Browsing by Author "Lau, Yuen-Sum"
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Item Association of GRK3 with stress resilience and stress susceptibility: Behavioral and pharmacological evidence(2011-08) Taneja, Manish 1978-; Eikenburg, Douglas C.; Standifer, Kelly M.; De Biasi, Mariella; Bond, Richard A.; Lau, Yuen-SumOn exposure to stress, persistent stimulation of alpha2A-adrenoceptors (α2A-AR) and corticotrophin-releasing factor 1 receptors (CRF1-R) increase the receptor signaling in locus coeruleus (LC) and amygdala (two critical brain regions involved in stress response. If this stimulation remains uncontrolled, it initiates the adverse consequences of stress. G protein-coupled receptor kinase-3 (GRK3) mediated desensitization of α2A-AR and CRF1-R, which terminates the enhanced signaling, is considered an adaptive response. It is not known if there are any biochemical alterations in this adaptive response in stress resilient individuals which make them resistant to the negative consequences of stress. The purpose of this research was to understand the stress-induced alterations of GRK3 levels and their relationship with α2A-AR/ CRF1-R levels in LC/ amygdala of stress susceptible and stress-resilient rats. The model utilized, exposure of rats to a single bout of 100 unpredictable inescapable tail shocks, resulted in two distinct behaviors: learned helpless (LH) behavior, (stress susceptible, escape deficits≥ controls) and non-helpless (NH) behavior (stress resilient, escape behavior ≈ controls). A single bout of stress produced readily reversible behavioral changes. Thus, the present study examined time-dependent correlates of GRK3, α2A-AR/CRF1-R levels from the appearance to the disappearance of LH behavior. In order to evaluate the differences between readily reversible and prolonged LH behavior, a new model of repeated bouts of tail shocks was created. This model showed prolonged behavioral changes. Finally, the efficacy of desipramine treatment in reversing repeated stress-induced behavioral and biochemical changes was assessed. LH behavior induced by a single stress was associated with reduced levels of GRK3 and relatively higher levels of α2A-AR /CRF1-R in LC. These changes appear as early as 1h-post stress and disappear when LH behavior is no longer present. Amygdala showed similar changes compared to LC, but the biochemical distinctions don’t appear at 1h post-stress. Instead, the global effects of single stress are seen. Repeated bout of stress (Day 1, 4, 7) generated a bimodal population distribution among stressed rats with prolonged NH and LH behavior (14 days). Levels of GRK3 and α2A-AR/ CRF1-R were affected similarly to single stress LH rats. In contrast to GRK3, GRK2 also was reduced which was unchanged during single stress. Amygdala showed similar changes after repeated stress compared to LC except that there was no change in GRK2 levels. Desipramine treatment (5mg/Kg bid/14 days) reversed the behavioral deficits of repeated stress LH rats. The levels of GRK3/2 were normalized in LC along with down-regulation of α2A-AR and CRF1-Rs. Amygdala also showed restoration of GRK3 levels with no receptor down-regulation. Collectively this data suggest that LH behavior (single and repeated stress), an index of stress susceptibility, is associated with reduced GRK3 levels accompanied by relative increase in α2A-AR and CRF1-R levels in LC. The strength of this association is indicated by the fact that cluster analysis of these proteins, collectively, can predict rat behavior post-stress, independent of behavioral testing.Item Changes in GRK3 and Norepinephrine Responsiveness in Locus Coeruleus Neurons are Associated with Learned Helplessness After Repeated Forced Swim Stress(2011-08) Saha, Kaustuv; Eikenburg, Douglas C.; Knoll, Brian J.; Ziburkus, Jokubas; Standifer, Kelly M.; Lau, Yuen-SumIn brain, locus coeruleus plays an important role in mediating the stress responses. Two important neurotransmitter/hormones released in locus coeruleus (LC) during exposure to stress include corticotrophin releasing factor (CRF) and norepinephrine (NE). CRF and NE predominantly act on G protein-coupled receptors (GPCR), the corticotrophin-releasing factor type 1 receptor (CRF1-R) and the alpha2A–adrenoceptors (α2A-AR), respectively. Activation of CRF1-R increases LC neuronal firing and activation of postsynaptic α2A-AR inhibits firing of LC neurons. Additionally, presynaptic α2A-ARs act as autoreceptors inhibiting release of NE in LC. Both the agonist-occupied CRF1-R and α2A-AR are preferentially desensitized by G protein-coupled receptor kinase 3 (GRK3). This desensitization contributes to termination of the signaling of CRF1-R and α2A-AR, observed during the persistent presence of neurotransmitters during stress. At present, there is a gap in knowledge as to what changes in GPCR signaling occur during single and repeated stress. The present study provides a contribution towards filling this gap. This study observed the effects of single and repeated forced swim stress on the escape task performance of rats in a shuttle-box. The study also observed the effects of GRK3 and NE responsiveness in LC neurons in slices of rat brainstem. Both single and repeated forced swim stress segregated the stressed rats into two clusters based on their performance in the escape task. One cluster showed impaired escape behavior compared to controls and was designated Learned Helpless (LH), showing susceptibility to the adverse effects of stress. The other cluster of stressed rats showed escape behavior similar to the controls and was termed Non-Helpless (NH), showing resilience against the adverse consequences of stress. Thus this study demonstrated that a milder stress than inescapable electric shock, the stress paradigm of forced swim, could induce deficits in escape behavior. These deficits are a well-established index of depression-associated behavior. Biochemical analysis showed that single forced swim stress did not cause any change in the levels of GRK3, CRF1-R and α2A-AR in the LC of the LH rats compared to the control and NH rats. However, repeated forced swim stress caused a decrease in the levels of GRK3 and an increase in the levels of CRF1-R and α2A-AR in the LC of LH rats compared to the control and NH rats. Also, repeated forced swim stress was accompanied by an increase in the responsiveness of α2A-AR upon application of lower concentrations of NE as observed by measuring the changes in membrane current in response to different concentrations of NE in single LC neuron. Moreover, the increases in immobility, LH behavior, decreases in GRK3 and increase in CRF1-R and α2A-AR in LC after repeated forced swim stress alone were not observed in rats pretreated with desipramine (DMI). In conclusion, a much milder and more physiological stressor than electric shock, repeated forced swim stress, enables the identification of a sub-population of stress-susceptible rats that display LH. This LH behavior was associated with a decrease in GRK3 and an increase in α2A-AR levels and responsiveness in LC, accompanied by an increase in CRF1-R levels. The repeated forced swim-induced changes in responsiveness of the postsynaptic α2A-AR may indicate that when the stressful stimuli are removed there is a rebound compensatory mechanism by which the α2A-AR may reduce LC hyperactivity. Although, the method used in this study measured only postsynaptic α2A-AR function, if similar changes in the presynaptic α2A-AR occur, this would decrease NE release in LC during stress. Thus the pre- and postsynaptic α2A-ARs would cancel each other functionally. This would lead to predominance of excitatory effects of CRF1-R, potentially contributing to the hyperresponsiveness of LC to CRF and to hyperactivity of the LC that is characteristically observed on exposure to stress. DMI pretreatment, by increasing the availability of norepinephrine in the LC, will maintain an inhibitory tone on the neurons and prevent the hyperactivity of LC neurons associated with exposure to repeated stress. This will lead to prevention of repeated forced swim stress-induced decrease in GRK3 and increase in the levels and responsiveness α2A-AR and CRF1-Rs in the LC, resulting in the prevention of subsequent impairment of escape behavior in rats.Item CHRONIC STRESS REVEALS COGNITIVE IMPAIRMENT IN A SUBTHRESHOLD AMYLOID-BETA MODEL OF ALZHEIMER’S DISEASE(2010-05) Tran, Trinh T. 1982-; Alkadhi, Karim A.; De Biasi, Mariella; Lau, Yuen-Sum; Rea, Michael A.; Salim, SaminaAlthough it is generally accepted that Aβ contributes to the pathogenesis of Alzheimer's disease (AD), other factors that impact the severity and time of onset of the disease are not well known. Aside from genetic factors, environmental factors, such as stress, may also play a critical role in the manifestation of AD. Epidemiological studies indicate that individuals suffering from chronic stress are at an increased risk for developing AD. The present study investigated the effect of chronic psychosocial stress in an at-risk, subthreshold Aβ (subAβ) rat model of AD by three techniques: learning and memory tests in the radial arm water maze, electrophysiological recordings of long-term potentiation (LTP) and long-term depression (LTD) in anesthetized rats, and immunoblot analyses of learning- and memory-related signaling and AD-related molecules. Chronic psychosocial stress was induced using a rat intruder model. The subAβ rat model of AD was induced by continuous i.c.v. infusion of 160 pmol/day Aβ1-42 via a 14-day mini-osmotic pump. Behavioral tests, electrophysiological recordings, and molecular analyses showed that subAβ rats were not significantly different from control rats, thus validating this model as an at-risk model of AD without phenotypic characteristics or cognitive deficits commonly associated with AD. However, chronically stressed subAβ-infused rats showed significantly greater impairment of cognitive functions and synaptic plasticity than that caused by stress alone. Molecular analyses of essential signaling molecules showed that animals subjected to stress have reduced basal levels of p-CaMKII, decreased p-CaMKII/CaMKII ratio, and increased basal levels of calcineurin. The infusion of subAβ into the cerebral ventricle of chronically stressed rats also decreased basal levels of p-CREB, total CREB and BDNF and increased basal levels of BACE. Furthermore, multiple high frequency stimulation failed to increase levels of p-CREB and BDNF during the late-phase of long-term potentiation. However, paired pulse stimulation produced a decrease in levels of BDNF during long-term depression in the stress/subAβ animals. Together, the results of our behavioral, electrophysiological, and molecular studies suggest that prior and concomitant exposure of subAβ-infused rats to chronic stress intensify the severity of stress-induced cognitive and synaptic plasticity deficits. Thus, chronic stress may accelerate the impairment of learning, memory, and synaptic plasticity in individuals “at-risk” for AD.Item Low-level human equivalent gestational lead exposure produces sex-specific motor and coordination abnormalities and late-onset obesity in year-old mice(Environmental Health Perspectives, 2008-03) Leasure, J. Leigh; Giddabasappa, Anand; Chaney, Shawnta Y.; Johnson, Jerry E., Jr.; Pothakos, Konstantinos; Lau, Yuen-Sum; Fox, Donald A.Background. Low-level developmental lead exposure is linked to cognitive and neurological disorders in children. However, the long-term effects of gestational lead exposure (GLE) have received little attention. Objectives. Our goals were to establish a murine model of human equivalent GLE and to determine dose–response effects on body weight, motor functions, and dopamine neurochemistry in year-old offspring. Methods. We exposed female C57BL/6 mice to water containing 0, 27 (low), 55 (moderate), or 109 ppm (high) of lead from 2 weeks prior to mating, throughout gestation, and until postnatal day 10 (PN10). Maternal and litter measures, blood lead concentrations ([BPb]), and body weights were obtained throughout the experiment. Locomotor behavior in the absence and presence of amphetamine, running wheel activity, rotarod test, and dopamine utilization were examined in year-old mice. Results. Peak [BPb] were < 1, ≤ 10, 24–27, and 33–42 μg/dL in control, low-, moderate- and high-dose GLE groups at PN0–10, respectively. Year-old male but not female GLE mice exhibited late-onset obesity. Similarly, we observed male-specific decreased spontaneous motor activity, increased amphetamine-induced motor activity, and decreased rotarod performance in year-old GLE mice. Levels of dopamine and its major metabolite were altered in year-old male mice, although only forebrain utilization increased. GLE-induced alterations were consistently larger in low-dose GLE mice. Conclusions. Our novel results show that GLE produced permanent male-specific deficits. The nonmonotonic dose-dependent responses showed that low-level GLE produced the most adverse effects. These data reinforce the idea that lifetime measures of dose–response toxicant exposure should be a component of the neurotoxic risk assessment process.Item Neuronal and Mitochondrial Protection in Chronic Parkinsonism(2010-08) Patki, Gaurav; Lau, Yuen-Sum; Alkadhi, Karim A.; Eriksen, Jason; Le, Wei-dong; Widger, William R.Among the several plausible neuropathological hypotheses underlying the progression of aging and neurodegenerative diseases such as Parkinson’s disease (PD), oxidative stress and mitochondrial damage have emerged as one of the attractive biochemical mechanisms. However, most of the past studies linking mitochondrial dysfunction to neuronal degeneration have been carried out in vitro or in acute in vivo studies. It is not known whether mitochondrial dysfunction is an immediate response to cytotoxic-inducing agents or is sustained as a long-term consequence of neuronal death. The purpose of our research was to first validate the chronic mouse model of Parkinson’s disorder (MPD), which has been developed and characterized by our laboratory as a suitable animal model for investigating neuronal and mitochondrial dysfunctions and then to examine the protective effects of endurance exercise and melatonin treatment on this model. Male, C57/BL retired breeder mice at 6-10 months of age were used in the present study. The aged chronic MPD was treated with of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (15 mg/kg, s.c), twice a week for 5 weeks. MPTP was co-administered with probenecid (250 mg/kg, i.p), an adjuvant that is known to inhibit the peripheral and neuronal clearance of MPTP and potentiate the neurotoxicity of MPTP. The chronic MPD was previously shown to display neurochemical, histological, behavioral and pathological features resembling those of PD-like neurodegeneration lasting for at least 6 months. Six to twelve weeks after chronic MPTP treatment, aged mice showed sustained decrease in striatal mitochondrial respiration as well as loss of antioxidant enzymes, Cu-Zn superoxide dismutase (SOD), Mn SOD and cytochrome c (cyt c) expression. Striatal mitochondrial dysfunction correlated with dopamine neuron and behavioral deficits in the aged chronic MPD. When the chronic MPD was exercise-trained on a motorized treadmill 5 days/week for 18 weeks, the dopamine neuronal, mitochondrial and behavioral deficits as seen in the sedentary chronic MPD were prevented. Melatonin (5 mg/kg, i.p), a known natural antioxidant and free radical scavenger was injected to the chronic MPD 5 days/week for 18 weeks. Melatonin alone did not alter the striatal neuronal, mitochondrial and motor functions in normal mice. However, melatonin was effective to reverse dopaminergic, mitochondrial and motor impairment as exercise did to the chronic MPD. We conclude that endurance exercise training and melatonin treatment are effective neuroprotective and mitochondrial protective measures in the chronic MPD. Exercise and melatonin treatment may have the potential to slow the progression of PD related neurodegeneration.Item The Effects of Treadmill Exercise in the P301S Mouse Model of Tau Pathology(2015-08) Ohia, Odochi Iquo; Eriksen, Jason; Alkadhi, Karim A.; Lau, Yuen-Sum; Leasure, J. Leigh; McConnell, Bradley K.Tauopathies are a group of neurodegenerative disorders characterized by severe cognitive and motor deficits that are associated with the development of neurofibrillary tangles (NFTs), intracellular protein aggregates composed of hyperphosphorylated tau (a microtubule associated protein). The accumulation of NFTs (along with senile plaques) is one of the neuropathological hallmarks of Alzheimer's disease (AD), and there is evidence that NFT accumulation is positively correlated with the severity of AD symptoms (Arriagada et al., 1992; Ghoshal et al., 2002; Mitchell et al., 2002). Current FDA-approved pharmacological treatments do not alter AD progression and only temporarily alleviate symptoms. However, recent evidence suggests that physical exercise may slow the progression of AD and other tauopathies. The following dissertation project investigated the impact of treadmill exercise in a transgenic mouse model of neurodegenerative tauopathy. The central hypothesis was that endurance treadmill exercise would slow the development of neurodegenerative tau pathology and associated behavioral impairments in the P301S-tau transgenic mouse model of tauopathy. Old (7-month old) and young (3-month old) P301S mice were subjected to 12- and 24-weeks of exercise, respectively. Following exercise, mice were given behavioral assessments. Immunohistochemical and biochemical analysis was also performed to assess the impact of exercise on behavior and pathology. When old P301S mice with advanced tau pathology where introduced to treadmill exercise for 12 weeks: 1) enhanced exploratory locomotion, 2) a decrease in pathological tau hyperphosphorylation and 3) reduction of aggregated (insoluble) tau, which was confirmation of the central hypothesis. When young P301S without advanced pathology where introduced to treadmill exercise for 24 weeks, the following changes were observed: 1) reduced hyperactivity, 2) enhanced muscular strength, 3) restoration of normal anxiety-like behavior, 3) improved associative memory 4) a decrease in pathological tau hyperphosphorylation and 5) reduction of aggregated (insoluble) tau, which also confirmed the central hypothesis. Despite the numerous benefits of this exercise regimen before and after the onset of significant tau pathology and behavioral dysfunction, exercise had no impact on cell loss. Additionally, it was observed that the majority of changes associated with therapeutic exercise occurred in the spinal cord, whereas preventative exercise appeared to have greater benefits in the brain. These observations offer insight on the impact of consistent and regular exercise in tau-related dementias. Moreover, these observations add to the growing body of literature on the importance of incorporating physical activity into a healthy lifestyle, to help combat the onset and progression of dementia.Item THE PROTECTIVE EFFECTS OF CHRONIC CAFFEINE TREATMENT ON THE COGNITIVE FUNCTION AND SYNAPTIC PLASTICITY IN ACUTE SLEEP DEPRIVATION(2010-05) Alhaider, Ibrahim; Alkadhi, Karim A.; Lau, Yuen-Sum; Hussain, Tahir; Leasure, J. Leigh; Aleisa, Abdulaziz M.Study objectives: Accumulating evidence has shown that caffeine and sleep deprivation have opposing effects on learning and memory; therefore, this study was undertaken to provide a detailed account of the effect of chronic, low-dose caffeine treatment on the deleterious effects of sleep loss on hippocampus-dependent learning and memory. Experimental design: We investigated the effects of chronic (4 weeks) caffeine treatment (0.3 g/l in drinking water) on memory impairment in acutely (24 hr) sleep-deprived rats. Sleep deprivation was induced using the modified multiple platform model. The effects of caffeine on sleep deprivation-induced hippocampus-dependent learning and memory deficits were studied using three approaches: learning and memory performance in the radial arm water maze task; electrophysiological recordings in the Cornu Ammonis (CA1) and dentate gyrus (DG) regions of the hippocampus; and western blot analysis to measure the levels of memory- and synaptic plasticity-related signaling molecules. Results: Our results showed that chronic caffeine treatment prevented impairment of hippocampus-dependent learning, short-term memory and early phase- long-term potentiation (E-LTP) of the CA1 and DG areas in the sleep-deprived rats. In correlation, caffeine treatment prevented a sleep deprivation-associated decrease in the basal levels of phosphorylated calcium/calmodulin-dependent protein kinase II (P-CaMKII) and brain-derived neurotrophic factor (BDNF). In addition, caffeine treatment of sleep-deprived rats increased the levels of P-CaMKII during the expression of E-LTP. The results also showed that chronic caffeine treatment prevented the impairment of long-term memory and late phase-LTP (L-LTP) in the CA1 and DG regions of the sleep-deprived rats. Additionally, caffeine treatment prevented a sleep deprivation-associated decrease in the basal levels of the phosphorylated cAMP response element binding protein (P-CREB) as well as total CREB. Treating sleep-deprived rats chronically with caffeine enables multiple high frequency stimulation to increase the levels of P-CREB during L-LTP expression. Conclusions: The results suggest that long-term use of a low dose of caffeine protects against the harmful changes in the basal levels of P-CaMKII, P-CREB and BDNF associated with sleep deprivation and as a result contributes to the revival of hippocampus-dependent learning and memory as well as LTP in the CA1 and DG regions.Item The Role of Rac1 in Synaptic Plasticity, Learning and Memory(2012-05) Bongmba, Odelia; Tejada-Simon, Maria V.; Lau, Yuen-Sum; Alkadhi, Karim A.; Alcantara, Adriana A.; Spencer, Corinne M.During the process of learning and memory, neuronal synapses undergo changes involving gene expression, protein synthesis, and cytoarchitectural remodeling, referred to as synaptic plasticity. Changes in the morphology of synapses are necessary for learning and memory storage, and require the rearrangement of the actin cytoskeleton at dendrites and actin rich dendritic spines which are the loci excitatory of synaptic transmission in the central nervous system. Rac1, a protein of the Rho subfamily of GTP binding proteins (GTPases), is largely known for its involvement in cytoskeleton remodeling, and has been implicated in neuronal development, participating in the morphological changes required for migration of newborn neurons to characteristic locations, extension of axons and dendrites into proper target regions, and formation of synapses with appropriate partners. However, the functional role of Rac1 in adult neuronal signaling has been relatively unclear. Our laboratory previously demonstrated that that Rac1 is highly expressed in the adult mouse hippocampus, a part of the brain, which is very crucial for memory acquisition. In vitro studies in hippocampal slices indicated that activation of the hippocampal N-methyl-D-aspartate (NMDA) receptor, the receptor that was modified to produce the “smart mouse” results in membrane translocation and activation of Rac1. Moreover, our laboratory has observed that translocation and activation of Rac1 are associated with fear learning in the adult mice. The purpose of this study was to examine whether Rac1 is required for regulation of the cytoskeletal dynamics leading to morphological plasticity observed at neuronal synapses during hippocampal learning and memory. To evaluate the importance of Rac1 in plasticity and learning we generated a mouse bearing a conditional inactivation of the rac1 gene in the hippocampus (referred herein as Rac1 knockouts [KO] or mutants) using the Cre/LoxP system. We showed that the disappearance of Rac1 in the Rac1 knock out (KO) is time dependent, with a 16% significant decrease at two months and 90% at six months as compared to their wild type (WT) littermates. No differences in protein levels were observed between the wild type and heterozygous littermates. Next, we studied neuronal morphology in hippocampal slices using the rapid Golgi-Cox technique to determine whether Rac1 was necessary for the neuroanatomical and cytoarchitectural changes associated with synaptic plasticity in the adult mice. We showed that loss of Rac1 leads to a significant reduction in spine density in Rac1 mutant mice as compared to the wild type controls. In an attempt to correlate this effect with an alteration in the actin dynamics pathway, we performed Western blot analysis, which showed in the Rac1 mutant significant reduction in p-PAK-1, p-LIMK-1 and p-Cofilin-1, all proteins downstream of Rac1 and essential for cytoskeletal rearrangements leading to dendritic spine development. In order to evaluate the involvement of Rac1 in long term synaptic plasticity (LTP and LTD), hippocampal slices from age matched wild type and Rac1 mutant were given high frequency stimulation (HFS) to generate LTP and low frequency stimulation (LFS) to induce LTD. Rac1 deficient mice showed impaired LTP and LTD as compared to their littermate controls. Furthermore, to assess whether Rac1 is associated with, and necessary for hippocampus-dependent learning and memory in the intact animal, Rac1 mutant mice and their littermate controls were examined in a battery of behavioral tests beginning with six control tests namely, the Open Field Activity, Rotating Rod, Pre-pulse Inhibition of Startle Response, Hot Plate test, Light-dark, Elevated Plus Maze, and ending with two learning and memory tests, the Morris Water Maze and Fear conditioning paradigm. Rac1 deficient mice showed the same performance as the wild type and the heterozygotes in control tests, however, they showed impaired learning in the learning and memory tests. Collectively, these data suggest that Rac1 is an important protein required for proper dendritic spine morphogenesis, long-term synaptic plasticity, as well as learning and memory. These phenomena are abnormal in some autistic disorders, making Rac1 an interesting target in the study of these diseases.