: 10.1016/j.biopsych.2014.09.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 09/18/2014] [Indexed: 12/22/2022]
Affiliation(s)
- Raffaele Iorio
- Institute of Neurology, Department of Geriatrics, Neuroscience and Orthopedics, Catholic University, Rome, Italy.
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105
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Janke C, Bumb JM, Aksay SS, Thiel M, Kranaster L, Sartorius A. [Ketamine as anesthetic agent in electroconvulsion therapy]. Anaesthesist 2015; 64:357-64. [PMID: 25943498 DOI: 10.1007/s00101-015-0027-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Revised: 03/20/2015] [Accepted: 03/21/2015] [Indexed: 11/30/2022]
Abstract
BACKGROUND Electroconvulsive therapy (ECT) is a well-established, safe and effective treatment for severe psychiatric disorders. Ketamine is known as a core medication in anesthesiology and has recently gained interest in ECT practice as there are three potential advantages: (1) ketamine has no anticonvulsive actions, (2) according to recent studies ketamine could possess a unique intrinsic antidepressive potential and (3) ketamine may exhibit neuroprotective properties, which again might reduce the risk of cognitive side effects associated with ECT. OBJECTIVES The use of ketamine in psychiatric patients has been controversially discussed due to its dose-dependent psychotropic and psychotomimetic effects. This study was carried out to test if the occurrence of side effects is comparable and if seizure quality is better with ketamine when compared to thiopental. MATERIAL AND METHODS This retrospective study analyzed a total of 199 patients who received ketamine anesthesia for a total of 2178 ECT sessions. This cohort was compared to patients who were treated with thiopental for 1004 ECT sessions. RESULTS AND DISCUSSION A repeated measurement multiple logistic regression analysis revealed significant advantages in the ketamine group for seizure concordance and postictal suppression (both are surrogates for central inhibition). S-ketamin also necessitated the use of a higher dose of urapidil and a higher maximum postictal heart frequency. Clinically relevant psychiatric side effects were rare in both groups. No psychiatric side effects occurred in the subgroup of patients with schizophrenia (ketamine: n = 30). The mean dose of S-ketamine used increased in the first years but stabilized at 63 mg per patient in 2014. From these experiences it can be concluded that S-ketamine can be recommended at least as a safe alternative to barbiturates.
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Affiliation(s)
- C Janke
- Klinik für Anästhesiologie und Intensivmedizin, Universitätsklinikum Heidelberg, Heidelberg, Deutschland
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106
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Wiebking C, de Greck M, Duncan NW, Tempelmann C, Bajbouj M, Northoff G. Interoception in insula subregions as a possible state marker for depression-an exploratory fMRI study investigating healthy, depressed and remitted participants. Front Behav Neurosci 2015; 9:82. [PMID: 25914633 PMCID: PMC4392695 DOI: 10.3389/fnbeh.2015.00082] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Accepted: 03/17/2015] [Indexed: 12/16/2022] Open
Abstract
Background: Interoceptive awareness (iA), the awareness of stimuli originating inside the body, plays an important role in human emotions and psychopathology. The insula is particularly involved in neural processes underlying iA. However, iA-related neural activity in the insula during the acute state of major depressive disorder (MDD) and in remission from depression has not been explored. Methods: A well-established fMRI paradigm for studying (iA; heartbeat counting) and exteroceptive awareness (eA; tone counting) was used. Study participants formed three independent groups: patients suffering from MDD, patients in remission from MDD or healthy controls. Task-induced neural activity in three functional subdivisions of the insula was compared between these groups. Results: Depressed participants showed neural hypo-responses during iA in anterior insula regions, as compared to both healthy and remitted participants. The right dorsal anterior insula showed the strongest response to iA across all participant groups. In depressed participants there was no differentiation between different stimuli types in this region (i.e., between iA, eA and noTask). Healthy and remitted participants in contrast showed clear activity differences. Conclusions: This is the first study comparing iA and eA-related activity in the insula in depressed participants to that in healthy and remitted individuals. The preliminary results suggest that these groups differ in there being hypo-responses across insula regions in the depressed participants, whilst non-psychiatric participants and patients in remission from MDD show the same neural activity during iA in insula subregions implying a possible state marker for MDD. The lack of activity differences between different stimulus types in the depressed group may account for their symptoms of altered external and internal focus.
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Affiliation(s)
- Christine Wiebking
- Cluster of Excellence in Cognitive Sciences, Department of Sociology of Physical Activity and Health, University of Potsdam Potsdam, Germany ; Mind, Brain Imaging and Neuroethics, Institute of Mental Health Research, University of Ottawa Ottawa, ON, Canada
| | - Moritz de Greck
- Department of Psychosomatic Medicine and Psychotherapy, University Medicine Mainz Mainz, Germany
| | - Niall W Duncan
- Mind, Brain Imaging and Neuroethics, Institute of Mental Health Research, University of Ottawa Ottawa, ON, Canada ; Centre for Cognition and Brain Disorders, Hangzhou Normal University Hangzhou, China ; Graduate Institute of Humanities in Medicine, Taipei Medical University Taipei, Taiwan ; Brain and Consciousness Research Center, Taipei Medical University-Shuang Ho Hospital New Taipei City, Taiwan
| | - Claus Tempelmann
- Department of Neurology, Otto-von-Guericke University Magdeburg Magdeburg, Germany
| | - Malek Bajbouj
- Cluster of Excellence "Languages of Emotion" and Dahlem Institute for Neuroimaging of Emotion, Freie Universität Berlin Berlin, Germany ; Department of Psychiatry, Charité-Universitätsmedizin, Campus Benjamin Franklin Berlin, Germany
| | - Georg Northoff
- Mind, Brain Imaging and Neuroethics, Institute of Mental Health Research, University of Ottawa Ottawa, ON, Canada ; Centre for Cognition and Brain Disorders, Hangzhou Normal University Hangzhou, China ; Graduate Institute of Humanities in Medicine, Taipei Medical University Taipei, Taiwan ; Brain and Consciousness Research Center, Taipei Medical University-Shuang Ho Hospital New Taipei City, Taiwan ; Department of Psychology, National Chengchi University Taipei, Taiwan
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107
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Antidepressant-like effects of rosmarinic acid through mitogen-activated protein kinase phosphatase-1 and brain-derived neurotrophic factor modulation. J Funct Foods 2015. [DOI: 10.1016/j.jff.2015.03.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
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108
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Barth C, Villringer A, Sacher J. Sex hormones affect neurotransmitters and shape the adult female brain during hormonal transition periods. Front Neurosci 2015; 9:37. [PMID: 25750611 PMCID: PMC4335177 DOI: 10.3389/fnins.2015.00037] [Citation(s) in RCA: 379] [Impact Index Per Article: 42.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Accepted: 01/26/2015] [Indexed: 12/21/2022] Open
Abstract
Sex hormones have been implicated in neurite outgrowth, synaptogenesis, dendritic branching, myelination and other important mechanisms of neural plasticity. Here we review the evidence from animal experiments and human studies reporting interactions between sex hormones and the dominant neurotransmitters, such as serotonin, dopamine, GABA and glutamate. We provide an overview of accumulating data during physiological and pathological conditions and discuss currently conceptualized theories on how sex hormones potentially trigger neuroplasticity changes through these four neurochemical systems. Many brain regions have been demonstrated to express high densities for estrogen- and progesterone receptors, such as the amygdala, the hypothalamus, and the hippocampus. As the hippocampus is of particular relevance in the context of mediating structural plasticity in the adult brain, we put particular emphasis on what evidence could be gathered thus far that links differences in behavior, neurochemical patterns and hippocampal structure to a changing hormonal environment. Finally, we discuss how physiologically occurring hormonal transition periods in humans can be used to model how changes in sex hormones influence functional connectivity, neurotransmission and brain structure in vivo.
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Affiliation(s)
- Claudia Barth
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences Leipzig, Germany
| | - Arno Villringer
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences Leipzig, Germany ; Clinic of Cognitive Neurology, University of Leipzig Leipzig, Germany ; Leipzig Research Center for Civilization Diseases, University of Leipzig Leipzig, Germany ; Integrated Research and Treatment Center Adiposity Diseases, University of Leipzig Leipzig, Germany ; Berlin School of Mind and Brain, Mind and Brain Institute Berlin, Germany
| | - Julia Sacher
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences Leipzig, Germany ; Clinic of Cognitive Neurology, University of Leipzig Leipzig, Germany
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109
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Hertz L, Rothman DL, Li B, Peng L. Chronic SSRI stimulation of astrocytic 5-HT2B receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift. Front Behav Neurosci 2015; 9:25. [PMID: 25750618 PMCID: PMC4335176 DOI: 10.3389/fnbeh.2015.00025] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 01/23/2015] [Indexed: 11/13/2022] Open
Abstract
It is firmly believed that the mechanism of action of SSRIs in major depression is to inhibit the serotonin transporter, SERT, and increase extracellular concentration of serotonin. However, this undisputed observation does not prove that SERT inhibition is the mechanism, let alone the only mechanism, by which SSRI's exert their therapeutic effects. It has recently been demonstrated that 5-HT2B receptor stimulation is needed for the antidepressant effect of fluoxetine in vivo. The ability of all five currently used SSRIs to stimulate the 5-HT2B receptor equipotentially in cultured astrocytes has been known for several years, and increasing evidence has shown the importance of astrocytes and astrocyte-neuronal interactions for neuroplasticity and complex brain activity. This paper reviews acute and chronic effects of 5-HT2B receptor stimulation in cultured astrocytes and in astrocytes freshly isolated from brains of mice treated with fluoxetine for 14 days together with effects of anti-depressant therapy on turnover of glutamate and GABA and metabolism of glucose and glycogen. It is suggested that these events are causally related to the mechanism of action of SSRIs and of interest for development of newer antidepressant drugs.
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Affiliation(s)
- Leif Hertz
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University Shenyang, China
| | - Douglas L Rothman
- Magnetic Resonance Research Center, Diagnostic Radiology and Biomedical Engineering, Yale University New Haven, CT, USA
| | - Baoman Li
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University Shenyang, China
| | - Liang Peng
- Laboratory of Brain Metabolic Diseases, Institute of Metabolic Disease Research and Drug Development, China Medical University Shenyang, China
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110
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Ketamine and other potential glutamate antidepressants. Psychiatry Res 2015; 225:1-13. [PMID: 25467702 DOI: 10.1016/j.psychres.2014.10.028] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2014] [Revised: 09/29/2014] [Accepted: 10/28/2014] [Indexed: 11/24/2022]
Abstract
The need for rapid acting antidepressants is widely recognised. There has been much interest in glutamate mechanisms in major depressive disorder (MDD) as a promising target for the development of new antidepressants. A single intravenous infusion of ketamine, a N-methyl-d-aspartate (NMDA) receptor antagonist anaesthetic agent, can alleviate depressive symptoms in patients within hours of administration. The mechanism of action appears to be in part through glutamate release onto non-NMDA receptors including α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and metabotropic receptors. However these are also reported effects on 5-HT, dopamine and intracellular effects on the mammalian target of rapamycin (mTOR) pathway. The effects of SSRI (Selective Serotonin Reuptake Inhibitor) antidepressants may also involve alterations in NMDA function. The article reviews the effect of current antidepressants on NMDA and examines the efficacy and mechanism of ketamine. Response to ketamine is also discussed and comparison with other glutamate drugs including lamotrigine, amantadine, riluzole, memantine, traxoprodil, GLYX-13, MK-0657, RO4917523, AZD2066 and Coluracetam. Future studies need to link the rapid antidepressant effects seen with ketamine to inflammatory theories in MDD.
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111
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Potential involvement of the mitochondrial unfolded protein response in depressive-like symptoms in mice. Neurosci Lett 2015; 588:166-71. [PMID: 25576703 DOI: 10.1016/j.neulet.2015.01.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Revised: 12/16/2014] [Accepted: 01/05/2015] [Indexed: 01/22/2023]
Abstract
Many evidences strongly suggest that a mitochondrial deficit is implicated in major depression. A mitochondrial deficit leads to mitochondrial stress responses, including the mitochondrial unfolded protein response (UPRmt), which is associated with certain brain disorders such as spastic paraplegia and Parkinson's disease. However, there is no evidence regarding the relationship between depressive disorder and UPRmt. Mice treated with chronic restraint stress showed significant depressive-like behaviors in the tail suspension and forced swim tests, decreased oxygen consumption rate, and increased levels of molecules associated with UPRmt such as Hspa9, Hspd1, Ubl5, Abcb10, and ClpP. All of the UPRmt-related molecules were significantly correlated with depressive-like behavior in the forced swim test. Thus, the present study is to reveal a relationship between the UPRmt and depressive disorder, suggesting that the UPRmt is a potential drug target for depressive disorders.
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112
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Du X, Pang TY. Is Dysregulation of the HPA-Axis a Core Pathophysiology Mediating Co-Morbid Depression in Neurodegenerative Diseases? Front Psychiatry 2015; 6:32. [PMID: 25806005 PMCID: PMC4353372 DOI: 10.3389/fpsyt.2015.00032] [Citation(s) in RCA: 112] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 02/16/2015] [Indexed: 01/19/2023] Open
Abstract
There is increasing evidence of prodromal manifestation of neuropsychiatric symptoms in a variety of neurodegenerative diseases such as Parkinson's disease (PD) and Huntington's disease (HD). These affective symptoms may be observed many years before the core diagnostic symptoms of the neurological condition. It is becoming more apparent that depression is a significant modifying factor of the trajectory of disease progression and even treatment outcomes. It is therefore crucial that we understand the potential pathophysiologies related to the primary condition, which could contribute to the development of depression. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signaling system involved in physiological homeostasis and stress response. Disturbances of this system lead to severe hormonal imbalances, and the majority of such patients also present with behavioral deficits and/or mood disorders. Dysregulation of the HPA-axis is also strongly implicated in the pathology of major depressive disorder. Consistent with this, antidepressant drugs, such as the selective serotonin reuptake inhibitors have been shown to alter HPA-axis activity. In this review, we will summarize the current state of knowledge regarding HPA-axis pathology in Alzheimer's, PD and HD, differentiating between prodromal and later stages of disease progression when evidence is available. Both clinical and preclinical evidence will be examined, but we highlight animal model studies as being particularly useful for uncovering novel mechanisms of pathology related to co-morbid mood disorders. Finally, we purpose utilizing the preclinical evidence to better inform prospective, intervention studies.
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Affiliation(s)
- Xin Du
- Mental Health Division, Florey Institute of Neuroscience and Mental Health, University of Melbourne , Melbourne, VIC , Australia
| | - Terence Y Pang
- Behavioural Neurosciences Division, Florey Institute of Neuroscience and Mental Health, University of Melbourne , Melbourne, VIC , Australia
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113
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Shulman RG, Hyder F, Rothman DL. Insights from neuroenergetics into the interpretation of functional neuroimaging: an alternative empirical model for studying the brain's support of behavior. J Cereb Blood Flow Metab 2014; 34:1721-35. [PMID: 25160670 PMCID: PMC4269754 DOI: 10.1038/jcbfm.2014.145] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Revised: 06/12/2014] [Accepted: 07/21/2014] [Indexed: 02/05/2023]
Abstract
Functional neuroimaging measures quantitative changes in neurophysiological parameters coupled to neuronal activity during observable behavior. These results have usually been interpreted by assuming that mental causation of behavior arises from the simultaneous actions of distinct psychological mechanisms or modules. However, reproducible localization of these modules in the brain using functional magnetic resonance imaging (MRI) and positron emission tomography (PET) imaging has been elusive other than for sensory systems. In this paper, we show that neuroenergetic studies using PET, calibrated functional magnetic resonance imaging (fMRI), (13)C magnetic resonance spectroscopy, and electrical recordings do not support the standard approach, which identifies the location of mental modules from changes in brain activity. Of importance in reaching this conclusion is that changes in neuronal activities underlying the fMRI signal are many times smaller than the high ubiquitous, baseline neuronal activity, or energy in resting, awake humans. Furthermore, the incremental signal depends on the baseline activity contradicting theoretical assumptions about linearity and insertion of mental modules. To avoid these problems, while making use of these valuable results, we propose that neuroimaging should be used to identify observable brain activities that are necessary for a person's observable behavior rather than being used to seek hypothesized mental processes.
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Affiliation(s)
- Robert G Shulman
- Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA
| | - Fahmeed Hyder
- Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA
- Departments of Diagnostic Radiology, Yale University, New Haven, Connecticut, USA
- Biomedical Engineering, Yale University, New Haven, Connecticut, USA
- Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut, USA
| | - Douglas L Rothman
- Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA
- Departments of Diagnostic Radiology, Yale University, New Haven, Connecticut, USA
- Biomedical Engineering, Yale University, New Haven, Connecticut, USA
- Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut, USA
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