The Expensive-Tissue Hypothesis in Vertebrates: Gut Microbiota Effect, a Review

Oxygen and the Spark of Human Brain Evolution: Complex Interactions of Metabolism and Cortical Expansion across Development and Evolution

Scientific theories on the functioning and dysfunction of the human brain require an understanding of its development-before and after birth and through maturation to adulthood-and its evolution. Here we bring together several accounts of human brain evolution by focusing on the central role of oxygen and brain metabolism. We argue that evolutionary expansion of human transmodal association cortices exceeded the capacity of oxygen delivery by the vascular system, which led these brain tissues to rely on nonoxidative glycolysis for additional energy supply. We draw a link between the resulting lower oxygen tension and its effect on cytoarchitecture, which we posit as a key driver of genetic developmental programs for the human brain-favoring lower intracortical myelination and the presence of biosynthetic materials for synapse turnover. Across biological and temporal scales, this protracted capacity for neural plasticity sets the conditions for cognitive flexibility and ongoing learning, supporting complex group dynamics and intergenerational learning that in turn enabled improved nutrition to fuel the metabolic costs of further cortical expansion. Our proposed model delineates explicit mechanistic links among metabolism, molecular and cellular brain heterogeneity, and behavior, which may lead toward a clearer understanding of brain development and its disorders.

A role for the serotonin 2A receptor in the expansion and functioning of human transmodal cortex

Integrating independent but converging lines of research on brain function and neurodevelopment across scales, this article proposes that serotonin 2A receptor (5-HT2AR) signalling is an evolutionary and developmental driver and potent modulator of the macroscale functional organization of the human cerebral cortex. A wealth of evidence indicates that the anatomical and functional organization of the cortex follows a unimodal-to-transmodal gradient. Situated at the apex of this processing hierarchy-where it plays a central role in the integrative processes underpinning complex, human-defining cognition-the transmodal cortex has disproportionately expanded across human development and evolution. Notably, the adult human transmodal cortex is especially rich in 5-HT2AR expression and recent evidence suggests that, during early brain development, 5-HT2AR signalling on neural progenitor cells stimulates their proliferation-a critical process for evolutionarily-relevant cortical expansion. Drawing on multimodal neuroimaging and cross-species investigations, we argue that, by contributing to the expansion of the human cortex and being prevalent at the apex of its hierarchy in the adult brain, 5-HT2AR signalling plays a major role in both human cortical expansion and functioning. Owing to its unique excitatory and downstream cellular effects, neuronal 5-HT2AR agonism promotes neuroplasticity, learning and cognitive and psychological flexibility in a context-(hyper)sensitive manner with therapeutic potential. Overall, we delineate a dual role of 5-HT2ARs in enabling both the expansion and modulation of the human transmodal cortex.

Caffeic acid improves intestinal barrier functions by regulating colonic bacteria and tight junction protein expression and alleviating inflammation in weaning piglets

The experiment investigated the effect of caffeic acid on bacteria, short-chain fatty acids (SCFA), and the expression of tight junction protein and inflammation related genes in the colon of weaning piglets. Thirty-six weaning piglets were allocated to three treatment groups, which were fed with a basal diet, a basal diet supplemented with 250 mg/kg or 500 mg/kg caffeic acid for 28 days. The results showed that caffeic acid treatment increased the contents of acetate acid, propionate acid and total SCFA. Moreover, real-time quantitative PCR showed that the number of Bifidobacterium (p < 0.05) and Lactobacillus (p < 0.05) were increased and the number of Escherichia coli (p < 0.05) was decreased by caffeic acid in colonic mucosa. Real-time quantitative PCR also showed that the mRNA levels of zonula occludens-1 (p < 0.01), claudin-1 (p < 0.01), occludin (p < 0.01), mucin 1 (MUC1) (p < 0.01), MUC2 (p < 0.01), interleukin 4 (IL-4) (p < 0.01) and IL-10 (p < 0.05) were increased, while the mRNA expression levels of histone deacetylases (p < 0.01), IL-1 (p < 0.01), IL-6 (p < 0.01) and tumor necrosis factor-α (TNF-α) (p < 0.01) were decreased, by caffeic acid in colonic mucosa. These results suggested that caffeic acid could improve intestinal barrier function in weaned pigs, which might be mediated by regulating colonic bacteria and tight junction protein expression and alleviating inflammation.

A Comparative Perspective on the Cerebello-Cerebral System and Its Link to Cognition

The longstanding idea that the cerebral cortex is the main neural correlate of human cognition can be elaborated by comparative analyses along the vertebrate phylogenetic tree that support the view that the cerebello-cerebral system is suited to support non-motor functions more generally. In humans, diverse accounts have illustrated cerebellar involvement in cognitive functions. Although the neocortex, and its transmodal association cortices such as the prefrontal cortex, have become disproportionately large over primate evolution specifically, human neocortical volume does not appear to be exceptional relative to the variability within primates. Rather, several lines of evidence indicate that the exceptional volumetric increase of the lateral cerebellum in conjunction with its connectivity with the cerebral cortical system may be linked to non-motor functions and mental operation in primates. This idea is supported by diverging cerebello-cerebral adaptations that potentially coevolve with cognitive abilities across other vertebrates such as dolphins, parrots, and elephants. Modular adaptations upon the vertebrate cerebello-cerebral system may thus help better understand the neuroevolutionary trajectory of the primate brain and its relation to cognition in humans. Lateral cerebellar lobules crura I-II and their reciprocal connections to the cerebral cortical association areas appear to have substantially expanded in great apes, and humans. This, along with the notable increase in the ventral portions of the dentate nucleus and a shift to increased relative prefrontal-cerebellar connectivity, suggests that modular cerebellar adaptations support cognitive functions in humans. In sum, we show how comparative neuroscience provides new avenues to broaden our understanding of cerebellar and cerebello-cerebral functions in the context of cognition.

The Impact of Hormesis, Neuronal Stress Response, and Reproduction, upon Clinical Aging: A Narrative Review

INTRODUCTION

The primary objective of researchers in the biology of aging is to gain a comprehensive understanding of the aging process while developing practical solutions that can enhance the quality of life for older individuals. This involves a continuous effort to bridge the gap between fundamental biological research and its real-world applications.

PURPOSE

In this narrative review, we attempt to link research findings concerning the hormetic relationship between neurons and germ cells, and translate these findings into clinically relevant concepts.

METHODS

We conducted a literature search using PubMed, Embase, PLOS, Digital Commons Network, Google Scholar and Cochrane Library from 2000 to 2023, analyzing studies dealing with the relationship between hormetic, cognitive, and reproductive aspects of human aging.

RESULTS

The process of hormesis serves as a bridge between the biology of neuron-germ cell interactions on one hand, and the clinical relevance of these interactions on the other. Details concerning these processes are discussed here, emphasizing new research which strengthens the overall concept.

CONCLUSIONS

This review presents a scientifically and clinically relevant argument, claiming that maintaining a cognitively active lifestyle may decrease age-related degeneration, and improve overall health in aging. This is a totally novel approach which reflects current developments in several relevant aspects of our biology, technology, and society.

Counter-gradient variation and the expensive tissue hypothesis explain parallel brain size reductions at high elevation in cricetid and murid rodents

To better understand functional morphological adaptations to high elevation (> 3000 m above sea level) life in both North American and African mountain-associated rodents, we used microCT scanning to acquire 3D images and a 3D morphometric approach to calculate endocranial volumes and skull lengths. This was done on 113 crania of low-elevation and high-elevation populations in species of North American cricetid mice (two Peromyscus species, n = 53), and African murid rodents of two tribes, Otomyini (five species, n = 49) and Praomyini (four species, n = 11). We tested two distinct hypotheses for how endocranial volume might vary in high-elevation populations: the expensive tissue hypothesis, which predicts that brain and endocranial volumes will be reduced to lessen the costs of growing and maintaining a large brain; and the brain-swelling hypothesis, which predicts that endocranial volumes will be increased either as a direct phenotypic effect or as an adaptation to accommodate brain swelling and thus minimize pathological symptoms of altitude sickness. After correcting for general allometric variation in cranial size, we found that in both North American Peromyscus mice and African laminate-toothed (Otomys) rats, highland rodents had smaller endocranial volumes than lower-elevation rodents, consistent with the expensive tissue hypothesis. In the former group, Peromyscus mice, crania were obtained not just from wild-caught mice from high and low elevations but also from those bred in common-garden laboratory conditions from parents caught from either high or low elevations. Our results in these mice showed that brain size responses to elevation might have a strong genetic basis, which counters an opposite but weaker environmental effect on brain volume. These results potentially suggest that selection may act to reduce brain volume across small mammals at high elevations but further experiments are needed to assess the generality of this conclusion and the nature of underlying mechanisms.

Foregut Exclusion Enhances Incretin and Insulin Secretion After Roux-en-Y Gastric Bypass in Adults With Type 2 Diabetes

INTRODUCTION

Patients with type 2 diabetes experience resolution of hyperglycemia within days after Roux-en-Y gastric bypass (RYGB) surgery. This is attributed, in part, to enhanced secretion of hindgut factors following exclusion of the gastric remnant and proximal intestine during surgery. However, evidence of the mechanisms of remission remain limited due to the challenges of metabolic evaluation during the early postoperative period. The purpose of this investigation was to determine the role of foregut exclusion in the resolution of type 2 diabetes after RYGB.

METHODS

Patients with type 2 diabetes (n = 15) undergoing RYGB had a gastrostomy tube (G-tube) placed in their gastric remnant at time of surgery. Patients were randomized to receive a mixed meal tolerance test via oral or G-tube feeding immediately prior to and 2 weeks after surgery in a repeated measures crossover design. Plasma glucose, insulin, C-peptide, incretin responses, and indices of meal-stimulated insulin secretion and sensitivity were determined.

RESULTS

Body weight, fat mass, fasting glucose and insulin, and circulating lipids were significantly decreased 2 weeks after surgery. The glycemic response to feeding was reduced as a function of total area under the curve but not after adjustment for the reduction in fasting glucose. Oral feeding significantly enhanced insulin and incretin secretion after RYGB, which was entirely ablated by G-tube feeding.

CONCLUSION

Foregut exclusion accounts for the rise in incretin and insulin secretion but may not fully explain the early improvements in glucose metabolism after RYGB surgery.

Domestication-induced reduction in eye size revealed in multiple common garden experiments: The case of Atlantic salmon (Salmo salar L.)

Domestication leads to changes in traits that are under directional selection in breeding programmes, though unintentional changes in nonproduction traits can also arise. In offspring of escaping fish and any hybrid progeny, such unintentionally altered traits may reduce fitness in the wild. Atlantic salmon breeding programmes were established in the early 1970s, resulting in genetic changes in multiple traits. However, the impact of domestication on eye size has not been studied. We measured body size corrected eye size in 4000 salmon from six common garden experiments conducted under artificial and natural conditions, in freshwater and saltwater environments, in two countries. Within these common gardens, offspring of domesticated and wild parents were crossed to produce 11 strains, with varying genetic backgrounds (wild, domesticated, F1 hybrids, F2 hybrids and backcrosses). Size-adjusted eye size was influenced by both genetic and environmental factors. Domesticated fish reared under artificial conditions had smaller adjusted eye size when compared to wild fish reared under identical conditions, in both the freshwater and marine environments, and in both Irish and Norwegian experiments. However, in parr that had been introduced into a river environment shortly after hatching and sampled at the end of their first summer, differences in adjusted eye size observed among genetic groups were of a reduced magnitude and were nonsignificant in 2-year-old sea migrating smolts sampled in the river immediately prior to sea entry. Collectively, our findings could suggest that where natural selection is present, individuals with reduced eye size are maladapted and consequently have reduced fitness, building on our understanding of the mechanisms that underlie a well-documented reduction in the fitness of the progeny of domesticated salmon, including hybrid progeny, in the wild.

Seasonal Variation in Gut Microbiota Related to Diet in Fejervarya limnocharis

Organisms adapt to environmental fluctuations by varying their morphology and structural, physiological, and biochemical characteristics. Gut microbiome, varying rapidly in response to environmental shifts, has been proposed as a strategy for adapting to the fluctuating environment (e.g., new dietary niches). Here, we explored the adaptive mechanism of frog intestinal microbes in response to environmental changes. We collected 170 Fejervarya limnocharis during different seasons (spring, summer, autumn, and pre-hibernation) to study the compositional and functional divergence of gut microbiota and analysed the effects of seasonal feeding habits and body condition on intestinal microorganisms using 16S rRNA high-throughput sequencing, Tax4Fun function prediction analysis, and bioinformatics analysis. The results showed no significant dietary difference in various seasons and between males and females. However, a significantly positive correlation was detected between dietary diversity and food niche width. Host condition (body size, body mass, and body condition) also revealed seasonal changes. The frogs were colonised by 71 bacterial phyla and dominated by Proteobacteria, Firmicutes, and Bacteroidetes. Stenotrophomonas was the most abundant genus in the Proteobacteria. The composition, diversity, and function of intestinal microorganisms in different seasons were significantly different. Significant differences were observed in composition and function but not in the microbial diversity between sexes. Furthermore, seasonal foods and body mass were significantly correlated with gut microbial composition. Our results suggest that gut microbiomes of F. limnocharis vary seasonally in response to diet under fluctuating environments.

Microbiota Detection Patterns Correlate With Presence and Severity of Barrett's Esophagus

Background

The microbiome has been increasingly associated with different disease processes, but its role in esophagus is largely unknown. Our goal was to determine the associations of the esophageal microbiota with Barrett’s esophagus.

Methods

A total of 74 patients were included in this prospective study, including 34 patients with Barrett’s esophagus and 40 patients without Barrett’s esophagus. Esophageal swabs were obtained from the uvula, and mucosal biopsies were obtained from the proximal esophagus and distal esophagus in each patient. The microbiome of each sample was assessed using a customized Esophageal Microbiome qPCR array (EMB). For each clinical sample, we completed a detection/non-detection analysis for each organism in the EMB. The limit of detection (LOD) for each target was established by analysis of plasmid dilutions.

Results

Average age was 60.2 years. There were significantly different microbial detection patterns in patients with Barrett’s esophagus compared to the control population. There were a greater number of organisms which had different likelihoods of detection in the distal esophagus, compared to the proximal esophagus or uvula. In addition, as the length of the Barrett’s column increased, multiple organisms were less likely to be detected. This decreased likelihood occurred only in the distal esophagus. Beside Barrett’s esophagus, no other demographic factors were associated with differences in detection patterns.

Conclusions

Microbial community structures differ between patients with and without Barrett’s esophagus. Certain organisms are less likely to be detected as the severity of Barrett’s esophagus worsens. These results suggest that particular organisms may have a protective effect against the development of Barrett’s esophagus.

Novel Ex Vivo Model to Examine the Mechanism and Relationship of Esophageal Microbiota and Disease

Rates of esophageal cancer have increased over the last 40 years. Recent clinical research has identified correlations between the esophageal microbiome and disease. However, mechanisms of action have been difficult to elucidate performing human experimentation. We propose an ex vivo model, which mimics the esophagus and is ideal for mechanistic studies on the esophageal microbiome and resultant transcriptome. To determine the microbiome and transcriptome profile of the human distal esophagus, the microbiome was assessed in 74 patients and the transcriptome profile was assessed in 37 patients with and without Barrett’s esophagus. Thereafter, an ex vivo model of the esophagus was created using an air–liquid interfaced (ALI) design. This design created a sterile apical surface and a nutrient-rich basal surface. An epithelial layer was grown on the apical surface. A normal microbiome and Barrett’s microbiome was harvested and created from patients during endoscopic examination of the esophagus. There was a distinct microbiome in patients with Barrett’s esophagus. The ex vivo model was successfully created with a squamous epithelial layer on the apical surface of the ex vivo system. Using this ex vivo model, multiple normal esophageal and Barrett’s esophageal cell lines will be created and used for experimentation. Each microbiome will be inoculated onto the sterile apical surface of each cell line. The resultant microbiome and transcriptome profile on each surface will be measured and compared to results in the human esophagus to determine the mechanism of the microbiome interaction.

The gut–brain axis in vertebrates: implications for food intake regulation

The gut and brain are constantly communicating and influencing each other through neural, endocrine and immune signals in an interaction referred to as the gut–brain axis. Within this communication system, the gastrointestinal tract, including the gut microbiota, sends information on energy status to the brain, which, after integrating these and other inputs, transmits feedback to the gastrointestinal tract. This allows the regulation of food intake and other physiological processes occurring in the gastrointestinal tract, including motility, secretion, digestion and absorption. Although extensive literature is available on the mechanisms governing the communication between the gut and the brain in mammals, studies on this axis in other vertebrates are scarce and often limited to a single species, which may not be representative for obtaining conclusions for an entire group. This Review aims to compile the available information on the gut–brain axis in birds, reptiles, amphibians and fish, with a special focus on its involvement in food intake regulation and, to a lesser extent, in digestive processes. Additionally, we will identify gaps of knowledge that need to be filled in order to better understand the functioning and physiological significance of such an axis in non-mammalian vertebrates.

Effects of proton pump inhibitor use on the esophageal microbial community

BACKGROUND

Changes in the esophageal microbiome correlate with esophageal disease, but the effects of proton pump inhibitor (PPI) drugs are incompletely characterized. Our objective was to identify the effects of PPI use on the microbial community of the esophagus.

METHODS

Mucosal biopsies of the distal esophagus were analyzed using a customized esophageal microbiome qPCR panel array (EMB). Patient demographics, use of PPIs, duration of use and dose were recorded.

RESULTS

Fifty-eight patients were included. Mean age was 60.5 years. Ninety percent (52/58) of patients were on PPIs. Mean dose was 42.7 mg. Mean duration of use was 2.5 years. The use of PPIs led to a significant difference in absolute levels of only one organism, Actinomyces, in the entire array (p < 0.01). Among patients who used proton pump inhibitors, there was no significant association between dose and absolute levels of any organism. Similarly, there was no association between duration of use and absolute levels of any organism.

CONCLUSIONS

PPI use does not seem to cause significant changes in the distal esophageal microbial community. Future studies with larger sample sizes and esophageal pH testing should be performed to determine the level of acidity and its relationship to the microbial community.

High-throughput sequencing reveals the core gut microbiota of the mud crab (Scylla paramamosain) in different coastal regions of southern China

Background

Scylla paramamosain is a commercially important mud crab. The microbiota is a community that inhabits the crab intestine, and is important for physiological functional and host health.

Results

Proteobacteria, Firmicutes, Bacteroidetes, Tenericutes, Spirochaetae and Fusobacteria were the dominant phyla of the 36 representative phyla. Eleven genera of the 820 representative genera were considered as core gut microbiota and were distributed in the five dominant phyla. The core genus of the Proteobacteria included Arcobacter, Photobacterium, Vibrio, Shewanella and Desulfovibrio. The other four phyla contained one or two genera. Male and female crab samples had two different core genera, (male samples: Psychrilyobacter & Lactococcus; female samples: Clostridium_sensu_stricto_11 and Candidatus_Bacilloplasma).

Conclusions

This is the first time core intestinal microbiota have been identified in crab from nine coastal regions of southern China. This study provides sequencing data related to the gut microbiota of S. paramamosain, and may contribute to probiotic development for S. paramamosain aquaculture industries.

Associations of the microbiome and esophageal disease

The incidence of esophageal diseases such as esophageal adenocarcinoma (EAC) and gastroesophageal reflux disease (GERD) have been increasing over the last 40 years. The esophageal microbiome appears to have a role in the development of some disease processes, and could also serve as markers of early diseases of the esophagus. A literature review was performed examining the role of the microbiome in the development of esophageal disease. In addition, the results of several studies and experiments were included in the review. Both EAC and GERD have increased in incidence over the last 40 years. Barrett's esophagus (BE) is a risk factor for EAC. Patients with BE appear to have a microbiome expression pattern distinct from patients without BE. The distinct pattern may be related to factors within the distal esophagus such as a more acidic environment, intraluminal stasis and other elements. It remains unclear whether the change in microflora leads to esophageal disease, or whether the disease process within the esophagus allows these particular organisms to experience overgrowth compared to other microflora. Patient factors such as body mass index (BMI), diet and geographic location also appear to affect the esophageal microbiome. There is an association with the esophageal microbiome and several esophageal diseases. Future studies should examine these correlations more closely. The distinct patterns may be able to serve as a marker of early disease, and possibly lead to a mechanism for the development of esophageal disease.