Researchers divided Sprague-Dawley rats into sham-operated, MIRI, and sevoflurane-plus-MIRI groups. They measured myocardial infarct size with 2,3,5-triphenyltetrazolium chloride staining, examined cardiac tissue with hematoxylin and eosin staining, and detected apoptotic nuclei using TUNEL staining. Quantitative reverse-transcription PCR and western blotting were used to quantify circ_SMG6 and TLR4/mTOR expression.

In the rat experiment, MIRI increased the myocardial apoptotic index, infarct size, and structural cardiac damage while elevating circ_SMG6 and TLR4/mTOR signaling. These changes were reduced with sevoflurane, although the abstract states that they were not entirely restored. In AC16 and HCM cardiomyocyte models, hypoxia-reoxygenation increased circ_SMG6, reduced cell viability, increased production of TNF-α, IL-1β, and IL-6, and increased the measured TLR4/mTOR signaling readout.

The investigators also tested circ_SMG6 overexpression and knockdown 48 hours before hypoxia-reoxygenation, with or without sevoflurane. Knockdown reversed the measured effects of hypoxia-reoxygenation, whereas overexpression further aggravated the reported injury, supporting the involvement of circ_SMG6 in the inflammatory and apoptotic responses in these cell models. Sevoflurane produced changes similar to circ_SMG6 silencing at the functional and signaling levels. These findings come from rat and cell experiments and do not establish clinical efficacy or safety in patients with myocardial infarction or MIRI; the assessment here is limited to the published abstract.

Subject of Research: Preclinical testing of sevoflurane, circ_SMG6, and TLR4/mTOR signaling in myocardial ischemia-reperfusion models

Article Title: Sevoflurane suppresses circ_SMG6 to inhibit TLR4/mTOR signaling and attenuate myocardial ischemia-reperfusion injury

Article References: Feng, M., Li, W., Chen, B., & Sun, Y. (2026). Sevoflurane suppresses circ_SMG6 to inhibit TLR4/mTOR signaling and attenuate myocardial ischemia-reperfusion injury. Molecular Biology Reports, 53(1), Article 1590. https://doi.org/10.1007/s11033-026-12758-y

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12758-y

Keywords: sevoflurane, myocardial ischemia-reperfusion injury, circ_SMG6, TLR4/mTOR signaling, cardioprotection, Sprague-Dawley rats, cardiomyocytes, hypoxia-reoxygenation, inflammation, apoptosis, suppresses, circ

The particles at the center of the study came from Okhla Industrial Area-I in New Delhi, a location that blends industrial emissions with residential sources and therefore represents a realistic mixture of what millions of residents breathe daily. The researchers sampled continuously for twenty-four-hour periods between November 22, 2018 and June 30, 2019, capturing seasonal variation across Delhi’s notorious winter pollution episodes and the comparatively cleaner summer months. PM1 refers to particles with an aerodynamic diameter of one micrometer or less, a size class so fine that individual particles are invisible under ordinary light microscopes and can penetrate deep into lung tissue. Because these particles carry adsorbed toxic metals on their surfaces, toxicologists consider the chemical composition of PM1, not merely its mass, to be the primary driver of its harm.

To prepare the exposure material, the collected PM1 samples were extracted from their filters and processed both for chemical analysis and for injection. Eighteen male Sprague-Dawley rats were divided into three equal groups: a control group receiving saline, a low-dose group receiving 80.5 micrograms per kilogram of body weight, and a high-dose group receiving 244.6 micrograms per kilogram. The two exposed groups were dosed intravenously once a week for seventy days, a regimen designed to simulate the sustained systemic delivery of particle-associated metals that occurs when inhaled ultrafine particles cross from the lungs into the circulation. This route of administration is a deliberate departure from conventional inhalation studies, and the researchers are explicit that it does not fully replicate the physiology of breathing polluted air, a caveat they flag as a key limitation of the design.

After the seventy-day exposure window closed, the animals were euthanized and their organs harvested for analysis. The team used inductively coupled plasma optical emission spectroscopy, or ICP-OES, a technique that excites metal atoms in a plasma torch and reads the characteristic wavelengths of light they emit, allowing precise quantification of twelve metals: aluminum, iron, nickel, chromium, copper, lead, manganese, molybdenum, zinc, cobalt, cadmium and vanadium. To test whether differences between groups were statistically meaningful, the researchers applied one-way analysis of variance with a significance threshold of p less than 0.05, followed by Tukey’s post hoc test for multiple comparisons between the control, low-dose and high-dose cohorts. This analytical pipeline let them rank the metals not only by how much they accumulated overall but by where in the body each one preferentially settled.

The resulting hierarchy, ordered from highest to lowest concentration across the rats’ tissues, placed aluminum and iron at the top, followed by nickel, chromium, copper, lead, manganese, molybdenum, zinc, cobalt, cadmium and vanadium. Aluminum showed particularly high accumulation in the kidneys, the spleen and the cerebellum, the part of the brain responsible for motor coordination. Iron, an element whose overload is known to catalyze the production of damaging reactive oxygen species, concentrated significantly in the liver, spleen, heart and cerebellum. The convergence of both elements in the cerebellum is notable, because iron-driven oxidative stress and aluminum’s association with neurodegenerative processes have each been examined extensively in prior toxicological literature, and the metal-ranking framework in this study provides a systematic basis for pursuing those links in the context of real-world particulate exposures.

Perhaps the most consequential finding concerns lead. The study documented substantial accumulation of lead in the bloodstream and in vital organs including the lungs, heart, kidneys, liver and brain, indicating that once it detaches from its particle carrier, lead is highly mobile and disseminates widely through the body. Lead is a neurotoxin with no known safe exposure threshold, and its molecular targets include synaptotagmin I, a protein central to neurotransmitter release. The observation that intravenously delivered PM1-borne lead reached both the cerebrum and cerebellum underscores why lead remains the pollutant of greatest concern in this exposure scenario, even though it ranked only sixth in overall concentration across tissues.

Chromium and copper told their own organ-specific stories. Chromium accumulated significantly in the blood, kidneys, heart, cerebrum and cerebellum, consistent with its status as a carcinogenic metal whose hexavalent form can cross cellular membranes and damage DNA. Copper concentrated in the blood, lungs and heart, a distribution that resonates with clinical observations linking elevated myocardial copper to heart failure. The study also identified clear single-organ specialists: cobalt localized primarily in the spleen, nickel in the heart, and zinc in the kidneys. Vanadium, another transition metal associated with cardiopulmonary toxicity in earlier inhalation studies, was found at high levels in the lungs, kidneys and heart. Each of these patterns suggests that the health consequences of breathing metal-laden air may depend less on the total metal dose than on which organs each specific element finds hospitable.

Not every notorious toxin behaved as expected. Cadmium, a metal infamous for kidney damage, bone disease and endocrine disruption, showed no significant organ-level accumulation, and neither did certain other toxic trace metals. The authors suggest three non-exclusive explanations: constrained bioavailability of the metal in the particle matrix, limited cellular uptake once in circulation, or distinct metabolic clearance pathways that removed the element before it could lodge in tissue. This null result is scientifically valuable, because it demonstrates that the toxicity of particulate matter cannot be predicted simply by summing the hazardous reputations of its constituents. The same particle that delivers lead to the brain may carry cadmium that the body efficiently eliminates, meaning risk assessments must be element-specific rather than mass-based.

The intravenous delivery method deserves careful interpretation. By bypassing the respiratory tract entirely, the design isolates what happens after particles and their dissolved metals enter the blood, which is precisely the step most relevant to the emerging paradigm that air pollution’s deadliest effects, from heart attacks to strokes, arise from particles that escape the lungs rather than damage them directly. But the trade-off is realism: inhaled particles face filtration in the nose and airways, deposition patterns in the alveoli, interactions with lung immune cells and variable rates of translocation into circulation. The doses delivered by injection likely exceed what translocation alone would achieve, and the weekly bolus schedule differs from continuous low-level exposure. The authors acknowledge this limitation directly, positioning the study as a controlled probe of systemic metal fate rather than a model of the full inhalation pathway.

Even with those caveats, the study’s organ-specific metal map carries weighty implications for public health in Delhi and other megacities where PM1 concentrations routinely soar. It suggests that chronic exposure to submicron particulate matter could quietly load the kidneys, spleen, cerebellum, liver and heart with aluminum and iron, seed the heart with nickel, and circulate lead and chromium throughout the vasculature and brain. Research cited by the team connects these metals to oxidative stress, inflammation, hypertension, atherosclerosis, hepatic fibrosis, kidney damage and neurodegeneration, so each localization pattern hints at a plausible disease pathway waiting to be tested. As the authors and their collaborators continue this line of work, the challenge will be bridging the gap between this controlled murine model and the messier reality of human exposure, where inhalation, diet, genetics and comorbidities all shape the same toxic ledger that seventy days of injections so cleanly revealed.

Subject of Research: Organ-specific accumulation of metals associated with submicron particulate matter (PM1) following intravenous exposure in rats

Article Title: Preferential accumulation of PM₁-associated metals in Sprague-Dawley rats’ tissues/organs as a consequence of intravenous administration of Delhi’s airborne PM₁

Article References: Mehta, D., Kumar, M., Kumar, N., & Srivastava, A. (2026). Preferential accumulation of PM₁-associated metals in Sprague-Dawley rats’ tissues/organs as a consequence of intravenous administration of Delhi’s airborne PM₁. Air Quality, Atmosphere & Health, 19(10), Article 236. https://doi.org/10.1007/s11869-026-02125-y

Image Credits: AI Generated

DOI: 10.1007/s11869-026-02125-y

Keywords: PM1, particulate matter, air pollution, Delhi, heavy metals, toxicology, Sprague-Dawley rats, intravenous exposure, ICP-OES, organ accumulation, lead, neurotoxicity

Zinc is one of the most abundant trace elements in the male reproductive tract, and its importance is difficult to overstate. The metal is a structural component of countless enzymes and transcription factors, it stabilizes sperm chromatin, and it acts as a cofactor in the biosynthesis of testosterone. When dietary zinc falls short, the consequences for male fertility are well documented: spermatogenesis falters, sperm quality declines, and hormone profiles shift in ways that undermine the entire reproductive axis. At the same time, clinicians and livestock breeders face a parallel problem in the fertility laboratory. Sperm destined for storage must survive both the violent osmotic and thermal stresses of freeze-thaw cycling and the subtler insult of heat shock, and the reactive oxygen species generated during these events can fragment DNA and strip away motility. Conventional cryoprotective media address some of this damage but do little to control microbial contamination or to replenish the zinc that sperm and the testes so heavily depend on.

The new work rests on a deceptively simple idea. The eggshell membrane is a naturally occurring three-dimensional network of interwoven protein fibers, dominated by collagen types I, V, and X along with smaller amounts of osteopontin, sialoprotein, and lysozyme. This fibrous architecture is chemically rich in amino and carboxyl functional groups, which means it can bind metal ions and then serve as a nucleation template for growing inorganic nanocrystals directly on its surface. Rather than grinding the membrane into powder, the team kept the intact 3D fibrous scaffold and grew zinc oxide nanostructures uniformly across it, producing a hybrid material in which the organic and inorganic phases are intimately interlocked. The researchers prepared several versions of the nanocomposite using different synthesis routes, including chemical, thermal, and biogenic methods, and then systematically compared their physicochemical properties.

The comparison produced a clear winner. The thermally synthesized variant, designated ESM-ZnO-T, displayed the most favorable combination of characteristics. Microscopy confirmed that distinct zinc oxide nanostructures were anchored evenly across the nanocrystalline fibrous network, and the material showed improved colloidal stability compared with its chemically and biogenically synthesized counterparts. Most importantly for a material intended to deliver a biological payload of zinc, ESM-ZnO-T exhibited a sustained, gradual release of zinc ions rather than a burst. That slow-release behavior matters because uncontrolled zinc dosing can be cytotoxic, while a steady trickle of the ion can support cellular metabolism and tissue regeneration over time. The thermal route also conferred the strongest antimicrobial performance, with the composite inhibiting both bacterial and fungal growth in the assays the team conducted.

With the optimized formulation in hand, the researchers moved to the first of two experimental phases: testing whether the material could actually protect sperm under the two most punishing conditions a fertility laboratory can impose. They exposed sperm samples to heat shock and to freeze-thaw cycles in the presence of the nanocomposite and then measured a battery of endpoints, including viability, motility, morphological characteristics, DNA integrity, and the generation of reactive oxygen species. The results showed that ESM-ZnO-T effectively preserved sperm viability, morphology, motility, and DNA integrity across both stress conditions. The protective effect appears to stem from a dual mechanism: the composite acts as a scavenger of the reactive oxygen species that accumulate during thermal stress, while the steady release of zinc ions supports the enzymatic antioxidant machinery that sperm use to defend themselves. The team quantified the diagnostic power of their measurements using receiver operating characteristic analysis, and the optimized formulation achieved an area under the curve of 0.84 following cryopreservation, a figure that indicates strong discriminatory performance in distinguishing well-preserved from damaged samples.

The antimicrobial dimension of the material deserves particular attention because it addresses a chronic weakness of conventional sperm storage. Semen and extended semen samples are notorious vectors for bacterial and fungal contamination, and antibiotics added to cryopreservation media carry their own drawbacks, including allergic reactions and the selection of resistant strains. A cryoprotective platform that simultaneously suppresses microbial growth while shielding sperm from oxidative damage could simplify the logistics of sperm banking, particularly in veterinary and agricultural settings where large volumes of semen are processed daily and where the cost of contamination losses runs into enormous figures. The eggshell membrane scaffold itself contributes to this function, since the proteins it contains are known to interact with microbial membranes.

The second phase of the study took the question out of the culture dish and into living animals. The team turned to male Sprague-Dawley rats, a standard rodent model for reproductive toxicology, and evaluated the biological efficacy of the optimized nanocomposite through reproductive, biochemical, and histological analyses. The animals that received the treatment showed improved reproductive hormone profiles compared with control groups, along with evidence of enhanced spermatogenesis, better sperm morphology, and healthier testicular histology. In other words, the material did not merely protect sperm in a test tube; it appeared to support the biological machinery that produces sperm in the first place. The researchers attribute this to the gradual zinc ion release, which they suggest supports testicular regeneration and healthy spermatogenesis, consistent with the established role of zinc in Leydig cell function and seminiferous tubule integrity.

Perhaps the most surprising findings concerned organs far removed from the reproductive system. The study also examined the effects of the nanocomposite under conditions of hypokalemia, a dangerous drop in blood potassium, and hyperoxaluria, an excess of oxalate in the urine that is closely linked to kidney stone formation and renal injury. The treated animals showed regulation of the biochemical alterations associated with these conditions, and the material supported normal liver and kidney function even under controlled hyperoxaluric stress. The research highlights accompanying the paper note that ESM-ZnO-T enhances renal and liver function under these stress conditions, suggesting that the composite’s antioxidant and ion-regulating properties extend into systemic physiology. This metabolic dimension transforms the material from a niche fertility tool into something closer to a general-purpose zinc supplementation platform with built-in antimicrobial activity.

The study was conducted under rigorous ethical oversight. Semen analyses followed World Health Organization 2021 guidelines, informed consent was obtained from all participants with confidentiality maintained, and the animal experiments complied with the ARRIVE guidelines, the UK Animals (Scientific Procedures) Act of 1986, the EU Directive 2010/63/EU, and the guidelines of the Committee for the Purpose of Control and Supervision of Experiments on Animals, with approval from the relevant Indian animal ethics committee. The work received partial support from a JSPS KAKENHI grant and was based in part on a project commissioned by Japan’s New Energy and Industrial Technology Development Organization, with open access funding provided by Shinshu University.

Much work remains before an eggshell membrane zinc oxide nanohybrid could reach a fertility clinic or a livestock breeding center. The published study demonstrates efficacy in rats and in vitro sperm models, and translation to human sperm banking, clinical zinc deficiency therapy, or veterinary artificial insemination would require dose optimization, long-term safety studies, and regulatory review. Yet the conceptual leap is striking. The researchers have taken one of the world’s most abundant food-industry waste streams, preserved its natural three-dimensional protein architecture, and used it as the backbone for a multifunctional biomaterial that simultaneously fights microbes, protects the genome of frozen sperm, replenishes a critical trace element, and supports the health of the testes, liver, and kidneys. If the findings hold up at larger scales, the papery lining of a discarded eggshell may prove to be one of the most versatile reproductive biomaterials yet described, and a vivid reminder that the raw materials for the next generation of medical technology are often hiding in plain sight, or in this case, in the compost bin.

Subject of Research: Eggshell membrane-derived zinc oxide nanocomposites for sperm cryopreservation and treatment of zinc deficiency-related male infertility

Article Title: Protein-rich fibrous eggshell membrane derived ZnO 3D-nanohybrid for cryoprotectant, reproductive scavengers against Zn deficiency and hypokalemic effects in rats

Article References: Mayakrishnan, G., Ranganathan, P., Pichandi, M. K., Ranaganathan, B., Xiong, J., Sarwar, M. N., Ullah, A., Cha, H. J., & Soo, K. I. (2026). Protein-rich fibrous eggshell membrane derived ZnO 3D-nanohybrid for cryoprotectant, reproductive scavengers against Zn deficiency and hypokalemic effects in rats. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02090-1

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02090-1

Keywords: eggshell membrane, zinc oxide nanoparticles, nanocomposite, sperm cryopreservation, male infertility, zinc deficiency, spermatogenesis, reactive oxygen species, antimicrobial biomaterial, hypokalemia, hyperoxaluria, Sprague-Dawley rats

The research team, led by Anja Schroff of the Department of Medical Radiation Sciences, set out to answer a deceptively simple question with major implications for both medicine and emergency preparedness. Iodine-131 is a workhorse of nuclear medicine, used for decades to treat hyperthyroidism and certain thyroid cancers, because the thyroid gland eagerly hoards iodine to build its hormones. But the same isotope is also a signature component of nuclear accident fallout. Understanding exactly how much radiation each organ receives after exposure — and whether that dose differs between males and females, or between the young and the grown — is essential both for optimizing therapy and for refining risk estimates after a nuclear emergency.

To probe the question, the researchers gave male and female Sprague–Dawley rats a controlled internal exposure of 0.36 megabecquerels of iodine-131 at one of two life stages: five weeks of age, representing a young, still-developing animal, and seventeen weeks of age, representing adulthood. Over the following six days, they measured the activity concentration of the isotope in sixteen vital tissues at six time points, ranging from one hour to 144 hours after injection. From these time-activity data, they calculated the mean absorbed dose delivered to each organ, using both analytical methods and Monte Carlo simulations to cross-check their estimates.

The results were striking. As expected, the thyroid gland dominated the picture, showing the highest iodine-131 activity concentration of any tissue in every group — peaking at 18 hours after exposure in males and 24 hours in females, regardless of whether the animals were young or adult. Every other tissue lagged far behind, with the stomach, which also expresses iodine-transporting machinery, coming in a distant second. But the real story lay in the differences between groups, which proved to be anything but subtle.

Female rats consistently accumulated more iodine-131 in their thyroids than males, and — critically — they retained it longer. That combination of higher uptake and slower clearance translated directly into higher radiation dose. The absorbed dose to the thyroid ranged across the study groups from 23 gray per megabecquerel in adult males to a staggering 100 gray per megabecquerel in young females — a more than fourfold difference driven entirely by biological sex and age at exposure. Statistically significant sex differences emerged in all sixteen tissues examined, with the most pronounced effect in the thyroid itself.

Age mattered too, though in a sex-specific way. The most notable age-related differences in thyroid uptake and absorbed dose appeared in males: young males showed markedly higher iodine-131 uptake than adult males, resulting in a substantially greater thyroid dose. In females, whose thyroid uptake was already elevated, the age effect was less prominent. This pattern suggests that the developing thyroid — or the hormonal and metabolic milieu surrounding it — handles iodine differently depending on both its maturity and the animal’s sex, compounding rather than simply adding to the sex effect.

To understand the mechanism behind these differences, the team turned to the sodium-iodide symporter, or NIS, the membrane protein responsible for actively pumping iodide into thyroid cells. Using immunohistochemistry and western blot analysis, they quantified NIS protein expression in thyroid tissue across all groups. The result was a surprise: despite the dramatic differences in uptake and dose, NIS protein levels showed high individual variability but no clear, consistent difference between the groups. Whatever drives females and young animals to accumulate and retain more radioactive iodine, it appears not to be a simple matter of having more of the iodine transporter — hinting at deeper biological factors, perhaps involving hormone regulation, thyroid size, iodine turnover kinetics, or clearance pathways that have yet to be pinned down.

The implications reach well beyond the laboratory. After Chernobyl, epidemiological studies documented a surge in thyroid cancer among people exposed as children to iodine-131 fallout, with the increase particularly pronounced among young girls — a pattern that has long suggested some combination of biological susceptibility and dosimetric difference. This study provides the first rigorous experimental evidence that the dose itself may differ systematically by sex and age, meaning that part of the observed cancer excess could reflect the fact that young females simply received more radiation to their thyroids from the same environmental exposure. The authors are careful to note that dosimetry alone cannot explain everything — biology at the cellular level certainly contributes — but the fourfold dose range they measured is far too large to ignore in risk models.

For nuclear medicine, the findings carry a more immediate practical message. Radioiodine therapy is prescribed to patients of both sexes and all ages, yet dosing protocols have historically been built on assumptions that may not hold uniformly across the population. If sex and age influence thyroid uptake and retention as strongly in humans as they do in rats, personalized dose planning — adjusting administered activity for patient sex and age — could improve therapeutic efficacy while sparing healthy tissue. The study also underscores the value of including both sexes and multiple age groups in preclinical radiopharmaceutical research, a practice that remains inconsistent across the field.

The Gothenburg team, whose work was supported by the Swedish Radiation Safety Authority, the Swedish Research Council, and the Swedish Cancer Society, among others, emphasizes that further research is needed to clarify the underlying biological and mechanistic drivers of the observed differences. Untangling whether hormonal status, thyroid growth dynamics, renal clearance, or other factors govern the sex- and age-dependent handling of iodine will be the next step. But the core conclusion stands on its own: when it comes to radioactive iodine, who you are and how old you are when exposure happens can change the dose your thyroid receives by a factor of four — a biological reality that both radiation oncologists and emergency planners can no longer afford to overlook.

Subject of Research: How sex and age at exposure influence the biodistribution and absorbed dose of radioactive iodine-131 in rats

Article Title: Sex and age at exposure influence 131I biodistribution and dosimetry in Sprague–Dawley rats

Article References: Schroff, A., Insulander Björk, K., Rassol, N., Johansson, J., Lundberg, T., Bakr, H., Andersson, M., Spetz, J., & Forssell-Aronsson, E. (2026). Sex and age at exposure influence 131I biodistribution and dosimetry in Sprague–Dawley rats. Biology of Sex Differences. https://doi.org/10.1186/s13293-026-00989-4

Image Credits: AI Generated

DOI: 10.1186/s13293-026-00989-4

Keywords: radioiodine, iodine-131, thyroid, dosimetry, biodistribution, sex differences, Chernobyl, thyroid cancer, sodium-iodide symporter, radiation protection, Sprague-Dawley rats, nuclear medicine

The research, conducted by Christopher J. Petty of the University of Georgia, Mindy Isaman and Linnea R. Freeman of Furman University, and colleagues at Furman and Clemson University, was published in the journal Biology of Sex Differences. The team set out to address two intertwined problems: the persistent excess of severe obesity among women compared with men, and the growing but still murky evidence that the gut microbiome shapes feeding behavior. Individuals with obesity are known to carry an altered gut microbiome, but whether those microbial differences actually drive overeating—or merely accompany it—has remained an open question, particularly with respect to sex differences.

To measure hedonic feeding with real precision, the researchers turned to an approach borrowed from economics rather than simple food-intake counts. Male and female Sprague-Dawley rats were trained in a de-escalating fixed ratio operant task built on behavioral economics principles. In this paradigm, animals work—pressing a lever—to earn high-fat, palatable reward pellets, and the price of those pellets, measured in effort, steadily increases. The design allows researchers to estimate two key parameters. The first is demand elasticity, denoted alpha, which captures how quickly an animal’s demand for the reward falls as the price of obtaining it rises. The second is demand at null cost, or Q0, an extrapolated prediction of how much the animal would consume if the reward required no effort at all. Together, these values describe not just how much an animal eats, but how much it values the food—an economic signature of hedonic drive.

The baseline results were clear and consistent with the team’s earlier work: female rats showed a significantly higher demand at null cost for the high-fat palatable pellets than male rats. In plain terms, when effort was stripped away, females valued and would consume more of the palatable reward than males. Because hedonic feeding is a well-recognized contributor to chronic overconsumption in environments saturated with calorie-dense foods, this kind of sex-linked difference in reward valuation is exactly the sort of biological signal that could help explain why severe obesity disproportionately affects women.

The next question was what might be driving that difference. Emerging evidence suggests the gut microbiome influences feeding behavior through several channels, including the production of short chain fatty acids, metabolites generated when gut bacteria ferment dietary fiber, and through effects on bile acids, molecules synthesized from cholesterol that aid fat digestion and also act as signaling agents in the gut and beyond. The researchers therefore administered an antibiotic cocktail in the rats’ drinking water to disrupt the gut microbiome, then re-ran the behavioral economics task to see whether wiping out the microbial community would change hedonic feeding in either sex.

The outcome was striking in its restraint. Female rats given antibiotics continued to show a higher demand at null cost compared with untreated male control rats, and—critically—the researchers found no statistically significant difference between antibiotic-treated males and females. In other words, disrupting the microbiome did not erase or meaningfully reshape the sex difference in hedonic reward valuation. The antibiotic treatment did do its biological job: when the team characterized the fecal microbiome at the genus level before and after antibiotic administration, they documented clear disruption to the bacterial community, alongside measured changes in fecal short chain fatty acid levels. They also profiled serum short chain fatty acid and bile acid levels at the end of the study, providing a metabolomic snapshot of the systemic consequences of microbial disruption.

What makes the finding conceptually important is what it rules out, or at least renders less likely as a simple explanation. If baseline differences in gut bacterial composition between males and females were the primary engine of the female rats’ stronger hedonic drive, collapsing that composition with antibiotics should have narrowed the gap. It did not. The authors also report that they did not observe striking baseline sex differences in fecal microbiome diversity and composition in the first place, which further weakens the notion that straightforward differences in which bacterial genera dominate the gut could account for the behavioral divergence. The study’s own conclusion is deliberately measured: these results bring into question whether the gut microbiome contributes to sex differences in hedonic feeding at all.

That said, the researchers are careful not to close the book on microbial influence. The gut microbiome is not a single variable but a network of interacting communities and metabolites, and antibiotics are a blunt instrument. The team points to network factors—such as the interplay between the microbiome and bile acids, which themselves show sex differences and can modulate feeding—as avenues requiring further investigation. Serum bile acid profiles measured at the study’s endpoint suggest that downstream signaling pathways, rather than raw bacterial composition, may be where sex-specific microbial effects on appetite ultimately reside, if they exist.

The work also carries a methodological lesson for the field. Behavioral economics approaches like the de-escalating fixed ratio task distinguish between consumption and motivation, two things that simple access-feeding experiments conflate. An animal that eats more of a tasty food at zero cost but gives up quickly when effort increases is economically different from one that persists at high prices, and only the second pattern reflects a genuine shift in reward valuation. By anchoring sex comparisons in demand curve parameters rather than grams consumed, studies of this kind can pinpoint whether the sexes differ in how much they value palatable food, in how sensitive they are to its cost, or both. In this case, the female-male difference lived specifically in the null-cost demand estimate.

For human health, the implications are cautious but meaningful. The finding that female rats place a higher intrinsic value on high-fat palatable food parallels epidemiological patterns in which women face higher rates of severe obesity, and it reinforces the idea that any intervention aimed at curbing pleasure-driven eating may need to account for sex as a fundamental biological variable rather than an afterthought. At the same time, the negative result on the microbiome tempers enthusiasm for microbial therapies—probiotics, targeted antibiotics, or fecal transplants—as quick fixes for hedonic overeating, at least until the relevant mechanisms are better mapped. Obesity, the authors note, remains a pressing public health issue, and hedonic feeding, while not its sole culprit, is one of its major contributing forces. Untangling which biological threads—hormonal, neural, microbial, or metabolic—woven together produce the sex difference in reward valuation will demand the kind of systematic, multi-dimensional profiling this study models: behavior, bacterial census, and metabolites measured in the same animals, before and after perturbation. The microbiome may yet play a role in appetite, but this careful experiment suggests that if it does, it operates through subtler, networked pathways than the simple presence or absence of particular gut bacteria.

Subject of Research: Sex differences in hedonic feeding and the effects of antibiotic-induced gut microbiome disruption in rats

Article Title: Sex differences in hedonic feeding and characterizing the effects of antibiotic-induced microbiome disruption

Article References: Petty, C. J., Isaman, M., Pallas Perez, L., Millard, S., Ortiz, M., & Freeman, L. R. (2026). Sex differences in hedonic feeding and characterizing the effects of antibiotic-induced microbiome disruption. Biology of Sex Differences. https://doi.org/10.1186/s13293-026-00970-1

Image Credits: AI Generated

DOI: 10.1186/s13293-026-00970-1

Keywords: hedonic feeding, gut microbiome, sex differences, behavioral economics, obesity, antibiotics, short chain fatty acids, bile acids, operant conditioning, Sprague-Dawley rats, microbiome disruption, food reward