Outcomes of patients with pre-existing disability managed by mobile stroke units: A sub-analysis of the BEST-MSU study

BACKGROUND

Few data exist on acute stroke treatment in patients with pre-existing disability (PD) since they are usually excluded from clinical trials. A recent trial of mobile stroke units (MSUs) demonstrated faster treatment and improved outcomes, and included PD patients.

AIM

To determine outcomes with tissue plasminogen activator (tPA), and benefit of MSU versus management by emergency medical services (EMS), for PD patients.

METHODS

Primary outcomes were utility-weighted modified Rankin Scale (uw-mRS). Linear and logistic regression models compared outcomes in patients with versus without PD, and PD patients treated by MSU versus standard management by EMS. Time metrics, safety, quality of life, and health-care utilization were compared.

RESULTS

Of the 1047 tPA-eligible ischemic stroke patients, 254 were with PD (baseline mRS 2-5) and 793 were without PD (baseline mRS 0-1). Although PD patients had worse 90-day uw-mRS, higher mortality, more health-care utilization, and worse quality of life than non-disabled patients, 53% returned to at least their baseline mRS, those treated faster had better outcome, and there was no increased bleeding risk. Comparing PD patients treated by MSU versus EMS, 90-day uw-mRS was 0.42 versus 0.36 (p = 0.07) and 57% versus 46% returned to at least their baseline mRS. There was no interaction between disability status and MSU versus EMS group assignment (p = 0.67) for 90-day uw-mRS.

CONCLUSION

PD did not prevent the benefit of faster treatment with tPA in the BEST-MSU study. Our data support inclusion of PD patients in the MSU management paradigm.

Global Impact of the COVID-19 Pandemic on Stroke Volumes and Cerebrovascular Events: A 1-Year Follow-up

BACKGROUND AND OBJECTIVES

Declines in stroke admission, IV thrombolysis (IVT), and mechanical thrombectomy volumes were reported during the first wave of the COVID-19 pandemic. There is a paucity of data on the longer-term effect of the pandemic on stroke volumes over the course of a year and through the second wave of the pandemic. We sought to measure the effect of the COVID-19 pandemic on the volumes of stroke admissions, intracranial hemorrhage (ICH), IVT, and mechanical thrombectomy over a 1-year period at the onset of the pandemic (March 1, 2020, to February 28, 2021) compared with the immediately preceding year (March 1, 2019, to February 29, 2020).

METHODS

We conducted a longitudinal retrospective study across 6 continents, 56 countries, and 275 stroke centers. We collected volume data for COVID-19 admissions and 4 stroke metrics: ischemic stroke admissions, ICH admissions, IVT treatments, and mechanical thrombectomy procedures. Diagnoses were identified by their ICD-10 codes or classifications in stroke databases.

RESULTS

There were 148,895 stroke admissions in the 1 year immediately before compared with 138,453 admissions during the 1-year pandemic, representing a 7% decline (95% CI [95% CI 7.1-6.9]; p < 0.0001). ICH volumes declined from 29,585 to 28,156 (4.8% [5.1-4.6]; p < 0.0001) and IVT volume from 24,584 to 23,077 (6.1% [6.4-5.8]; p < 0.0001). Larger declines were observed at high-volume compared with low-volume centers (all p < 0.0001). There was no significant change in mechanical thrombectomy volumes (0.7% [0.6-0.9]; p = 0.49). Stroke was diagnosed in 1.3% [1.31-1.38] of 406,792 COVID-19 hospitalizations. SARS-CoV-2 infection was present in 2.9% ([2.82-2.97], 5,656/195,539) of all stroke hospitalizations.

DISCUSSION

There was a global decline and shift to lower-volume centers of stroke admission volumes, ICH volumes, and IVT volumes during the 1st year of the COVID-19 pandemic compared with the prior year. Mechanical thrombectomy volumes were preserved. These results suggest preservation in the stroke care of higher severity of disease through the first pandemic year.

TRIAL REGISTRATION INFORMATION

This study is registered under NCT04934020.

Hemorrhage Enlargement Is More Frequent in the First 2 Hours: A Prehospital Mobile Stroke Unit Study

Background:

Hematoma enlargement (HE) after intracerebral hemorrhage (ICH) is a therapeutic target for improving outcomes. Hemostatic therapies to prevent HE may be more effective the earlier they are attempted. An understanding of HE in first 1 to 2 hours specifically in the prehospital setting would help guide future treatment interventions in this time frame and setting.

Methods:

Patients with spontaneous ICH within 4 hours of symptom onset were prospectively evaluated between May 2014 and April 2020 as a prespecified substudy within a multicenter trial of prehospital mobile stroke unit versus standard management. Baseline computed tomography scans obtained <1, 1 to 2, and 2 to 4 hours postsymptom onset on the mobile stroke unit in the prehospital setting were compared with computed tomography scans repeated 1 hour later and at 24 hours in the hospital. HE was defined as >6 mL if baseline ICH volume was < 20 mL and 33% increase if baseline volume >20 mL. The association between time from symptom onset to baseline computed tomography (hours) and HE was investigated using Wilcoxon rank-sum test when time was treated as a continuous variable and using Fisher exact test when time was categorized. Kruskal-Wallis and Wilcoxon rank-sum tests evaluated differences in baseline volumes and HE. Univariable and multivariable logistic regression analyses were conducted to identify factors associated with HE and variable selection was performed using cross-validated L1-regularized (Lasso regression). This study adhered to STROBE guidelines (Strengthening the Reporting of Observational Studies in Epidemiology) for cohort studies.

Results:

One hundred thirty-nine patients were included. There was no difference between baseline ICH volumes obtained <1 hour (n=43) versus 1 to 2 hour (n=51) versus >2 hours (n=45) from symptom onset (median [interquartile range], 13 mL [6–24] versus 14 mL [6–30] versus 12 mL [4–19]; P =0.65). However, within the same 3 time epochs, initial hematoma growth (volume/time from onset) was greater with earlier baseline scanning (median [interquartile range], 17 mL/hour [9–35] versus 9 mL/hour [5–23]) versus 4 mL/hour [2–7]; P <0.001). Forty-nine patients had repeat scans 1 hour after baseline imaging (median, 2.3 hours [interquartile range. 1.9–3.1] after symptom onset). Eight patients (16%) had HE during that 1-hour interval; all of these occurred in patients with baseline imaging within 2 hours of onset (5/18=28% with baseline imaging within 1 hour, 3/18=17% within 1–2 hour, 0/13=0% >2 hours; P =0.02). HE did not occur between the scans repeated at 1 hour and 24 hours. No association between baseline variables and HE was detected in multivariable analyses.

Conclusions:

HE in the next hour occurs in 28% of ICH patients with baseline imaging within the first hour after symptom onset, and in 17% of those with baseline imaging between 1 and 2 hours. These patients would be a target for ultraearly hemostatic intervention.

Global impact of COVID-19 on stroke care

Background

The COVID-19 pandemic led to profound changes in the organization of health care systems worldwide.

Aims

We sought to measure the global impact of the COVID-19 pandemic on the volumes for mechanical thrombectomy, stroke, and intracranial hemorrhage hospitalizations over a three-month period at the height of the pandemic (1 March–31 May 2020) compared with two control three-month periods (immediately preceding and one year prior).

Methods

Retrospective, observational, international study, across 6 continents, 40 countries, and 187 comprehensive stroke centers. The diagnoses were identified by their ICD-10 codes and/or classifications in stroke databases at participating centers.

Results

The hospitalization volumes for any stroke, intracranial hemorrhage, and mechanical thrombectomy were 26,699, 4002, and 5191 in the three months immediately before versus 21,576, 3540, and 4533 during the first three pandemic months, representing declines of 19.2% (95%CI, −19.7 to −18.7), 11.5% (95%CI, −12.6 to −10.6), and 12.7% (95%CI, −13.6 to −11.8), respectively. The decreases were noted across centers with high, mid, and low COVID-19 hospitalization burden, and also across high, mid, and low volume stroke/mechanical thrombectomy centers. High-volume COVID-19 centers (−20.5%) had greater declines in mechanical thrombectomy volumes than mid- (−10.1%) and low-volume (−8.7%) centers (p < 0.0001). There was a 1.5% stroke rate across 54,366 COVID-19 hospitalizations. SARS-CoV-2 infection was noted in 3.9% (784/20,250) of all stroke admissions.

Conclusion

The COVID-19 pandemic was associated with a global decline in the volume of overall stroke hospitalizations, mechanical thrombectomy procedures, and intracranial hemorrhage admission volumes. Despite geographic variations, these volume reductions were observed regardless of COVID-19 hospitalization burden and pre-pandemic stroke/mechanical thrombectomy volumes.

Integrated Stroke System Model Expands Availability of Endovascular Therapy While Maintaining Quality Outcomes

BACKGROUND AND PURPOSE

The optimal endovascular stroke therapy (EVT) care delivery structure is unknown. Here, we present our experience in creating an integrated stroke system (ISS) to expand EVT availability throughout our region while maintaining hospital and physician quality standards.

METHODS

We identified all consecutive patients with large vessel occlusion acute ischemic stroke treated with EVT from January 2014 to February 2019 in our health care system. In October 2017, we implemented the ISS, in which 3 additional hospitals (4 total) became EVT-performing hospitals (EPHs) and physicians were rotated between all centers. The cohort was divided by time into pre-ISS and post-ISS, and the primary outcome was time from stroke onset to EPH arrival. Secondary outcomes included hospital and procedural quality metrics. We performed an external validation using data from the Southeast Texas Regional Advisory Council.

RESULTS

Among 513 patients with large vessel occlusion acute ischemic stroke treated with EVT, 58% were treated pre-ISS and 43% post-ISS. Over the study period, EVT procedural volume increased overall but remained relatively low at the 3 new EPHs (<70 EVT/y). After ISS, the proportion of patients who underwent interhospital transfer decreased (46% versus 37%; P<0.05). In adjusted quantile regression, ISS implementation resulted in a reduction of time from stroke onset to EPH arrival by 40 minutes (P<0.01) and onset to groin puncture by 29 minutes (P<0.05). Rates of postprocedural hemorrhage, modified Thrombolysis in Cerebral Infarction (TICI) 2b/3, and 90-day modified Rankin Scale were comparable at the higher and lower volume EPHs. The improvement in onset-to-arrival time was not reflective of overall improvement in secular trends in regional prehospital care.

CONCLUSIONS

In our system, increasing EVT availability decreased time from stroke onset to EPH arrival. The ISS provides a framework to maintain quality in lower volume hospitals.

Abstract TP79: Do Early Ischemic Changes Occur on CT Within the First Hour of Acute Ischemic Stroke

Introduction: Early ischemic changes (EIC) on non-contrast computed tomography (NCCT) can appear within 6 hours of last known normal (LKN), and can be quantified using the Alberta Stroke Program Early CT Score (ASPECTS). However, there is lack of data describing when EIC first appear. We leveraged our Mobile Stroke Unit (MSU) to determine the incidence of EIC on NCCT within 1 hour of LKN.

Methods: Prospectively derived data were analyzed from patients on our MSU who were independently adjudicated as tissue plasminogen activator (tPA) eligible, had NCCT within 1 hour of LKN, and had definite strokes based on subsequent testing. EIC, defined as ASPECTS ≤ 7, was measured and correlated to time from LKN, stroke severity (National Institutes of Health Stroke Scale, NIHSS), and presence of large vessel occlusion (LVO) on neuroimaging. All scans were obtained on an 8 slice Ceretom (Neurologica Corp) and graded by a Vascular Neurology fellow, with random scans compared with a Vascular Neurology attending (κ=0.69).

Results: 80 tPA eligible patients with NCCT within 1 hour of LKN were identified. 57 had definite strokes and/or strokes reversed by tPA. Of these, 54 (95%) had NCCT with sufficient diagnostic quality. Mean ASPECTS was 9.2 (median 10, interquartile range (IQR) 9-10) with a mean of 45.3 minutes (median 46, IQR 39-52) from LKN. Average NIHSS was 14.9. EIC (e.g. ASPECTS 6, 6, 7, 7) was identified in 4 patients (7%). There was no association between ASPECTS and time from LKN to CT (p=0.63), stroke severity (p=0.12) or presence of LVO (p= 0.09); the LVO analysis was limited by the small number of EIC patients (n=4).

Conclusions: Based on our experience, EIC may be present but ASPECTS is not < 6 within the first hour after LKN. Close scrutiny of NCCT for EIC within this timeframe may not be necessary for determining eligibility for tPA or endovascular thrombectomy.

Thyroid hormones and functional outcomes after ischemic stroke

Background

Stroke is the fifth leading cause of death and the primary cause of long-term adult disability in the United States. Increasing evidence suggests that low T3 levels immediately following acute ischemic stroke are associated with greater stroke severity, higher mortality rates, and poorer functional outcomes. Prognosis is also poor in critically ill hospitalized patients who have non-thyroidal illness syndrome (NTIS), where T3 levels are low, but TSH is normal. However, data regarding the association between TSH levels and functional outcomes are contradictory. Thus, this study investigated the role of TSH on stroke outcomes, concomitantly with T3 and T4.

Findings

In this work, blood was collected from patients with radiologically confirmed acute ischemic stroke at 24±6 hours post-symptom onset and serum levels of TSH, free T3, and free T4 were measured. Stroke outcomes were measured at discharge, 3 and 12 months using the modified Rankin scale and modified Barthel Index as markers of disability. Though we found that lower levels of free T3 were associated with worse prognosis at hospital discharge, and at 3 and 12 months post-stroke, none of these outcomes held after multivariate analysis. Thus, it is likely that thyroid hormones are associated with other factors that impact stroke outcomes, such as sex, age and stroke etiology.

Conclusions

This study found that lower levels of free T3 were associated with poorer outcomes at hospital discharge, and at 3 and 12 months post stroke, however, these associations diminished after correction for other known predictors of stroke outcome. Thyroid hormones have a complex relationship with ischemic stroke and stroke recovery, which merits further larger investigations.

Abstract W MP59: Thyroid Hormones And Functional Outcomes After Ischemic Stroke

Background: Hypothyroidism can lead to hypertension, hypercholesterolemia, and cardiac dysfunction, which are risk factors for stroke. Activity of the hypothalamic-pituitary-thyroid axis may contribute to functional stroke outcomes. Low levels of thyroid stimulating hormone (TSH) correlate with an increased risk of ischemic stroke. However, once a stroke occurs, hypothyroidism is associated with more favorable outcomes. It is well known that thyroid hormone levels drop rapidly in critically ill patients (“sick-euthryoid” syndrome), which may be prevented by the exogenous thyroid replacement provided to hypothyroid patients. We directly assessed thyroid function with measurements of TSH, free T3 (fT3) and free T4 (fT4) in patients with ischemic stroke and evaluated acute and long-term outcomes.

Methods: Blood was collected prospectively from patients with radiologically confirmed ischemic stroke (AIS) (n=136) 24 hours after symptom onset. Serum levels of TSH, fT4, and fT3 were quantified by ELISA. Primary outcomes were in-hospital mortality and admission NIH Stroke Scale (NIHSS). Secondary outcomes were admission to discharge change in NIHSS, modified Barthel Index (mBI) and modified Rankin score (mRs) at 3 and 12 months (mo), and mortality at 3 and 12 mo.

Results: AIS patients show a negative correlation in fT3 with age (r=-.332, p<0.01 ). AIS patients with a higher pre-stroke mRS had higher levels of fT3, and fT4 , p=0.01, p=0.03 ). Patients that died or went to hospice had significantly lower levels of fT3 and TSH (1.99pg/ml (1.75-2.48), 0.52 pg/ml (0.30-0.76)).TSH levels were lower in AIS patients with worsened NIHSS (0.72 pg/ml (0.36-1.12)). Higher fT3 levels were significantly associated with better mRS and mBI at 3 and 12 mo ( p=0.01, p=0.01, p=0.03, p=0.02 ), whereas lower levels of TSH were significant for worse mRS at 3mo (0.87pg/ml (0.59-1.48)).

Conclusion: While higher levels of fT3 correlate with stroke risk factors, high fT3 is seen in patients with better functional outcome at 3 and 12mo post-stroke. Ischemic stroke patients with low TSH levels at 24 hrs have higher mortality. Thus, monitoring the hypothalamus-pituitary-thyroid axis during acute stroke may improve long-term stroke outcomes.

β-Blockers associated with no class-specific survival benefit in acute intracerebral hemorrhage

OBJECTIVES

Despite the high mortality, there is currently no specific treatment for intracerebral hemorrhage (ICH). Research investigating optimum degree of blood pressure control in patients presenting with ICH and hypertension is ongoing. However, there is limited understanding of the potential benefits of specific classes of antihypertensive therapy. β-Adrenergic antagonists may provide neuroprotection from inflammation-induced injury by inhibiting sympathetic nervous system mediated immune activation. We examined mortality in ICH patients receiving β-adrenergic antagonists to determine whether this class of antihypertensive therapy was associated with improved survival.

METHODS

A retrospective analysis of a large, prospectively collected database of patients presenting with acute ICH was performed. Patients were grouped by inpatient β-blocker treatment to determine an effect on mortality during the inpatient stay and at 3 months of follow-up. Additional analysis was conducted comparing β-blocker therapy to any other antihypertensive treatment to determine a class-specific association of β-blocker treatment with mortality.

RESULTS

The study population included 426 patients with acute, spontaneous ICH. Inpatient β-blocker use was independently associated with decreased rates of inpatient death and mortality at 3 months of follow-up. However, univariate and multivariable analyses comparing β-blocker use to other antihypertensives failed to show any class-specific reduction in mortality at either time point.

DISCUSSION

Our study demonstrates that the improvement seen in patients treated with β-adrenergic antagonists is not an effect unique to this class. This supports ongoing trials to determine optimum levels of blood pressure control using multiple classes of antihypertensives.

Peripheral leukocyte counts and outcomes after intracerebral hemorrhage

Background

Intracerebral hemorrhage (ICH) is a devastating disease that carries a 30 day mortality of approximately 45%. Only 20% of survivors return to independent function at 6 months. The role of inflammation in the pathophysiology of ICH is increasingly recognized. Several clinical studies have demonstrated an association between inflammatory markers and outcomes after ICH; however the relationship between serum biomarkers and functional outcomes amongst survivors has not been previously evaluated. Activation of the inflammatory response as measured by change in peripheral leukocyte count was examined and assessment of mortality and functional outcomes after ICH was determined.

Findings

Patients with spontaneous ICH admitted to a tertiary care center between January 2005 and April 2010 were included. The change in leukocyte count was measured as the difference between the maximum leukocyte count in the first 72 hours and the leukocyte count on admission. Mortality was the primary outcome. Secondary outcomes were mortality at 1 year, discharge disposition and the modified Barthel index (MBI) at 3 months compared to pre-admission MBI. 423 cases were included. The in-hospital mortality was 30.4%. The change in leukocyte count predicted worse discharge disposition (OR = 1.258, p = 0.009). The change in leukocyte count was also significantly correlated with a decline in the MBI at 3 months. These relationships remained even after removal of all patients with evidence of infection.

Conclusions

Greater changes in leukocyte count over the first 72 hours after admission predicted both worse short term and long term functional outcomes after ICH.

RasGRP3, a Ras activator, contributes to signaling and the tumorigenic phenotype in human melanoma

RasGRP3, an activator for H-Ras, R-Ras and Rap1/2, has emerged as an important mediator of signaling downstream from receptor coupled phosphoinositide turnover in B and T cells. Here, we report that RasGRP3 showed a high level of expression in multiple human melanoma cell lines as well as in a subset of human melanoma tissue samples. Suppression of endogenous RasGRP3 expression in these melanoma cell lines reduced Ras-GTP formation as well as c-Met expression and Akt phosphorylation downstream from HGF or EGF stimulation. RasGRP3 suppression also inhibited cell proliferation and reduced both colony formation in soft agar and xenograft tumor growth in immunodeficient mice, demonstrating the importance of RasGRP3 for the transformed phenotype of the melanoma cells. Reciprocally, overexpression of RasGRP3 in human primary melanocytes altered cellular morphology, markedly enhanced cell proliferation, and rendered the cells tumorigenic in a mouse xenograft model. Suppression of RasGRP3 expression in these cells inhibited downstream RasGRP3 responses and suppressed cell growth, confirming the functional role of RasGRP3 in the altered behavior of these cells. The identification of the role of RasGRP3 in melanoma highlights its importance, as a Ras activator, in the phosphoinositide signaling pathway in human melanoma and provides a new potential therapeutic target.

The synthetic bryostatin analog Merle 23 dissects distinct mechanisms of bryostatin activity in the LNCaP human prostate cancer cell line

Bryostatin 1 has attracted considerable attention both as a cancer chemotherapeutic agent and for its unique activity. Although it functions, like phorbol esters, as a potent protein kinase C (PKC) activator, it paradoxically antagonizes many phorbol ester responses in cells. Because of its complex structure, little is known of its structure-function relations. Merle 23 is a synthetic derivative, differing from bryostatin 1 at only four positions. However, in U-937 human leukemia cells, Merle 23 behaves like a phorbol ester and not like bryostatin 1. Here, we characterize the behavior of Merle 23 in the human prostate cancer cell line LNCaP. In this system, bryostatin 1 and phorbol ester have contrasting activities, with the phorbol ester but not bryostatin 1 blocking cell proliferation or tumor necrosis factor alpha secretion, among other responses. We show that Merle 23 displays a highly complex pattern of activity in this system. Depending on the specific biological response or mechanistic change, it was bryostatin-like, phorbol ester-like, intermediate in its behavior, or more effective than either. The pattern of response, moreover, varied depending on the conditions. We conclude that the newly emerging bryostatin derivatives such as Merle 23 provide powerful tools to dissect subsets of bryostatin mechanism and response.

Abstract 4500: What distinguishes a PKC activator like phorbol ester from a PKC functional antagonist like bryostatin 1? Bryologues permit mechanistic insight

Bryostatin 1, a promising anticancer agent in clinical trials, is a potent PKC activator in vitro that paradoxically often antagonizes the effects of the typical PKC activator phorbol 12-myristate 13-acetate (PMA) in cellular systems. Understanding the underlying mechanism(s) responsible for this functional PKC antagonism should afford a new generation of drugs for PKC, a validated therapeutic target. We use the synthetic bryostatin look-alike (bryologue) Merle 23 that differs structurally from bryostatin 1 to only a modest degree as a tool to dissect mechanisms responsible for the unique effects of bryostatin 1. We have previously reported that Merle 23 is PMA like, bryostatin-1 like, intermediate or unique in its behavior depending on the system and response examined. In LNCaP prostate cancer cells Merle 23 is bryostatin 1 like in failing to inhibit cell proliferation, to induce apoptosis, or to induce secretion of TNF-alpha, responses induced by PMA. Using siRNAs and PKC inhibitors we show that PKC delta, but not PKC alpha or epsilon, was responsible for induction of apoptosis. Nuclear localized PKC delta was previously shown to be responsible for the apoptotic response, and we found that Merle 23 resembled bryostatin 1 and was unlike PMA in that failed to induce translocation of PKC delta and phospho-PKD1 to the nucleus. In contrast, Merle 23 was PMA-like in inducing nuclear translocation of PKC alpha and PKC epsilon. Bryostatin 1 is unique in down-regulating PKC alpha very efficiently in LNCaP cells and Merle 23 is unique for quick and very efficient down-regulation of PKC delta. If proteosome inhibitors were used to prevent down-regulation of PKC delta, the bryostatin 1-like effects of Merle 23 on proliferation and TNF-alpha secretion were transformed to PMA-like effects: Merle 23 inhibited LNCaP cell proliferation and induced secretion of TNF-alpha when co-applied with lactacystin or MG-132. Similarly, for tyrosine phosphorylation of PKC delta at position 311 and for cFos activation, responses where Merle 23 had effects intermediate between bryostatin 1 and PMA, Merle 23 became more PMA-like when co-applied with proteosome inhibitors. Finally, consistent with stability of PKC signaling elements varying between ligands, we found that phosphorylation of ERK, Mek1 and Mek2, and AKT in response to bryostatin 1, PMA, and Merle 23 was similar at 30 min but returned to the basal level at 150 min for bryostatin 1, but not PMA or Merle 23, as determined using capillary iso-electrofocusing immune-assay. We conclude that differential regulation of PKC isoforms by bryostatin and the bryologues is an important contributor to their differential biological activity relative to PMA.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4500.

Neuroblast protuberances in the subventricular zone of the regenerative MRL/MpJ mouse

The MRL mouse is unique in its capacity for regenerative healing of wounds. This regenerative ability includes complete closure, with little scarring, of wounds to the ear pinna and repair of cardiac muscle, without fibrosis, following cryoinjury. Here, we examine whether neurogenic zones within the MRL brain show enhanced regenerative capacity. The largest neurogenic zone in the adult brain, the subventricular zone (SVZ), lies adjacent to the lateral wall of the lateral ventricle and is responsible for replacement of interneuron populations within the olfactory bulb. Initial gross observation of the anterior forebrain in MRL mice revealed enlarged lateral ventricles; however, little neurodegeneration was detected within the SVZ or surrounding tissues. Instead, increased proliferation within the SVZ was observed, based on incorporation of the thymidine analogue bromodeoxyuridine. Closer examination using electron microscopy revealed that a significant number of SVZ astrocytes interpolated within the ependyma and established contact with the ventricle. In addition, subependymal, protuberant nests of cells, consisting primarily of neuroblasts, were found along the anterior SVZ of MRL mice. Whole mounts of the lateral wall of the lateral ventricle stained for the neuroblast marker doublecortin revealed normal formation of chains of migratory neuroblasts along the entire wall and introduction of enhanced green fluorescent protein-tagged retrovirus into the lateral ventricles confirmed that newly generated neuroblasts were able to track into the olfactory bulb.