F.R. Walker

Cognitive deficits develop 1 month after diffuse brain injury and are exaggerated by microglia-associated reactivity to peripheral immune challenge

UNLABELLED Traumatic brain injury (TBI) elicits immediate neuroinflammatory events that contribute to acute cognitive, motor, and affective disturbance. Despite resolution of these acute complications, significant neuropsychiatric and cognitive issues can develop and progress after TBI. We and others have provided novel evidence that these complications are potentiated by repeated injuries, immune challenges and stressors. A key component to this may be increased sensitization or priming of glia after TBI. Therefore, our objectives were to determine the degree to which cognitive deterioration occurred after diffuse TBI (moderate midline fluid percussion injury) and ascertain if glial reactivity induced by an acute immune challenge potentiated cognitive decline 30 days post injury (dpi). In post-recovery assessments, hippocampal-dependent learning and memory recall were normal 7 dpi, but anterograde learning was impaired by 30 dpi. Examination of mRNA and morphological profiles of glia 30 dpi indicated a low but persistent level of inflammation with elevated expression of GFAP and IL-1β in astrocytes and MHCII and IL-1β in microglia. Moreover, an acute immune challenge 30 dpi robustly interrupted memory consolidation specifically in TBI mice. These deficits were associated with exaggerated microglia-mediated inflammation with amplified (IL-1β, CCL2, TNFα) and prolonged (TNFα) cytokine/chemokine expression, and a marked reactive morphological profile of microglia in the CA3 of the hippocampus. Collectively, these data indicate that microglia remain sensitized 30 dpi after moderate TBI and a secondary inflammatory challenge elicits robust microglial reactivity that augments cognitive decline. STATEMENT OF SIGNIFICANCE Traumatic brain injury (TBI) is a major risk factor in development of neuropsychiatric problems long after injury, negatively affecting quality of life. Mounting evidence indicates that inflammatory processes worsen with time after a brain injury and are likely mediated by glia. Here, we show that primed microglia and astrocytes developed in mice 1 month following moderate diffuse TBI, coinciding with cognitive deficits that were not initially evident after injury. Additionally, TBI-induced glial priming may adversely affect the ability of glia to appropriately respond to immune challenges, which occur regularly across the lifespan. Indeed, we show that an acute immune challenge augmented microglial reactivity and cognitive deficits. This idea may provide new avenues of clinical assessments and treatments following TBI.

124. A comparative examination of the anti-inflammatory effects of SSRI and SNRI antidepressants on microglia

Selective serotonin and serotonin norepinephrine reuptake inhibitors (SSRI; SNRI) are the frontline pharmacological treatment options for major depression. While these drugs have long been assumed to exert their antidepressant effects because of their ability to alter central monoamine levels, they have also been shown to exert anti-inflammatory effects. Recently it has become apparent that these drugs can also exert anti-inflammatory effects on microglia, the principal cells within the CNS that regulate and respond to inflammatory factors. From a pharmacological standpoint, much critical information remains unknown. In particular, the relative efficacy of these drugs in modulating microglial responses is yet to be determined. To address these issues, we evaluated the ability of different SSRIs (fluoxetine, sertraline, paroxetine, fluvoxamine and citalopram) and one SNRI (venlafaxine) to suppress microglial responses to an inflammatory stimulus. Specifically, we examined their ability to alter tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) production after stimulation with lipopolysaccharide. Our results indicated that the SSRIs potently inhibited microglial TNF-alpha and NO production. We then investigated whether these effects might involve either beta-adrenoceptor or cAMP signalling. Using the protein kinase A inhibitor Rp-CAMPs, we found evidence to suggest that cAMP signalling may be partially involved in regulating the anti-inflammatory response. Findings such as these could suggest that antidepressants may owe at least some of their therapeutic effectiveness to their anti-inflammatory properties.

Frequent, short bouts of light-intensity exercises while standing decreases systolic blood pressure: Breaking Up Sitting Time after Stroke (BUST-Stroke) trial:

Background Stroke survivors sit for long periods each day. Uninterrupted sitting is associated with increased risk of cardiovascular disease. Breaking up uninterrupted sitting with frequent, short bouts of light-intensity physical activity has an immediate positive effect on blood pressure and plasma clotting factors in healthy, overweight, and type 2 diabetic populations. Aim We examined the effect of frequent, short bouts of light-intensity physical activity on blood pressure and plasma fibrinogen in stroke survivors. Methods Prespecified secondary analyses from a three-armed randomized, within-participant, crossover trial. Participants were 19 stroke survivors (nine female, aged 68 years old, 90% able to walk independently). The experimental conditions were sitting for 8 h uninterrupted, sitting with 3 min bouts of light-intensity exercise while standing every 30 min, or sitting with 3 min of walking every 30 min. Blood pressure was measured every 30 min over 8 h and plasma fibrinogen at the beginning, middle, and end of each day. Intention-to-treat analyses were performed using linear mixed models including fixed effects for condition, period, and order, and a random intercept for participant to account for repeated measures and missing data. Results Sitting with 3 min bouts of light-intensity exercise while standing every 30 min decreased systolic blood pressure by 3.5 mmHg (95% CI 1.7–5.4) compared with sitting for 8 h uninterrupted. For participants not taking antihypertensive medications, sitting with 3 min of walking every 30 min decreased systolic blood pressure by 5.0 mmHg (95% CI −7.9 to 2.0) and sitting with 3 min bouts light-intensity exercise while standing every 30 min decreased systolic blood pressure by 4.2 mmHg (95% CI −7.2 to −1.3) compared with sitting for 8 h uninterrupted. There was no effect of condition on diastolic blood pressure (p = 0.45) or plasma fibrinogen levels (p = 0.91). Conclusion Frequent, short bouts of light-intensity physical activity decreases systolic blood pressure in stroke survivors. However, before translation into clinical practice, the optimal duration and timing of physical activity bouts needs to be determined. Clinical trial registration Australian and New Zealand Clinical Trials Registry http://www.anzctr.org.au ANZTR12615001189516.

Abstract # 1760 Secondary neurodegeneration after stroke is exacerbated by stress: A new opportunity for preserving viable brain tissue

As our population ages stroke is becoming an ever more prevalent condition, afflicting tens of thousands of people every year. The initial stroke event results in a very significant loss of brain tissue at the site of infarction. Unfortunately, however, viable brain tissue continues to be lost after the primary infarction process is complete, in a process known as secondary neurodegeneration (SND). SND involves the progressive death of brain regions that were connected to the original infarcted territories. To better understand SND we have developed a highly controllable model of SND. Specifically, we induce a small stroke within the somatosensory cortex with the assistance of a custom built intrinsic optical signal imaging tandem lens macroscope. This procedure initiates a tightly constrained SND process. We have identified that SND-linked neuroinflammatory disturbances spread out from the injury site, as indicated by significantly enhanced pro-inflammatory signalling (mRNA and protein levels), microglial morphology, neuronal loss (histology), and infiltration of peripheral immune cells (flow cytometry). We have identified that these events are significantly suppressed by chronic stress, or by corticosterone alone, which is in-turn associated with greater cell loss at sites of SND. Collectively, these results suggest that detailed monitoring of stress loads and stress reduction strategies may be warranted in patients recovering from stroke.

Understanding ‘stress x microglial interactions’ in stroke-induced secondary neurodegeneration: A major opportunity for the preservation of viable brain tissue.

Stroke patients experience persistently high levels of psychological stress. As there is very little evidence to indicate that stress can modify longer-term recovery processes, we decided to utilize an experimental model of stroke to determine whether exposure to chronic stress could modify the development of secondary thalamic neurodegeneration (STND), a commonly reported complication associated with stroke induced cortical damage. We focused on the involvement of microglia-like cells, as several studies have linked microglial activation to the development of STND. One month following stroke, in male mice, we identified that numbers of microglial-like cells, as well as putative markers of microglial structural reorganization (Iba-1), complement processing (CD11b), phagocytosis (CD68), and antigen presentation (MHC-II) were all elevated in response to occlusion ( p 0.05 ). Occluded animals that were also exposed to chronic stress exhibited lower levels of Iba-1 positive cells and a reduced expression of Iba-1 and CD11b compared to the ‘occlusion-alone’ group ( p 0.05 ). The dampened expression of microglial-like markers observed in stressed animals was associated with significant additional loss of neurons, indicating a potential neuroprotective role for microglia ( p 0.05 ). We will also present new findings concerning the effect of the microglial-modulator minocycline on these phenomena. Together, our results suggest that STND can be negatively modified, potentially in a microglial dependent manner, by exposure to chronic stress.

92. Improving the quantitative analysis of immunohistochemically and immunofluorescently labelled glia

Immunohistochemical or immunofluorescent labelling has the advantage of being able to identify differences between treatment groups with a high degree of locational specificity. Accurate quantification of resulting images requires that certain assumptions be met. For instance, all immunolabelling procedures have to be undertaken simultaneously under identical conditions. Assuming these requirements are met, the most common procedure used to quantify group differences is a process known as thresholding. This image analysis technique involves defining a single intensity set-point, which is considered to demarcate signal from noise in an image. Normally this set-point, however, is chosen in an arbitrary manner. Indeed, it is frequently the case that within published literature the set-point is not described. Interestingly, we have discovered that the relative magnitude of the differences can vary dramatically depending upon where across the intensity spectrum the set-point is chosen. The importance of this issue is significant given that were a set-point is chosen can reveal huge between group differences or none at all. Accordingly, without appropriate consideration of the relative proportion of material that is captured by a threshold it is essentially impossible to have any confidence in the actual accuracy of the provided results. This presentation will describe both the limitations associated with traditional single point thresholding approaches and discuss a variety of solutions to that maybe useful in circumventing the limitations of this approach.

126. What have microglia got to do with it? New directions in the neurobiology of depression

biomarkers of stress and inflammation, and poor pregnancy outcome. Two hundred women were recruited from Denver Health Medical Center during their first trimester of pregnancy and followed until delivery. Early and late in pregnancy, women completed a series of psychosocial assessments and provided a blood sample. Assessments included measures of pregnancy-specific distress and support, overall stress, major life events, and self-efficacy. Serum levels of TNF-a, IL-6, IL-10, and CRP were measured via ELISA at each timepoint. Data on complications, delivery, and infant outcome were obtained through chart extraction. Elevated proinflammatory markers were related to lower social support, higher pregnancy-specific distress, and lower self-efficacy. Early elevations in TNF-a, IL-6, and CRP were predictive of preterm birth and increased frequency of complications overall. Similarly, higher distress and lower support were also related to more complications and preterm birth. This work provides some of the first data showing that stress and psychosocial factors are related to increases in stress and inflammation-related biomarkers, and that these increases, in turn, are associated with increased likelihood of pregnancy complications and premature delivery.

Postnatal exposure to a bacterial mimetic increases microglial activation and histone H3 acetylation in rats

11. Postnatal exposure to a bacterial mimetic increases microglial activation and histone H3 acetylation in rats L. Sominsky , A.K. Walker , L.K. Ong , F.R. Walker , D.M. Hodgson a a Laboratory of Neuroimmunology, School of Psychology, Faculty of Science and IT, The University of Newcastle, Callaghan, NSW 2308, Australia b School of Biomedical Sciences & Pharmacy, The University of Newcastle, Australia c Priority Research Centre for Brain and Mental Health Research, University of Newcastle, Australia Hunter Medical Research Institute, Newcastle, Australia