Title: Chronic Stress and Depression Background. Chronic exposure to severe or persistent stress is a risk factor for the development of mood disorders including major depression. Major depression is a serious and debilitating disease that has a life time risk of 15-20% in the United States alone. According to the World Health Organization, by the year 2020 depression will become the 2nd leading cause of disability worldwide second only to heart disease. It is estimated that the total cost of mental illness in the US averaged over $156 billion in 1996 alone. Serotonin is a brain chemical that controls many brain functions and behavior including mood control, sleep, anxiety, satiety etc. Any disruption in the synthesis, metabolism or uptake of this chemical is known to lead to lead to mood lowering effects and may lead to depression. There appears to be a complex relationship between stress, our mind and how we individually respond to stress and the onset of depression. It is now clear that some individuals develop depression after chronic or persistent stress in their lives. Events such as death of a loved one, loss of a job can cause great stress for some people and make them susceptible to depression. One way to study stress and stress related disorder will be to use animal stress models; these models not only tell us how the human brain may change during stress but also provide clues about stress induced disorders like depression. Because of this, it is important that we develop animal models that have the greatest validity in studying depression. Many patients with major depressive disorder (MDD) have elevated stress hormone (cortisol) levels. Interestingly, patients with Cushing’s disease characterized by elevated cortisol levels exhibit a high rate of MDD and depressive symptoms are a frequent side effect of corticosteroid treatment, indicating that endogenous production of cortisol may be one mechanism by which stressful life events precipitate depression. Thus a repeated corticosterone (CORT) injection paradigm in rodents may provide a useful way to study the effect of prolonged exposure to stress. Advance. At the University of Mississippi Medical Center, we are working on projects using various animal models of stress to study the relationship between stress, the serotonin system and depression. One of the biggest problems with experimenter-applied stress models is the lack of uniformity and control over individual differences in responsivity to physical and psychological stressors. We have successfully shown that in a modified repeated CORT injection paradigm in rodents, which includes a wash-out period of 14 days during which no CORT is injected, CORT injected rats exhibit significantly less preference for sucrose demonstrating anhedonia - a core symptom of human depression. An advantage of this model is that we can now begin to study the mechanisms involved in the dysregulation of the serotonin system especially under the direct influence of glucocorticoids and how this may lead to the development of depressive symptomatology. Public impact statement/significance. This model represents an advance that is capable of providing answers to the basic mechanisms responsible for serotonin dysfunction in humans especially where elevated glucocorticoids are involved. It opens up a new vista in the study of depression and could lead to the development new antidepressants especially where elevated glucocorticoids are involved. Grant support. P20 RR017701-08 (COBRE: Center for Psychiatric Neuroscience)
Title: Measuring Newborn Neurons with Flow Cytometry: Implications for Speeding up Neurogenic Drug Development Background. Research conducted over the last twenty years has shattered the belief that the human brain gets its quota of nerve cells shortly after birth and stands by helplessly as our brain cells die one by one. On the contrary, neurogenesis, or the birth of new nerve cells, occurs throughout the life span of mammals, including humans. Debilitating diseases such as Alzheimer’s disease, Parkinson’s disease and depression are caused, at least in part, because something went awry in the generation of new nerve cells in the brain. As a matter of fact, reduced neurogenesis (resulting in fewer functioning brain cells) occurs in the hippocampus of patients diagnosed with these devastating disorders. Drug development to reverse the neurogenic deficits observed in patients with these diseases holds the promise of more effective treatments or possibly even cures. Unfortunately, measuring newly born nerve cells requires a large number of samples and the methods are currently both time- and labor-intensive. This has created a bottleneck in developing new drugs to treat neurodegenerative diseases and in evaluating their therapeutic effectiveness. Until recently, measuring brain neurogenesis was a monumental task involving labeling newborn cells with 5-bromo-2-deoxyuridine (BrdU), cutting brain sections, performing antibody reaction, mounting these sections on microscope slides and finally counting the BrdU positive cells under the microscope. In 2009, a group of researchers at the University of Pennsylvania developed a fast and effective method to evaluate neurogenesis in the mouse brain by incorporating BrdU in vivo (requiring animal injections) and using flow cytometry to measure neurogenesis, allowing analysis of data in a single day as opposed to the several weeks using the old method. Although the flow cytometric method has considerably speeded up analyses, there are a couple of disadvantages. Namely, BrdU is toxic to new born neurons and nonspecifically labels DNA damage in older neurons. Advance. Investigators at the University Mississippi Medical Center, supported by NCRR’s Institutional Development Award Program, have developed an approach of counting the cells which contain Ki-67 in the mouse hippocampus by flow cytometry. Ki-67 is a naturally occurring protein in the dividing cell that is strictly associated with cell division. Since it is naturally-occurring, it doesn’t have to be injected and it is not toxic to new born neurons; since it specifically labels dividing cells, measurement of new born cells is more accurate. This modified method represents an incremental advance in analyzing hippocampal cell proliferation and can be applied to postmortem human tissue, allowing the flow of scientific advances to clear the bottleneck between laboratory discoveries and patient health. Public impact statement/significance. This method will enhance the development of antidepressants and other anti-neurodegenerative disease drugs. Grant support. P20 RR017701-08 (COBRE: Center for Psychiatric Neuroscience) IIRG - Alzheimer’s Association Publication. Henry S, Bigler S, Wang JM. High throughput analysis of neural progenitor cell proliferation in adult rodent hippocampus. Biosci Trends. 2009 Dec;3(6):233-8. PMCID: PMC2830061.
Title: Glutamate Receptors: Potential Biomarkers for Depression? Background. Researchers studying clinical depression tend to look at several aspects of brain function including specific brain regions implicated in the pathophysiology of depression (such as the amygdala, the locus coeruleus, and the prefrontal cortex), along with the function of neurotransmitters within neurons. The past decade has seen a steady accumulation of compelling evidence implicating the neurotransmitter glutamate and its receptors in the pathophysiology of depression and antidepressant activity. Glutamate is the major excitatory neurotransmitter in the brain, with receptors on both presynaptic and postsynaptic neurons. Any dysfunction in glutamate neurotransmission might potentially disrupt information processing in the brain and ultimately lead to cognitive decline and possibly depression. University of Mississippi COBRE investigator, Dr. Beata Karolewicz, and her research team study glutamatergic neurotransmission in postmortem human brain tissue from both depressed and healthy control subjects. They are particularly interested in the ionotropic glutamate N-methyl-D-aspartate (NMDA) receptor, which is made up of several different subunits (NR1, NR2A, NR2B, NR2C). In brain regions implicated in the pathophysiology of depression, she observed significant increases in the NMDA receptor subunit NR2A in the lateral amygdala and in the NR2C subunit in the locus coeruleus of depressed subjects when compared to healthy control subjects. Consistent with Dr. Karolewicz’s findings, brain imaging studies reveal altered glutamate levels (reduced or increased - depending on the brain region) in living depressed patients. Recent clinical studies show that a single dose of ketamine, an antagonist of the NMDA receptor, produced rapid and substantial antidepressive effects in patients with treatment-resistant depression. There is no evidence to date of any other pharmacological intervention that consistently reproduces results in such a rapid manner. Moreover, antagonists of the other type of glutamate receptors - metabotropic glutamate receptors (mGlu1 or mGlu5) - exhibit antidepressant-like properties in animal screenings. Together, these findings suggest disruption of glutamate signaling in depression, and its regulation in critical brain circuits may offer a strategy for the development of effective and rapidly acting antidepressants. Advance. Dr. Karolewicz’s more recent focus on glutamatergic neurotransmission in the prefrontal cortex provides first evidence of reduced levels of the NMDA receptor subunits NR2A and NR2B in this brain region in depressed subjects as compared to healthy controls. She has further observed significantly reduced levels of the mGlu5 receptor in this same brain region in depressed subjects as compared to controls that is consistent with neuroimaging findings showing reduced binding to the mGlu5 receptor in the prefrontal cortex of living depressed patients. These findings strongly implicate glutamate receptors as uniquely suited targets for the discovery of novel antidepressant medications. Public impact statement / significance. Recent studies identify the glutamate system as uniquely ranked among other neurotransmitters as a candidate system for the development of clinically and biologically plausible endophenotypes or biomarkers for depression. Publications:
Title: The Novel Role of GAPDH in Alcohol-Induced Cellular Damage Background: Alcoholism is a major psychiatric condition elicited, at least in part, by ethanol-induced cell damage. Although brain cell loss has been reported in subjects with alcoholism, the molecular mechanism is unclear. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and monoamine oxidase B (MAO B) reportedly play a role in cellular dysfunction under stress conditions and therefore may contribute to ethanol-induced cell damage. GAPDH is a multifunctional protein. Studies from our group and others indicate that GAPDH translocates to the nucleus and mediates stress signaling, resulting in cellular dysfunction and death. Although GAPDH protein levels were reportedly increased in brains from subjects with alcoholism, its significance in alcoholism remains elusive. MAO B degrades neurotransmitters, phenylethylamine and dopamine, and generates toxic hydrogen peroxide (H2O2), which causes cellular dysfunction and death. An MAO B transcriptional activator, transforming growth factor-beta-inducible early gene 2 (TIEG2), induces MAO B expression. TIEG2 reportedly inhibits cell growth. Thus, the TIEG2-MAO B cascade has a role in cell dysfunction and damage. Selegiline (deprenyl) has been used mainly for treatment of Parkinson’s disease, because this compound inhibits MAO B and prevents degradation of dopamine. In addition to MAO B inhibition, selegiline binds to GAPDH and blocks its nuclear translocation. Advance: Recently we found that both protein levels of GAPDH and MAO B are significantly increased in human brains from subjects with alcoholism. We also discovered that GAPDH interacts with MAO B-activator TIEG2, and augments TIEG2-mediated MAO B induction, which results in cell damage in neuronal cells exposed to ethanol. Treatment with selegiline (an MAO B inhibitor) can block this cascade. Public impact statement/significance: Ethanol-elicited GAPDH augments TIEG2-mediated MAO B and may play a role in brain damage in subjects with alcoholism. Compounds that block GAPDH-TIEG2-MAO B cascade are potential candidates for therapeutic strategies to fight against alcohol-induced brain damage. Grant support: P20 RR017701, MH67996, an NARSAD Young Investigator Award and an Intramural Research Support grant from The University of Mississippi Medical Center. Publications:
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