Alterations of norepinephrine levels in plasma and CSF of patients after traumatic brain injury in relation to disruption of the blood-brain barrier

Long-Term Impact of Diffuse Traumatic Brain Injury on Neuroinflammation and Catecholaminergic Signaling: Potential Relevance for Parkinson's Disease Risk

Traumatic brain injury (TBI) is associated with an increased risk of developing Parkinson's disease (PD), though the exact mechanisms remain unclear. TBI triggers acute neuroinflammation and catecholamine dysfunction post-injury, both implicated in PD pathophysiology. The long-term impact on these pathways following TBI, however, remains uncertain. In this study, male Sprague-Dawley rats underwent sham surgery or Marmarou's impact acceleration model to induce varying TBI severities: single mild TBI (mTBI), repetitive mild TBI (rmTBI), or moderate-severe TBI (msTBI). At 12 months post-injury, astrocyte reactivity (GFAP) and microglial levels (IBA1) were assessed in the striatum (STR), substantia nigra (SN), and prefrontal cortex (PFC) using immunohistochemistry. Key enzymes and receptors involved in catecholaminergic transmission were measured via Western blot within the same regions. Minimal changes in these markers were observed, regardless of initial injury severity. Following mTBI, elevated protein levels of dopamine D1 receptors (DRD1) were noted in the PFC, while msTBI resulted in increased alpha-2A adrenoceptors (ADRA2A) in the STR and decreased dopamine beta-hydroxylase (DβH) in the SN. Neuroinflammatory changes were subtle, with a reduced number of GFAP+ cells in the SN following msTBI. However, considering the potential for neurodegenerative outcomes to manifest decades after injury, longer post-injury intervals may be necessary to observe PD-relevant alterations within these systems.

Label free impedance based acetylcholinesterase enzymatic biosensors for the detection of acetylcholine

Realtime monitoring of neurotransmitters is of great interest for understanding their fundamental role in a wide range of biological processes in the central and peripheral nervous system, as well as their role, in several degenerative brain diseases. The measurement of acetylcholine in the brain is particularly challenging due to the complex environment of the brain and the low concentration and short lifetime of acetylcholine. In this paper, we demonstrated a novel, label-free biosensor for the detection of Ach using a single enzyme, acetylcholinesterase (ACHE), and electrochemical impedance spectroscopy (EIS). Acetylcholinesterase was covalently immobilized onto the surface of gold microelectrodes through an amine-reactive crosslinker dithiobis(succinimidyl propionate) (DSP). Passivation of the gold electrode with SuperBlock eliminated or reduced any non-specific response to other major interfering neurotransmitter molecules such as dopamine (DA), norepinephrine (NE) and epinephrine (EH). The sensors were able to detect acetylcholine over a wide concentration range (5.5-550 μM) in sample volumes as small as 300 μL by applying a 10 mV AC voltage at a frequency of 500 Hz. The sensors showed a linear relationship between Ach concentration and ΔZmod(R2 = 0.99) in PBS. The sensor responded to acetylcholine not only when evaluated in a simple buffer (PBS buffer) but in several more complex environments such as rat brain slurry and rat whole blood. The sensor remained responsive to acetylcholine after being implanted ex vivo in rat brain tissue. These results bode well for the future application of these novel sensors for real time in vivo monitoring of acetylcholine.

The Current State of Traumatic Brain Injury Biomarker Measurement Methods

Traumatic brain injury (TBI) is associated with high rates of morbidity and mortality partially due to the limited tools available for diagnosis and classification. Measuring panels of protein biomarkers released into the bloodstream after injury has been proposed to diagnose TBI, inform treatment decisions, and monitor the progression of the injury. Being able to measure these protein biomarkers at the point-of-care would enable assessment of TBIs from the point-of-injury to the patient's hospital bedside. In this review, we provide a detailed discussion of devices reported in the academic literature and available on the market that have been designed to measure TBI protein biomarkers in various biofluids and contexts. We also assess the challenges associated with TBI biomarker measurement devices and suggest future research directions to encourage translation of these devices to clinical use.

Endothelial glycocalyx in traumatic brain injury associated coagulopathy: potential mechanisms and impact

Traumatic brain injury (TBI) remains one of the leading causes of death and disability worldwide; more than 10 million people are hospitalized for TBI every year around the globe. While the primary injury remains unavoidable and not accessible to treatment, the secondary injury which includes oxidative stress, inflammation, excitotoxicity, but also complicating coagulation abnormalities, is potentially avoidable and profoundly affects the therapeutic process and prognosis of TBI patients. The endothelial glycocalyx, the first line of defense against endothelial injury, plays a vital role in maintaining the delicate balance between blood coagulation and anticoagulation. However, this component is highly vulnerable to damage and also difficult to examine. Recent advances in analytical techniques have enabled biochemical, visual, and computational investigation of this vascular component. In this review, we summarize the current knowledge on (i) structure and function of the endothelial glycocalyx, (ii) its potential role in the development of TBI associated coagulopathy, and (iii) the options available at present for detecting and protecting the endothelial glycocalyx.

β-Blockers for traumatic brain injury: A systematic review and meta-analysis

BACKGROUND

Paroxysmal sympathetic hyperactivity (PSH) and catecholamine surge, which are associated with poor outcome, may be triggered by traumatic brain injury (TBI).β Adrenergic receptor blockers (β-blockers), as potential therapeutic agents to prevent paroxysmal sympathetic hyperactivity and catecholamine surge, have been shown to improve survival after TBI. The principal aim of this study was to investigate the effect of β-blockers on outcomes in patients with TBI.

METHODS

For this systematic review and meta-analysis, we searched MEDLINE, EMBASE, and Cochrane Library databases from inception to September 25, 2020, for randomized controlled trials, nonrandomized controlled trials, and observational studies reporting the effect of β-blockers on the following outcomes after TBI: mortality, functional measures, and cardiopulmonary adverse effects of β-blockers (e.g., hypotension, bradycardia, and bronchospasm). With use of random-effects model, we calculated pooled estimates, confidence intervals (CIs), and odds ratios (ORs) of all outcomes.

RESULTS

Fifteen studies with 12,721 patients were included. Exposure to β-blockers after TBI was associated with a significant reduction in adjusted in-hospital mortality (OR, 0.39; 95% CI, 0.30-0.51; I2 = 66.3%; p < 0.001). β-Blockers significantly improved the long-term (≥6 months) functional outcome (OR, 1.75; 95% CI, 1.09-2.80; I2 = 0%; p = 0.02). Statistically significant difference was not seen for cardiopulmonary adverse events (OR, 0.91; 95% CI, 0.55-1.50; I2 = 25.9%; p = 0.702).

CONCLUSION

This meta-analysis demonstrated that administration of β-blockers after TBI was safe and effective. Administration of β-blockers may therefore be suggested in the TBI care. However, more high-quality trials are needed to investigate the use of β-blockers in the management of TBI.

LEVEL OF EVIDENCE

Systematic review and meta-analysis, level III.

When Two Wrongs Make a Right: The Effect of Acute and Chronic Binge Drinking on Traumatic Brain Injury Outcomes in Young Adult Female Rats

Alcohol is the most commonly abused drug by young adults across North America. Although alcohol consumption itself incurs a risk of neurological damage, it is also a significant risk factor for traumatic brain injury (TBI). TBI among young adults is described as a modern healthcare epidemic. The drastic changes occurring within their neurological networks put young adults at greater risk for developing long-term post-traumatic deficits. Contradictory findings have been indicated regarding the effects of alcohol consumption on TBI outcomes in adults, with some studies demonstrating detrimental effects, whereas others suggest neuroprotective abilities. However, little is known about the effects of alcohol consumption on TBI outcomes during the sensitive stage of early adulthood. Young adult female Sprague-Dawley rats were randomly assigned to one of six experimental conditions: Pre-injury alcohol+TBI; Pre-injury alcohol+Sham; Pre- and Post-injury alcohol+TBI; Pre- and Post-injury alcohol+Sham; No alcohol+TBI; No alcohol+Sham. Alcohol consumption groups received an amount of 10% v/v ethanol solution based on the animals' weight. Following the injury, the rats were subjected to a behavioral test battery to assess post-concussive symptomology. Overall, chronic binge drinking significantly improved TBI outcomes related to motor coordination and balance, whereas binge drinking in general significantly decreased anxiety-like behaviors. Additionally, in many cases, chronic binge drinking appears to return the TBI animal's behavioral outcomes to levels comparable to those of the no alcohol sham animals. Thus, the results suggest that alcohol may exhibit neuroprotective abilities in the context of early adulthood TBI.

Beta-adrenergic blockade for attenuation of catecholamine surge after traumatic brain injury: a randomized pilot trial

Background

Beta-blockers have been proven in multiple studies to be beneficial in patients with traumatic brain injury. Few prospective studies have verified this and no randomized controlled trials. Additionally, most studies do not titrate the dose of beta-blockers to therapeutic effect. We hypothesize that propranolol titrated to effect will confer a survival benefit in patients with traumatic brain injury.

Methods

A randomized controlled pilot trial was performed during a 24-month period. Patients with traumatic brain injury were randomized to propranolol or control group for a 14-day study period. Variables collected included demographics, injury severity, physiologic parameters, urinary catecholamines, and outcomes. Patients receiving propranolol were compared with the control group.

Results

Over the study period, 525 patients were screened, 26 were randomized, and 25 were analyzed. Overall, the mean age was 51.3 years and the majority were male with blunt mechanism. The mean Injury Severity Score was 21.8 and median head Abbreviated Injury Scale score was 4. Overall mortality was 20.0%. Mean arterial pressure was higher in the treatment arm as compared with control (p=0.021), but no other differences were found between the groups in demographics, severity of injury, severity of illness, physiologic parameters, or mortality (7.7% vs. 33%; p=0.109). No difference was detected over time in any variables with respect to treatment, urinary catecholamines, or physiologic parameters. Glasgow Coma Scale (GCS), Sequential Organ Failure Assessment, and Acute Physiology and Chronic Health Evaluation scores all improved over time. GCS at study end was significantly higher in the treatment arm (11.7 vs. 8.9; p=0.044). Finally, no difference was detected with survival analysis over time between groups.

Conclusions

Despite not being powered to show statistical differences between groups, GCS at study end was significantly improved in the treatment arm and mortality was improved although not at a traditional level of significance. The study protocol was safe and feasible to apply to an appropriately powered larger multicenter study.

Level of evidence

Level 2—therapeutic.

Identification of novel acetylcholinesterase inhibitors designed by pharmacophore-based virtual screening, molecular docking and bioassay

In this study, pharmacophore based 3D QSAR models for human acetylcholinesterase (AChE) inhibitors were generated, with good significance, statistical values (r2training = 0.73) and predictability (q2training = 0.67). It was further validated by three methods (Fischer's test, decoy set and Güner-Henry scoring method) to show that the models can be used to predict the biological activities of compounds without costly and time-consuming synthesis. The criteria for virtual screening were also validated by testing the selective AChE inhibitors. Virtual screening experiments and subsequent in vitro evaluation of promising hits revealed a novel and selective AChE inhibitor. Thus, the findings reported herein may provide a new strategy for the discovery of selective AChE inhibitors. The IC50 value of compounds 5c and 6a presented selective inhibition of AChE without inhibiting butyrylcholinesterase (BChE) at uM level. Molecular docking studies were performed to explain the potent AChE inhibition of the target compounds studies to explain high affinity.

The Neurological Wake-up Test-A Role in Neurocritical Care Monitoring of Traumatic Brain Injury Patients?

The most fundamental clinical monitoring tool in traumatic brain injury (TBI) patients is the repeated clinical examination. In the severe TBI patient treated by continuous sedation in a neurocritical care (NCC) unit, sedation interruption is required to enable a clinical evaluation (named the neurological wake-up test; NWT) assessing the level of consciousness, pupillary diameter and reactivity to light, and presence of focal neurological deficits. There is a basic conflict regarding the NWT in the NCC setting; can the clinical information obtained by the NWT justify the risk of inducing a stress response in a severe TBI patient? Furthermore, in the presence of advanced multimodal monitoring and neuroimaging, is the NWT necessary to identify important clinical alterations? In studies of severe TBI patients, the NWT was consistently shown to induce a stress reaction including brief increases in intracranial pressure (ICP) and changes in cerebral perfusion pressure (CPP). However, it has not been established whether these short-lived ICP and CPP changes are detrimental to the injured brain. Daily interruption of sedation is associated with a reduced ventilator time, shorter hospital stay and reduced mortality in many studies of general intensive care unit patients, although such clinical benefits have not been firmly established in TBI. To date, there is no consensus on the use of the NWT among NCC units and systematic studies are scarce. Thus, additional studies evaluating the role of the NWT in clinical decision-making are needed. Multimodal NCC monitoring may be an adjunct in assessing in which TBI patients the NWT can be safely performed. At present, the NWT remains the golden standard for clinical monitoring and detection of neurological changes in NCC and could be considered in TBI patients with stable baseline ICP and CPP readings. The focus of the present review is an overview of the existing literature on the role of the NWT as a clinical monitoring tool for severe TBI patients.

An Analysis of Beta-Blocker Administration Pre-and Post-Traumatic Brain Injury with Subanalyses for Head Injury Severity and Myocardial Injury

A growing body of literature indicates that beta-blocker administration after traumatic brain injury (TBI) is cerebroprotective, limiting secondary injury; however, the effects of preinjury beta blocker status remain poorly understood. We sought to characterize the effects of pre- and post-injury beta-blocker administration on mortality with subanalyses accounting for head injury severity and myocardial injury. In a Level II trauma center, all admissions of patients ≥18 years with a head Abbreviated Injury Scale Score ≥2, Glasgow Coma Scale ≤13 from May 2011 to May 2013 were queried. Demographic, injury-specific, and outcome variables were analyzed using univariate analyses. Subsequent multivariate analyses were conducted to determine adjusted odds of mortality for beta-blocker usage controlling for age, Injury Severity Score, head Abbreviated Injury Scale, arrival Glasgow Coma Scale, ventilator use, and intensive care unit stay. A total of 214 trauma admissions met inclusion criteria: 112 patients had neither pre- nor postinjury beta-blocker usage, 46 patients had preinjury beta-blocker usage, and 94 patients had postinjury beta-blocker usage. Both unadjusted and adjusted odds ratios of preinjury beta-blocker were insignificant with respect to mortality. However, postinjury in-hospital administration of beta blockers was found to significantly in the decrease of mortality in both univariate ( P = 0.002) and multivariate analyses ( P = 0.001). Our data indicate that beta-blocker administration post-TBI in hospital reduces odds of mortality; however, preinjury beta-blocker usage does not. Additionally, myocardial injury is a useful indicator for beta-blocker administration post-TBI. Further research into which beta blockers confer the best benefits as well as the optimal period of beta-blocker administration post-TBI is recommended.

Catecholaminergic based therapies for functional recovery after TBI

Among the many pathophysiologic consequences of traumatic brain injury are changes in catecholamines, including dopamine, epinephrine, and norepinephrine. In the context of TBI, dopamine is the one most extensively studied, though some research exploring epinephrine and norepinephrine have also been published. The purpose of this review is to summarize the evidence surrounding use of drugs that target the catecholaminergic system on pathophysiological and functional outcomes of TBI using published evidence from pre-clinical and clinical brain injury studies. Evidence of the effects of specific drugs that target catecholamines as agonists or antagonists will be discussed. Taken together, available evidence suggests that therapies targeting the catecholaminergic system may attenuate functional deficits after TBI. Notably, it is fairly common for TBI patients to be treated with catecholamine agonists for either physiological symptoms of TBI (e.g. altered cerebral perfusion pressures) or a co-occuring condition (e.g. shock), or cognitive symptoms (e.g. attentional and arousal deficits). Previous clinical trials are limited by methodological limitations, failure to replicate findings, challenges translating therapies to clinical practice, the complexity or lack of specificity of catecholamine receptors, as well as potentially counfounding effects of personal and genetic factors. Overall, there is a need for additional research evidence, along with a need for systematic dissemination of important study details and results as outlined in the common data elements published by the National Institute of Neurological Diseases and Stroke. Ultimately, a better understanding of catecholamines in the context of TBI may lead to therapeutic advancements. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Ethanol and isolated traumatic brain injury

The aim of this systematic review was to determine whether ethanol is neuroprotective or associated with adverse effects in the context of traumatic brain injury (TBI). Approximately 30-60% of TBI patients are intoxicated with ethanol at the time of injury. We performed a systematic review of the literature using a combination of keywords for ethanol and TBI. Manuscripts were included if the population studied was human subjects with isolated moderate to severe TBI, acute ethanol intoxication was studied as an exposure variable and mortality reported as an outcome. The included studies were assessed for heterogeneity. A meta-analysis was performed and the pooled odds ratio (OR) for the association between ethanol and in-hospital mortality reported. There were seven studies eligible for analysis. A statistically significant association favouring reduced mortality with ethanol intoxication was found (OR 0.78; 95% confidence interval 0.73-0.83). Heterogeneity among selected studies was not statistically significant (p=0.25). Following isolated moderate-severe TBI, ethanol intoxication was associated with reduced in-hospital mortality. The retrospective nature of the studies, varying definitions of brain injury, degree of intoxication and presence of potential confounders limits our confidence in this conclusion. Further research is recommended to explore the potential use of ethanol as a therapeutic strategy following TBI.

Association between sympathetic response, neurogenic cardiomyopathy, and venous thromboembolization in patients with primary subarachnoid hemorrhage

INTRODUCTION

Sympathetic activation promotes hemostasis, and subarachnoid hemorrhage (SAH) is associated with pronounced sympathetic activation. This investigation will assess whether catecholaminergic activity relates to venous thrombotic events in patients with acute SAH.

METHODS

Observational study of consecutive SAH grade 3-5 patients requiring ventriculostomy insertion who did not undergo open surgical treatment of cerebral aneurysm. Cerebrospinal fluid (CSF) samples were obtained within 48 h of hemorrhage for assay of catecholamines, which were related to occurrence of deep venous thrombosis (DVT) and pulmonary embolization (PE).

RESULTS

Of the 92 subjects, mean age was 57 years, 76% were female, and 57% Caucasian; 11% experienced lower extremity (LE) DVT, 12% developed upper extremity (UE) or LE DVT, and 23% developed any DVT/PE. Mean time to occurrence of UE/LE DVT was 7.8 days (+/-5.9 days), and mean time to development of PE was 8.8 days (+/-5.4 days). In hazards analysis models, independent predictors of LE DVT included neurogenic cardiomyopathy (NC) [HR 4.97 (95%CI 1.32-18.7)], norepinephrine/3,4-dihydroxyphenylglycol ratio (NE/DHPG) [3.81 (2.04-7.14)], NE [5.91 (2.14-16.3)], and dopamine (DA) [2.27 (1.38-3.72)]. Predictors of UE/LE DVT included NC [5.78 (1.70-19.7)], cerebral infarction [4.01 (1.18-13.7)], NE [3.58 (1.40-9.19)], NE/DHPG [3.38 (1.80-6.33)] and DA [2.01 (1.20-3.35)]. Predictors of DVT/PE included Hunt-Hess grade (H/H) [3.02 (1.19-7.66)], NE [2.56 (1.23-5.37)] and 3,4-dihydroxyphenylalanine (DOPA) [3.49 (1.01-12.0)].

CONCLUSIONS

In severe SAH, central sympathetic activity and clinical manifestations of (nor)adrenergic activity relate to the development of venous thromboemboli. Catecholamine activation may promote hemostasis, or may represent a biomarker for venous thromboses.

Overpressure blast-wave induced brain injury elevates oxidative stress in the hypothalamus and catecholamine biosynthesis in the rat adrenal medulla

Explosive overpressure brain injury (OBI) impacts the lives of both military and civilian population. We hypothesize that a single exposure to OBI results in increased hypothalamic expression of oxidative stress and activation of the sympatho-adrenal medullary axis. Since a key component of blast-induced organ injury is the primary overpressure wave, we assessed selective biochemical markers of autonomic function and oxidative stress in male Sprague Dawley rats subjected to head-directed overpressure insult. Rats were subjected to single head-directed OBI with a 358kPa peak overpressure at the target. Control rats were exposed to just noise signal being placed at ~2m distance from the shock tube nozzle. Sympathetic nervous system activation of the adrenal medullae (AM) was evaluated at 6h following blast injury by assessing the expression of catecholamine biosynthesizing enzymes, tyrosine hydroxylase (TH), dopamine-β hydroxylase (DβH), neuropeptide Y (NPY) along with plasma norepinephrine (NE). TH, DβH and NPY expression increased 20%, 25%, and 91% respectively, following OBI (P<0.05). Plasma NE was also significantly elevated by 23% (P<0.05) following OBI. OBI significantly elevated TH (49%, P<0.05) in the nucleus tractus solitarius (NTS) of the brain stem while AT1 receptor expression and NADPH oxidase activity, a marker of oxidative stress, was elevated in the hypothalamus following OBI. Collectively, the increased levels of TH, DβH and NPY expression in the rat AM, elevated TH in NTS along with increased plasma NE suggest that single OBI exposure results in increased sympathoexcitation. The mechanism may involve the elevated AT1 receptor expression and NADPH oxidase levels in the hypothalamus. Taken together, such effects may be important factors contributing to pathology of brain injury and autonomic dysfunction associated with the clinical profile of patients following OBI.

Beta blockers exposure and traumatic brain injury: a literature review

Traumatic brain injury (TBI) continues to carry a significant public health burden and is anticipated to worsen worldwide over the next century. Recently the authors of several articles have suggested that exposure to beta blockers may improve mortality rates following TBI. The exact mechanism through which beta blockers mediate this effect is unknown. In this paper, the authors review the literature regarding the safety of beta blockers in patients with TBI. The findings of several recent retrospective cohort studies are examined and implications for future investigation are discussed. Future questions to be addressed include: the specific indications for the use of beta blockers in patients with TBI, the optimal type and dose of beta blocker given, the end point of beta blocker therapy, and the safety of beta blockers in cases of severe TBIs.

Low perfusion pressure during CPB may induce cerebral metabolic and ultrastructural changes

BACKGROUND

Recently we reported on cerebral metabolic changes suggesting ischemia in piglets during nitroprusside-induced low-pressure CPB. We here investigated whether a mean arterial pressure (MAP) of 40-45 mmHg could provoke similar changes by a NO-independent intervention.

METHODS

Piglets underwent 60 minutes normothermic followed by 90 minutes hypothermic CPB. The LP-group (n=8) had MAP of 40-45 mmHg by phentolamine while the HP-group (n=8) had MAP of 60-80 mmHg by norepinephrine. Cerebral glucose, lactate, pyruvate and glycerol were determined. In the last two animals of each group, cerebral tissue was examined by electron microscopy.

RESULTS

Cerebral lactate was higher in the LP-group than the HP-group during normothermic CPB. Compared with baseline, cerebral glucose of the LP-group decreased whereas lactate/pyruvate-ratio, lactate and glycerol-concentrations increased during normothermic CPB. In the HP-group these parameters remained unchanged. Electron microscopy showed 31.2% and 8.3% altered mitochondria in the cortical micrographs taken from the LP- and the HP-group, respectively (p<0.001).

CONCLUSION

MAP below 45 mmHg during CPB was associated with cerebral biochemical and morphological changes consistent with anaerobic metabolism and subcellular injury.

Nicotine and cotinine modulate cerebral microvascular permeability and protein expression of ZO-1 through nicotinic acetylcholine receptors expressed on brain endothelial cells

The blood-brain barrier (BBB) adapts to a variety of pathological processes. Little is known about the effects of nicotine exposure on BBB function and the ability to adapt to stroke conditions. We have demonstrated, using a well-characterized in vitro BBB model, bovine brain microvessel endothelial cells (BBMEC) model, that nicotine and its major metabolite, cotinine, modulate BBB integrity by opening the paracellular route of solute entry into the brain. Additionally, nicotine and cotinine together increase the permeability change observed after 6 h of hypoxia/aglycemia, an in vitro model of stroke. This has important implications for how the BBB initially adapts to stroke in an environment that is previously exposed to nicotine. Nicotine and cotinine exposure also resulted in reduced ZO-1 immunoreactivity (tight junctional protein) that occurred in a time-dependent manner. Interestingly, attenuation of bovine brain microvessel endothelial cell (BBMEC) ZO-1 protein expression was reversed using 10 nM BGT, an alpha7 nicotinic acetycholine receptor (nAChR) antagonist, suggesting that the effects of nicotine on BBMEC protein expression of ZO-1 protein are mediated by nAChR expressed on brain endothelial cells. In addition to alpha7, we found that BBMEC also contain positive immunoreactivity for the alpha3, alpha5, beta2, beta3 nAChR subunit. Both alpha7 and beta2 nAChR subunit protein levels decreased with prior nicotine and cotinine exposure. These data provide evidence that nicotine and cotinine alter BBB permeability and tight junctional protein expression of ZO-1, thereby altering the BBB response to stroke conditions. These changes in brain endothelial cell paracellular permeability are believed to be associated with nicotine binding to nAChRs present at the BBB.