Movement of cerebrospinal fluid tracer into brain parenchyma and outflow to nasal mucosa is reduced at 24 h but not 2 weeks post-stroke in mice

BACKGROUND

Recent data indicates that cerebrospinal fluid (CSF) dynamics are disturbed after stroke. Our lab has previously shown that intracranial pressure rises dramatically 24 h after experimental stroke and that this reduces blood flow to ischaemic tissue. CSF outflow resistance is increased at this time point. We hypothesised that reduced transit of CSF through brain parenchyma and reduced outflow of CSF via the cribriform plate at 24 h after stroke may contribute to the previously identified post-stroke intracranial pressure elevation.

METHODS

Using a photothrombotic permanent occlusion model of stroke in C57BL/6 adult male mice, we examined the movement of an intracisternally infused 0.5% Texas Red dextran throughout the brain and measured tracer efflux into the nasal mucosa via the cribriform plate at 24 h or two weeks after stroke. Brain tissue and nasal mucosa were collected ex vivo and imaged using fluorescent microscopy to determine the change in CSF tracer intensity in these tissues.

RESULTS

At 24 h after stroke, we found that CSF tracer load was significantly reduced in brain tissue from stroke animals in both the ipsilateral and contralateral hemispheres when compared to sham. CSF tracer load was also reduced in the lateral region of the ipsilateral hemisphere when compared to the contralateral hemisphere in stroke brains. In addition, we identified an 81% reduction in CSF tracer load in the nasal mucosa in stroke animals compared to sham. These alterations to the movement of CSF-borne tracer were not present at two weeks after stroke.

CONCLUSIONS

Our data indicates that influx of CSF into the brain tissue and efflux via the cribriform plate are reduced 24 h after stroke. This may contribute to reported increases in intracranial pressure at 24 h after stroke and thus worsen stroke outcomes.

The Hunter-8 scale prehospital triage workflow for identification of large vessel occlusion and brain haemorrhage

ObjectiveThe Hunter-8 prehospital stroke scale predicts large vessel occlusion in hyperacute ischemic stroke patients (LVO) at hospital admission. We wished to test its performance in the hands of paramedics as part of a prehospital triage algorithm. We aimed to determine a) the proportion of patients identified by the Hunter-8 algorithm, receiving reperfusion therapies, b) whether a call to stroke team improved this, and c) performance for LVO detection using an expanded LVO definition.MethodsA prehospital workflow combining pre-morbid functional status, time from symptom onset, and the Hunter-8 scale was implemented from July 2019. A telephone call to the stroke team was prompted for potential treatment candidates. Classic LVO was defined as a proximal middle cerebral artery (MCA-M1), terminal internal carotid artery, or tandem occlusion. Extended LVO added proximal MCA-M2 and basilar occlusions.ResultsFrom July 2019 to April 2021, there were 363 Hunter-8 activations, 320 analysed: 181 (56.6%) had confirmed ischemic strokes, 13 (4.1%) transient ischemic attack, 91 (28.5%) stroke mimics, and 35 (10.9%) intracranial haemorrhage. Fifty-two patients (16.3%) received reperfusion therapies, 35 with Hunter-8 ≥ 8. The stroke doctor changed the final destination for 76 patients (23.7%), and five received reperfusion therapies. The AUCs for classic and extended LVO were 0.73 (95% CI 0.66-0.79) and 0.72 (95% CI 0.65-0.77), respectively.ConclusionThe Hunter-8 workflow resulted in 28.7% of confirmed ischemic stroke patients receiving reperfusion therapies, with no secondary transfers to the comprehensive stroke centre. The role of communication with stroke team needs to be further explored.

Aging alters signaling properties in the mouse spinal dorsal horn

A well-recognized relationship exists between aging and increased susceptibility to chronic pain conditions, underpinning the view that pain signaling pathways differ in aged individuals. Yet despite the higher prevalence of altered pain states among the elderly, the majority of preclinical work studying mechanisms of aberrant sensory processing are conducted in juvenile or young adult animals. This mismatch is especially true for electrophysiological studies where patch clamp recordings from aged tissue are generally viewed as particularly challenging. In this study, we have undertaken an electrophysiological characterization of spinal dorsal horn neurons in young adult (3–4 months) and aged (28–32 months) mice. We show that patch clamp data can be routinely acquired in spinal cord slices prepared from aged animals and that the excitability properties of aged dorsal horn neurons differ from recordings in tissue prepared from young animals. Specifically, aged dorsal horn neurons more readily exhibit repetitive action potential discharge, indicative of a more excitable phenotype. This observation was accompanied by a decrease in the amplitude and charge of spontaneous excitatory synaptic input to dorsal horn neurons and an increase in the contribution of GABAergic signaling to spontaneous inhibitory synaptic input in aged recordings. While the functional significance of these altered circuit properties remains to be determined, future work should seek to assess whether such features may render the aged dorsal horn more susceptible to aberrant injury or disease-induced signaling and contribute to increased pain in the elderly.

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.

Purinergic modulation of glutamate transmission: An expanding role in stress-linked neuropathology

Chronic stress has been extensively linked to disturbances in glutamatergic signalling. Emerging from this field of research is a considerable number of studies identifying the ability of purines at the pre-, post-, and peri-synaptic levels to tune glutamatergic neurotransmission. While the evidence describing purinergic control of glutamate has continued to grow, there has been relatively little attention given to how chronic stress modulates purinergic functions. The available research on this topic has demonstrated that chronic stress can not only disturb purinergic receptors involved in the regulation of glutamate neurotransmission, but also perturb glial-dependent purinergic signalling. This review will provide a detailed examining of the complex literature relating to glutamatergic-purinergic interactions with a focus on both neuronal and glial contributions. Once these detailed interactions have been described and contextualised, we will integrate recent findings from the field of stress research.

An analysis of signal processing algorithm performance for cortical intrinsic optical signal imaging and strategies for algorithm selection

Intrinsic Optical Signal (IOS) imaging has been used extensively to examine activity-related changes within the cerebral cortex. A significant technical challenge with IOS imaging is the presence of large noise, artefact components and periodic interference. Signal processing is therefore important in obtaining quality IOS imaging results. Several signal processing techniques have been deployed, however, the performance of these approaches for IOS imaging has never been directly compared. The current study aims to compare signal processing techniques that can be used when quantifying stimuli-response IOS imaging data. Data were gathered from the somatosensory cortex of mice following piezoelectric stimulation of the hindlimb. The effectiveness of each technique to remove noise and extract the IOS signal was compared for both spatial and temporal responses. Careful analysis of the advantages and disadvantages of each method were carried out to inform the choice of signal processing for IOS imaging. We conclude that spatial Gaussian filtering is the most effective choices for improving the spatial IOS response, whilst temporal low pass and bandpass filtering produce the best results for producing temporal responses when periodic stimuli are an option. Global signal regression and truncated difference also work well and do not require periodic stimuli.

A combined cumulative threshold spectra and digital reconstruction analysis reveal structural alterations of microglia within the prefrontal cortex following low-dose LPS administration

Sickness behaviors have become the focus of great interest in recent years as they represent a clear case of how peripheral disturbances in immune signaling can disrupt quite complex behaviors. In the current study, we were interested in examining whether we could identify any significant morphological disturbances in microglia associated with these sickness-like behaviors in adult male Sprague-Dawley rats. We chose lipopolysaccharide (LPS 100 μg/kg/i.p.), to induce sickness-like behaviors as it is the most well-validated approach to do so in rodents and humans. We were particularly interested in examining changes in microglia within the prefrontal cortex (PFC) as several recent neuroimaging studies have highlighted significant functional changes in this region following peripheral LPS administration. Paraformaldehyde-fixed tissue was collected from animals 24h post LPS administration and labeled immunohistochemically with an antibody directed to bind to Iba-1, a protein known to be involved in the structural remodeling of microglia. To analyze changes, we have made use of two recently described image analysis procedures. The first is known as cumulative threshold spectra (CTS) analysis. The second involves the unsupervised digital reconstruction of microglia. We undertook these complementary analysis of microglial cells in the both the pre- and infralimbic divisions of the PFC. Our results indicated that microglial soma size was significantly enlarged, while cell processes had contracted slightly following LPS administration. To our knowledge this study is to first to definitely demonstrate substantial microglial disturbances within the PFC following LPS delivered at a dose that was sufficient to induce significant sickness-like behavior.

Astrocyte and microglial control of glutamatergic signalling: a primer on understanding the disruptive role of chronic stress

It is now well established that chronic stress can induce significant structural remodelling of astrocytes and microglia. Until recently, however, the full significance of these morphological disturbances has remained unclear. Clues to the significance of astroglial re-organisation following stress are beginning to emerge from a compelling literature describing how astrocytes contribute to glutamatergic neurotransmission. The present review briefly summarises these two fields of research, identifies points of overlap and, in doing so, pin-points future research directions for stress neurobiology. Ultimately, understanding how chronic stress can disrupt the interactions of astrocytes and microglia with neurones has the potential in the future to improve the development of therapeutics designed to treat stress-related illnesses such as depression.

Calorie restriction increases lipopolysaccharide-induced neuropeptide Y immunolabeling and reduces microglial cell area in the arcuate hypothalamic nucleus

Calorie restriction (CR) increases longevity and elicits many health promoting benefits including delaying immunosenescence and reducing the incidence of age-related diseases. Although the mechanisms underlying the health-enhancing effects of CR are not known, a likely contributing factor is alterations in immune system functioning. CR suppresses lipopolysaccharide (LPS)-induced release of pro-inflammatory cytokines, blocks LPS-induced fever, and shifts hypothalamic signaling pathways to an anti-inflammatory bias. Furthermore, we have recently shown that CR attenuates LPS-stimulated microglial activation in the hypothalamic arcuate nucleus (ARC), a brain region containing neurons that synthesize neuropeptide Y (NPY), an orexigenic neuropeptide that is upregulated by a CR diet and has anti-inflammatory properties. To determine if increased NPY expression in the ARC following CR was associated with changes in microglial activation, a set of brain sections from mice that were exposed to 50% CR or ad libitum feeding for 28 days before being injected with LPS were immunostained for NPY. The density of NPY-immunolabeling was assessed across the rostrocaudal extent of the ARC and hypothalamic paraventricular nucleus (PVN). An adjacent set of sections were immunostained for ionized calcium-binding adapter molecule-1 (Iba1) and immunostained microglia in the ARC were digitally reconstructed to investigate the effects of CR on microglial morphology. We demonstrated that exposure to CR increased NPY expression in the ARC, but not the PVN. Digital reconstruction of microglia revealed that LPS increased Iba1 intensity in ad libitum fed mice but had no effect on Iba1 intensity in CR mice. CR also decreased the size of ARC microglial cells following LPS. Correlational analyses revealed strong associations between NPY and body temperature, and body temperature and microglia area. Together these results suggest that CR-induced changes in NPY are not directly involved in the suppression of LPS-induced microglial activation, however, NPY may indirectly affect microglial morphology through changes in body temperature.

Microglial activation in the injured and healthy brain: what are we really talking about? Practical and theoretical issues associated with the measurement of changes in microglial morphology

Recently it has become apparent that microglia play a role not only in responding to insults within the central nervous system but also in responding to changes in synaptic activity and potentially modulating synaptic function. This has led to an enormous expansion of interest in how microglia respond to both pathological and nonpathological challenges, with activities that are associated with unique morphological transformations. Examining changes in microglial morphology can provide direct insight into the cells' functional activities, as morphological status is recognized to be tightly coupled with function. Despite these advances in knowledge, many of the image-based morphometric procedures used to investigate changes in microglial morphology have not kept pace. This has created a situation in which morphometric approaches that have been extensively employed in the past can no longer provide accurate information on the complex transformations that microglia can undergo, particularly under non-pathological conditions. This review critically examines the strengths and weaknesses of existing morphometric analysis procedures. This review further examines efforts to improve the utility of existing approaches and discusses new developments, such as digital reconstruction, that yield more accurate and specific information on how microglia remodel themselves. Ultimately, an improved understanding of the strengths and limitations of existing, and emerging, morphometric approaches will greatly facilitate efforts to understand how microglia remodel themselves in response to the full spectrum of challenges that they are known to encounter.

Increased microglial activation in the rat brain following neonatal exposure to a bacterial mimetic

Neonatal lipopolysaccharide (LPS) exposure increases anxiety-like behaviour in adulthood. Our current aim was to examine whether neonatal LPS exposure is associated with changes in microglial activation, and whether these alterations correspond with alterations in behaviour. In adulthood, LPS-treated animals exhibited significantly increased anxiety-like behaviour and hippocampal microglial activation. The efficacy of the LPS challenge was confirmed by increased neonatal plasma corticosterone and tyrosine hydroxylase (TH) phosphorylation in the adrenal medulla. These findings suggest a neuroimmune pathway which may underpin the long-term behavioural and neuroendocrine changes following neonatal infection.

Evidence that microglia mediate the neurobiological effects of chronic psychological stress on the medial prefrontal cortex

Psychological stress contributes to the development of clinical depression. This has prompted many preclinical studies to investigate the neurobiology of this relationship, however, the effects of stress on glia remain unclear. In this study, we wished to determine, first, how exposure to chronic psychological stress affects microglial activity within the prefrontal cortex (PFC) and, second, whether the observed changes were meaningfully related to corresponding changes in local neuronal activity and PFC-regulated behavior. Therefore, we examined markers of microglial activation, antigen presentation, apoptosis, and persistent neuronal activation within the PFC after exposure to repeated restraint stress. We also examined the effect of stress on spatial working memory, a PFC-dependent function. Finally, we tested the ability of a microglial activation inhibitor (minocycline) to alter the impact of chronic stress on all of these endpoints. Stressor exposure produced positively correlated increases in microglial and long-term neuronal activation in the PFC but not antigen presentation or apoptosis. As expected, it also impaired spatial working memory. Importantly, minocycline reduced the impact of stress on neuronal activation and working memory, as well as microglial activation. These results suggest a role for microglia in mediating the effects of stress on PFC neuronal function and PFC-regulated behavior.

Coping with defeat: acute glucocorticoid and forebrain responses to social defeat vary with defeat episode behaviour

Individuals vary in the way in which they cope with stressful situations. It has been suggested that 'active' coping behaviour, characterised by aggression and territorial control, is more effective in moderating the stress associated with social defeat than 'passive' coping behaviour, as characterised by immobility, decreased reactivity, and low aggression. We used the rodent 'resident/intruder' paradigm to determine whether individual differences in coping behaviour modulate the acute adrenocortical response to social defeat. During the 10 min conflict episode, behaviours displayed by the intruder were recorded and subsequently scored. Intruders that engaged in large numbers of fights and/or frequently used physical structures to block the resident's approach (a behaviour referred to as 'guarding'), displayed smaller corticosterone responses to defeat than other intruders. Corticosterone responses to defeat were unrelated to a measure of coping style preferences (defensive burying test) obtained prior to the defeat encounter. We further chose to investigate the neurobiological basis of this observation by comparing the patterns of defeat-induced neuronal activation in the forebrains of intruders that displayed high versus low numbers of defensive behaviours during the defeat episode. The results of this analysis indicated that 'low fight' and 'low guard' intruders, i.e. those that achieved a fight or a guard score below the 20th percentile, had significantly higher numbers of Fos-positive neurons in forebrain regions such as the medial prefrontal cortex and the amygdala than did control animals exposed to an empty resident's cage. In summary, the present data suggest that 'active' coping behaviour is associated with both a smaller adrenocortical response and a lower level of 'neural activation' following social defeat. This outcome differs from that of earlier studies, a difference that we suggest is due to the fact that the present study is the first to assess coping on the basis of behaviour actually displayed during the conflict interaction.

Neonatal endotoxin exposure influences HPA responsivity and impairs tumor immunity in Fischer 344 rats in adulthood

Recent research in rodents has demonstrated that exposure to bacterial endotoxin during the neonatal period alters the development of the hypothalamic-pituitary-adrenal axis resulting in hypersecretion of corticosterone after stress-exposure in adulthood. Given the known interactions between glucocorticoids and the immune system it was hypothesized that such alterations may impact on immune outcomes. Fischer 344 rats were treated with endotoxin (50 microg/kg Salmonella enteritidis, i.p.) or the vehicle on postpartum d 1, 3, 5, and 7. In adulthood, animals were subjected to chronic stress (6 x 10 h/d restraint stress), and the effect on resistance to tumor colonization (experiment 1) and natural killer cell activity (experiment 2) was assessed. Experiment 3 assessed corticosterone responses to acute stress in adulthood after neonatal endotoxin or saline treatment. Neonatal endotoxin exposure resulted in a 2-fold increase in tumor colonization (p < 0.001) and a significant impairment in the activity of natural killer cells (p < 0.01), cells critically involved in the surveillance and eradication of tumor cells. Neonatal endotoxin exposure also resulted in a significant decrease in gain weight that persisted into adulthood (p < 0.05), and potentiation of corticosterone responses to acute stress in adulthood (p < 0.05). We conclude that neonatal endotoxin exposure produces long-term changes in the hypothalamic-pituitary-adrenal axis, and has significant long-term effects on immune function, specifically in terms of resistance to tumor colonization in adulthood.

Laboratory and in-situ reductions of soluble phosphorus in swine waste slurries

Laboratory and field experiments were conducted using magnesium chloride (MgCl2) to force the precipitation of struvite (MgNH4PO4 x 6H2O) and reduce the concentration of soluble phosphorus (SP) in swine waste. In laboratory experiments, reductions of SP of 76% (572 to 135 mg P l(-1)) were observed in raw swine manure after addition of magnesium chloride (MgCl2) at a rate calculated to provide a 1.6:1 molar ratio of magnesium (Mg) to total phosphorus. Adjusting the pH of the treated manure to pH 9.0 with sodium hydroxide (NaOH) increased SP reduction to 91% (572 to 50 mg P l(-1)). X-ray diffraction of the precipitate recovered from swine waste slurry treated only with MgCl2 confirmed the presence ofstruvite. The molar N:P:Mg ratio of the recovered precipitate was 1:1.95:0.24, suggesting that compounds in addition to struvite were formed. In a field experiment conducted in a swine manure holding pond, a 90% reduction in SP concentration was observed in approximately 140,000 l of swine manure slurry treated before land application with 2,000 l MgCl2 (64% solution) at ambient slurry temperatures ranging from 5 to 10 degrees C.