Seasonal plasticity of gut morphology and small intestinal enzymes in free-living Mongolian gerbils

Phenotypic flexibility in metabolic adjustments and digestive function in white-shouldered starlings: responses to short-term temperature acclimation

Changing the intrinsic rate of metabolic heat production is the main adaptive strategy for small birds to cope with different ambient temperatures. In this study, we tested the hypothesis that the small passerine the white-shouldered starling (Sturnus sinensis) can modulate basal metabolism under temperature acclimation by changing the morphological, physiological and biochemical state of its tissues and organs. We measured the effects of temperature on body mass, basal metabolic rate (BMR), wet mass of various internal organs, state 4 respiration (S4R) and cytochrome c oxidase (CCO) activity in the pectoral muscle and organs, metabolites in the pectoral muscle, energy intake, histological dynamics and the activity of duodenal digestive enzymes. Warm acclimation decreased BMR to a greater extent than cold acclimation. At the organ level, birds in the cold-acclimated group had significantly heavier intestines but significantly lighter pectoral muscles. At the cellular level, birds in the cold-acclimated group showed significantly higher S4R in the liver and heart and CCO activity in the liver and kidney at both the mass-specific and whole-organ levels. A metabolomic analysis of the pectoral tissue revealed significantly higher lipid decomposition, amino acid degradation, ATP hydrolysis, and GTP and biotin synthesis in cold-acclimated birds. Acclimation to cold significantly increased the gross energy intake (GEI), feces energy (FE) and digestive energy intake (DEI) but significantly decreased the digestive efficiency of these birds. Furthermore, cold-acclimated birds had a higher maltase activity and longer villi in the duodenum. Taken together, these data show that white-shouldered starlings exhibit high phenotypic flexibility in metabolic adjustments and digestive function under temperature acclimation, consistent with the notion that small birds cope with the energy challenges presented by a cold environment by modulating tissue function in a way that would affect BMR.

Seasonal flexibility of the gut structure and physiology in Eremias multiocellata

Although gut seasonal plasticity has been extensively reported, studies on physiological flexibility, such as water-salt transportation and motility in reptiles, are limited. Therefore, this study investigated the intestinal histology and gene expression involved in water-salt transport (AQP1, AQP3, NCC, and NKCC2) and motility regulation (nNOS, CHRM2, and ADRB2) in desert-dwelling Eremias multiocellata during winter (hibernating period) and summer (active period). The results showed that mucosal thickness, the villus width and height, the enterocyte height of the small intestine, and the mucosal and submucosal thicknesses of the large intestine were greater in winter than in summer. However, submucosal thickness of the small intestine and muscularis thickness of the large intestine were lower in winter than in summer. Furthermore, AQP1, AQP3, NCC, nNOS, CHRM2, and ADRB2 expressions in the small intestine were higher in winter than in summer; AQP1, AQP3, and nNOS expressions in the large intestine were lower in winter than in summer, with the upregulation of NCC and CHRM2 expressions; no significant seasonal differences were found in intestinal NKCC2 expression. These results suggest that (i) intestinal water-salt transport activity is flexible during seasonal changes where AQP1, AQP3 and NCC play a vital role, (ii) the intestinal motilities are attenuated through the concerted regulation of nNOS, CHRM2, and ADRB2, and (iii) the physiological flexibility of the small and large intestine may be discrepant due to their functional differences. This study reveals the intestinal regulation and adaptation mechanisms in E. multiocellata in response to the hibernation season.

Seasonal changes of rumen and intestine morphology of the Qinghai yak (Bos grunniens)

Aim:

The aim of the current study was to investigate the effects of seasonal changes in grass quality on the ruminal and intestinal morphology of male Qinghai yaks.

Materials and Methods:

A total of four male yaks with the same age of 4 years old from each season (summer and winter) were randomly selected and slaughtered to determine the effect of different season on intestinal morphology of yak in the Qinghai-Tibetan Plateau.

Results:

The histological analysis shows that male yak has the longer and wider papillae in rumen in green season. The height of villi in duodenum and jejunum was significantly higher in green season, and the width of villi on duodenum, jejunum, ileum, and rectum was significantly wider in green season. Surface area of villi and crypt depth in duodenum, jejunum, and ileum was significantly larger and deeper in green season. Submucosa thickness of duodenum, jejunum, ileum, and rectum was significantly thicker in green season. The muscular thickness of jejunum, cecum, and rectum was significantly thicker in green season.

Conclusion:

According to this research, we found that the seasonal changes of ruminal and intestinal morphology of yak showed different length and width papillae, villi, crypt, and submucosa. This fact was confirmed the functional advantages resulting from the ability to successfully adapt to a dry climate and diets, flat, open, and cold grassland may allow yak to overcome both water shortage and energy deficiency in winter.

Dietary Fat, but Not Protein or Carbohydrate, Regulates Energy Intake and Causes Adiposity in Mice

The impacts of different macronutrients on body weight regulation remain unresolved, with different studies suggesting increased dietary fat, increased carbohydrates (particularly sugars), or reduced protein may all stimulate overconsumption and drive obesity. We exposed C57BL/6 mice to 29 different diets varying from 8.3% to 80% fat, 10% to 80% carbohydrate, 5% to 30% protein, and 5% to 30% sucrose. Only increased dietary fat content was associated with elevated energy intake and adiposity. This response was associated with increased gene expression in the 5-HT receptors, and the dopamine and opioid signaling pathways in the hypothalamus. We replicated the core findings in four other mouse strains (DBA/2, BALB/c, FVB, and C3H). Mice regulate their food consumption primarily to meet an energy rather than a protein target, but this system can be over-ridden by hedonic factors linked to fat, but not sucrose, consumption.

Seasonal changes in digestive enzymes in five bird species

Most animals must cope with seasonal fluctuations in environmental conditions, including variations in food availability and composition. Accordingly, it is expected that most species should exhibit reversible seasonal phenotypic adjustments in their physiology. Here, we assessed seasonal variation in the activity of three digestive enzymes (sucrase, maltase, and aminopeptidase-N) in one omniviorous bird species (Rufous-collared Sparrow (Zonotrichia capensis (P. L. Statius Müller, 1776))), three granivorous bird species (Black-chinned Siskin (Carduelis barbata (Molina, 1782)), Common Diuca Finch (Diuca diuca (Molina, 1782)), and Mourning Sierra Finch (Phrygilus fruticeti (Kittlitz, 1833))), and one insectivorous bird species (Plain-mantled Tit-Spinetail (Leptasthenura aegithaloides (Kittlitz, 1830))). Based on the adaptive modulation hypothesis, we predicted that the omnivorous species should exhibit the largest seasonal variation in the activity of its digestive enzymes in relation to granivorous and insectivorous species. We found that Z. capensis adjusts total activities of disaccharidases, total sucrase activity varied between seasons in C. barbata, and total activity of aminopeptidase-N only changed seasonally in L. aegithaloides. Moreover, this last species modified the tissue-specific activity of both disaccharidases as well as the wet mass of its intestine. Taken together, our results suggest that seasonal dietary changes occur in most of the species, regardless of the trophic categories in which they belong. Consequently, a better knowledge of the diet and its seasonal variation is necessary to better account for the results recorded in this study.

Implication of metabolomic profiles to wide thermoneutral zone in Mongolian gerbils (Meriones unguiculatus)

Mongolian gerbils (Meriones unguiculatus) have evolved a wide thermoneutral zone (26.5-38.9 °C) and high upper critical temperature, and appear to have a high tolerance for heat exposure. Here, we use a metabolomic approach to measure global metabolite profiles for gerbils between lower (27 °C) and upper critical temperatures (38 °C) to investigate the role of metabolomic characterization in maintaining basal metabolic rates within a wide thermoneutral zone. We found that in serum and liver, 14 and 19 metabolites were significantly altered, respectively. In the aerobic respiration-related tricarboxylic cycle (TCA), 5 intermediates (isocitric acid, cis-aconitic acid, α-ketoglutaric acid, fumaric acid and malic acid) were increased in serum in 38 °C animals; however, no such increase was found in the liver. A stable level of hepatic TCA cycle intermediates may be related to the steady state of aerobic respiration at 38 °C. Metabolomic results also revealed that acute heat exposure caused increased oxidative stress and low molecular weight antioxidants in Mongolian gerbils. Increased methionine and 2-hydroxybutyrate suggest an accelerated synthesis of glutathione. Increased urate and its precursors, inosine and hypoxanthine, were detected at 38 °C. Glucuronate, threonate and oxalate involved in ascorbate synthesis and degradation were increased in serum at 38 °C. In conclusion, although dramatic metabolomic variation was found, a stable hepatic TCA cycle may contribute to maintaining a constant basal metabolic rate within a wide thermoneutral zone in Mongolian gerbils.

Insights into embryo defenses of the invasive apple snail Pomacea canaliculata: egg mass ingestion affects rat intestine morphology and growth

Background

The spread of the invasive snail Pomacea canaliculata is expanding the rat lungworm disease beyond its native range. Their toxic eggs have virtually no predators and unusual defenses including a neurotoxic lectin and a proteinase inhibitor, presumably advertised by a warning coloration. We explored the effect of egg perivitellin fluid (PVF) ingestion on the rat small intestine morphology and physiology.

Methodology/Principal Findings

Through a combination of biochemical, histochemical, histopathological, scanning electron microscopy, cell culture and feeding experiments, we analyzed intestinal morphology, growth rate, hemaglutinating activity, cytotoxicity and cell proliferation after oral administration of PVF to rats. PVF adversely affects small intestine metabolism and morphology and consequently the standard growth rate, presumably by lectin-like proteins, as suggested by PVF hemaglutinating activity and its cytotoxic effect on Caco-2 cell culture. Short-term effects of ingested PVF were studied in growing rats. PVF-supplemented diet induced the appearance of shorter and wider villi as well as fused villi. This was associated with changes in glycoconjugate expression, increased cell proliferation at crypt base, and hypertrophic mucosal growth. This resulted in a decreased absorptive surface after 3 days of treatment and a diminished rat growth rate that reverted to normal after the fourth day of treatment. Longer exposure to PVF induced a time-dependent lengthening of the small intestine while switching to a control diet restored intestine length and morphology after 4 days.

Conclusions/Significance

Ingestion of PVF rapidly limits the ability of potential predators to absorb nutrients by inducing large, reversible changes in intestinal morphology and growth rate. The occurrence of toxins that affect intestinal morphology and absorption is a strategy against predation not recognized among animals before. Remarkably, this defense is rather similar to the toxic effect of plant antipredator strategies. This defense mechanism may explain the near absence of predators of apple snail eggs.

Filled with nutritious substances to nourish the embryos, eggs of most animals are often the targets of pathogens and predators. An exception are the eggs of Pomacea canaliculata –known as the apple snail– which have hardly any predators. This freshwater snail is a serious aquatic crop pest in several continents, listed among the 100 worst invasive species. It is the host of a roundworm responsible for the rat lungworm disease causing human eosinophilic meningitis. The spread of this emerging infectious disease has been associated with the expansion of apple snails. They lay eggs above water level in bright pink-reddish masses, presumably a warning coloration. Indeed, eggs have chemical defenses, including neurotoxic and antinutritive proteins. The authors found that the ingestion of egg extracts adversely affects rat small intestine inducing large, reversible changes in the intestinal wall that limits the ability to absorb egg nutrients causing a diminished growth rate. Apple snail eggs are the first animal known to deter predators by this mechanism, but remarkably this defense is rather similar to the toxic effect of plant seeds proteins. These overlapping egg defenses that predators have not managed to overcome yet may partially explain the reproductive success of P. canaliculata.