Ventilatory responses of the ground squirrel, Spermophilus tridecemlineatus, to various levels of hypoxia

1. Minute ventilation (VE) in the semifossorial ground squirrel (Spermophilus tridecemlineatus) increased with increased levels of hypoxia. 2. The increase in VE was brought about primarily by an increase in breathing frequency (f). There was no significant change in tidal volume (VT). 3. The PiO2 threshold for the ventilatory response to hypoxia and position of the ventilatory response curve in the ground squirrel were closer to the semifossorial echidna (Tachyglossus aculeatus) than the completely fossorial mole rate (Spalax ehrenbergi); both the ground squirrel and echidna had a higher PiO2 threshold than the mole rat. 4. The ventilatory response curve was shifted to the left in the mole rat. 5. These observations indicate that the mole rat is the least responsive to hypoxia of the three species.     

Persistence of weight gain and hibernation onset in juvenile thirteen-lined ground squirrels (Spermophilus tridecemlineatus) in spite of long-term administration of naloxone

Sexual differences in body weight of juvenile thirteen-lined ground squirrels (Spermophilus tridecemlineatus) were significant (P less than 0.05) at all weeks of age except weeks 0-4, 6, 7, 9, 20 and 24. Hibernation onset between sexes did not differ significantly. Naloxone administration did not alter weight gain nor onset of hibernation when compared to saline controls.     

Antioxidant defense in hibernation: cloning and expression of peroxiredoxins from hibernating ground squirrels, Spermophilus tridecemlineatus

Mammalian hibernation is characterized by prolonged torpor bouts interspersed by brief arousal periods. Adequate antioxidant defenses are needed both to sustain cell viability over weeks of deep torpor and to defend against high rates of oxyradical formation associated with massive oxygen-based thermogenesis during arousal. The present study shows that up-regulation of peroxiredoxins contributes to antioxidant defense during torpor in thirteen-lined ground squirrels, Spermophilus tridecemlineatus. Expression levels of three isozymes of the 2-Cys peroxiredoxin (Prdx) family were quantified by Western blotting, the results showing 4.0- and 12.9-fold increases in Prdx1 protein in brown adipose tissue (BAT) and heart, respectively, during hibernation compared with euthermia. Comparable increases in Prdx2 were 2.4- and 3.7-fold whereas Prdx3 rose by 3.1-fold in heart of torpid animals. Total 2-Cys peroxiredoxin enzymatic activity also rose during hibernation by 1.5-fold in heart and 3.5-fold in BAT. Furthermore, RT-PCR showed that prdx2 mRNA levels increased by 1.7- and 3.7-fold in BAT and heart, respectively, during hibernation. A partial nucleotide sequence of prdx2 from ground squirrels was obtained by PCR amplification, the deduced amino acid sequence showing 96-97% identity with Prdx2 from other mammals. Some unique amino acid substitutions were identified that might contribute to stabilizing Prdx2 conformation at the near 0 degrees C body temperatures during torpor.     

A non-LTR retroelement extinction in Spermophilus tridecemlineatus

The typical mammalian genome is dominated by two types of transposable elements (TEs), the autonomous and non-autonomous non-LTR retrotransposons, i.e. LINEs and SINEs, and with few exceptions there is a sole active LINE family (L1). During an ongoing investigation of TEs in rodents we determined that overall transposon activity has been steadily declining in Spermophilus tridecemlineatus. More specifically, the typically ubiquitous L1 activity of mammals has decreased drastically within the last 26MY. Indeed, only three L1 insertions with intact ORF1 sequences were readily identifiable and no intact ORF2 sequences were identified. The last L1 and SINE insertions date to ~5.3MYA and 4MYA, respectively. Based on our inability to computationally identify recently inserted L1 elements we suggest that S. tridecemlineatus is experiencing a quiescence or extinction of non-LTR retrotransposon activity. Such a finding represents only the fourth instance of a loss of non-LTR retrotransposon activity identified in mammals and, as such, represents an important additional data point to guide our understanding of LINE dynamics in eutherians.     

Thirteen-lined Ground Squirrel (Sciuridae: Spermophilus tridecemlineatus) Antipredator Vigilance: Monitoring the Sky for Aerial Predators

Despite the success of antipredator vigilance research, the specific focus of this vigilance has been difficult to determine. We have previously shown that thirteen-lined ground squirrels ( Spermophilus tridecemlineatus ) increase their vigilance when their lateral field of view is obstructed. In this paper, we describe an experiment in which we attempt to determine the predator class for which this vigilance is directed. Using six differentially occluded Plexiglas foraging boxes with hinged 'eaves', we were able to obstruct the squirrels' view of the sky while not obstructing their view of terrestrial threats. In general, across the box types, when their sky view was obstructed, ground squirrels increased their vigilance by increasing the percentage of time spent withdrawn from the boxes. This result suggests that a significant portion of ground squirrel antipredator vigilance is directed at the sky and is surveillance for aerial predators.     

Diabetes mellitus in the 13-lined ground squirrel (Citellus tridecemlineatus).

Spontaneous diabetes mellitus was diagnosed in six of 126, 13-lined ground squirrels, Citellus tridecemlineatus. Serum glucose values were significantly higher in the diabetic ground squirrels than in the non-diabetic ground squirrels, while serum insulin values of fasted diabetic squirrels were significantly lower than fasted nondiabetic ground squirrels. In addition, the classic diabetic signs of poly-dipsia, polyuria, glycosuria, ketonuria, polyphasia, and weight loss were present. The proportion of islet tissue to total pancreatic area in diabetic ground squirrels was less than 25% of that in the nondiabetic ground squirrels. Both the number and size of the islets of Langerhans in diabetic ground squirrels were less than those in nondiabetic ground squirrels.     

Cycle of period gene expression in a diurnal mammal (Spermophilus tridecemlineatus): implications for nonphotic phase shifting.

Ground squirrels, Spermophilus tridecemlineatus, were kept in a 12:12 h light-dark cycle. As expected for a diurnal species, their locomotor activity occurred almost entirely in the daytime. Expression of mPer1 and mPer2 in the suprachiasmatic nucleus was studied at six time points by in situ hybridization. For both these genes, mRNA was highest in the first part of the subjective day (about zeitgeber time 5). This is close to the time when mPer1 and mPer2 expression is maximal in nocturnal rodents. These results have implications for understanding nonphotic phase response curves in diurnal species and thereby for guiding research on nonphotic phase shifting in people.     

Placement, Retrieval, and Memory of Caches by Thirteen-Lined Ground Squirrels

Mechanisms governing placement and retrieval of scatter hoards were investigated in 13-lined ground squirrels ( Spermophilus tridecemlineatus ). The squirrels used several placement tactics, including relatively deep burial of seeds, avoidance of prominent objects, and cryptic placement, which would reduce chance discovery by competitors but that might also increase the difficulty of retrieval for the hoarder. Nevertheless, scatter hoards were unfailingly retrieved within a day or two after placement, despite experimental elimination or displacement of local sensory cues emanating from the sites. Artificial caches placed close to true caches were not discovered, indicating that recovery attempts were quite precise. These results imply that 13-lined ground squirrels rely heavily on spatial memory for retrieval and are the first experimental demonstration of the importance of memory for cache recovery in a natural population of mammals.     

Potential of Kidney Cell Cultures from Nonhibernating Thirteen-Lined Ground Squirrels (Citellus tridecemlineatus) for Virus Propagation

Kidney cells were cultured in vitro from nonhibernating thirteen-lined ground squirrels (Citellus tridecemlineatus). These primary ground squirrel kidney cultures were tested for the ability to support the replication of 13 viruses representing nine virus groups. The cultures were shown to be susceptible to every virus tested, either by an increase in infectious virus or by the cytopathic effect produced.     

Host usage and seasonal activity patterns of Ixodes kingi and I. sculptus (Acari: Ixodidae) nymphs in a Colorado prairie landscape, with a summary of published North American host records for all life stages.

We examined host usage and seasonal activity patterns of the nymphal stage of the ticks Ixodes kingi and I. sculptus within a prairie rodent community in north-central Colorado. Ixodes kingi was commonly encountered on both northern grasshopper mice (Onychomys leucogaster) and thirteen-lined ground squirrels (Spermophilus tridecemlineatus), whereas I. sculptus frequently infested S. tridecemlineatus but was absent from O. leucogaster. Low numbers of ticks of both species were collected from deer mice (Peromyscus maniculatus) and Ord's kangaroo rats (Dipodomys ordii). Nymphal loads of I. kingi and I. sculptus increased dramatically on commonly infested rodent species from spring (May-June) to summer (July-August). Further, rodents trapped on prairie-dog towns tended to experience increased nymphal loads of I. kingi (O. leucogaster, S. tridecemlineatus) but decreased loads of I. sculptus (S. tridecemlineatus) following plague epizootics among prairie dog populations. A summary of published North American host records revealed that I. kingi has been recorded from humans, domestic animals (cat, dog), 17 species of carnivores, 40 species of rodents, and four species of lagomorphs, and that I. sculptus has been recorded from humans, domestic animals (cat, dog, goat), 13 species of carnivores, 34 species of rodents, and three species of lagomorphs. In accordance with our observations from Colorado, I. kingi commonly has been found to infest heteromyid and murid rodents (such as grasshopper mice), whereas I. sculptus most frequently has been collected from ground-dwelling sciurid rodents, especially Spermophilus ground squirrels. The potential roles of I. kingi and I. sculptus as enzootic vectors of human pathogens, particularly the agents of tularemia (Francisella tularensis), Q fever (Coxiella burnetii), and Colorado tick fever (CTF virus), are discussed.     

Trypanosomes and Haemobartonella in Wild Rodents in Illinois

SYNOPSIS. Trypanosoma microti and Haemobartonella microti were found in 1 (17%) of 6 yellow-bellied voles Microtus ochrogastev , and T. iowensis was found in 7 (11.5%) of 60 thirteen-lined ground squirrels Spermophilus tridecemlineatus in Illinois. Reports of lewisi group trypanosomes from Microtus and Spermophilus are summarized. Those from different rodent host genera are considered to belong to different species. All of the 6 species named from the host genus Sperinophilus may belong to a single species; if so, their correct name would be T. otospermophili. However, until adequate cross transmission studies are carried out, it is considered preferable to retain the names originally assigned to the North American species.     

Ubiquitin conjugate dynamics in the gut and liver of hibernating ground squirrels

Protein synthesis is severely depressed in hibernating mammals. In the absence of significant protein synthesis, the continued turnover of proteins as a function of normal cellular activity would result in the net depletion of protein pools. We measured levels of ubiquitylated proteins in the gut of thirteen-lined ground squirrels ( Spermophilus tridecemlineatus) and liver of golden-mantled ground squirrels ( Spermophilus lateralis). In both tissues, ubiquitin conjugate concentrations increased during entrance into torpor and were elevated 2-3 fold by late torpor compared with levels in active animals. The data are consistent with a depression of proteolysis with a resultant high level of ubiquitylated proteins during the natural hypothermia of torpor. The periodic returns to euthermy during the hibernation season allow for degradation of these conjugated proteins and may serve to restore protein pools.     

Epigenetic regulation by DNA methyltransferases during torpor in the thirteen-lined ground squirrel Ictidomys tridecemlineatus

Molecular and Cellular Biochemistry - The thirteen-lined ground squirrel, Ictidomys tridecemlineatus, is a mammal capable of lowering its Tb to almost 0 °C while undergoing deep...     

Effect of 7,12-dimethylbenz(a)anthracene on the integument of the hibernating and nonhibernating 13-lined ground squirrel

1. DMBA, a chemical carcinogen, was topically applied to skin patches of hibernating and nonhibernating ground squirrels (Spermophilus tridecemlineatus). 2. Macroscopically, hyperpigmentation, hair loss and excessive skin sloughing were evident in all treated nonhibernator skin patches. 3. Histological sections of skin revealed hyperkeratosis, epidermal vesicles, acanthosis, an indistinct basal layer and increased vascularization in nonhibernators. 4. Skin patches on hibernators were unaffected by treatment showing hibernation confers protection from the pathological effects of DMBA.     

Effect of cooling on vascular smooth muscle from the thirteen-lined ground squirrel

Peripheral vascular resistance in the ground squirrel (Spermophilus tridecemlineatus) increases when the animal enters hibernation. The goals of this study were to determine if a change in vascular reactivity contributes to this hemodynamic response, and to compare the effects of temperature on vascular responsiveness in a hibernator (ground squirrel) and a nonhibernating mammal (rat). Helically cut strips of aortae and femoral arteries were mounted in organ chambers (37 degrees C) and isometric contractions were recorded. The arteries were made to contract in response to exogenous norepinephrine (5.9 X 10(-7) M). Cooling the organ chamber (11 degrees C) potentiated contractions to norepinephrine (5-15% increase) in ground squirrel femoral arteries but depressed those (80-100% decrease) in ground squirrel aortae and rat aortae and femoral arteries. Contractions in response to depolarizing concentrations of potassium in ground squirrel femoral arteries were depressed by cooling (11 degrees C), suggesting that the augmented response to norepinephrine at low temperature is specific. Treatment with indomethacin, propanolol, and ouabain did not alter the potentiating effect of temperature on contractions to norepinephrine in ground squirrel femoral arteries. Apparently, the potentiation is not related to prostaglandins generated in the vascular wall, to blockade of beta-adrenergic receptors, nor to inhibition of the electrogenic sodium pump. The observations are consistent with the hypothesis that a change in vascular responsiveness contributes to the regional control of blood flow in hibernation. This adaptive response is specific in that it does not occur in the aorta of the ground squirrel and the response is not present in the vasculature of the rat, a nonhibernating mammal.