Divergent gene expression patterns in alcohol and opioid use disorders lead to consistent alterations in functional networks within the Dorsolateral Prefrontal Cortex.

Substance Use Disorders (SUDs) manifest as persistent drug-seeking behavior despite adverse consequences, with Alcohol Use Disorder (AUD) and Opioid Use Disorder (OUD) representing prevalent forms associated with significant mortality rates and economic burdens. The co-occurrence of AUD and OUD is common, necessitating a deeper comprehension of their intricate interactions. While the causal link between these disorders remains elusive, shared genetic factors are hypothesized. Leveraging public datasets, we employed genomic and transcriptomic analyses to explore conserved and distinct molecular pathways within the dorsolateral prefrontal cortex associated with AUD and OUD. Our findings unveil modest transcriptomic overlap at the gene level between the two disorders but substantial convergence on shared biological pathways. Notably, these pathways predominantly involve inflammatory processes, synaptic plasticity, and key intracellular signaling regulators. Integration of transcriptomic data with the latest genome-wide association studies (GWAS) for problematic alcohol use (PAU) and OUD not only corroborated our transcriptomic findings but also confirmed the limited shared heritability between the disorders. Overall, our study indicates that while alcohol and opioids induce diverse transcriptional alterations at the gene level, they converge on select biological pathways, offering promising avenues for novel therapeutic targets aimed at addressing both disorders simultaneously.

Unlocking the complete blood count as a risk stratification tool for breast cancer using machine learning: a large scale retrospective study.

Optimizing early breast cancer (BC) detection requires effective risk assessment tools. This retrospective study from Brazil showcases the efficacy of machine learning in discerning complex patterns within routine blood tests, presenting a globally accessible and cost-effective approach for risk evaluation. We analyzed complete blood count (CBC) tests from 396,848 women aged 40-70, who underwent breast imaging or biopsies within six months after their CBC test. Of these, 2861 (0.72%) were identified as cases: 1882 with BC confirmed by anatomopathological tests, and 979 with highly suspicious imaging (BI-RADS 5). The remaining 393,987 participants (99.28%), with BI-RADS 1 or 2 results, were classified as controls. The database was divided into modeling (including training and validation) and testing sets based on diagnostic certainty. The testing set comprised cases confirmed by anatomopathology and controls cancer-free for 4.5-6.5 years post-CBC. Our ridge regression model, incorporating neutrophil-lymphocyte ratio, red blood cells, and age, achieved an AUC of 0.64 (95% CI 0.64-0.65). We also demonstrate that these results are slightly better than those from a boosting machine learning model, LightGBM, plus having the benefit of being fully interpretable. Using the probabilistic output from this model, we divided the study population into four risk groups: high, moderate, average, and low risk, which obtained relative ratios of BC of 1.99, 1.32, 1.02, and 0.42, respectively. The aim of this stratification was to streamline prioritization, potentially improving the early detection of breast cancer, particularly in resource-limited environments. As a risk stratification tool, this model offers the potential for personalized breast cancer screening by prioritizing women based on their individual risk, thereby indicating a shift from a broad population strategy.

Solvate Suite: A Command-Line Interface for Molecular Simulations and Multiscale Microsolvation Modeling.

In this work, we introduce the Solvate Suite, a comprehensive and modular command-line interface designed for molecular simulation and microsolvation modeling. The suite interfaces with widely used scientific software, streamlining computational experiments for liquid systems through the automated creation of simulation boxes and topology with adjustable simulation parameters. Furthermore, it has features for graphical and statistical analysis of simulated properties and extraction of trajectory configurations with various filters. Additionally, it introduces innovative strategies for microsolvation modeling with a multiscale approach, employing equilibrated dynamics to identify favorable solute-solvent interactions and enabling full cluster optimization for free-energy calculations without imaginary frequency contamination.

MicroRNAs as Diagnostic Biomarkers and Predictors of Antidepressant Response in Major Depressive Disorder: A Systematic Review.

Despite the hardships of major depressive disorder (MDD), biomarkers for the diagnosis and pharmacological management of this condition are lacking. MicroRNAs are epigenetic mechanisms that could provide promising MDD biomarkers. Our aim was to summarize the findings and provide validation for the selection and use of specific microRNAs as biomarkers in the diagnosis and treatment of MDD. A systematic review was conducted using the PubMed/Medline, Cochrane, PsycINFO, Embase, and LILACS databases from March 2022 to November 2023, with clusters of terms based on "microRNA" and "antidepressant". Studies involving human subjects, animal models, and cell cultures were included, whereas those that evaluated herbal medicines, non-pharmacological therapies, or epigenetic mechanisms other than miRNA were excluded. The review revealed differences in the expression of various microRNAs when considering the time of assessment (before or after antidepressant treatment) and the population studied. However, due to the heterogeneity of the microRNAs investigated, the limited size of the samples, and the wide variety of antidepressants used, few conclusions could be made. Despite the observed heterogeneity, the following microRNAs were determined to be important factors in MDD and the antidepressant response: mir-1202, mir-135, mir-124, and mir-16. The findings indicate the potential for the use of microRNAs as biomarkers for the diagnosis and treatment of MDD; however, more homogeneous studies are needed.

Biodiversity dataset and atlas of the special area of conservation Montesinho/Nogueira, Portugal.

Background: The special area of conservation Montesinho/Nogueira (SAC-MN) is a key area for biodiversity conservation in the Iberian Peninsula. Covering an area of approximately 1081 km² in the northeast of Portugal mainland, the SAC-MN is home to a wide range of species, including several endemic and endangered species and priority habitats. Despite its ecological significance and importance for conservation, there is a lack of publicly available biodiversity data, which urges the need to create a comprehensive and up-to-date biodiversity dataset for the SAC-MN. New information: To bridge the knowledge gap on biodiversity in SAC-MN, we undertook a thorough data collection process, including species occurrence records and conservation status information at regional (Portugal) and European levels, from multiple sources. We collected and compiled this information for five major taxonomic groups (amphibians, birds, flora - vascular plants, mammals and reptiles) in SAC-MN, resulting in a total of 31,871 records with 1,312 documented species. In addition, we developed an easy-to-navigate web-based geographic information system (Web GIS). In this article, we present an in-depth report on the process of compiling and preparing data, as well as the development and design of our Web GIS to increase awareness and enhance understanding of the importance of preserving biodiversity in SAC-MN.

Association of socioeconomic deprivation with outcomes in critically ill adult patients: an observational prospective multicenter cohort study.

BACKGROUND: The influence of socioeconomic deprivation on health inequalities is established, but its effect on critically ill patients remains unclear, due to inconsistent definitions in previous studies. METHODS: Prospective multicenter cohort study conducted from March to June 2018 in eight ICUs in the Greater Paris area. All admitted patients aged ≥ 18 years were enrolled. Socioeconomic phenotypes were identified using hierarchical clustering, based on education, health insurance, income, and housing. Association of phenotypes with 180-day mortality was assessed using Cox proportional hazards models. RESULTS: A total of 1,748 patients were included. Median age was 62.9 [47.4-74.5] years, 654 (37.4%) patients were female, and median SOFA score was 3 [1-6]. Study population was clustered in five phenotypes with increasing socioeconomic deprivation. Patients from phenotype A (n = 958/1,748, 54.8%) were without socioeconomic deprivation, patients from phenotype B (n = 273/1,748, 15.6%) had only lower education levels, phenotype C patients (n = 117/1,748, 6.7%) had a cumulative burden of 1[1-2] deprivations and all had housing deprivation, phenotype D patients had 2 [1-2] deprivations, all of them with income deprivation, and phenotype E patients (n = 93/1,748, 5.3%) included patients with 3 [2-4] deprivations and included all patients with health insurance deprivation. Patients from phenotypes D and E were younger, had fewer comorbidities, more alcohol and opiate use, and were more frequently admitted due to self-harm diagnoses. Patients from phenotype C (predominant housing deprivation), were more frequently admitted with diagnoses related to chronic respiratory diseases and received more non-invasive positive pressure ventilation. Following adjustment for age, sex, alcohol and opiate use, socioeconomic phenotypes were not associated with increased 180-day mortality: phenotype A (reference); phenotype B (hazard ratio [HR], 0.85; 95% confidence interval CI 0.65-1.12); phenotype C (HR, 0.56; 95% CI 0.34-0.93); phenotype D (HR, 1.09; 95% CI 0.78-1.51); phenotype E (HR, 1.20; 95% CI 0.73-1.96). CONCLUSIONS: In a universal health care system, the most deprived socioeconomic phenotypes were not associated with increased 180-day mortality. The most disadvantaged populations exhibit distinct characteristics and medical conditions that may be addressed through targeted public health interventions.

Biochar obtained from eucalyptus, rice hull, and native bamboo as an alternative to decrease mobility of hexazinone, metribuzin, and quinclorac in a tropical soil.

Mobile herbicides have a high potential for groundwater contamination. An alternative to decrease the mobility of herbicides is to apply materials with high sorbent capacity to the soil, such as biochars. The objective of this research was to evaluate the effect of eucalyptus, rice hull, and native bamboo biochar amendments on sorption and desorption of hexazinone, metribuzin, and quinclorac in a tropical soil. The sorption-desorption was evaluated using the batch equilibrium method at five concentrations of hexazinone, metribuzin, and quinclorac. Soil was amended with eucalyptus, rice hull, and native bamboo biochar at a rate of 0 (control-unamended) and 1% (w w-1), corresponding to 0 and 12 t ha-1, respectively. The amount of sorbed herbicides in the unamended soil followed the decreasing order: quinclorac (65.9%) > metribuzin (21.4%) > hexazinone (16.0%). Native bamboo biochar provided the highest sorption compared to rice hull and eucalyptus biochar-amended soils for the three herbicides. The amount of desorbed herbicides in the unamended soil followed the decreasing order: metribuzin (18.35%) > hexazinone (15.9%) > quinclorac (15.1%). Addition of native bamboo biochar provided the lowest desorption among the biochar amendments for the three herbicides. In conclusion, the biochars differently affect the sorption and desorption of hexazinone, metribuzin, and quinclorac mobile herbicides in a tropical soil. The addition of eucalyptus, rice hull, and native bamboo biochars is a good alternative to increase the sorption of hexazinone, metribuzin, and quinclorac, thus, reducing mobility and availability of these herbicides to nontarget organisms in soil.

Niche analyses and the potential distribution of four invasive bumblebees worldwide.

The introduction of bees for agricultural production in distinct parts of the world and poor management have led to invasion processes that affect biodiversity, significantly impacting native species. Different Bombus species with invasive potential have been recorded spreading in different regions worldwide, generating ecological and economic losses. We applied environmental niche and potential distribution analyses to four species of the genus Bombus to evaluate the similarities and differences between their native and invaded ranges. We found that B. impatiens has an extended environmental niche, going from dry environmental conditions in the native range to warmer and wetter conditions in the invaded range. Bombus ruderatus also exhibited an extended environmental niche with drier and warmer conditions in the invaded range than in its native range. Bombus subterraneus expanded its environmental niche from cooler and wetter conditions in the native range to drier and warmer conditions in the invaded range. Finally, B. terrestris showed the most significant variation in the environmental niche, extending to areas with similar and different environmental conditions from its native range. The distribution models agreed with the known distributions for the four Bombus species, presenting geographic areas known to be occupied by each species in different regions worldwide. The niche analysis indicate shifts in the niches from the native to the invaded distribution area of the bee species. Still, niche similarities were observed in the areas of greatest suitability in the potential distribution for B. ruderatus, B. subterraneus, and B. terrestris, and to a lesser degree in the same areas with B. impatiens. These species require similar environmental conditions as in their native ranges to be established in their introduced ranges. Still, they can adapt to changes in temperature and humidity, allowing them to expand their ranges into new climatic conditions.

Novel Fe3O4 Nanoparticles with Bioactive Glass-Naproxen Coating: Synthesis, Characterization, and In Vitro Evaluation of Bioactivity.

Immune response to biomaterials, which is intimately related to their surface properties, can produce chronic inflammation and fibrosis, leading to implant failure. This study investigated the development of magnetic nanoparticles coated with silica and incorporating the anti-inflammatory drug naproxen, aimed at multifunctional biomedical applications. The synthesized nanoparticles were characterized using various techniques that confirmed the presence of magnetite and the formation of a silica-rich bioactive glass (BG) layer. In vitro studies demonstrated that the nanoparticles exhibited bioactive properties, forming an apatite surface layer when immersed in simulated body fluid, and biocompatibility with bone cells, with good viability and alkaline phosphatase activity. Naproxen, either free or encapsulated, reduced nitric oxide production, an inflammatory marker, while the BG coating alone did not show anti-inflammatory effects in this study. Overall, the magnetic nanoparticles coated with BG and naproxen showed promise for biomedical applications, especially anti-inflammatory activity in macrophages and in the bone field, due to their biocompatibility, bioactivity, and osteogenic potential.

Cyclooxygenase-2 inhibitors alleviated depressive and anxious-like behaviors in mice exposed to lipopolysaccharide: Involvement of oxidative stress and neuroinflammation.

Depression and anxiety disorders have their pathophysiologies linked to inflammation and oxidative stress. In this context, celecoxib (CLX) and etoricoxib (ETR) inhibit cyclooxygenase 2 (COX-2), an enzyme expressed by cells involved in the inflammatory process and found in the brain. Studies have been using CLX as a possible drug in the treatment of depression, although its mechanisms at the central nervous system level are not fully elucidated. In this study, the effects of CLX and ETR on behavioral, oxidative, and inflammatory changes induced by systemic exposure to Escherichia coli lipopolysaccharide (LPS) were evaluated in adult male swiss mice. For ten days, the animals received intraperitoneal injections of LPS at 0.5 mg/kg. From the sixth to the tenth day, one hour after LPS exposure, they were treated orally with CLX (15 mg/kg), ETR (10 mg/kg), or fluoxetine (FLU) (20 mg/kg). Twenty-four hours after the last oral administration, the animals underwent evaluation of locomotor activity (open field test), predictive tests for depressive-like behavior (forced swim and tail suspension tests), and anxiolytic-like effect (elevated plus maze and hole board tests). Subsequently, the hippocampus, prefrontal cortex and striatum were dissected for the measurement of oxidative and nitrosative parameters (malondialdehyde, nitrite, and glutathione) and quantification of pro-inflammatory cytokines (IL-1ß and IL-6). LPS induced depressive and anxious-like behavior, and treatment with CLX or ETR was able to reverse most of the behavioral changes. It was evidenced that nitrosative stress and the degree of lipid peroxidation induced by LPS were reduced in different brain areas after treatment with the drugs, as well as the endogenous defense system against free radicals was strengthened. CLX and ETR also significantly reduced LPS-induced cytokine levels. These data are expected to expand information on the role of inflammation in depression and anxiety and provide insights into possible mechanisms of COX-2 inhibitors in psychiatric disorders with a neurobiological basis in inflammation and oxidative stress.

Entrevista motivacional como estrategia de mejoramiento de la salud bucal de niños y cuidadores. Revisión en sombrilla / Motivational interviewing as a strategy to improve the oral health of children and caregivers. Umbrella review

Objetivo: demostrar la efectividad de la entrevista motivacional (EM) en el mejoramiento de algunos indicadores de salud bucal en niños de 0 a 12 años y sus cuidadores. Material y métodos: estudio de revisión en sombrilla (umbrella review). Se realizó búsqueda en bases de datos electrónicas (PubMed, MEDLINE, SCOPUS, EBSCO) y Google Scholar desde el año 2010 hasta el año 2020, con las siguientes palabras clave: ('motivational interviewing' OR 'motivational interview' OR 'motivational interviewing style' OR 'motivational intervention' OR 'motivational counseling' OR 'brief motivational counseling' OR 'maternal counseling' OR 'behavioral intervention') AND (“caries” OR 'dental caries' OR 'tooth decay' OR 'dental decay' OR 'carious lesions' OR 'DMFT index' OR “ICDAS”) AND ('gingival diseases' OR “gingivitis” OR “CPITN” OR 'gingival bleeding' OR 'dental calculus') AND (“children” OR “families” OR “caregivers”). Se incluyeron artículos originales sobre la efectividad de la entrevista motivacional en salud bucal (EMSB) en niños de hasta 12 años y cuidadores, tipo revisión sistemática de la literatura y metanálisis, desde el año 2010 hasta el 2020. Resultados: 69 artículos (2 revisiones sistemáticas y 4 metanálisis). Los indicadores encontrados fueron: cambios en la presentación de caries de la infancia temprana, higiene bucal, condiciones gingivales y frecuencia de visitas a la consulta odontológica, con resultados alentadores y, en otros, contradictorios. Conclusiones: la evidencia sobre la efectividad de la entrevista motivacional en comparación con la educación convencional muestra cambios positivos en indicadores de salud bucal, como mejoramiento de la higiene dental y de la presentación de la caries en la primera infancia. (AU)

Objective: to demonstrate, the effectiveness of motivational interviewing in improving oral health indicators in children aged 0 to 12 years and their caregivers. Material and method: an umbrella review design. Search in electronic databases (PubMed, MEDLINE, SCOPUS, EBSCO) and Google Scholar since 2010 to 2020, with the following keywords: ('Motivational interviewing' OR 'motivational interview' OR 'motivational interviewing style' OR 'motivational intervention' OR 'motivational counseling' OR 'brief motivational counseling' OR 'maternal counseling' OR 'behavioral intervention') AND (“caries” OR 'dental caries' OR 'tooth decay' OR 'dental decay' OR 'carious lesions' OR 'DMFT index' OR “ICDAS”) AND ('gingival diseases' OR “gingivitis” OR “CPITN” OR 'gingival bleeding' OR 'dental calculus') AND (“children” OR “families” OR “caregivers”), original articles on the effectiveness of motivational interviewing in oral health (EMSB) in children between 0 and 12 years of age and caregivers, type systematic review of the literature and metaanalysis. Results: 69 articles were found (2 systematic reviews and 4 metaanalysis). The indicators found: change in early childhood caries, oral hygiene, gingival conditions and frequency of visits to the dental office with promise results and others contradictories. Conclusion: the evidence on the effectiveness of motivational interviewing compared to conventional education shows positive changes in oral health indicators such as improvement in dental hygiene and the presentation of caries in early childhood, among others. (AU)

Herbicide Leaching in Soil with Different Properties: Perspectives from Commercial Formulations and Analytical Standards.

The leaching of herbicides into the soil is essential to control germinating seeds and parts of vegetative weeds. However, herbicide transportation to deeper soil layers can result in groundwater contamination and, consequently, environmental issues. In this research, our objective was to investigate differences in herbicide leaching between commercial formulations and analytical standards using three different soils. Leaching experiments were carried out for diuron, hexazinone, and sulfometuron-methyl herbicides isolated and in binary and ternary mixtures. The herbicide residue quantification was performed by ultra-high-performance liquid chromatography coupled to a mass spectrometer (LC-MS/MS). Diuron had less mobility in soils and was retained in the most superficial layers. Hexazinone and sulfometuron-methyl were more mobile and leached into deeper layers. The leaching process was more intense for hexazinone and sulfometuron-methyl. The additives present in the commercial formulation favored the leaching in soils of diuron, hexazinone, and sulfometuron-methyl herbicides isolated and mixture compared to the analytical standard. This fact highlights the importance of considering these effects for the positioning of herbicides in the field to increase the efficiency of weed control and minimize the potential for environmental contamination.

Long-term administration of omeprazole in mice: a study of behavior, inflammatory, and oxidative stress alterations with focus on central nervous system.

Chronic use of omeprazole has been linked to central effects alongside with the global concern of increasing appearance of neuropsychiatric disorders. This study aimed to identifying behavioral, inflammatory, and oxidative stress alterations after long-term administration of omeprazole. C57BL/6 mice were divided in groups: OME and Sham, each received either solutions of omeprazole or vehicle, administered for 28 days by gavage. Results observed in the omeprazole-treated mice: Decrease in the crossing parameter in the open field, no change in the motor performance assessed by rotarod, an immobility time reduction in the forced swimming test, improved percentage of correct alternances in the Ymaze and an exploration time of the novel object reduction in the novel object recognition. Furthermore, a reduced weight gain and hippocampal weight were observed. There was an increase in the cytokine IL1-ß levels in both prefrontal cortex (PFC) and serum, whereas TNF-α increased only in the PFC. Nitrite levels increased in the hippocampus (HP) and PFC, while malondialdehyde (MDA) and glutathione (GSH) levels decreased. These findings suggest that omeprazole improves depressive-like behavior and working memory, likely through the increase in nitrite and reduction in MDA levels in PFC and HP, whereas, the impairment of the recognition memory is more likely to be related to the reduced hippocampal weight. The diminished weight gain might be associated with the IL-1ß increased levels in the peripheral blood. Altogether, omeprazole showed to have the potential to impact at central level and inflammatory and oxidative parameters might exert a role between it.

Radiologic and computed tomography evaluation of the beaks from three bird species.

This study aimed to evaluate the beaks of three species of birds using radiography and computed tomography (CT). The mean lengths of maxillary and mandibular rostra on radiographs were highest for toco toucan, followed by buff-necked ibis, and least for red-legged seriema birds. The height and width of maxillary and mandibular rostra measured on CT had mean values highest for toco toucans, followed by red-legged seriema, and least for buff-necked ibis. Except for the proximal region of the maxillary rostrum, the HU values were positive for other regions of the maxillary and mandibular rostra in the buff-necked ibis and red-legged seriema and negative in all for the toco toucan.

Impact of feeding native Caatinga pasture on the rumen histomorphometry of sheep raised in semi-extensive management.

In the northeastern region of Brazil, sheep and goat farming, encompassing around 20 million animals, is predominantly a subsistence activity. Forage quality plays a crucial role in animal productivity, posing a complex interplay between plant and animal aspects. The Caatinga biome, vital for livestock in the region, serves as a significant source for animal diet through pastures. This study aimed to conduct a histomorphometric evaluation of sheep rumens in a semi-extensive system, comparing those feeding on native Caatinga pastures to those on cultivated pastures. Histological processing followed standard protocols, with morphometry focusing on six viable rumen papillae and the submucosa and muscular layer thickness. Statistical correlation analysis revealed morphological differences in papillae across various rumen regions. Morphometric data indicated no significant difference in papillae area between the groups, with average values in Group A surpassing those in Group B, except for width. This study establishes a morphological and morphometric pattern for rumen regions linked to diet types-native or cultivated. The findings not only enhance understanding of the dietary foundation in the Caatinga's extensive system, but also contribute valuable insights for formulating nutritional strategies to enhance sheep production in the region. This research sheds light on the intricacies of forage-based animal nutrition, particularly in semi-extensive systems, offering a foundation for future studies and practices to optimise livestock management in the northeastern Brazilian context.

Correction: Cotovio et al. Regulatory Clearance and Approval of Therapeutic Protocols of Transcranial Magnetic Stimulation for Psychiatric Disorders. Brain Sci. 2023, 13, 1029.

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Oral health challenges in patients with chronic kidney disease: A comprehensive clinical assessment.

Loss of kidney function causes oral manifestations and multiple complications that have implications for dental treatment and patients' systemic conditions. We aimed to determine the clinical condition, epidemiological profile, and incidence of dental caries in patients with chronic kidney disease (CKD). This was an observational, cross-sectional, field study using a quantitative and epidemiological approach. The sample consisted of 45 randomly selected patients with CKD from a total of 114 patients. Data were collected through oral clinical examination, anamnesis, and medical records compiled in a clinical file specially developed for this research. Clinical evaluation was performed, including a Decayed, Missing, and Filled Teeth (DMFT) index examination. Data were analyzed using the Shapiro-Wilk test, Mann-Whitney test, and Spearman's rho coefficient. All analyses were performed using IBM SPSS Statistics software version 20.0, with a confidence interval of 95 % and significance level of 5 % (p < 0.05). The results indicated that CKD is more prevalent in the 5th decade of life, with a slight predilection for men. Oral cavity alterations were observed in 77.8 % of patients. The study population had a very high DMFT index, with a high number of missing teeth and a low number of decayed and filled teeth. Poor oral health in patients with CKD indicates a lack of care that supports the necessity of installing a preventive and therapeutic oral program and a regular follow-up aimed at this group of patients.

Reducing motor evoked potential amplitude variability through normalization.

Background: Transcranial Magnetic Stimulation (TMS) is used for in vivo assessment of human motor cortical excitability, with application of TMS pulses over the motor cortex resulting in muscle responses that can be recorded with electromyography (EMG) as Motor Evoked Potentials (MEPs). These have been widely explored as potential biomarkers for neuropsychiatric disorders but methodological heterogeneity in acquisition, and inherent high variability, have led to constraints in reproducibility. Normalization, consisting in scaling the signal of interest to a known and repeatable measurement, reduces variability and is standard practice for between-subject comparisons of EMG. The effect of normalization on variability of MEP amplitude has not yet been explored and was assessed here using several methods. Methods: Three maximal voluntary isometric contractions (MVICs) and 40 MEPs were collected from the right hand in healthy volunteers, with a retest session conducted 4 to 8 weeks later. MEP amplitude was normalized using either external references (MVICs) or internal references (extreme MEPs). Iterative re-sampling of 30 normalized MEPs per subject was repeated 5,000 times to define, for each normalization method, distributions for between-subject coefficients of variation (CV) of the mean MEP amplitude. Intra-class correlation coefficients (ICC) were used to assess the impact of normalization on test­retest stability of MEP amplitude measurements. Results: In the absence of normalization, MEPs collected from the right hand of 47 healthy volunteers were within reported values regarding between-subject variability (95% confidence intervals for the CV: [1.0567,1.0577]) and showed good temporal stability (ICC = 0.77). Internal reference normalization substantially reduced between-subject variability, by values of up to 64%, while external reference normalization had no impact or increased between-subject variability. Normalization with the smallest references reduced test­retest stability, with use of the largest references resulting in slight reduction or improvement of ICCs. Internal reference normalization using the largest MEPs was found to be robust to several sensitivity analyses. Conclusion: Internal, but not external, reference normalization reduces between-subject variability of MEP amplitude, and has a minimal impact on within-subject variability when conducted with the largest references. Additional research is necessary to further validate these normalization methods toward potential use of MEPs as biomarkers of neuropsychiatric disorders.