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- Creators: Barrett, The Honors College
Description
Monoamine neurotransmitters (e.g., serotonin, norepinephrine, and dopamine) are powerful modulators of mood and cognitive function in health and disease. We have been investigating the modulation of monoamine clearance in select brain regions via organic cation transporters (OCTs), a family of nonselective monoamine transporters. OCTs are thought to complement the actions of selective monoamine transporters in the brain by helping to clear monoamines from the extracellular space; thus, assisting to terminate the monoamine signal. Of particular interest, stress hormones (corticosterone; CORT) inhibit OCT3-mediated transport of monoamine, to putatively lead to prolonged monoamine signaling. It has been demonstrated that stress levels of CORT block OCT3 transport in the rat hypothalamus, an effect that likely underlies the rapid, stress-induced increase in local monoamines. We examined the effect of chronic variable stress (CVS) on the development of mood disorders and OCT3 expression in limbic and hypothalamic regions of the rat brain. Animals subjected to CVS (14-days with random stressor exposure two times/day) showed reduced body weight gain, indicating that CVS was perceived as stressful. However, behavioral tests of anxiety and depressive-like behaviors in rats showed no group differences. Although there were no behavioral effects of stress, molecular analysis revealed that there were stress-related changes in OCT3 protein expression. In situ hybridization data confirmed that OCT3 mRNA is expressed in the hippocampus, amygdala, and hypothalamus. Analysis of Western blot data by two-way ANOVA revealed a significant treatment effect on OCT3 protein levels, with a significant decrease in OCT3 protein in the amygdala and hippocampus in CVS rats, compared to controls. These data suggest an important role for CORT sensitive OCT3 in the reduction of monoamine clearance during stress.
ContributorsBoyll, Piper Savannah (Author) / Orchinik, Miles (Thesis director) / Conrad, Cheryl (Committee member) / Talboom, Joshua (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
The stress response facilitates our ability to deal effectively with threatening situations, but exposure to severe or chronic stressors can lead to undesirable neural, physiological, and behavioral outcomes. Chronic stress is associated with structural changes in the rat hippocampus, with corresponding deficits in learning and memory. Recent studies have uncovered an inherent neuroplasticity that allows the hippocampus to recover from these stress-induced neural changes. Underlying mechanisms likely involve several different cellular and molecular pathways. In order to gain a more comprehensive understanding of these pathways, we investigated differences in protein expression throughout the timeline of chronic stress and recovery. Male Sprague-Dawley rats were randomly assigned to chronic restraint stress for 6hr/d/10d or 6hr/d/21d, stress for 6hr/d/21d followed by a recovery period of no stress for 10 or 21 days, or a control group. The proteome from the hippocampus of these rats was sequenced using liquid chromatography tandem mass spectrometry (LC-MS/MS) and analyzed. We hypothesized that chronic stress alters interneuronal signaling in the hippocampus by enhancing or attenuating the expression of proteins responsible for synaptic plasticity (functional) and neuronal structure (morphology). So far we have found that structural proteins, such as alpha-internexin, homer protein homolog 3, neurofilament light, and vimentin were significantly altered by chronic stress and recovery. In contrast, proteins necessary for or associated with myelination such as 2',3'-cyclic-nucleotide 3'-phosphodiesterase, myelin-associated glycoprotein, myelin basic protein S, and myelin proteolipid protein were significantly downregulated by chronic stress. Collectively, these results will provide a resource for further investigations into the mechanisms of the brain's recovery from chronic stress.
ContributorsKachemov, Marketta Marilyn (Author) / Orchinik, Miles (Thesis director) / Pirrotte, Patrick (Committee member) / Conrad, Cheryl (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Chronic stress often leads to cognitive deficits, especially within the spatial memory domain mediated by the hippocampus. When chronic stress ends and a no-stress period ensues (i.e., washout, WO), spatial ability improves, which can be better than non-stressed controls (CON). The WO period is often the same duration as the chronic stress paradigm. Given the potential benefit of a post-stress WO period on cognition, it is important to investigate whether this potential benefit of a post-stress WO period has long-lasting effects. In this project, chronic restraint (6hr/d/21d) in Sprague-Dawley rats was used, as it is the minimum duration necessary to observe spatial memory deficits. Two durations of post-stress WO were used following the end of chronic restraint, 3 weeks (STR-WO3) and 6 weeks (STR-WO6). Immediately after chronic stress (STR-IMM) or the WO periods, rats were tested on various cognitive tests. We corroborated past studies that chronic stress impaired spatial memory (STR-IMM vs CON). Interestingly, STR-WO3 and STR-WO6 failed to demonstrate improved spatial memory on a radial arm water maze task, performing similarly as STR-IMM. Performance outcomes were unlikely from differences in anxiety or motivation because rats from all conditions performed similarly on an open field task and on a simple object recognition paradigm, respectively. However, performance on object placement was unusual in that very few rats explored, suggesting some degree of anxiety or fear in all groups. One possible interpretation of the unusual results of the 3 week washout group may be attributed to the different spatial memory tasks used across studies or external factors from the study. Further exploration of these other factors led to the conclusion that they did not play a role and the STR-WO3 RAWM data were anomalous to other studies. This suggests that a washout period following chronic stress may not be fully understood.
ContributorsFlegenheimer, Aaron Embden (Author) / Conrad, Cheryl (Thesis director) / Bimonte-Nelson, Heather (Committee member) / Ortiz, J. Bryce (Committee member) / School of Life Sciences (Contributor) / School of Human Evolution and Social Change (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Chronic stress impairs spatial working memory, attention set-shifting, and response inhibition. The relationship between these functions and the potential underlying neurocircuitry, such as the medial prefrontal cortex (mPFC), needs further research to understand how chronic stress impacts these functions. This study focused on the infralimbic (IL) and prelimbic (PRL) regions of the mPFC, to examine its involvement in two behavioral tasks, fixed minimum interval (FMI) and radial arm water maze (RAWM), following chronic stress, and the relationship between the two paradigms. A previous study failed to find a significant correlation between spatial working memory and response, both functions mediated by the PFC, even though chronic stress disrupted both outcomes. Thus, the purpose of this study was to investigate the functional activation of the mPFC, following chronic stress in these two paradigms, in order to gain an understanding of the neurocircuitry involved within this region. The behavioral outcomes were performed prior to my involvement in the project, and the results corroborate previous findings that chronic stress impairs response inhibition on FMI and spatial working memory on RAWM. My honors thesis involved quantifying the immunohistochemistry-stained tissue to assess the functional activation of the mPFC. Over the course of six months, my work involved identifying the border between IL and PRL regions by overlaying captured images of tissues, starting at a lower magnification of 40x. Afterwards, images were recaptured at higher magnifications (100x) to quantify Fos-like counts of functional activation. No overt changes were found following chronic stress in Fos-like counts after performance on FMI or RAWM. However, response inhibition on the FMI task showed a relationship with the IL function; non-stressed rats displayed a positive correlation between response inhibition and Fos-like profiles. In contrast, chronically stressed rats revealed a negative correlation between response inhibition and Fos-like profiles. The IL cortex is revealed to facilitate extinction of a learned behavior. Thus, these results present a possible interpretation that there is an association, non-stressed rats suppressing a previously learned response, being formed.
ContributorsLe, Brittany Quynh (Author) / Conrad, Cheryl (Thesis director) / Sanabria, Federico (Committee member) / Judd, Jessica (Committee member) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Chronic restraint stress leads to apical dendritic retraction in CA3 pyramidal neurons and often no quantifiable changes in CA1 dendritic complexity. When chronic stress ends, a post-stress recovery period results in an enhancement in CA3 dendritic complexity. We investigated the relationship between CA3 and CA1 pyramidal neurons to determine whether dendritic restructuring in CA3 neurons leads to region-specific changes in the dendritic complexity of CA1 neurons. Adult male Sprague-Dawley rats were restrained (wire mesh, 6h/d/21d) and brains were removed soon after restraint ended (Str-Imm) or after a 21d post-stress recovery period (Str-Rec). In addition, BDNF downregulation targeting the CA3 region prevents enhancement in dendritic complexity following recovery in chronically stressed rats, providing robust conditions to investigate the CA3-CA1 relationship. Consequently, rats were infused into the CA3 area with either an AAV vector with a coding sequence against BDNF (shRNA) or a sequence with no known mRNA complements (Scr). Apical and basal dendritic complexity of CA3 and CA1 was quantified by counting total dendritic bifurcations and dendritic intersections using the Sholl analysis (20 µm distances from soma). Please note that the quantification of the CA3 dendritic arbors was not part of this thesis project. The outcome of that investigation revealed that apical CA3 dendritic retraction was found in Str-Imm-Scr and Str-Rec-shRNA. For the CA1 apical area, gross dendritic bifurcation differences were not detected, but the Sholl quantification revealed regionally-enhanced dendritic complexity that varied by distance from the soma at the distal apical dendrites (Str-Imm-Scr) and proximal basal dendrites (Str-Rec-shRNA). For the latter, significant increases in basal branch points were detected with total branch point quantification method. Moreover, a correlation using all groups revealed a significant inverse relationship between CA3 apical dendritic complexity and CA1 basal dendritic complexity. The results demonstrate that chronic stress-induced CA3 apical dendritic retraction may relate to region-specific changes in CA1 dendritic complexity. The inability of past studies to detect changes in CA1 dendritic complexity may be due to the shortcoming of gross dendritic arbor measures in accounting for subtle region-specific alterations. To address this, the current study included a cohort with BDNF downregulated in the CA3 region. Overall, this suggests that decreased levels of BDNF in the hippocampus provide robust conditions in which changes to CA1 dendritic complexity can be detected.
ContributorsDaas, Eshaan Jatin (Author) / Conrad, Cheryl (Thesis director) / Orchinik, Miles (Committee member) / Ortiz, J. Bryce (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
The stress levels of the average person in today's society are extremely high and this can have a massive effect on health, especially on the cardiovascular system. The two most common types of stress, acute and chronic, effect the cardiovascular system differently. Acute stress comes from a short term source of perceived danger, such as giving a presentation in front of a crowd, or being chased by a wild animal. Chronic stress is the dull anxiety that hangs around consistently and comes from long-term sources of stress, such as a negative work environment or feeling trapped in a poor relationship. A review of the available research literature shows that while acute stress can have positive or negative effects on the body, chronic stress is consistently damaging to cardiovascular health. The adrenaline rush associated with acute stress can increase focus and improve performance through a variety of physiological reactions such as increased heart rate and changes in blood flow to support the most vital organs. Chronic stress sufferers have an increased chance of heart disease, heart attack, and a variety of other problems due to the negative consequences of chronic stress such as high blood pressure. The high negative impact chronic stress and excessive amounts of acute stress can have leads to the conclusion that stress needs to be regulated and limited. Prioritizing health by getting sufficient sleep, taking time to exercise, and practicing relaxation techniques such as meditation can all help to minimize stress levels and the dangerous potential consequences of excess stress.
ContributorsJarrett, Jacqalyn Renee (Author) / Oberstein, Bruce (Thesis director) / Murphree, Julie (Committee member) / College of Letters and Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Stress is a necessary and functional part of human physiology. From responding to life-threatening situations to getting people out of bed in the morning, stress serves a major purpose in human survival. However, when consistent and high levels of stress are experienced, it can pose a threat to human health. One of the major mediators of physiological stress is a hormone called cortisol. Cortisol is a well-defined substance and its function in normal physiology is well understood. Scientific research indicates that consistent and high levels of this hormone may be an aid in cancer’s ability to evade the human immune response. Despite this, there is not much known about its relationship with cancer. I used immunofluorescence to determine cell-to-cell variability of vimentin expression and DNA content for cells that were exposed to cortisol at consistent and frequent doses overtime and those not exposed to cortisol to determine if cortisol altered the variability of vimentin expression and DNA content. I observed no change in the variability in vimentin expression across both cell conditions. I did observe variability in DNA content across both cell conditions, with more variability in the population affected by cortisol. These results suggest that there might be a relationship between the stress induced by cortisol, taking place at the genomic level but may have no impact on specific protein expression. Potential implications of the research conducted are looks to preventative medicine in the context of stress experienced by members of marginalized groups as a way of preventing cancer development.
ContributorsWarthen, Alexander (Author) / Quaranta, Kimberly (Thesis director) / Bussey, Kimberly (Thesis director) / Cunningham, Anna (Committee member) / Barrett, The Honors College (Contributor) / College of Health Solutions (Contributor)
Created2023-05
Description
Women are twice as likely as men to develop Major Depressive Disorder (MDD), and current MDD therapies are only effective for about a third of patients. Hormonal transitions, specifically those involving estradiol (E2), have been found to contribute to this increased vulnerability in women. This study aimed to investigate potential mechanisms underlying the sex differences seen in MDD vulnerability, specifically the role of E2. The brain region-specific changes induced by chronic stress differ for female rats than for male rats. Therefore, we aimed to determine the effects of sex and chronic stress on E2 expression in four brain regions: the hippocampus, medial prefrontal cortex, amygdala, and cerebellum. Sprague-Dawley rats (n = 48, 24 males, 24 females; n=12/Tx group) were subjected to daily wire mesh restraint stress (6 h/21 days), and were euthanized and dissected the day following the end of chronic restraint stress (day 22). Ultra high-pressure liquid chromatography-mass spectroscopy was used to directly measure E2 in the brain regions. Quantitative real-time PCR was used to indirectly assess E2 expression via mRNA for aromatase (ARO-L) and estrogen receptors (ERβ, ERɑ, and GPR30), as well as expression of inflammatory cytokines (IL-1β and TNF-ɑ). Our findings suggest that chronic stress may lead to changes in local estradiol expression in the brain that are both sex-dependent and brain region-specific, while the data are preliminary given the small sample size. We found that expression of ARO-L mRNA, a measure of local E2 production, tended to increase in the HIPP, but decrease in the mPFC following chronic stress, and in the mPFC this pattern was only observed in males. Local estradiol production in the brain seems to act as a potential compensatory mechanism in the hippocampus, but as a protective mechanism in the mPFC, which is highly sensitive to chronic stress.
ContributorsSmith, Elliot Ann (Author) / Conrad, Cheryl (Thesis director) / Presson, Clark (Committee member) / Department of Psychology (Contributor) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Major Depressive Disorder (MDD) is a widespread mood disorder that affects more than 300 million people worldwide and yet, high relapse rates persist. This current study aimed to use an animal model for depression, unpredictable intermittent restraint (UIR), to investigate changes in a subset of neurons within the hippocampus, a region of high susceptibility in MDD. Adult male and female Sprague-Dawley rats were randomly assigned to four treatment groups based on sex (n = 48, n = 12/group). Half of the rats underwent UIR that involved restraint with orbital shaking (30 min or 1 h) for 2-6 consecutive days, followed by one or two days of no stressors; the other half of the rats were undisturbed (CON). UIR rats were stressed for 28 days (21 days of actual stressors) before behavioral testing began with UIR continuing between testing days for nearly 70 days. Rats were then euthanized between 9 and 11 days after the last UIR session. Brains were processed for Golgi stain and long-shaft (LS) neurons within the hippocampal CA3a and CA3b regions were quantified for dendritic complexity using a Camera Lucida attachment. Our findings failed to support our hypothesis that UIR would produce apical dendritic retraction in CA3 hippocampal LS neurons in both males and females. Given that UIR failed to produce CA3 apical dendritic retraction in males, which is commonly observed in the literature, we discuss several reasons for these findings including, time from the end of UIR to when brains were sampled, and the effects of repeated cognitive testing. Given our published findings that UIR impaired spatial ability in males, but not females, we believe that UIR holds validity as a chronic stress paradigm, as UIR attenuated body weight gain in both males and females and produced reductions in thymus gland weight in UIR males. These findings corroborate UIR as an effective stressor in males and warrant further research into the timing of UIR-induced changes in hippocampal CA3 apical dendritic morphology.
ContributorsReynolds, Cindy Marie (Author) / Conrad, Cheryl D. (Thesis director) / Olive, M. Foster (Committee member) / School of Molecular Sciences (Contributor) / Department of English (Contributor) / Barrett, The Honors College (Contributor)
Created2020-12