Prolactin and testosterone inhibit torpor in Siberian hamsters

1993 ◽  
Vol 264 (1) ◽  
pp. R123-R128 ◽  
Author(s):  
N. F. Ruby ◽  
R. J. Nelson ◽  
P. Licht ◽  
I. Zucker
Keyword(s):  
Food Intake ◽  
Suprachiasmatic Nucleus ◽  
Daily Torpor ◽  
Osmotic Minipumps ◽  
Siberian Hamsters ◽  
Long Day ◽  
Discontinuation Of Treatment ◽  
Plasma Prl

Female Siberian hamsters maintained in a winter photoperiod (8 h light/day) ceased to undergo daily torpor during infusion of prolactin (PRL) from osmotic minipumps; winter torpor was reinstated within 3 days of discontinuation of treatment. By contrast, PRL infusion was ineffective in suppressing daily torpor elicited by restricting food intake in female hamsters housed in a summer photoperiod (16 h light/day). Summer daily torpor was, however, completely inhibited in long-day gonadectomized male hamsters treated with testosterone (T). We suggest that the hyperprolactinemia, which in previous studies is characteristic of hamsters that sustain ablation of the suprachiasmatic nucleus, is incompatible with winter torpor. Summer torpor may be controlled by a mechanism less responsive to variations in plasma PRL concentration. Both winter and summer torpor are inhibited by exogenous T; it remains uncertain, however, whether sustained decreases in endogenous T secretion are as essential for the expression of summer as they are for winter torpor.

Control of torpor and body weight patterns by a seasonal timer in Siberian hamsters

1989 ◽  
Vol 257 (1) ◽  
pp. R142-R149 ◽  
Author(s):  
T. J. Bartness ◽  
J. A. Elliott ◽  
B. D. Goldman
Keyword(s):  
Body Weight ◽  
Food Intake ◽  
Implant Removal ◽  
Daily Torpor ◽  
Short Day ◽  
Siberian Hamsters ◽  
Long Day ◽  
Preparatory Phase ◽  
Pelage Color ◽  
Seasonal Responses

Two experiments were designed to assess whether the short-day-induced patterns of shallow daily torpor, body weight, and other seasonal responses (food intake and pelage pigmentation) exhibited by Siberian hamsters (Phodopus sungorus sungorus) are under the control of a "seasonal timekeeping mechanism" that is independent of reproductive status [testosterone, (T)]. We examined whether the patterning and expression of these seasonal responses were altered by decreases in serum T that accompany gonadal regression during the first 8 wk of short-day exposure (i.e., the "preparatory phase" of the torpor season) or by experimental increases in serum T after this phase. Short-day-housed, castrated hamsters bearing T implants had long-day levels of the hormone and did not exhibit torpor. Appropriate seasonal patterns and levels of torpor, body weight, pelage color stage, and food intake were exhibited after T implant removal although serum T was clamped to long-day levels during the preparatory phase. In animals that were gonad intact during the preparatory phase and were subsequently castrated and given T implants, torpor did not occur as long as the implants were in place. However, the patterns and levels of daily torpor, food intake, and body weight rapidly returned to appropriate seasonal values compared with the castrated, blank-implanted controls on T implant removal; these effects occurred whether the T implants were removed when torpor frequency was increasing, at its peak, or decreasing across the torpor season. T did not affect pelage color stage under any condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Daily torpor in the absence of the suprachiasmatic nucleus in Siberian hamsters

1992 ◽  
Vol 263 (2) ◽  
pp. R353-R362 ◽  
Author(s):  
N. F. Ruby ◽  
I. Zucker
Keyword(s):  
Suprachiasmatic Nucleus ◽  
Food Restriction ◽  
Temporal Organization ◽  
Daily Torpor ◽  
Short Day ◽  
Siberian Hamsters ◽  
Random Fashion ◽  
Before And After ◽  
Ad Libitum ◽  
Short Days

Siberian hamsters express torpor spontaneously after several weeks of exposure to short days. In long days, torpor is expressed only when food intake is restricted. Hamsters maintained in a long photoperiod (16 h light/day) at 15 degrees C expressed daily torpor during food restriction both before and after bilateral ablation of the suprachiasmatic nucleus (SCN). Hamsters housed in short days (8 h light/day, ambient temperature 15 degrees C) and fed ad libitum displayed torpor before, but not after, ablation of the SCN (SCNX). Torpor was reinstated in all short-day SCNX hamsters during postoperative food restriction and persisted in several animals even after ad libitum feeding was reinstated. Torpor was entrained to the light-dark cycle in both long- and short-day hamsters preoperatively but appeared to occur in a temporally random fashion in SCNX animals. SCNX hamsters, unlike control animals, displayed multiple torpor bouts per 24 h. The SCN is not essential for the expression of torpor but plays a crucial role in its temporal organization.

scholarly journals The Chemistry of Cold: Mechanisms of Torpor Regulation in the Siberian Hamster

Physiology ◽  
2016 ◽  
Vol 31 (1) ◽  
pp. 51-59 ◽  
Author(s):  
Ceyda Cubuk ◽  
Jonathan H. H. Bank ◽  
Annika Herwig
Keyword(s):  
Physiological State ◽  
Daily Torpor ◽  
Brain Areas ◽  
Siberian Hamster ◽  
Siberian Hamsters ◽  
Save Energy

Siberian hamsters use spontaneous daily torpor, a state of hypometabolism and hypothermia, to save energy during winter. Multiple neuroendocrine signals set the scene for spontaneous torpor to occur, and several brain areas have been identified as potential sites for torpor regulation. Here, we summarize the known mechanisms of a fascinating physiological state in the Siberian hamster.

Energy intake and fur in summer- and winter-acclimated Siberian hamsters (Phodopus sungorus)

2001 ◽  
Vol 281 (2) ◽  
pp. R519-R527 ◽  
Author(s):  
Alexander S. Kauffman ◽  
Alessandra Cabrera ◽  
Irving Zucker
Keyword(s):  
Food Intake ◽  
Energy Intake ◽  
Ventral Surface ◽  
Phodopus Sungorus ◽  
Ambient Temperatures ◽  
Siberian Hamsters ◽  
Daily Food ◽  
Brown Adipose ◽  
Wide Range ◽  
The Impact

Few studies have directly addressed the impact of fur on seasonal changes in energy intake. The daily food intake of Siberian hamsters ( Phodopus sungorus) was measured under simulated summer and winter conditions in intact animals and those with varying amounts of pelage removed. Energy intake increased up to 44% above baseline control values for approximately 2–3 wk after complete shaving. Increases in food intake varied with condition and were greater in hamsters housed in short than long day lengths and at low (5°C) than moderate (23°C) ambient temperatures. Removal of 8 cm2 of dorsal fur, equivalent to 30% of the total dorsal fur surface, increased food intake, but removal of 4 cm2 had no effect. An 8-cm2 fur extirpation from the ventral surface did not increase food consumption. Food intake was not influenced differentially by fur removal from above brown adipose tissue hot spots. Fur plays a greater role in energy balance in winter- than summer-acclimated hamsters and conserves energy under a wide range of environmental conditions.

Thermoregulation, growth, and reproduction in Alaskan collared lemmings: role of short day and cold

1991 ◽  
Vol 261 (3) ◽  
pp. R522-R530 ◽  
Author(s):  
H. A. Maier ◽  
D. D. Feist
Keyword(s):  
Food Intake ◽  
Thermal Conductance ◽  
Reproductive Condition ◽  
Reproductive Morphology ◽  
Short Day ◽  
Long Day ◽  
Dicrostonyx Groenlandicus ◽  
Before And After ◽  
Growth And Reproduction

To assess factors controlling seasonal thermoregulatory and reproductive changes, collared lemmings (Dicrostonyx groenlandicus) were exposed for 16 wk to long day (LD, 22 h light: 2 h dark) and warm (15 +/- 3 degrees C), LD and cold (1 +/- 0.5 degrees C), short day (SD, 4 h light: 20 h dark) and warm, SD and cold or acclimatized to outdoor winter conditions (OUT). Hair length and color, body mass, and food intake were monitored weekly. Resting metabolic rates (RMR) and nonshivering thermogenesis (NST) were estimated several times by measuring oxygen consumption before and after norepinephrine injections. Body composition and reproductive condition were determined at the end of the experiment. SD and OUT groups had a 15.8% lower (P less than 0.01) RMR at 7 degrees C than the LD groups. Lower thermal conductance in SD and OUT animals appears due to molt to white winter pelage, which occurred by week 3 in SD but not in LD groups. Neither SD, cold, nor OUT altered NST or reproductive morphology. SD-exposed lemmings showed 19.2% greater growth than those in LD, resulting primarily from a 29.2 and 15.0% increase in lean and ash components, respectively. Cold exposure increased food intake by 34.7%. Results suggest that the pineal gland, which mediates SD effects, may influence molt and growth but not NST or reproductive morphology.

Photoperiod modulates the effects of norepinephrine on lymphocyte proliferation in Siberian hamsters

2003 ◽  
Vol 285 (4) ◽  
pp. R873-R879 ◽  
Author(s):  
Gregory E. Demas ◽  
Timothy J. Bartness ◽  
Randy J. Nelson ◽  
Deborah L. Drazen
Keyword(s):  
Lymphocyte Proliferation ◽  
Splenic Tissue ◽  
Splenocyte Proliferation ◽  
Short Day ◽  
Siberian Hamsters ◽  
Long Day ◽  
Β Adrenergic Receptors ◽  
Short Days

Siberian hamsters ( Phodopus sungorus) rely on photoperiod to coordinate seasonally appropriate changes in physiology, including immune function. Immunity is regulated, in part, by the sympathetic nervous system (SNS), although the precise role of the SNS in regulating photoperiodic changes in immunity remains unspecified. The goal of the present study was to examine the contributions of norepinephrine (NE), the predominant neurotransmitter of the SNS, to photoperiodic changes in lymphocyte proliferation. In experiment 1, animals were maintained in long [16:8-h light-dark cycle (16:8 LD)] or short days (8:16 LD) for 10 wk, and splenic NE content was determined. In experiment 2, in vitro splenocyte proliferation in response to mitogenic stimulation (concanavalin A) was assessed in spleen cell suspensions taken from long- or short-day hamsters in which varying concentrations of NE were added to the cultures. In experiment 3, splenocyte proliferation was examined in the presence of NE and selective α- and β-noradrenergic receptor antagonists (phenoxybenzamine and propranolol, respectively) in vitro. Short-day animals had increased splenic NE content compared with long-day animals. Long-day animals had higher proliferation compared with short-day animals independent of NE. NE (1 μM) further suppressed splenocyte proliferation in short but not long days. Last, NE-induced suppression of proliferation in short-day hamsters was blocked by propranolol but not phenoxybenzamine. The present results suggest that NE plays a role in photoperiodic changes in lymphocyte proliferation. Additionally, the data suggest that the effects of NE on proliferation are specific to activation of β-adrenergic receptors located on splenic tissue. Collectively, these results provide further support that photoperiodic changes in immunity are influenced by changes in SNS activity.

Regional differences in fat pad responses to short days in Siberian hamsters

1989 ◽  
Vol 257 (6) ◽  
pp. R1533-R1540 ◽  
Author(s):  
T. J. Bartness ◽  
J. M. Hamilton ◽  
G. N. Wade ◽  
B. D. Goldman
Keyword(s):  
Body Weight ◽  
Body Fat ◽  
Subcutaneous Fat ◽  
Short Photoperiod ◽  
Fat Pad ◽  
Initial Exposure ◽  
Short Day ◽  
Siberian Hamsters ◽  
Long Day ◽  
Induced Changes

Siberian hamsters exhibit decreased body weight and fat after initial exposure to short photoperiods and increased body weight and fat after extended short photoperiod exposure. The purpose of the present experiments was to determine if uniform changes in white adipose tissue (WAT) pad weights and lipid metabolism correspond to these short photoperiod-induced changes in body fat. Carcass lipid content and testes and fat pad weights [retroperitoneal WAT (RWAT), epididymal WAT (EWAT), and inguinal and dorsal subcutaneous WAT, respectively] were decreased in male hamsters relative to their long day counterparts after 6 and 12 wk of short-day exposure. Moreover, EWAT and RWAT weight, EWAT specific lipoprotein lipase activity, and specific and total lipogenesis were disproportionately decreased relative to the subcutaneous fat pads. The changes in fat pad weight and metabolism were generally reversed coincident with the return to a long-day-like reproductive status after prolonged short-day exposure (24 and 30 wk). In a less detailed experiment, female Siberian hamsters had decreased body, fat pad, and uterine weights after 6 wk of short-day exposure; however, no fat pad-specific changes in weight were observed. The results of these experiments demonstrate that short-day-exposed male Siberian hamsters may be a useful model for examining mechanisms underlying fat pad-specific responses. In addition, gender appears to influence the pattern of short-day-induced lipid depletion in this species.

Short-day-like body weight changes do not prevent fat pad compensation after lipectomy in Siberian hamsters

1997 ◽  
Vol 272 (1) ◽  
pp. R68-R77 ◽  
Author(s):  
M. M. Mauer ◽  
T. J. Bartness
Keyword(s):  
Body Weight ◽  
Food Restriction ◽  
Adipocyte Size ◽  
Weight Changes ◽  
Fat Pad ◽  
Body Weight Changes ◽  
Siberian Hamsters ◽  
Long Day ◽  
Long Duration ◽  
Short Days

Long-day (LD)-housed Siberian hamsters show compensatory increases in white adipose tissue (WAT) weight after lipectomy, whereas hamsters exposed to short days (SDs) for a long duration (22 wk) do not. We tested whether SD-induced body weight changes prevent fat pad compensation after lipectomy. In experiment 1, hamsters with lesions of the paraventricular nucleus of the hypothalamus (PVNx) rapidly increased body weight similarly to 22-wk SD-exposed hamsters. In experiment 2, LD-housed hamsters were food restricted for 22 wk and then pair fed with SD-housed hamsters for 12 wk to produce body weight changes mimicking those of ad libitum-fed SD-exposed animals. Epididymal WAT (EWAT) lipectomy (EWATx) of PVNx or food-restricted hamsters elicited compensatory increases in retroperitoneal and inguinal WAT (RWAT and IWAT) weights. Unlike other fat pads, EWAT was less affected by food restriction or PVNx than by SD exposure. In general, food restriction decreased adipocyte number, whereas SD exposure decreased adipocyte size. PVNx increased RWAT adipocyte size and IWAT adipocyte number. These results suggest that the lack of body fat compensation by EWATx hamsters exposed to SDs for a long duration is due to SD-associated responses other than body weight changes per se.

Diminished satiation in rats exposed to elevated levels of endogenous or exogenous cholecystokinin

2001 ◽  
Vol 280 (2) ◽  
pp. R331-R337 ◽  
Author(s):  
Mihai Covasa ◽  
Jeremy K. Marcuson ◽  
Robert C. Ritter
Keyword(s):  
Body Weight ◽  
Food Intake ◽  
Body Fat ◽  
Peritoneal Cavity ◽  
Dietary Protein ◽  
High Protein ◽  
High Fat ◽  
Low Fat ◽  
Osmotic Minipumps ◽  
Fat Composition

Rats maintained on a high-fat (HF) diet exhibit reduced sensitivity to the satiation-producing effect of exogenous CCK. Because more CCK is released in response to HF meals than low-fat (LF) meals, we hypothesized that increased circulating CCK associated with ingestion of HF diets contributes to the development of decreased CCK sensitivity. To test this hypothesis, we implanted osmotic minipumps filled with either NaCl or CCK octapeptide into the peritoneal cavity. Subsequently, we examined the effect of intraperitoneal NaCl or CCK (0.5 μg/kg) injection on 30-min food intake. CCK significantly reduced 30-min food intake less in rats implanted with CCK-releasing minipumps compared with those with NaCl-releasing minipumps. Because dietary protein is a potent releaser of endogenous CCK, we hypothesized that rats adapted to a high-protein (HP) diet might also exhibit reduced sensitivity to exogenous CCK. Therefore, in a second experiment, we examined CCK-induced reduction of food intake in rats maintained on LF and rats maintained on HF or HP. Ingestion of LF stimulates very little endogenous CCK secretion, whereas both HF and HP markedly increase plasma CCK concentrations. Both doses of CCK reduced food intake significantly less in HF and HP rats compared with LF rats. There were no differences in 24-h food intake, body weight, or body fat composition among LF-, HF-, and HP-fed rats. These results are consistent with the hypothesis that sustained elevation of CCK either by infusion of exogenous CCK or by dietary-induced elevation of plasma CCK contributes to the development of reduced sensitivity to exogenous CCK.

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