Golden-mantled Ground Squirrel Spermophilus Lateralis Research Articles

Plasma ghrelin concentrations change with physiological state in a sciurid hibernator ( Spermophilus lateralis)

Ghrelin is a recently discovered hormone which has profound effects on food intake and lipogenesis in mammals. In all mammals studied thus far, plasma ghrelin concentrations are increased before a meal and decrease immediately following a meal; ghrelin levels increase with fasting. The golden-mantled ground squirrel Spermophilus lateralis (also known as Callospermophilus lateralis (see Helgen et al., 2009) is a diurnal hibernator which has a robust annual cycle of body mass gain and loss that is primarily controlled by food intake. We hypothesized that in spring, summer, and autumn, the endogenous ghrelin concentrations of hibernators would be similar to those of non-hibernators, but that during the winter hibernation season, plasma ghrelin concentrations would be low or undetectable. We found that peripherally injected ghrelin significantly increased food intake in June. Plasma ghrelin concentrations were significantly increased through 5 days of fasting during a short-term fast in summer. Over a 24 h period, ghrelin concentrations increased at night and decreased during the day with drops corresponding to times when squirrels were eating. In January, ghrelin concentrations are low but measurable even while animals are at low body temperature (Tb). This is the first report of ghrelin concentrations in a non-photoperiodic hibernator. We suggest that ghrelin may be important for the regulation of food intake and the body mass cycle in mammals that hibernate.

An Appraisal of Operative Temperature Mounts as Tools for Studies of Ecological Energetics

Taxidermic mounts are frequently used to quantify the operative temperature or standard operative temperature of complex natural environments. These thermal indices are subsequently used to estimate the metabolic heat production of freeliving animals. Such use has often entailed violation of two standards for biological data collection: that multiple samples be analyzed and that instruments be calibrated under the range of conditions used in empirical analyses. To explore the consequences of these practices, we compared the responses of both heated and unheated taxidermic mounts with those of live animals when exposed to combinations of wind and radiation that normally could be experienced in nature. Two mammals, the rock squirrel Spermophilus variegatus and the golden-mantled ground squirrel Spermophilus lateralis, as well as a bird, the verdin, Auriparus flaviceps, were studied. For all species, there was substantial individual variation in mount responses. Under a single set of environmental conditions, coefficients of variance for mount response were as high as 71%, and the range of values between mounts typically equaled the change in the group's average standard operative temperature that was produced by two-to fourfold increases in wind speed. For predicting physiological responses of animals, the adequacy of taxidermic mounts varied widely with species, type of mount, and environmental conditions. In some cases, predictions closely matched animal responses. In other cases, predictions using data from mounts produced errors of up to 28.5°C in the estimate of standard operative temperature. The types of error observed, combined with the extensive investment of time and resources required to construct and determine the utility of mounts as operative temperature thermometers for a particular species, greatly reduces the attractiveness of this technique for quantifying the thermal environments of animals in nature.

Regional changes in central monoamine and metabolite levels during the hibernation cycle in the golden-mantled ground squirrel

We assayed various brain regions for levels of monoamines and their metabolites throughout the hibernation cycle of the golden-mantled ground squirrel Spermophilus lateralis. The tissue concentrations of serotonin, dopamine, norepinephrine and their metabolites were determined in the parietal cortex, striatum, midbrain, hippocampus, hypothalamus, and pons. Telencephalic regions exhibited the most significant variations in biogenic amine content. Cortical serotonin (5-HT) levels increased significantly at entrance ( P < 0.0001) relative to other period of the hibernation cycle, suggesting a role for 5-HT in the initiation of hibernation. Among striatal dopamine (DA) metabolites, 3-methoxytyramine was detectable only during euthermia and arousal; from entrance through arousal, homovanillic acid (HVA) levels were half that found during euthermia ( P = 0.0001); and dihydroxyphenylacetic acid (DOPAC) levels increased during day 1 of hibernation ( P < 0.0005). Midbrain DA ( P = 0.0295) and hippocampal HVA ( P = 0.0194) levels also changed significantly across the hibernation bout. The absence of a consistent change in any monoamine or metabolite throughout the brain precludes the possibility of preferential temperature-dependent impairment of an enzyme involved in biogenic amine synthesis or degradation and suggests that the levels observed reflect changes in neural activity specific to each brain region. Together with previous studies of brain 2-deoxyglucose uptake throughout the hibernation cycle, these data indicate that a transient change in afferent monoaminergic metabolism and neurotransmission in the forebrain is a necessary component for the entrance to hibernation.

Changes in renal morphology and renin secretion in the golden-mantled ground squirrel (Spermophilus lateralis) during activity and hibernation

Chronological changes in renal glomerular morphology and plasma renin activity were investigated during active and hibernating periods in the golden-mantled ground squirrel Spermophilus lateralis. The objective of this study was to determine whether the glomerular endothelium, visceral epithelium (podocytes), basement membrane, mesangial cells, proximal convoluted tubule cells and plasma renin activity exhibit measurable sequential differences between as well as within active and hibernating states at various time points. Limitations in the size of the experimental population prevented an evaluation of changes in these parameters during other important periods such as periodic arousal between hibernation bouts. In this study, glomerular endothelial pore number and epithelial filtration slit number significantly decreased by early hibernation when compared to those during summer activity, and then they increased back toward summer levels by late hibernation. In contrast, podocytic pedicel width along the glomerular basement membrane increased from summer activity to early hibernation, before significantly decreasing again by late hibernation. Mesangial cell and proximal convoluted tubule cell activity appeared increased during hibernation as compared to summer activity, whereas the width of the glomerular basement membrane showed no significant alterations throughout. Plasma renin activity significantly increased during early hibernation and mid-hibernation when compared to summer levels but had decreased by late hibernation toward summer values. The glomerular and plasma renin activity changes observed in this study clearly illustrate the drastic structural and functional adjustments which hibernating species make during torpor and also correlate well with the reported decrease in renal perfusion pressure and urine formation during hibernation.(ABSTRACT TRUNCATED AT 250 WORDS)

The golden-mantled ground squirrel (Spermophilus lateralis) as a model for the effects of environmental enrichment in solitary animals.

It has been proposed that the brain effects induced by laboratory environmental enrichment may be a product of the social stimulation inherent in the standard enriched environment. This experiment was conducted in order to study the suitability of the golden-mantled ground squirrel Spermophilus lateralis (a solitary-living species) for studies attempting to dissociate social factors from other effects in brain and behavioral effects of environmental enrichment. Juvenile Spermophilus lateralis, born in the laboratory of mothers wild-caught while pregnant, were assigned singly to individual enriched conditions (I-EC) or impoverished (IC) conditions at 55-62 days (an age at which wild individuals would disperse from the natal burrow and live alone). After 30 days, the subjects were videotaped in two 10-min opportunities for exploration; following this, they were sacrificed and their brains dissected. Multiple indications of isolation stress were observed, including unusual difficulty in handling, stereotyped pacing behavior, and escape behaviors in the exploration arena. Comparisons between I-EC and IC showed no differences in whole-brain weight or weights of several brain regions. These results indicate that S. lateralis is not suitable for this type of study; in addition, this species' reported nonsociality is questioned, based on these subjects' reactions to isolation housing and field observations of social interactions in this species.