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Bhargava A, Arnold AP, Bangasser DA, Denton KM, Gupta A, Hilliard Krause LM, Mayer EA, McCarthy M, Miller WL, Raznahan A, Verma R. Considering Sex as a Biological Variable in Basic and Clinical Studies: An Endocrine Society Scientific Statement. Endocr Rev 2021; 42:219-258. [PMID: 33704446 PMCID: PMC8348944 DOI: 10.1210/endrev/bnaa034] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Indexed: 02/08/2023]
Abstract
In May 2014, the National Institutes of Health (NIH) stated its intent to "require applicants to consider sex as a biological variable (SABV) in the design and analysis of NIH-funded research involving animals and cells." Since then, proposed research plans that include animals routinely state that both sexes/genders will be used; however, in many instances, researchers and reviewers are at a loss about the issue of sex differences. Moreover, the terms sex and gender are used interchangeably by many researchers, further complicating the issue. In addition, the sex or gender of the researcher might influence study outcomes, especially those concerning behavioral studies, in both animals and humans. The act of observation may change the outcome (the "observer effect") and any experimental manipulation, no matter how well-controlled, is subject to it. This is nowhere more applicable than in physiology and behavior. The sex of established cultured cell lines is another issue, in addition to aneuploidy; chromosomal numbers can change as cells are passaged. Additionally, culture medium contains steroids, growth hormone, and insulin that might influence expression of various genes. These issues often are not taken into account, determined, or even considered. Issues pertaining to the "sex" of cultured cells are beyond the scope of this Statement. However, we will discuss the factors that influence sex and gender in both basic research (that using animal models) and clinical research (that involving human subjects), as well as in some areas of science where sex differences are routinely studied. Sex differences in baseline physiology and associated mechanisms form the foundation for understanding sex differences in diseases pathology, treatments, and outcomes. The purpose of this Statement is to highlight lessons learned, caveats, and what to consider when evaluating data pertaining to sex differences, using 3 areas of research as examples; it is not intended to serve as a guideline for research design.
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Affiliation(s)
- Aditi Bhargava
- Center for Reproductive Sciences, San Francisco, CA, USA
- Department of Obstetrics and Gynecology, University of California, San Francisco, CA, USA
| | - Arthur P Arnold
- Department of Integrative Biology & Physiology, University of California, Los Angeles, Los Angeles, CA, USA
| | - Debra A Bangasser
- Department of Psychology and Neuroscience Program, Temple University, Philadelphia, PA, USA
| | - Kate M Denton
- Cardiovascular Disease Program, Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Victoria, Australia
| | - Arpana Gupta
- G. Oppenheimer Center for Neurobiology of Stress and Resilience, Division of Digestive Diseases, University of California, Los Angeles, Los Angeles, CA, USA
| | - Lucinda M Hilliard Krause
- Cardiovascular Disease Program, Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Victoria, Australia
| | - Emeran A Mayer
- G. Oppenheimer Center for Neurobiology of Stress and Resilience, Division of Digestive Diseases, University of California, Los Angeles, Los Angeles, CA, USA
| | - Margaret McCarthy
- Department of Pharmacology and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Walter L Miller
- Center for Reproductive Sciences, San Francisco, CA, USA
- Department of Pediatrics, University of California, San Francisco, CA, USA
| | - Armin Raznahan
- Section on Developmental Neurogenomics, Human Genetics Branch, National Institutes of Mental Health, Intramural Research Program, Bethesda, MD, USA
| | - Ragini Verma
- Diffusion and Connectomics In Precision Healthcare Research (DiCIPHR) lab, Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
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Abstract
Communication pathways of the hypothalamus with other brain regions and the periphery are critical to successfully control key physiological and psychological processes. With advanced functional magnetic resonance imaging (fMRI) techniques, it is possible to target hypothalamic function and infer discrete hypothalamus networks. Resting-state functional connectivity (RSFC) is a promising tool to study the functional organization of the brain and may act as a marker of individual differences and dysfunctions. Based on recent fMRI findings, the hypothalamus is mostly connected to parts of the striatum, midbrain, thalamus, insula, frontal, cingulate, and temporal cortices and the cerebellum. There is a strong interplay of the hypothalamus with these regions in response to different metabolic, hormonal, and nutritional states. In a state of hunger, hypothalamus RSFC increases with a strong shift to reward-related brain regions, especially in person with excessive weight. Nutrient signals and hormones, as insulin, act on these same connections conveying reward and internal signals to regulate homeostatic control. Moreover, dysfunctional hypothalamus communication has been documented in persons with neurological and psychiatric diseases. The results implicate that patients with depression, epilepsy, and neurodegenerative diseases show mostly a reduction in hypothalamus RSFC, whereas patients with migraine and headache display predominantly increased hypothalamus RSFC. The extent of these changes and regions affected depend on the disorder and symptom severity. Whether hypothalamus RSFC can serve as a marker for disease states or is a prodromal neurobiological feature still needs to be investigated.
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The interrelationship of body mass index with gray matter volume and resting-state functional connectivity of the hypothalamus. Int J Obes (Lond) 2019; 44:1097-1107. [PMID: 31796869 PMCID: PMC8643195 DOI: 10.1038/s41366-019-0496-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 10/26/2019] [Accepted: 11/06/2019] [Indexed: 11/08/2022]
Abstract
Background The hypothalamus plays an important role in regulating body weight through its interactions with multiple brain circuits involved in distinct aspects of feeding behavior. Yet, how hypothalamic gray matter volume (GMV) and connectivity may be related to individual differences in body weight remains unclear. We tested the hypothesis that the hypothalamus shows enhanced resting-state functional connectivity (rsFC) with regions of the reward, motivation, and motor circuits in positive correlation with body mass index (BMI) and the opposite with those associated with inhibitory control. We further examined the interdependent relationships between hypothalamic GMV, connectivity, and body weight. Methods Using seed-based rsFC and voxel-based morphometry analyses, we examined the relationship between the rsFC and GMV of the hypothalamus and BMI in 105 healthy humans. Additionally, we employed mediation analyses to characterize the inter-relationships between hypothalamic connectivity, GMV, and BMI. Results A whole-brain multiple regression showed that BMI was positively correlated with hypothalamic rsFC with the insula, thalamus, globus pallidus, and cerebellum, and negatively correlated with hypothalamic rsFC with the superior parietal lobule. Thus, higher BMI was associated with enhanced hypothalamic connectivity with regions involved in motivated feeding and reduced connectivity with those in support of cognitive control of food intake. A second whole-brain multiple regression revealed a positive correlation between hypothalamic GMV and the hypothalamus-posterior insula connectivity. Finally, the relationship between hypothalamic GMV and BMI was significantly and bidirectionally mediated by the hypothalamus-posterior insula connectivity. Conclusions The current findings suggest that the hypothalamus differentially interacts with the motivation, motor, and control circuits to regulate BMI. We further found evidence for the interdependence of hypothalamic structure, function, and body weight, which provides potential insights into the brain mechanisms of obesity.
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Krolick KN, Zhu Q, Shi H. Effects of Estrogens on Central Nervous System Neurotransmission: Implications for Sex Differences in Mental Disorders. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2018; 160:105-171. [PMID: 30470289 PMCID: PMC6737530 DOI: 10.1016/bs.pmbts.2018.07.008] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Nearly one of every five US individuals aged 12 years old or older lives with certain types of mental disorders. Men are more likely to use various types of substances, while women tend to be more susceptible to mood disorders, addiction, and eating disorders, all of which are risks associated with suicidal attempts. Fundamental sex differences exist in multiple aspects of the functions and activities of neurotransmitter-mediated neural circuits in the central nervous system (CNS). Dysregulation of these neural circuits leads to various types of mental disorders. The potential mechanisms of sex differences in the CNS neural circuitry regulating mood, reward, and motivation are only beginning to be understood, although they have been largely attributed to the effects of sex hormones on CNS neurotransmission pathways. Understanding this topic is important for developing prevention and treatment of mental disorders that should be tailored differently for men and women. Studies using animal models have provided important insights into pathogenesis, mechanisms, and new therapeutic approaches of human diseases, but some concerns remain to be addressed. The purpose of this chapter is to integrate human and animal studies involving the effects of the sex hormones, estrogens, on CNS neurotransmission, reward processing, and associated mental disorders. We provide an overview of existing evidence for the physiological, behavioral, cellular, and molecular actions of estrogens in the context of controlling neurotransmission in the CNS circuits regulating mood, reward, and motivation and discuss related pathology that leads to mental disorders.
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Affiliation(s)
- Kristen N Krolick
- Center for Physiology and Neuroscience, Department of Biology, Miami University, Oxford, OH, United States
| | - Qi Zhu
- Center for Physiology and Neuroscience, Department of Biology, Miami University, Oxford, OH, United States
| | - Haifei Shi
- Center for Physiology and Neuroscience, Department of Biology, Miami University, Oxford, OH, United States; Cellular, Molecular and Structural Biology, Miami University, Oxford, OH, United States.
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Kumar S, Grundeis F, Brand C, Hwang HJ, Mehnert J, Pleger B. Satiety-induced enhanced neuronal activity in the frontal operculum relates to the desire for food in the obese female brain. Exp Brain Res 2018; 236:2553-2562. [PMID: 29934780 DOI: 10.1007/s00221-018-5318-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Accepted: 06/19/2018] [Indexed: 11/27/2022]
Abstract
In the present pilot study, we questioned how eating to satiety affects cognitive influences on the desire for food and corresponding neuronal activity in the obese female brain. During EEG recording, lean (n = 10) and obese women (n = 10) self-rated the ability to reappraise visually presented food. All women were measured twice, when hungry and after eating to satiety. After eating to satiety, reappraisal of food was easier than when being hungry. Comparing the EEG data of the sated to the hungry state, we found that only in obese women the frontal operculum was involved not only in the reappraisal of food but also in admitting the desire for the same food. The right frontal operculum in the obese female brain, assumed to primarily host gustatory processes, may be involved in opposing cognitive influences on the desire for food. These findings may help to find potential brain targets for non-invasive brain stimulation or neurofeedback studies that aim at modulating the desire for food.
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Affiliation(s)
- Saurabh Kumar
- Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1, 04103, Leipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital Leipzig, Liebigstraße 18, 04103, Leipzig, Germany.,Department of System Neuroscience, Universal Medical Center, Hamburg-Eppendorf, Martinistr. 52, 20246, Hamburg, Germany
| | - Felicitas Grundeis
- Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1, 04103, Leipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital Leipzig, Liebigstraße 18, 04103, Leipzig, Germany
| | - Cristin Brand
- Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1, 04103, Leipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital Leipzig, Liebigstraße 18, 04103, Leipzig, Germany
| | - Han-Jeong Hwang
- Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1, 04103, Leipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital Leipzig, Liebigstraße 18, 04103, Leipzig, Germany.,Department of Medical IT Convergence Engineering, Kumoh National Institute of Technology, Gumi, Republic of Korea
| | - Jan Mehnert
- Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1, 04103, Leipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital Leipzig, Liebigstraße 18, 04103, Leipzig, Germany.,Department of System Neuroscience, Universal Medical Center, Hamburg-Eppendorf, Martinistr. 52, 20246, Hamburg, Germany
| | - Burkhard Pleger
- Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstraße 1, 04103, Leipzig, Germany. .,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital Leipzig, Liebigstraße 18, 04103, Leipzig, Germany. .,Department of Neurology, BG University Clinic Bergmannsheil, Ruhr-University Bochum, Bürkle-de-la-Camp Place 1, 44789, Bochum, Germany. .,Collaborative Research Centre 874 "Integration and Representation of Sensory Processes", Ruhr-University Bochum, Universitätsstr. 150, 44780, Bochum, Germany. .,BMBF "nutriCARD", Friedrich-Schiller-University Jena (FSU), Dornburger Str. 25, 07743, Jena, Germany.
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Grundeis F, Brand C, Kumar S, Rullmann M, Mehnert J, Pleger B. Non-invasive Prefrontal/Frontal Brain Stimulation Is Not Effective in Modulating Food Reappraisal Abilities or Calorie Consumption in Obese Females. Front Neurosci 2017; 11:334. [PMID: 28676735 PMCID: PMC5476843 DOI: 10.3389/fnins.2017.00334] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 05/29/2017] [Indexed: 01/28/2023] Open
Abstract
Background/Objectives: Previous studies suggest that non-invasive transcranial direct current stimulation (tDCS) applied to the prefrontal cortex modulates food choices and calorie intake in obese humans. Participants/Methods: In the present fully randomized, placebo-controlled, within-subject and double-blinded study, we applied single sessions of anodal, cathodal, and sham tDCS to the left dorsolateral prefrontal cortex (DLPFC) and contralateral frontal operculum in 25 hungry obese women and investigated possible influences on food reappraisal abilities as well as calorie intake. We hypothesized that tDCS, (i) improves the ability to regulate the desire for visually presented foods and, (ii) reduces their consumption. Results: We could not confirm an effect of anodal or cathodal tDCS, neither on the ability to modulate the desire for visually presented foods, nor on calorie consumption. Conclusions: The present findings do not support the notion of prefrontal/frontal tDCS as a promising treatment option for obesity.
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Affiliation(s)
- Felicitas Grundeis
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital LeipzigLeipzig, Germany
| | - Cristin Brand
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital LeipzigLeipzig, Germany
| | - Saurabh Kumar
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital LeipzigLeipzig, Germany
| | - Michael Rullmann
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital LeipzigLeipzig, Germany
| | - Jan Mehnert
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital LeipzigLeipzig, Germany.,Department of Systems Neuroscience, University Medical Center Hamburg-EppendorfHamburg, Germany
| | - Burkhard Pleger
- Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany.,Collaborative Research Centre 1052 "Obesity Mechanisms", University Hospital LeipzigLeipzig, Germany.,Department of Neurology, BG University Clinic Bergmannsheil, Ruhr-University BochumBochum, Germany
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