Exploring dynamical phase transitions with cold atoms in an optical cavity.

Interactions between atoms and light in optical cavities provide a means of investigating collective (many-body) quantum physics in controlled environments. Such ensembles of atoms in cavities have been proposed for studying collective quantum spin models, where the atomic internal levels mimic a spin degree of freedom and interact through long-range interactions tunable by changing the cavity parameters1-4. Non-classical steady-state phases arising from the interplay between atom-light interactions and dissipation of light from the cavity have previously been investigated5-11. These systems also offer the opportunity to study dynamical phases of matter that are precluded from existence at equilibrium but can be stabilized by driving a system out of equilibrium12-16, as demonstrated by recent experiments17-22. These phases can also display universal behaviours akin to standard equilibrium phase transitions8,23,24. Here, we use an ensemble of about a million strontium-88 atoms in an optical cavity to simulate a collective Lipkin-Meshkov-Glick model25,26, an iconic model in quantum magnetism, and report the observation of distinct dynamical phases of matter in this system. Our system allows us to probe the dependence of dynamical phase transitions on system size, initial state and other parameters. These observations can be linked to similar dynamical phases in related systems, including the Josephson effect in superfluid helium27, or coupled atomic28 and solid-state polariton29 condensates. The system itself offers potential for generation of metrologically useful entangled states in optical transitions, which could permit quantum enhancement in state-of-the-art atomic clocks30,31.

Society for Cardiovascular Magnetic Resonance 2022 Cases of SCMR case series.

"Cases of SCMR" is a case series on the SCMR website (https://www.scmr.org) for the purpose of education. The cases reflect the clinical presentation, and the use of cardiovascular magnetic resonance (CMR) in the diagnosis and management of cardiovascular disease. The 2022 digital collection of cases are presented in this manuscript.

Clinically Suspected Myocarditis Temporally Related to COVID-19 Vaccination in Adolescents and Young Adults: Suspected Myocarditis After COVID-19 Vaccination.

BACKGROUND: Understanding the clinical course and short-term outcomes of suspected myocarditis after the coronavirus disease 2019 (COVID-19) vaccination has important public health implications in the decision to vaccinate youth. METHODS: We retrospectively collected data on patients <21 years old presenting before July 4, 2021, with suspected myocarditis within 30 days of COVID-19 vaccination. Lake Louise criteria were used for cardiac MRI findings. Myocarditis cases were classified as confirmed or probable on the basis of the Centers for Disease Control and Prevention definitions. RESULTS: We report on 139 adolescents and young adults with 140 episodes of suspected myocarditis (49 confirmed, 91 probable) at 26 centers. Most patients were male (n=126, 90.6%) and White (n=92, 66.2%); 29 (20.9%) were Hispanic; and the median age was 15.8 years (range, 12.1-20.3; interquartile range [IQR], 14.5-17.0). Suspected myocarditis occurred in 136 patients (97.8%) after the mRNA vaccine, with 131 (94.2%) after the Pfizer-BioNTech vaccine; 128 (91.4%) occurred after the second dose. Symptoms started at a median of 2 days (range, 0-22; IQR, 1-3) after vaccination. The most common symptom was chest pain (99.3%). Patients were treated with nonsteroidal anti-inflammatory drugs (81.3%), intravenous immunoglobulin (21.6%), glucocorticoids (21.6%), colchicine (7.9%), or no anti-inflammatory therapies (8.6%). Twenty-six patients (18.7%) were in the intensive care unit, 2 were treated with inotropic/vasoactive support, and none required extracorporeal membrane oxygenation or died. Median hospital stay was 2 days (range, 0-10; IQR, 2-3). All patients had elevated troponin I (n=111, 8.12 ng/mL; IQR, 3.50-15.90) or T (n=28, 0.61 ng/mL; IQR, 0.25-1.30); 69.8% had abnormal ECGs and arrhythmias (7 with nonsustained ventricular tachycardia); and 18.7% had left ventricular ejection fraction <55% on echocardiogram. Of 97 patients who underwent cardiac MRI at a median 5 days (range, 0-88; IQR, 3-17) from symptom onset, 75 (77.3%) had abnormal findings: 74 (76.3%) had late gadolinium enhancement, 54 (55.7%) had myocardial edema, and 49 (50.5%) met Lake Louise criteria. Among 26 patients with left ventricular ejection fraction <55% on echocardiogram, all with follow-up had normalized function (n=25). CONCLUSIONS: Most cases of suspected COVID-19 vaccine myocarditis occurring in persons <21 years have a mild clinical course with rapid resolution of symptoms. Abnormal findings on cardiac MRI were frequent. Future studies should evaluate risk factors, mechanisms, and long-term outcomes.

Gore Cardioform ASD device thrombus weeks after COVID-19 infection.

Device-related thrombosis and device-related endocarditis after atrial septal defect (ASD) transcatheter closure are extremely rare. It is known that COVID-19 infection could lead to a thrombotic microangiopathy-like phenomenon. We present the case of a 14-year-old female who developed fever and was found to have a thrombus on the right atrial side of the ASD closure device weeks after an asymptomatic COVID-19 infection and negative COVID-19 test 2 days before transcatheter ASD closure. Although there is no certainty that the thrombus was related to the prior COVID-19 infection, the possibility of an ongoing COVID-19-related hypercoagulable state should be entertained.

Two-dimensional photonic crystals for engineering atom-light interactions.

We present a 2D photonic crystal system for interacting with cold cesium (Cs) atoms. The band structures of the 2D photonic crystals are predicted to produce unconventional atom-light interaction behaviors, including anisotropic emission, suppressed spontaneous decay, and photon-mediated atom-atom interactions controlled by the position of the atomic array relative to the photonic crystal. An optical conveyor technique is presented for continuously loading atoms into the desired trapping positions with optimal coupling to the photonic crystal. The device configuration also enables application of optical tweezers for controlled placement of atoms. Devices can be fabricated reliably from a 200-nm silicon nitride device layer using a lithography-based process, producing predicted optical properties in transmission and reflection measurements. These 2D photonic crystal devices can be readily deployed to experiments for many-body physics with neutral atoms and engineering of exotic quantum matter.

Leftward and Posterior Deviation of the Septum Primum Predicts Morbidity in Patients with Hypoplastic Left Heart Syndrome.

Leftward posterior deviation of the atrial septum primum (LDSP) has been reported in up to 64% of patients with hypoplastic left heart syndrome (HLHS) but there are no published data on its impact on neonatal outcomes. We reviewed the prevalence of LDSP and its correlation with neonatal outcomes in our institution. This was a single-center retrospective study of neonates with HLHS from 2001 to 2019. Echocardiograms were reviewed and the presence or absence of LDSP was noted. To quantify the degree of deviation in patients with LDSP, a new measurement, the deviation index (DI) was calculated using both the subcostal long and short-axis views. Of ninety-four patients with HLHS, fifty-seven (61%) patients were noted to have LDSP. There was no statistically significant difference in gestational age (GA), birth weight (BW), or mortality between patients with and without LDSP. Patients with LDSP had an increased incidence of unplanned reoperation (p < 0.01), post-operative cardiac catheterization (p < 0.05), and post-operative infection (p < 0.05). After correction for GA, BW, HLHS subtype, and type of surgery, LDSP predicted reoperation (OR = 3.6, p < 0.01), catheterization (OR = 2.7, p = 0.05), and infection (OR = 3.4, p < 0.05). Higher degree of deviation predicted reoperation (DI > 0.17), catheterization (DI > 0.07), and infection (DI > 0.12). There was excellent inter-observer reproducibility of the DI (ICCabsolute-agreement = 0.82, ICCconsistency = 0.90). Patients with LDSP have a higher prevalence of post-operative morbidity. The degree of deviation was found to be predictive of post-operative complications. Pre-operative echocardiographic evaluation of LDSP in patients with HLHS may be helpful in risk stratification and counseling.

Protocol for Precise Field Sensing in the Optical Domain with Cold Atoms in a Cavity.

In the context of quantum metrology, optical cavity-QED platforms have primarily been focused on the generation of entangled atomic spin states useful for next-generation frequency and time standards. Here, we report a complementary application: the use of optical cavities to generate nonclassical states of light for electric field sensing below the standard quantum limit. We show that cooperative atom-light interactions in the strong collective coupling regime can be used to engineer generalized atom-light cat states which enable quantum enhanced sensing of small displacements of the cavity field even in the presence of photon loss. We demonstrate that metrological gains of 10-20 dB below the standard quantum limit are within reach for current cavity-QED systems operating with long-lived alkaline-earth atoms.

Evaluation of Residual Coarctation in Infants with a Single Right Ventricle after Stage I Palliation.

In infants with a single right ventricle (RV), stage I palliation involves aortic reconstruction, systemic-to-pulmonary shunt placement, and atrial septectomy. Many require re-intervention for residual coarctation of the aorta (CoA). Doppler echocardiography can detect residual CoA in most infants, but its ability to predict severity has not been studied. This study compares gradients from Doppler interrogation to those from cardiac catheterization in infants with residual CoA. We performed a retrospective study of infants after stage I palliation from 2000 to 2014. Infants with an echocardiogram and catheterization before the second-stage palliative surgery were included. Infants with an echocardiogram >30 days before catheterization were excluded. Doppler-derived gradients were compared to catheterization-derived gradients. Echocardiographic assessment of tricuspid valve (TV) and RV function were recorded. The cohort included 95 infants, and thirty-three (35%) had CoA. Doppler-derived and catheterization-derived gradients correlated weakly in infants with CoA (r = 0.37, p = 0.036) and without CoA (r = 0.35, p = 0.005). Among infants with CoA, 17/33 had none or trivial tricuspid regurgitation (TR) and normal RV function, and Doppler-derived gradients correlated with catheterization gradients in this group (r = 0.71, p = 0.001). In 16/33 infants with ≥moderate TR or RV dysfunction, gradients did not correlate (r = -0.003, p = 0.992). After a stage I palliation in infants with single RV and CoA, Doppler-derived gradients poorly predicted the severity of CoA. Infants with normal TV or RV function had Doppler-derived gradients more predictive of catheterization-derived gradients. Doppler-derived gradients have limited utility in determining the severity of CoA after a stage I palliation.

Safety and efficacy of lacosamide in the intensive care unit.

BACKGROUND: Seizures are common in critically ill patients and can impact morbidity and mortality. Traditional anti-epileptic drugs (AEDs) in this setting are not always effective and are associated with adverse events and drug interactions. Lacosamide (LCM) is a new AED which is available in parental form although few studies have evaluated the safety and efficacy of LCM in critically ill patients. METHODS: Critically ill patients at Emory University Hospital who received LCM from April 1, 2009 to February 1, 2010 were retrospectively reviewed. Primary outcome measure was incidence and time to seizure cessation. Adverse effects were also recorded. RESULTS: LCM was administered in 24 patients including 13 episodes of refractory status epilepticus (RSE) occurring in 10 patients and for treatment of isolated seizures or following resolution of RSE in an additional 14 patients. Seizure cessation was achieved in 5/13 (38%) episodes of RSE (mean 11.2 h) while there was at least a 50% decrease in seizure frequency in 7/13 (54%). 11/14 patients (76%) who received LCM for treatment of isolated seizures or prevention of seizure recurrence remained seizure free. Three patients experienced a decline in systolic blood pressure (> 20 mmHg) while one patient experienced unexplained fever and one patient had elevation of liver function tests. CONCLUSIONS: This preliminary data suggests that LCM may be a safe and effective alternative for treatment of seizures in critically ill patients. Further prospective, randomized controlled trials are needed to confirm these findings and further explore the incidence of adverse effects.

The Diagnostic Role of Echocardiographic Strain Analysis in Patients Presenting with Chest Pain and Elevated Troponin: A Multicenter Study.

BACKGROUND: Myocarditis presenting as acute chest pain with elevated troponins without significant cardiac compromise is rare in previously healthy children, often referred to as myopericarditis. Diagnosis is challenging, as conventional echocardiographic measures of systolic function can be normal. The aim of this study was to demonstrate the diagnostic utility of strain imaging in this scenario. METHODS: This was a multicenter, retrospective study including patients presenting with chest pain and elevated troponin from 10 institutions who underwent cardiac magnetic resonance imaging and transthoracic echocardiography within 30 days of each other (group 1). Findings were compared with those among 19 control subjects (group 2). Clinical data and conventional echocardiographic and cardiac magnetic resonance imaging data were collected. Echocardiography-derived strain was measured at the core laboratory. Group 1 was divided into subgroups as myocarditis positive (group 1a) or negative (group 1b) on cardiac magnetic resonance imaging on the basis of established criteria. RESULTS: Group 1 included 108 subjects (88 in group 1a, 20 in group 1b). Although all groups had normal mean fractional shortening and mean left ventricular ejection fraction, group 1 had significantly lower ejection fraction (56.8 ± 7.0%) compared with group 2 (62.3 ± 4.9%; P < .005) and fractional shortening (31.2 ± 4.9%) compared with group 2 (34.1 ± 3.5%; P < .05). Additionally, peak global longitudinal strain (GLS) was markedly abnormal in group 1 (-13.9 ± 3.4%) compared with group 2 (-19.8 ± 2.1%; P < .001). In subgroup analysis, GLS was markedly abnormal in group 1a (-13.2 ± 3.0%) compared with group 1b (-17.3 ± 2.6%; P < .001). Fifty-four subjects underwent follow-up echocardiography (46 in group 1a, eight in group 1b), with mean a follow-up time of 10 ± 11 months. At follow-up, whereas ejection fraction and fractional shortening returned to normal in all patients, abnormalities in strain persisted in group 1, with 22% still having abnormal GLS. Moreover, mean GLS was more abnormal in group 1a (-16.1 ± 2.6%) compared with group 1b (-17.4 ± 1.2%; P < .05). CONCLUSIONS: The present study demonstrates that echocardiographic GLS is significantly worse in subjects with myopericarditis presenting with chest pain and elevated troponins compared with control subjects even when conventional measures of systolic function are largely normal and that these abnormalities persisted over time.

Polyserositis as a Post-Covid-19 Complication.

INTRODUCTION: Polyserositis is described as inflammation with effusion of more than one serous membrane. There is very little published literature linking it to COVID-19 as a late complication. OBJECTIVE: Present and describe a case of post-COVID-19 polyserositis. METHODS: Data were collected from the medical record of a female patient admitted for fainting spells and marked weakness. The patient underwent a clinical evaluation, additional hematology, imaging and histopathology tests, and a surgical procedure. The new index, called the abdominal adipose deposit index, was obtained by multiplying the subcutaneous fat thickness by visceral fat thickness, both measured by ultrasound. A cutoff point was established that facilitated discernment of an unhealthy phenotype: normal weight but metabolically obese, a cardiometabolic risk factor. RESULTS: We present the case of a 57-year-old female patient admitted to hospital for fainting spells and marked weakness, four months after COVID-19 infection. She also had a history of obesity, asthma, type 2 diabetes mellitus and a cholecystectomy in December 1992 for gallstones. Clinical assessment revealed pericardial effusion and bilateral pleural effusion, in addition to a tumor-like lesion outside the pericardium, proximal to the right ventricular wall. A surgical procedure and findings from additional tests led to diagnoses of thymic remnants and polyserositis. CONCLUSIONS: This is a case of polyserositis in a post-COVID-19 patient. After other causes of polyserositis were ruled out, and since there is a likely physiological and pathogenic mechanism operating between the two diseases, the polyserositis was determined to be a late complication of COVID-19. To date, it is the second case reported in the world and the first reported in Cuba.

Accuracy of Cardiac Magnetic Resonance Imaging in Diagnosing Pediatric Cardiac Masses: A Multicenter Study.

BACKGROUND: After diagnosis of a cardiac mass, clinicians must weigh the benefits and risks of ascertaining a tissue diagnosis. Limited data are available on the accuracy of previously developed noninvasive pediatric cardiac magnetic resonance (CMR)-based diagnostic criteria. OBJECTIVES: The goals of this study were to: 1) evaluate the CMR characteristics of pediatric cardiac masses from a large international cohort; 2) test the accuracy of previously developed CMR-based diagnostic criteria; and 3) expand diagnostic criteria using new information. METHODS: CMR studies (children 0-18 years of age) with confirmatory histological and/or genetic diagnosis were analyzed by 2 reviewers, without knowledge of prior diagnosis. Diagnostic accuracy was graded as: 1) single correct diagnosis; 2) correct diagnosis among a differential; or 3) incorrect diagnosis. RESULTS: Of 213 cases, 174 (82%) had diagnoses that were represented in the previously published diagnostic criteria. In 70% of 174 cases, both reviewers achieved a single correct diagnosis (94% of fibromas, 71% of rhabdomyomas, and 50% of myxomas). When ≤2 differential diagnoses were included, both reviewers reached a correct diagnosis in 86% of cases. Of 29 malignant tumors, both reviewers indicated malignancy as a single diagnosis in 52% of cases. Including ≤2 differential diagnoses, both reviewers indicated malignancy in 83% of cases. Of 6 CMR sequences examined, acquisition of first-pass perfusion and late gadolinium enhancement were independently associated with a higher likelihood of a single correct diagnosis. CONCLUSIONS: CMR of cardiac masses in children leads to an accurate diagnosis in most cases. A comprehensive imaging protocol is associated with higher diagnostic accuracy.

Effects of sample collection and storage conditions on DNA damage in buccal cells from agricultural workers.

Buccal cells are becoming a widely used tissue source for monitoring human exposure to occupational and environmental genotoxicants. A variety of methods exist for collecting buccal cells from the oral cavity, including rinsing with saline, mouthwash, or scraping the oral cavity. Buccal cells are also routinely cryopreserved with dimethyl sulfoxide (DMSO), then examined later for DNA damage by the comet assay. The effects of these different sampling procedures on the integrity of buccal cells for measuring DNA damage are unknown. This study examined the influence of the collection and cryopreservation of buccal cells on cell survival and DNA integrity. In individuals who rinsed with Hank's balanced salt solution (HBSS), the viability of leukocytes (90%) was significantly (p<0.01) greater than that of epithelial cells (12%). Similar survival rates were found for leukocytes (88%) and epithelial cells (10%) after rinsing with Listerine(®) mouthwash. However, the viability of leukocytes after cryopreservation varied significantly (p<0.01) with DMSO concentration. Cell survival was greatest at 5% DMSO. Cryopreservation also influenced the integrity of DNA in the comet assay. Although tail length and tail moment were comparable in fresh or cryopreserved samples, the average head intensity for cryopreserved samples was ∼6 units lower (95% CI: 0.8-12 units lower) than for fresh samples (t(25)=-2.36, p=0.026). These studies suggest that the collection and storage of buccal samples are critical factors for the assessment of DNA damage. Moreover, leukocytes appear to be a more reliable source of human tissue for assessing DNA damage and possibly other biochemical changes.

Aortic size in children: Systolic measurements are different from diastolic measurements.

BACKGROUND: Current guidelines recommended aortic measurements during diastole in adults and during systole in children. Recent studies in adults have demonstrated noteworthy differences in aortic measurements during systole and diastole in the same subjects. In the present study, we aimed to characterize systolic and diastolic differences in aortic measurements in healthy children. MATERIALS AND METHODS: This retrospective study included 272 children who had a complete echocardiogram and no heart disease. Aortic measurements at the annulus (ANN), aortic root (AOR), sinotubular junction (STJ), and ascending aorta (AAO) were performed. Systolic and diastolic values were compared by calculating the mean systolic to diastolic (SD) percent difference for each segment; if the SD difference was >5%, it was considered clinically important. Similar measurements were conducted by another observer in 18% of the subjects. RESULTS: Systolic measurements were larger than diastolic measurements with mean SD percent differences >5% (P < 0.001) for the AOR (7.3% ± 5.5%), STJ (10.24% ± 7.1%), and AAO (9.8% ± 7.4%). There was no clinically significant SD difference for the ANN. There was an excellent intraclass correlation coefficient between observers (0.982-0.995). CONCLUSIONS: Systolic measurements for the AOR, STJ, and AAO were larger than diastolic measurements. Normal reference values are utilized to design treatment for patients with abnormal aortic sizes, and the timing in the cardiovascular cycle used to decide the reference values should be equivalent to the timing used to make measurements in clinical practice. This is particularly imperative as patients transition their care from a pediatric to an adult cardiologist.

Multi-isotope evidence of population aggregation in the Natufian and scant migration during the early Neolithic of the Southern Levant.

Human mobility and migration are thought to have played essential roles in the consolidation and expansion of sedentary villages, long-distance exchanges and transmission of ideas and practices during the Neolithic transition of the Near East. Few isotopic studies of human remains dating to this early complex transition offer direct evidence of mobility and migration. The aim of this study is to identify first-generation non-local individuals from Natufian to Pre-Pottery Neolithic C periods to explore the scope of human mobility and migration during the Neolithic transition in the Southern Levant, an area that is central to this historical process. The study adopted a multi-approach resorting to strontium (87Sr/86Sr), oxygen (δ18OVSMOW) and carbon (δ13C) isotope ratio analyses of tooth enamel of 67 human individuals from five sites in Jordan, Syria, and Israel. The isotope ratios point both to a significant level of human migration and/or mobility in the Final Natufian which is compatible with early sedentarism and seasonal mobility and with population aggregation in early sedentary hamlets. The current findings, in turn, offer evidence that most individuals dating to the Pre-Pottery Neolithic were local to their respective settlements despite certain evidence of non-locals. Interestingly, isotopic data suggest that two possible non-local individuals benefitted from particular burial practices. The results underscore a decrease in human mobility and migration as farming became increasingly dominant among the subsistence strategies throughout the Neolithic transition of the Southern Levant.

Repeating video/EEG monitoring: why and with what results?

Prolonged video/EEG monitoring is the main activity of referral tertiary epilepsy centers. Occasionally, monitoring is repeated in the same patient, but this subgroup has not been specifically studied. The purpose of this study was to analyze repeated video/EEG monitoring. We reviewed all sessions of inpatient video/EEG monitoring performed over 3 years (2005-2008), and selected the ones that were repeated in the same patient. A total of 1063 video/EEG monitoring sessions were performed. Of these, 43 (4.0%) were "redos." The most common indication for repeat video/EEG monitoring was evidence of focal epilepsy with no recorded seizures, followed by normal interictal EEG with no recorded episodes. The second session answered the question in 35 (81%) cases, whereas the question remained unanswered in 8 (19%). The repeated session was useful in 35 (81%) cases.

Cryptococcal meningitis misdiagnosed as Alzheimer's disease: complete neurological and cognitive recovery with treatment.

A sixty-two year old man, with a background of Alzheimer's disease for the past three years, acutely presented with imbalance, headaches, and dizziness. Examination revealed a profound frontal disinhibited and dysexecutive syndrome and brain imaging notable for leptomeningeal enhancement; laboratory data confirmed cryptococcal meningitis. Four months after treatment, the patient was normal neurologically, cognitively and neuroradiologically. The specific cognitive impairment and neuroradiological findings may be clues to differing dementia etiologies.

Organophosphate pesticide exposure and neurobehavioral performance in agricultural and non-agricultural Hispanic workers.

Our understanding of the health risks of farmworkers exposed to pesticides in their work and home environments is rapidly increasing, although studies designed to examine the possible neurobehavioral effects of low-level chronic pesticide exposure are limited. We measured dialkyl phosphate urinary metabolite levels, collected environmental dust samples from a subset of homes, obtained information on work practices, and conducted neurobehavioral tests on a sample of farmworkers in Oregon. Significant correlations between urinary methyl metabolite levels and total methyl organophosphate (azinphos-methyl, phosmet, malathion) house dust levels were observed. We found the neurobehavioral performance of Hispanic immigrant farmworkers to be lower than that observed in a nonagricultural Hispanic immigrant population, and within the sample of agricultural workers there was a positive correlation between urinary organophosphate metabolite levels and poorer performance on some neurobehavioral tests. These findings add to an increasing body of evidence of the association between low levels of pesticide exposure and deficits in neurobehavioral performance.

Genotoxicants target distinct molecular networks in neonatal neurons.

BACKGROUND: Exposure of the brain to environmental agents during critical periods of neuronal development is considered a key factor underlying many neurologic disorders. OBJECTIVES: In this study we examined the influence of genotoxicants on cerebellar function during early development by measuring global gene expression changes. METHODS: We measured global gene expression in immature cerebellar neurons (i.e., granule cells) after treatment with two distinct alkylating agents, methylazoxymethanol (MAM) and nitrogen mustard (HN2). Granule cell cultures were treated for 24 hr with MAM (10-1,000 microM) or HN2 (0.1-20 microM) and examined for cell viability, DNA damage, and markers of apoptosis. RESULTS: Neuronal viability was significantly reduced (p < 0.01) at concentrations > 500 microM for MAM and > 1.0 microM for HN2; this correlated with an increase in both DNA damage and markers of apoptosis. Neuronal cultures treated with sublethal concentrations of MAM (100 microM) or HN2 (1.0 microM) were then examined for gene expression using large-scale mouse cDNA microarrays (27,648). Gene expression results revealed that a) global gene expression was predominantly up-regulated by both genotoxicants; b) the number of down-regulated genes was approximately 3-fold greater for HN2 than for MAM; and c) distinct classes of molecules were influenced by MAM (i.e, neuronal differentiation, the stress and immune response, and signal transduction) and HN2 (i.e, protein synthesis and apoptosis). CONCLUSIONS: These studies demonstrate that individual genotoxicants induce distinct gene expression signatures. Further study of these molecular networks may explain the variable response of the developing brain to different types of environmental genotoxicants.