Hypoglycemia and torpor in Siberian hamsters

1999 ◽  
Vol 276 (3) ◽  
pp. R776-R781 ◽  
Author(s):  
John Dark ◽  
Daniel A. Lewis ◽  
Irving Zucker
Keyword(s):  
Blood Glucose ◽  
Body Temperature ◽  
Body Mass ◽  
Air Temperature ◽  
Day Length ◽  
Siberian Hamsters ◽  
Long Day ◽  
Necessary And Sufficient ◽  
Blood Glucose Concentrations ◽  
Torpor Bouts

We tested whether reduced blood glucose concentrations are necessary and sufficient for initiation of torpor in Siberian hamsters. During spontaneous torpor bouts, body temperature (Tb) decreases from the euthermic value of 37 to <31°C. Among hamsters that displayed torpor during maintenance in a short-day length (10 h light/day) at an air temperature of 15°C, blood glucose concentrations decreased significantly by 28% as Tb fell from 37 to <31°C and increased during rewarming so that by the time Tb first was >36°C, glucose concentrations had returned to the value preceding torpor. Hamsters did not display torpor when maintained in a long-day length (16 h light/day) and injected with a range of insulin doses (1–50 U/kg body mass), some of which resulted in sustained, pronounced hypoglycemia. We conclude that changes in blood glucose concentrations may be a consequence rather than a cause of the torpid state and question whether induction of torpor by 2-deoxy-d-glucose is due to its general glucoprivic actions.

scholarly journals MT1 Melatonin Receptors Mediate Somatic, Behavioral, and Reproductive Neuroendocrine Responses to Photoperiod and Melatonin in Siberian Hamsters (Phodopus sungorus)

Endocrinology ◽  
2010 ◽  
Vol 151 (2) ◽  
pp. 714-721 ◽  
Author(s):  
Brian J. Prendergast
Keyword(s):  
Reproductive Function ◽  
Melatonin Receptors ◽  
Day Length ◽  
Phodopus Sungorus ◽  
Receptor Subtypes ◽  
Gonadotropin Secretion ◽  
Siberian Hamsters ◽  
The Central Nervous System ◽  
Necessary And Sufficient ◽  
And Behavior

Environmental day length drives nocturnal pineal melatonin secretion, which in turn generates or entrains seasonal cycles of physiology, reproduction, and behavior. In mammals, melatonin (MEL) binds to a number of receptor subtypes including high-affinity (MT1 and MT2) and low-affinity (MT3, nuclear orphan receptors) binding sites, which are distributed throughout the central nervous system and periphery. The MEL receptors that mediate photoperiodic reproductive and behavioral responses to MEL have not been identified in a reproductively photoperiodic species. Here I tested the hypothesis that MT1 receptors are necessary and sufficient to engage photoperiodic responses by challenging male Siberian hamsters (Phodopus sungorus), a species that does not express functional MT2 receptors, with ramelteon (RAM), a specific MT1/MT2 receptor agonist. In hamsters housed in a long-day photoperiod, late-afternoon RAM treatment inhibited gonadotropin secretion, induced gonadal regression, and suppressed food intake and body mass, mimicking effects of MEL. In addition, chronic (24 h/d) RAM infusions were sufficient to obscure endogenous MEL signaling, and these treatments attenuated gonadal regression in short days. Together, the outcomes indicate that signaling at the MT1 receptor is sufficient and necessary to mediate the effects of photoperiod-driven changes in MEL on behavior and reproductive function in a reproductively photoperiodic mammal.

Hibernation in the Eastern Pygmy Possum, Cercartetus-Nanus (Marsupialia, Burramyidae)

1993 ◽  
Vol 41 (1) ◽  
pp. 67 ◽  
Author(s):  
F Geiser
Keyword(s):  
Oxygen Consumption ◽  
Body Temperature ◽  
Metabolic Rate ◽  
Air Temperature ◽  
The Body ◽  
Daily Torpor ◽  
Rate Of Oxygen Consumption ◽  
The Mean ◽  
Cercartetus Nanus ◽  
Torpor Bouts

The pattern of torpor was examined in the eastern pygmy possum, Cercartetus nanus (21 g). Animals displayed torpor regularly in the laboratory, and the occurrence of torpor increased with decreasing air temperature (T(a)). At high T(a) (18-degrees-C) animals usually exhibited daily torpor, but torpor bouts of up to 2 days were observed occasionally. The duration of torpor bouts lengthened with a lowering of T(a) and the mean bout duration at T(a) = 5-degrees-C was 17.0 +/- 2.5 days. The minimum metabolic rate (measured as rate of oxygen consumption) of torpid individuals was 0.018 +/- 0.003 mL O2 g-1 h-1, which is less than 2% of the basal metabolic rate. The body temperature (T(b)) Of torpid animals fell to a minimum of 1.3 +/- 0.4-degrees-C. These results clearly demonstrate that Cercartetus nanus is a deep hibernator.

Day length and body mass affect diet self-selection by siberian hamsters

1996 ◽  
Vol 59 (6) ◽  
pp. 1039-1050 ◽  
Author(s):  
Jacqueline B. Fine ◽  
Timothy J. Bartness
Keyword(s):  
Body Mass ◽  
Day Length ◽  
Siberian Hamsters ◽  
Self Selection

Photoperiod-driven variation in an allergic response is independent of allergen exposure

2012 ◽  
Vol 90 (9) ◽  
pp. 1086-1093
Author(s):  
Lynn B. Martin ◽  
Courtney A.C. Coon
Keyword(s):  
Seasonal Variation ◽  
Allergen Exposure ◽  
Day Length ◽  
Immune Functions ◽  
Siberian Hamsters ◽  
Long Day ◽  
Allergenic Component ◽  
Poison Ivy ◽  
Extended Exposure ◽  
Allergy Prevalence

Allergy prevalence and severity varies seasonally in humans, presumably due to intra-annual changes in allergen exposure. However, it is possible that seasonality of allergic responses is also influenced by seasonal changes in the immune system. Here, we asked whether extended exposure to different day lengths would alter allergic responses to pentadecylcatechol (PDC), an allergenic component of poison ivy ( Toxicodendron radicans (L.) Kuntze), in Siberian hamsters ( Phodopus sungorus (Pallas, 1773)), a species exhibiting extensive seasonal variation in immune functions. We found that contact dermatitis responses were larger in short day-length (SD) housed animals than in long day-length (LD) housed animals even though sensitization and challenge dosages of allergen were identical. Furthermore, SD animals were smaller and had regressed reproductive tissues compared with LD animals, results typically observed in this species in response to photoperiod. These data suggest that endogenous changes in immune functions, perhaps via melatonin, may underlie some seasonal variation in allergic responses.

Torpor shortens the period of Siberian hamster circadian rhythms

1993 ◽  
Vol 265 (4) ◽  
pp. R951-R956 ◽  
Author(s):  
E. M. Thomas ◽  
M. E. Jewett ◽  
I. Zucker
Keyword(s):  
Body Temperature ◽  
Circadian Rhythms ◽  
Body Mass ◽  
Short Term ◽  
Running Wheel ◽  
Siberian Hamster ◽  
Short Day ◽  
Siberian Hamsters ◽  
Wheel Activity

We investigated the influence of ambient and body temperature (Ta and Tb) on circadian rhythms of gonadectomized male Siberian hamsters. Animals that entered torpor (Tb < 30 degrees C) had significantly shorter circadian periods (tau s) than did nontorpid hamsters at a Ta of 13 degrees C (24.17 +/- 0.05 vs. 24.33 +/- 0.04 h). The tau s of homeothermic hamsters were not affected by Ta change. Short-term decreases in Tb, rather than changes in Ta, appear to affect tau. Access to activity wheels inhibited expression of torpor in short daylengths and was associated with significant increases in body mass. Running wheel activity can mask or block specific short-day responses.

scholarly journals Seasonal regulation of reproduction: altered role of melatonin under naturalistic conditions in hamsters

2010 ◽  
Vol 277 (1695) ◽  
pp. 2867-2874 ◽  
Author(s):  
Matthew P. Butler ◽  
Kevin W. Turner ◽  
Jin Ho Park ◽  
Elanor E. Schoomer ◽  
Irving Zucker ◽  
...  
Keyword(s):  
Body Weight ◽  
Day Length ◽  
Seasonal Transition ◽  
Siberian Hamsters ◽  
Long Day ◽  
Spring Equinox ◽  
Natural Photoperiod ◽  
History Of ◽  
Seasonal Regulation

The seasonal reproductive cycle of photoperiodic rodents is conceptualized as a series of discrete melatonin-dependent neuroendocrine transitions. Least understood is the springtime restoration of responsiveness to winter-like melatonin signals (breaking of refractoriness) that enables animals to once again respond appropriately to winter photoperiods the following year. This has been posited to require many weeks of long days based on studies employing static photoperiods instead of the annual pattern of continually changing photoperiods under which these mechanisms evolved. Maintaining Siberian hamsters under simulated natural photoperiods, we demonstrate that winter refractoriness is broken within six weeks after the spring equinox. We then test whether a history of natural photoperiod exposure can eliminate the requirement for long-day melatonin signalling. Hamsters pinealectomized at the spring equinox and challenged 10 weeks later with winter melatonin infusions exhibited gonadal regression, indicating that refractoriness was broken. A photostimulatory effect on body weight is first observed in the last four weeks of winter. Thus, the seasonal transition to the summer photosensitive phenotype is triggered prior to the equinox without exposure to long days and is thereafter melatonin-independent. Distinctions between photoperiodic and circannual seasonal organization erode with the incorporation in the laboratory of ecologically relevant day length conditions.

scholarly journals Is reproduction of male eastern rock sengis (Elephantulus myurus) from southern Africa affected by photoperiod?

2016 ◽  
Vol 94 (11) ◽  
pp. 747-752 ◽  
Author(s):  
K. Medger ◽  
C.T. Chimimba ◽  
N.C. Bennett
Keyword(s):  
Body Mass ◽  
Southern Africa ◽  
Day Length ◽  
Plasma Testosterone ◽  
Testosterone Concentration ◽  
Long Day ◽  
Seasonal Basis ◽  
The Tropics ◽  
Tubule Diameter

Many mammals use the change in day length to time physiological and behavioural activities on a seasonal basis. Particularly, mammals from temperate regions use photoperiod to regulate reproductive functions; however, information on the role of photoperiod in small mammals from the tropics and subtropics is scarce. We studied the response of the reproductive system of male eastern rock sengis (Elephantulus myurus Thomas and Schwann, 1906) from southern Africa to photoperiods of differing length. Elephantulus myurus breeds seasonally during the spring and summer months of the southern hemisphere despite its subtropical distribution. It is one of only three sengi species known to breed seasonally. Fourteen male E. myurus were subjected to either long-day (LD; 16 h light (L) : 8 h dark (D)) or short-day (SD; 8 h L : 16 h D) photoperiods and the photoperiodic effects on the testes, testosterone concentration, and body mass were examined. Testicular volume and mass, seminiferous tubule diameter, and body mass were not significantly different between LD and SD conditions. However, plasma testosterone concentration was significantly lower in males on LD photoperiods compared with SD photoperiods. Male E. myurus may not use photoperiod as a cue to control seasonal reproductive changes. Other environmental factors such as temperature, rainfall, food abundance, or social factors are possibly influencing seasonal reproduction in this species.

Exogenous T3 mimics long day lengths in Siberian hamsters

2007 ◽  
Vol 292 (6) ◽  
pp. R2368-R2372 ◽  
Author(s):  
David A. Freeman ◽  
Brett J. W. Teubner ◽  
Carlesia D. Smith ◽  
Brian J. Prendergast
Keyword(s):  
Gonadal Development ◽  
Day Length ◽  
Intermediate Step ◽  
Iodothyronine Deiodinase ◽  
Short Day ◽  
Siberian Hamsters ◽  
Long Day ◽  
Long Duration ◽  
Reproductive Response

Siberian hamsters ( Phodopus sungorus) exhibit seasonal cycles of reproduction driven by changes in day length. Day length is encoded endogenously by the duration of nocturnal melatonin (Mel) secretion from the pineal gland. Short-duration Mel signals stimulate reproduction and long-duration signals inhibit reproduction. The mechanism by which Mel signals are decoded at the level of neural target tissues remains uncharacterized. In Siberian hamsters, exposure to short day lengths or injections of Mel in long days results in a decrease in hypothalamic expression of type 2 iodothyronine deiodinase (Dio2) mRNA. Dio2 catalyzes the conversion of the thyroid hormone thyroxine to triiodothyronine (T3). Thus exposure to short and long day lengths should decrease and increase hypothalamic T3 concentrations, respectively. We tested the hypothesis that exogenous T3 administered to short-day hamsters would mimic exposure to long day lengths with respect to gonadal stimulation. Hamsters gestated and raised in short day lengths that exhibited photoinhibition of the testes were given daily subutaneous injections of T3 or saline vehicle for 4 wk beginning at week 12 of life. The results indicate that exogenous T3 induced gonadal growth in short-day hamsters and delayed spontaneous gonadal development by an interval equal to the number of weeks during which T3 was administered. T3 injections delayed gonadal regression if given coincident with the transfer of hamsters from long to short day lengths. These results suggest that T3 mimics long day exposure in Siberian hamsters and may serve as an intermediate step between the Mel rhythm and the reproductive response.

scholarly journals Ingesting a high-dose carbohydrate solution during the cycle section of a simulated Olympic-distance triathlon improves subsequent run performance

2012 ◽  
Vol 37 (4) ◽  
pp. 664-671 ◽  
Author(s):  
Kerry McGawley ◽  
Oliver Shannon ◽  
James Betts
Keyword(s):  
Blood Glucose ◽  
Oxygen Uptake ◽  
Body Mass ◽  
Time Trial ◽  
Peak Oxygen Uptake ◽  
High Dose ◽  
Stomach Upset ◽  
Single Discipline ◽  
Blood Glucose Concentrations ◽  
Carbohydrate Solution

The well-established ergogenic benefit of ingesting carbohydrates during single-discipline endurance sports has only been tested once within an Olympic-distance (OD) triathlon. The aim of the present study was to compare the effect of ingesting a 2:1 maltodextrin/fructose solution with a placebo on simulated OD triathlon performance. Six male and 4 female amateur triathletes (age, 25 ± 7 years; body mass, 66.8 ± 9.2 kg; peak oxygen uptake, 4.2 ± 0.6 L·min–1) completed a 1500-m swim time-trial and an incremental cycle test to determine peak oxygen uptake before performing 2 simulated OD triathlons. The swim and cycle sections of the main trials were of fixed intensities, while the run section was completed as a time-trial. Two minutes prior to completing every quarter of the cycle participants consumed 202 ± 20 mL of either a solution containing 1.2 g·min–1 of maltodextrin plus 0.6 g·min–1 of fructose at 14.4% concentration (CHO) or a sugar-free, fruit-flavored drink (PLA). The time-trial was 4.0% ± 1.3% faster during the CHO versus PLA trial, with run times of 38:43 ± 1:10 min:s and 40:22 ± 1:18 min:s, respectively (p = 0.010). Blood glucose concentrations were higher in the CHO versus PLA trial (p < 0.001), while perceived stomach upset did not differ between trials (p = 0.555). The current findings show that a 2:1 maltodextrin/fructose solution (1.8 g·min–1 at 14.4%) ingested throughout the cycle section of a simulated OD triathlon enhances subsequent 10-km run performance in triathletes.

scholarly journals Effect of food on seasonal response in Indian weaver bird (Ploceus philippinus)

2014 ◽  
Vol 15 (3) ◽  
pp. 19-28
Author(s):  
Shikha Malik ◽  
Rohit Kumar Pandey ◽  
Sanjay Kumar Bhardwaj
Keyword(s):  
Body Mass ◽  
Food Group ◽  
The Body ◽  
Day Length ◽  
Plumage Color ◽  
Supplementary Food ◽  
Short Day ◽  
Long Day ◽  
Group 5 ◽  
Group 2

We investigated the effect of normal (adlib) and supplementary food on body mass, testes growth, moult and plumage color in Indian weaver birds. Birds intially were kept under natural day length (NDL) and then exposed to short day lengths (8 h light: 16 h darkness) for at least 2 weeks before being subjected to an experimental regime. They were divided into five groups (n=4 each), groups 1 and 2 were held under SDL (Short day length -8L: 16D), groups 3 and 4 were exposed to LDL (Long daylength-16L: 8D) and simultaneously group 5 held under natural day length, served as control. One group of SDL (Group 2) and LDL (group 3) as well as group 5 (NDL) were fed on grain with supplement proteinaceous food and groups 2 and 4 were fed on adlib food (grain) only. Observations on body mass, testis growth, bodymolt and plumage color were recorded bi weekly. A significant change in the body mass under both photoperiodic groups (SDL; group 2 and LDL; group 4), but the testicular growth was noticed on long day lengths (LDL: 16L: 8D) and control (NDL) group. However the supplement food modulated the testes growth, body molt, beak pigmentation and body plumage regeneration. Early feather regeneration was found in supplementary food group under long day length. It is suggested that the supplementary food, affects the timing of the development of secondary sexual characteristics.

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