Sex-biased effects on hippocampal circuit development by perinatal SERT expression in CA3 pyramidal neurons.

Neurodevelopmental disorders ranging from autism to intellectual disability display sex-biased prevalence and phenotypical presentations. Despite increasing knowledge about temporospatial cortical map development and genetic variants linked to neurodevelopmental disorders, when and how sex-biased neural circuit derailment may arise in diseased brain remain unknown. Here, we identify in mice that serotonin uptake transporter (SERT) in non-serotonergic neurons - hippocampal and prefrontal pyramidal neurons - confers sex-biased effects specifically during neural circuit development. A set of gradient-patterned CA3 pyramidal neurons transiently express SERT to clear extracellular serotonin, coinciding with hippocampal synaptic circuit establishment. Ablating pyramidal neuron SERT (SERTPyramidΔ) alters dendritic spine developmental trajectory in the hippocampus, and precipitates sex-biased impairments in long-term activity-dependent hippocampal synaptic plasticity and cognitive behaviors. Transcriptomic analyses identify sex-biased alterations in gene sets associated with autism, dendritic spine structure, synaptic function and male-specific enrichment of dysregulated genes in glial cells in early postnatal SERTPyramidΔ hippocampus. Our data suggest that SERT function in these pyramidal neurons underscores a temporal- and brain region-specific regulation of normal sex-dimorphic circuit development and a source for sex-biased vulnerability to cognitive and behavioral impairments. This article has an associated 'The people behind the papers' interview.

Outcomes of acute ischemic stroke among patients with renal cell carcinoma: A nationwide analysis.

INTRODUCTION: Renal cell carcinoma (RCC) has been associated with an increased risk for acute ischemic stroke (AIS). As individuals with cancer who experience AIS tend to face higher mortality rates compared to AIS patients without cancer, recognizing the implications of RCC in AIS is crucial for identifying high-risk patients for major complications and directing management strategies. OBJECTIVE: To examine risk factors, interventions, and outcomes for patients with AIS stratified by their RCC diagnosis. METHODS: The National Inpatient Sample (NIS) database was queried for the period 2010-2019 using International Classification of Disease 10th Edition (ICD-10) codes for acute ischemic stroke and renal malignancies. We assessed demographic information, comorbidities, and clinical interventions between patients presenting with AIS, with and without renal malignancies. A logistic regression model was employed to further examine mortality outcomes. RESULTS: Among 1,609,817 patients identified with AIS, 2,068 (0.12%) had a concomitant diagnosis of RCC. AIS patients with RCC were older (72.09 yrs. vs. 70.9 yrs., p < 0.01), more often white (72.05% vs. 68.16%, p < 0.01), and had similar stroke severity scores. RCC patients received less tissue plasminogen activator (tPA; 4.98% vs. 6.2%, p = 0.02) but underwent endovascular mechanical thrombectomy (MT) at similar rates. RCC patients had more complications (p < 0.01) as well as longer hospital stays (8.19 days vs. 5.98 days, p < 0.01), and higher rates of mortality (11.27% vs. 5.63%, p < 0.01), when compared to their non-RCC counterparts. Propensity score-adjusted analysis largely confirmed these findings, with RCC being positively associated with in-hospital mortality (OR: 1.373, p < 0.01) and longer stays (OR: 2.591, p < 0.01). CONCLUSION: In addition to describing the demographics and clinical course of AIS patients diagnosed with RCC, our study underscores the substantial impact of RCC on AIS outcomes. Despite experiencing strokes of similar severity, AIS patients diagnosed with RCC are at a heightened risk of complications, including thromboembolic events and infections, leading to elevated in-hospital mortality rates and prolonged hospital stays.

Acute kidney injury in subarachnoid hemorrhage: Exploring its clinical significance and prognostic implications.

OBJECTIVES: Subarachnoid hemorrhage (SAH) from spontaneous aneurysm rupture is a debilitating condition with high morbidity and mortality. Patients with SAH remain understudied, particularly concerning the evaluation of incidence and consequences of subsequent acute kidney injury (AKI). In this study, we aim to explore the risk factors and outcomes of AKI in SAH patients. MATERIALS AND METHODS: International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) and International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) codes were used to query the National Inpatient Sample (NIS) for patients with a diagnosis of SAH between 2010-2019. Subgroup analysis was stratified by AKI diagnosis during the same hospitalization. AKI and non-AKI groups were assessed for baseline clinical characteristics, interventions, complications, and outcomes. Descriptive statistics, multivariate regressions, and propensity score-matching were performed using IBM SPSS 28. RESULTS: Of 76,553 patients diagnosed with nontraumatic SAH between 2010-2019, 10,634 (13.89 %) had a comorbid diagnosis of AKI. SAH patients with AKI were older (p < 0.01) and more often obese (p < 0.01) compared to the non-AKI group. A multivariate regression found the diagnosis of AKI to be independently correlated with poor functional outcome (p < 0.001), above average length of stay (p < 0.001), and in-hospital mortality (p < 0.001) when controlling for age, SAH severity, and other comorbidities. CONCLUSIONS: This study showed significant association between AKI and adverse outcomes in SAH patients, and a correlation between AKI and heightened complication rates, poor functional outcome, extended hospital stays, and elevated mortality rates. Early detection of AKI in SAH patients is vital to improve their chances of recovery.

Developmental Time Course of SNAP-25 Isoforms Regulate Hippocampal Long-Term Synaptic Plasticity and Hippocampus-Dependent Learning.

SNAP-25 is essential to activity-dependent vesicle fusion and neurotransmitter release in the nervous system. During early development and adulthood, SNAP-25 appears to have differential influences on short- and long-term synaptic plasticity. The involvement of SNAP-25 in these processes may be different at hippocampal and neocortical synapses because of the presence of two different splice variants, which are developmentally regulated. We show here that the isoform SNAP-25a, which is expressed first developmentally in rodent brain, contributes to developmental regulation of the expression of both long-term depression (LTD) and long-term potentiation (LTP) at Schaffer collateral-CA1 synapses in the hippocampus. In one month old mice lacking the developmentally later expressed isoform SNAP-25b, Schaffer collateral-CA1 synapses showed faster release kinetics, decreased LTP and enhanced LTD. By four months of age, SNAP-25b-deficient mice appeared to have compensated for the lack of the adult SNAP-25b isoform, now exhibiting larger LTP and no differences in LTD compared to wild type mice. Interestingly, learning a hippocampus-dependent task reversed the reductions in LTP, but not LTD, seen at one month of age. In four month old adult mice, learning prevented the compensatory up-regulation of LTD that we observed prior to training. These findings support the hypothesis that SNAP-25b promotes stronger LTP and weakens LTD at Schaffer collateral-CA1 synapses in young mice, and suggest that compensatory mechanisms can reverse alterations in synaptic plasticity associated with a lack of SNAP-25b, once mice reach adulthood.

Evaluation of the Safety of Liberalized Systolic Blood Pressure Goals in the Postoperative Period After Intracranial Tumor Resection.

BACKGROUND AND OBJECTIVES: Postoperative intracranial hemorrhage (POH) is a serious neurosurgical complication occurring in approximately 1.4% of patients after intracranial tumor resection. The convention across the United States is to maintain an immediate postoperative systolic blood pressure (SBP) of < 140 mm Hg to minimize this risk; however, this SBP goal lacks support in the literature despite widespread adoption. This study aims to investigate the safety of SBP liberalization to 160 mm Hg in the immediate postoperative setting after intracranial tumor resection. METHODS: A retrospective review was conducted on consecutive patients, aged 18 to 75 years, undergoing craniotomy for intracranial tumor resection from October 2020 until June 2023. Data were gathered from the electronic medical record per Institutional Review Board guidelines regarding demographics, operative details, perioperative vital signs, resource utilization, and complications. Pharmaceutical prices and insurance charges were approximated from costs provided by the institution's pharmacy. POH was defined as symptomatic hemorrhage within 48 hours requiring intervention. RESULTS: The study included 147 patients, with 104 in the liberalized cohort (SBP <160 mm Hg) and 43 in the standard cohort (SBP <140 mm Hg). The average age was 54.5 ± 14.9 years and 57.6 ± 10.6 years in the liberalized and standard groups, respectively (P = .23). Intensive care unit and hospital length of stay were not significantly different between groups. The liberalized group used $81.88 ± $280.19 (95% CI $53.01-$110.75) on as-needed antihypertensive medications vs $108.39 ± $215.91 (95% CI $75.96-$140.82) in the standard (P = .29), with significantly lower labetalol (P = .04). There was no POH in either cohort. CONCLUSION: Liberalization of SBP goals to <160 mm Hg appears safe in the immediate postoperative period after craniotomy for tumor resection without an increased POH risk. Liberalized SBP parameters may allow reduced antihypertensive medication usage, thereby avoiding excess hospital cost and medication side effects.

Atlantoaxial subluxation and Down syndrome: A cross-sectional analysis.

Background: Atlantoaxial subluxation (AAS) is a diagnosis describing misalignment of the C1 vertebra relative to C2. Excessive translation of this joint, located adjacent to the medullary brain stem, can lead to devastating neurological consequences. A higher prevalence of AAS within the Down syndrome (DS) population has been well-established. This study aims to establish a prevalence rate of DS in patients hospitalized for AAS and compare outcomes between AAS patients with and without DS. Methods: This study utilized the National Inpatient Sample (NIS) provided by the Healthcare Cost and Utilization Project (HCUP). In accordance with HCUP 2023 Clinical Classifications Software Refined files, data were queried using the International Classification of Diseases 10th Edition codes for DS and AAS. Demographics, comorbidities, hospital course, and outcomes were examined and compared using binary and linear multivariate regression. IBM SPSS software was used for data analysis. Results: Of the 213,095 patients in the NIS database admitted between 2016 and 2020 with AAS as their primary diagnosis, 7.2% were DS patients. DS patients were significantly younger (26.56 ± 20.81 vs. 49.39 ± 27.63, P < 0.01), less likely to be female (33.30% vs. 52.10%), and had fewer comorbidities (diabetes mellitus, hypertension, and hyperlipidemia) than non-DS patients. There was no significant difference in likelihood to undergo surgical fusion between DS patients and non-DS patients with AAS. Conclusion: This large-scale study using NIS data determined that 7.2% of all patients admitted to hospitals for AAS are DS patients. The analysis of demographics, hospital course, and outcomes can influence the development of treatment protocols for AAS in the DS population.

Nationwide Incidence and Trends in Central Retinal Arterial Occlusion Management: A 5000-Patient Analysis.

Central retinal artery occlusion (CRAO) is a rare and visually debilitating vascular condition characterized by sudden and severe vision loss. CRAO is a compelling target for intravenous alteplase (tPA) and endovascular mechanical thrombectomy (MT) due to pathophysiological similarities with acute ischemic stroke; however, the utility of these interventions in CRAO remains dubious due to limited sample sizes and potential risks. To assess usage and outcomes of tPA and MT in CRAO, we queried the National Inpatient Sample database using International Classification of Disease, Ninth and Tenth edition for patients with CRAO and acute ischemic stroke between 2010 and 2019. Our cohort of 5009 CRAO patients were younger with higher rates of obesity, hypertension, long-term anticoagulant use, and tobacco use compared to acute ischemic stroke patients. CRAO patients had lower rates of tPA administration (3.41% vs 6.21%) and endovascular MT (0.38% vs 1.31%) but fewer complications, including deep vein thrombosis, pneumonia, urinary tract infection, acute kidney injury, and acute myocardial infarction (all P < 0.01). CRAO patients had lower rates of poor functional outcome (31.74% vs 58.1%) and in-hospital mortality (1.2% vs 5.64%), but higher rates of profound blindness (9.24% vs 0.58%). A multivariate regression showed no relationship between tPA and MT and profound blindness, although the limited sample size of patients receiving interventions may have contributed to this apparent insignificance. Further investigation of larger patient cohorts and alternative treatment modalities could provide valuable insights for revascularization therapies in CRAO to optimize visual restoration and clinical outcomes.

Ultra-Early Hemostatic Therapy for Acute Intracerebral Hemorrhage: An Updated Review.

Intracerebral hemorrhage (ICH) is the second most common type of stroke, accounting for approximately 10-20% of all strokes, and is linked to severe neurological disability and death. Since the most accurate predictor of outcome in patients with ICH is hematoma volume, there is a great need for pharmacologic therapy that can reduce hematoma expansion and resultant mass effect and edema. This is especially critical within the ultra-early window of 3-4 hours after the presentation. Hemostatic therapies are exceptionally important for those patients taking antiplatelet or anticoagulant medications to reverse the effects of these medications and therefore prevent hematoma expansion. Furthermore, the recent publication of the 2023 Guideline for the Management of Patients with Aneurysmal Subarachnoid Hemorrhage by the American Heart Association/American Stroke Association, the first update to the guidelines since 2012, underscores the importance of optimizing anticoagulation reversal for this population. The purpose of this selective, nonsystematic review is to examine current literature regarding the use of hemostatic therapies in ICH, with particular attention paid to antiplatelet, anticoagulation, and antifibrinolytic therapies.

Mapping geographic disparities in treatment and clinical outcomes of high-grade aneurysmal subarachnoid hemorrhage in the United States.

BACKGROUND AND OBJECTIVE: Although high-grade (Hunt and Hess 4 and 5) aneurysmal subarachnoid hemorrhage (aSAH) typically portends a poor prognosis, early and aggressive treatment has previously been demonstrated to confer a significant survival advantage. This study aims to evaluate geographic, demographic, and socioeconomic determinants of high-grade aSAH treatment in the United States. METHODS: The National Inpatient Sample (NIS) was queried to identify adult high-grade aSAH hospitalizations during the period of 2015 to 2019 using the International Classification of Diseases, 10th Revision, Clinical Modification (ICD) codes. The primary clinical endpoint of this analysis was aneurysm treatment by surgical or endovascular intervention (SEI), while the exposure of interest was geographic region by census division. Favorable functional outcome (assessed by the dichotomous NIS-SAH Outcome Measure, or NIS-SOM) and in-hospital mortality were evaluated as secondary endpoints in treated and conservatively managed groups. RESULTS: Among 99 460 aSAH patients identified, 36 795 (37.0%) were high-grade, and 9210 (25.0%) of these were treated by SEI. Following multivariable logistic regression analysis, determinants of treatment by SEI included female sex (adjusted OR (aOR) 1.42, 95% CI 1.35 to 1.51), transfer admission (aOR 1.18, 95% CI 1.12 to 1.25), private insurance (ref: government-sponsored insurance) (aOR 1.21, 95% CI 1.14 to 1.28), and government hospital ownership (ref: private ownership) (aOR 1.17, 95% CI 1.09 to 1.25), while increasing age (by decade) (aOR 0.93, 95% CI 0.91 to 0.95), increasing mortality risk (aOR 0.60, 95% CI 0.57 to 0.63), urban non-teaching hospital status (aOR 0.66, 95% CI 0.59 to 0.73), rural hospital location (aOR 0.13, 95% CI 0.7 to 0.25), small hospital bedsize (aOR 0.68, 95% CI 0.60 to 0.76), and geographic region (South Atlantic (aOR 0.72, 95% CI 0.63 to 0.83), East South Central (aOR 0.75, 95% CI 0.64 to 0.88), and Mountain (aOR 0.72, 95% CI 0.61 to 0.85)) were associated with a lower likelihood of treatment. High-grade aSAH patients treated by SEI experienced significantly greater rates of favorable functional outcomes (20.1% vs 17.3%; OR 1.20, 95% CI 1.13 to 1.28, P<0.001) and lower rates of mortality (25.8% vs 49.1%; OR 0.36, 95% CI 0.34 to 0.38, P<0.001) in comparison to those conservatively managed. CONCLUSION: A complex interplay of demographic, socioeconomic, and geographic factors influence treatment patterns of high-grade aSAH in the United States.

Outcomes of heparin-induced thrombocytopenia type II in aneurysmal subarachnoid hemorrhage patients: A US nationwide analysis.

BACKGROUND: Despite the widespread use of heparin during and following endovascular procedures in the management of aneurysmal subarachnoid hemorrhage (SAH) patients, limited research has explored the incidence and impact of heparin-induced thrombocytopenia (HIT) on SAH. METHODS: Descriptive statistics, multivariate regressions, and propensity score-matching were employed to compare clinical characteristics, comorbidities, interventions, complications, and outcomes of HIT in SAH patients identified within the US National Inpatient Sample database from 2010 to 2019. RESULTS: Among 76 387 SAH patients from 2010 to 2019, 166 (0.22%) developed HIT. HIT was identified as a significant predictor of prolonged length of stay (OR 6.799, 95% CI 3.985 to 11.6, P<0.01) and poor functional outcomes (OR 2.541, 95% CI 1.628 to 3.966, P<0.01) after adjusting for relevant factors. HIT incidence was higher in patients with elevated SAH severity scores (1.42 vs 1.06, P<0.01), younger patients (58.04 vs 61.39 years, P=0.01), overweight individuals (0.4% vs 0.2%, P<0.01), those on long-term anticoagulants (10.84% vs 5.72%, P<0.01), or with a cerebrospinal fluid drainage device (external ventricular drain, ventriculoperitoneal shunt; P<0.01). HIT patients showed increased rates of endovascular coiling, ventricular drain placement, shunt placement, deep vein thrombosis, urinary tract infection, acute kidney injury, pulmonary embolism, venous sinus thrombosis, pneumonia, and cerebral vasospasm (all P<0.01). CONCLUSION: SAH patients with HIT exhibited various comorbidities and increased rates of complications, which may contribute to extended hospital stays. This nationwide study aids clinical suspicion and highlights HIT's impact on SAH patients.

Astrocyte and neuronal Panx1 support long-term reference memory in mice.

Pannexin 1 (Panx1) are ubiquitously expressed proteins that form plasma membrane channels permeable to anions and moderate sized signaling molecules (e.g., ATP, glutamate). In the nervous system, activation of Panx1 channels have been extensively shown to contribute to distinct neurological disorders (epilepsy, chronic pain, migraine, neuroAIDS, etc.) but knowledge of extent to which these channels have a physiological role remains restricted to three studies supporting their involvement in hippocampus dependent learning. Given that Panx1 channels may provide an important mechanism for activity-dependent neuron-glia interaction, we used Panx1 transgenic mice with global and cell-type specific deletions of Panx1 to interrogate their participation in working and reference memory. Using the 8-arm radial maze, we show that long-term spatial reference memory, but not spatial working memory, is deficient in Panx1-null mice and that both astrocyte and neuronal Panx1 contribute to the consolidation of long-term spatial memory. Field potential recordings in hippocampal slices of Panx1-null mice revealed an attenuation of both long-term potentiation (LTP) of synaptic strength and long-term depression (LTD) at Schaffer collateral - CA1 synapses without alterations basal synaptic transmission or pre-synaptic paired-pulse facilitation. Our results implicate both neuronal and astrocyte Panx1 channels as critical players for the development and maintenance of long-term spatial reference memory in mice.

Astrocyte and Neuronal Panx1 Support Long-Term Reference Memory in Mice.

Pannexin 1 (Panx1) is an ubiquitously expressed protein that forms plasma membrane channels permeable to anions and moderate-sized signaling molecules (e.g., ATP, glutamate). In the nervous system, activation of Panx1 channels has been extensively shown to contribute to distinct neurological disorders (epilepsy, chronic pain, migraine, neuroAIDS, etc.), but knowledge of the extent to which these channels have a physiological role remains restricted to three studies supporting their involvement in hippocampus dependent learning. Given that Panx1 channels may provide an important mechanism for activity-dependent neuron-glia interaction, we used Panx1 transgenic mice with global and cell-type specific deletions of Panx1 to interrogate their participation in working and reference memory. Using the eight-arm radial maze, we show that long-term spatial reference memory, but not spatial working memory, is deficient in Panx1-null mice and that both astrocyte and neuronal Panx1 contribute to the consolidation of long-term spatial memory. Field potential recordings in hippocampal slices of Panx1-null mice revealed an attenuation of both long-term potentiation (LTP) of synaptic strength and long-term depression (LTD) at Schaffer collateral-CA1 synapses without alterations of basal synaptic transmission or pre-synaptic paired-pulse facilitation. Our results implicate both neuronal and astrocyte Panx1 channels as critical players for the development and maintenance of long-term spatial reference memory in mice.

Frailty as a Predictor of Outcomes in Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis.

Frailty is an emerging concept in clinical practice used to predict outcomes and dictate treatment algorithms. Frail patients, especially older adults, are at higher risk for adverse outcomes. Aneurysmal subarachnoid hemorrhage (aSAH) is a neurosurgical emergency associated with high morbidity and mortality rates that have previously been shown to correlate with frailty. However, the relationship between treatment selection and post-treatment outcomes in frail aSAH patients is not established. We conducted a meta-analysis of the relevant literature in accordance with PRISMA guidelines. We searched PubMed, Embase, Web of Science, and Google Scholar using "Subarachnoid hemorrhage AND frailty" and "subarachnoid hemorrhage AND frail" as search terms. Data on cohort age, frailty measurements, clinical grading systems, and post-treatment outcomes were extracted. Of 74 studies identified, four studies were included, with a total of 64,668 patients. Percent frailty was 30.4% under a random-effects model in all aSAH patients (p < 0.001). Overall mortality rate of aSAH patients was 11.7% when using a random-effects model (p < 0.001). There was no significant difference in mortality rate between frail and non-frail aSAH patients, but this analysis only included two studies and should be interpreted cautiously. Age and clinical grading, rather than frailty, independently predicted outcomes and mortality in aSAH patients.

Neuroendovascular Surgery Applications in Craniocervical Trauma.

Cerebrovascular injuries resulting from blunt or penetrating trauma to the head and neck often lead to local hemorrhage and stroke. These injuries present with a wide range of manifestations, including carotid or vertebral artery dissection, pseudoaneurysm, occlusion, transection, arteriovenous fistula, carotid-cavernous fistula, epistaxis, venous sinus thrombosis, and subdural hematoma. A selective review of the literature from 1989 to 2023 was conducted to explore various neuroendovascular surgical techniques for craniocervical trauma. A PubMed search was performed using these terms: endovascular, trauma, dissection, blunt cerebrovascular injury, pseudoaneurysm, occlusion, transection, vasospasm, carotid-cavernous fistula, arteriovenous fistula, epistaxis, cerebral venous sinus thrombosis, subdural hematoma, and middle meningeal artery embolization. An increasing array of neuroendovascular procedures are currently available to treat these traumatic injuries. Coils, liquid embolics (onyx or n-butyl cyanoacrylate), and polyvinyl alcohol particles can be used to embolize lesions, while stents, mechanical thrombectomy employing stent-retrievers or aspiration catheters, and balloon occlusion tests and super selective angiography offer additional treatment options based on the specific case. Neuroendovascular techniques prove valuable when surgical options are limited, although comparative data with surgical techniques in trauma cases is limited. Further research is needed to assess the efficacy and outcomes associated with these interventions.

Socioeconomic characteristics of pediatric traumatic brain injury patients.

BACKGROUND: Traumatic brain injuries (TBIs) play a significant role in pediatric mortality and morbidity. Environment may play a role in the type, severity, and outcome of pediatric TBI (pTBI). Our objective was to characterize the impact of poor socioeconomic status (PSES) on the incidence, treatment, and outcomes of pTBI patients. METHODS: The Kids' Inpatient Database (KID) was queried from 2016 to 2019 for with TBI using International Classification of Disease, 10th revision (ICD 10) codes. Data defining demographics, complications, procedures, and outcomes was extracted. PSES was defined as Medicaid insurance and Q1 median income category. RESULTS: 26,417 patients had pTBI. 11,040 (41.8 %) of pTBI patients were on Medicaid insurance. 13,119 and 8165 (30.9 %) were in Q1 median income category. Land transport caused the majority of pTBI (41 %). Patients on Medicaid or Q1 median income were more likely to experience assault (OR 2.927, CI 95 % 2.455-3.491, p < 0.001 OR 2.033, CI 95 % 1.722-2.4000 p < 0.001 respectively). On propensity matched analysis, PSES was associated with increased mortality (OR 1.667, 95 % CI 1.322-2.100, p < 0.01), length of stay (LOS) (OR 1.369, 95 % CI 1.201-1.559, p < 0.01), and major complicated trauma (OR 1.354 95 % CI 1.090-1.682 p = 0.007). Total hospital charges were higher in pTBI patients on Medicaid ($112,101.52, +/- $203,716.35) versus non-Medicaid ($109,064.37 +/- $212,057.98) (p < 0.001). CONCLUSION: PSES is correlated with increased mortality, complications, and longer LOS. Healthcare coverage and clinical training should take these disparities into account to provide improved care and optimize healthcare resource utilization. LEVEL OF EVIDENCE: Level IV, Retrospective Database.

Life-long brain compensatory responses to galactic cosmic radiation exposure.

Galactic cosmic radiation (GCR) composed of high-energy, heavy particles (HZE) poses potentially serious hazards to long-duration crewed missions in deep space beyond earth's magnetosphere, including planned missions to Mars. Chronic effects of GCR exposure on brain structure and cognitive function are poorly understood, thereby limiting risk reduction and mitigation strategies to protect against sequelae from exposure during and after deep-space travel. Given the selective vulnerability of the hippocampus to neurotoxic insult and the importance of this brain region to learning and memory, we hypothesized that GCR-relevant HZE exposure may induce long-term alterations in adult hippocampal neurogenesis, synaptic plasticity, and hippocampal-dependent learning and memory. To test this hypothesis, we irradiated 3-month-old male and female mice with a single, whole-body dose of 10, 50, or 100 cGy 56Fe ions (600 MeV, 181 keV/µm) at Brookhaven National Laboratory. Our data reveal complex, dynamic, time-dependent effects of HZE exposure on the hippocampus. Two months post exposure, neurogenesis, synaptic plasticity and learning were impaired compared to sham-irradiated, age-matched controls. By six months post-exposure, deficits in spatial learning were absent in irradiated mice, and synaptic potentiation was enhanced. Enhanced performance in spatial learning and facilitation of synaptic plasticity in irradiated mice persisted 12 months post-exposure, concomitant with a dramatic rebound in adult-born neurons. Synaptic plasticity and spatial learning remained enhanced 20 months post-exposure, indicating a life-long influence on plasticity and cognition from a single exposure to HZE in young adulthood. These findings suggest that GCR-exposure can persistently alter brain health and cognitive function during and after long-duration travel in deep space.