The gut microbiota plays important roles in animal nutrition and health. This relationship is particularly dynamic in hibernating mammals where fasting drives the gut community to rely on host-derived nutrients instead of exogenous substrates. We used 16S rRNA pyrosequencing and caecal tissue protein analysis to investigate the effects of hibernation on the mucosa-associated bacterial microbiota and host responses in 13-lined ground squirrels. The mucosal microbiota was less diverse in winter hibernators than in actively feeding spring and summer squirrels. UniFrac analysis revealed distinct summer and late winter microbiota clusters, while spring and early winter clusters overlapped slightly, consistent with their transitional structures. Communities in all seasons were dominated by Firmicutes and Bacteroidetes, with lesser contributions from Proteobacteria, Verrucomicrobia, Tenericutes and Actinobacteria. Hibernators had lower relative abundances of Firmicutes, which include genera that prefer plant polysaccharides, and higher abundances of Bacteroidetes and Verrucomicrobia, some of which can survive solely on host-derived mucins. A core mucosal assemblage of nine operational taxonomic units shared among all individuals was identified with an average total sequence abundance of 60.2%. This core community, together with moderate shifts in specific taxa, indicates that the mucosal microbiota remains relatively stable over the annual cycle yet responds to substrate changes while potentially serving as a pool for 'seeding' the microbiota once exogenous substrates return in spring. Relative to summer, hibernation reduced caecal crypt length and increased MUC2 expression in early winter and spring. Hibernation also decreased caecal TLR4 and increased TLR5 expression, suggesting a protective response that minimizes inflammation.

Aims Burrowing mammals tend to be more hypoxia tolerant than non‐burrowing mammals and rely less on increases in ventilation and more on decreases in metabolic rate to tolerate hypoxia. Naked mole‐rats (Heterocephalus glaber, NMRs), eusocial mammals that live in large colonies, are among the most hypoxia‐tolerant mammals, and rely almost solely on decreases in metabolism with little change in ventilation during hypoxia. We hypothesized that the remarkable hypoxia tolerance of NMRs is an evolutionarily conserved trait derived from repeated exposure to severe hypoxia owing to their burrow environment and eusocial colony organization. Methods We used whole‐body plethysmography and indirect calorimetry to measure the hypoxic ventilatory and metabolic responses of eight mole‐rat species closely related to the NMR. Results We found that all eight species examined had a strong tolerance to hypoxia, with most species tolerating 3 kPa O2, Heliophobius emini tolerating 2 kPa O2 and Bathyergus suillus tolerating 5 kPa O2. All species examined employed a combination of increases in ventilation and decreases in metabolism in hypoxia, a response midway between that of the NMR and that of other fossorial species (larger ventilatory responses, lesser reductions in metabolism). We found that eusociality is not fundamental to the physiological response to hypoxia of NMRs as Fukomys damarensis, another eusocial species, was among this group. Conclusions Our data suggest that, while the NMR is unique in the pattern of their physiological response to hypoxia, eight closely related mole‐rat species share the ability to tolerate hypoxia like the current “hypoxia‐tolerant champion,” the NMR.

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Retinoic acid, a bioactive metabolite of vitamin A, plays key roles in immune function and vision and adipose tissue development. Our goal was to study the effect of vitamin A deficiency in physiologic changes seen in hibernating 13-lined ground squirrels (Ictidomys tridecemlineatus). In this study, we first developed a model of vitamin A deficiency that was based on published mouse models; we then examined the role of RA in the circannual cycle of and adipose accumulation in this hibernating species. Gravid female ground squirrels began consuming a deficient diet during the last 2 wk of their 4-wk gestation; pups received the diet until they were 8 wk old, when severe symptoms of hypovitaminosis were observed, requiring the animals' removal from the protocol. Body size and adipose mass were significantly lower in vitamin-deficient pups than controls. To avoid these complications, we developed a second model, in which pups started on the deficient diet after weaning. The revised model produced few symptoms of deficiency, and squirrels were able to remain on the diet through spring emergence. Liver retinol analysis showed that deficient squirrels essentially had no vitamin A stores. Our data suggest that 13-lined ground squirrels maintain higher concentrations of stored retinol than other rodent species, such that their dietary needs may differ from those of traditional laboratory rodent models. Our results indicate that ground squirrels are especially susceptible to vitamin A deficiency, and ground squirrels should not be fed a deficient diet until after weaning, to avoid severe symptoms. Interestingly, vitamin A deficiency does not seem to affect this species' ability to hibernate successfully.

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Sleep disordered breathing (SDB) during pregnancy is a growing concern because it causes adverse outcomes for infant offspring. Recently, our lab developed a rat model of SDB during pregnancy in which pregnant dams were exposed to gestational intermittent hypoxia (GIH; 15 episodes/hr of 10.5% oxygen for 8h daily from days 10-20 of pregnancy). Control dams were exposed in parallel to gestational intermittent normoxia (GNX). We found that male (but not female) GIH offspring had increased apneas in adulthood compared to their GNX control counterparts. Thus, in this study, we tested the hypothesis that GIH would increase respiratory instability (i.e. increase the number of apneas) in neonatal male, not female, offspring. Plethysmography was performed on GIH and GNX male and female pups at postnatal (P) days 0, 10, and 15, and the number of apneas was quantified. An apnea was defined as two missed breaths (2x the average period between breaths). Preliminary data suggest that apnea frequency was sexually dimorphic and changed both with development and treatment. At P10 and P15 male GIH offspring had more apneas compared to GNX offspring (p<0.05). However, at P0, male GIH offspring (16 ± 2.4 apneas/10m) had surprisingly fewer apneas compared to GNX offspring (28 ± 1.9 apneas/10m). In female offspring in contrast, there was no difference in apnea frequency between GIH and GNX treatment at P0, but at P10 and P15 respectively, female GIH offspring (17 ± 2.8 and 9 ± 2.3 apneas/10m) had more apneas compared to their GNX counterparts (8 ± 1.2 and 2.9 ± 0.57 apneas/10m). Apnea frequency decreased with increasing age in both sexes, regardless of GIH and GNX treatment. Together, as expected, these results suggest that the increased apnea phenotype observed in the adult GIH male emerges as early as postnatal day 10. Unexpected however is the observation that female neonatal GIH offspring also experience respiratory instability in during the postnatal period despite its absence in adult female GIH offspring. Studies are currently underway to better understand the mechanisms underlying these sex differences in respiratory neural control, and the protective responses utilized by adult female GIH offspring to mitigate these respiratory deficits induced by intermittent hypoxia exposure in utero. R01 HL142752 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.