Possible mechanisms of weight loss of Siberian hamsters (Phodopus sungorus sungorus) exposed to short photoperiod.

Several weeks of short day photoperiod (SD) exposure promote a dramatic decrease of white adipose tissue (WAT) mass in Siberian hamsters(Phodopus sungorus sungorus). This slimming effect is accompanied by changes in the adipocyte responsiveness to adrenergic stimulation that are still under debate. We investigated whether possible changes in the antilipolytic responses, and/or lipogenic activities could be involved in such lipid deposition/mobilisation imbalance.

Non-shivering thermogenesis activation and maintenance in the aging gray mouse lemur (Microcebus murinus).

The cold-induced enhancement of non-shivering thermogenesis (NST), involving brown-adipose tissue (BAT) metabolism, could participate to impair energy balance in the aged gray mouse lemur (Microcebus murinus). We first investigated the age-related modulations of cold-stimulated BAT cell morphology and contents. Then, NST was pharmacologically stimulated to assess whether aging impaired NST activation in the mouse lemur.

Brown fat and nonshivering thermogenesis in the gray mouse lemur (Microcebus murinus).

The gray mouse lemur Microcebus murinus is a rare example of a primate exhibiting daily torpor. In captive animals, we examined the metabolic rate during arousal from torpor and showed that this process involved nonshivering thermogenesis (NST). Under thermoneutrality (28 degrees C), warming-up from daily torpor (body temperature <33 degrees C) involved a rapid (<5 min) increase of O(2) consumption that was proportional to the depth of torpor (n = 8).

Evidence for a direct effect of melatonin on mitochondrial genome expression of Siberian hamster brown adipocytes.

Photoperiod variations are known to participate in the regulation of energy balance in different rodent species via melatonin, a neurosecretory product synthesized by the pineal gland during the night. A direct effect of melatonin on adipose tissue has been suggested since binding sites for the indole have been described on brown adipocytes. The aim of this study was to investigate a genetic effect of melatonin on isolated Siberian hamster brown adipocytes using differential display RT-PCR (DDRT-PCR).

Lipolytic and antilipolytic responses of the Siberian hamster (Phodopus sungorus sungorus) white adipocytes after weight loss induced by short photoperiod exposure.

Short day photoperiod promotes thermogenesis and extensive weight loss in Siberian hamsters (Phodopus sungorus sungorus). To determine whether a change in hormone-sensitive lipolysis occurs after short-photoperiod exposure, some lipolytic responses were measured on white adipocytes isolated from animals exposed in warm conditions to short or Long daylight photoperiod. The body mass of male Siberian hamsters exposed during 11 weeks to short days (SD; light: dark, 6:18 hr) reached only 50% of those kept in long days (LD; 16: 8 hr).

Characterization of a melatonin binding site in Siberian hamster brown adipose tissue.

Melatonin has been shown, in various rodent species, to mediate photoperiodic effects on body weight and, consequently, fat mass. Pharmacological investigations indicated that the brown adipose tissue of Siberian hamsters possesses a melatonin binding site with a dissociation constant of 570+/-300 pM and a density of 3.2+/-1.

Effects of both a melatonin agonist and antagonist on seasonal changes in body mass and energy intake in the garden dormouse.

Background: Many physiological functions including nycthemeral rhythm, reproductive cycles, body temperature and body mass are controlled by photoperiodic changes in different species. In the hibernating garden dormouse, both energy intake and body mass increase with the duration of the night. This seasonal mass gain is spontaneous and reversible.

Cellular changes during cold acclimatation in adipose tissues.

Cold exposure is a well-known physiological stimulus that activates the sympathetic nervous system and induces brown adipose tissue (BAT) hyperplasia. The effects of cold exposure or cold acclimatation have been extensively studied in interscapular BAT (IBAT). However, it has been recently shown that studied adipocytes are present in adipose deposits considered as white fat such as periovarian (PO) fat pad.

Antilipolytic effects of alpha 2-adrenergic agonists, neuropeptide Y, adenosine, and PGE1 in mammal adipocytes.

Lipolysis is stimulated by different hormones, depending on the species, but is also regulated by antilipolytic modulators, such as catecholamines (alpha 2-agonists), neuropeptide Y (NPY), adenosine, and prostaglandin E1 (PGE1), for which species-specific variations are poorly described. Comparison of the efficiency of these antilipolytic systems showed that PGE1 or phenylisopropyladenosine was able to totally inhibit lipolysis activation in nine mammalian species. However, the antilipolytic responses to clonidine or UK-14304 were fully developed in hamster and rabbit but blunted in the adipocytes of jerboa, rat, guinea pig, garden dormouse, and dormouse.

Predominance of beta 3-adrenergic component in catecholamine activation of lipolysis in garden dormouse adipocytes.

The beta 3-adrenoceptor (AR) agonists are potent activators of lipolysis in white adipose tissue. beta-AR agonists were tested here on the lipolytic activity of a hibernator, the garden dormouse (Eliomys quercinus L.).

Local sympathetic denervation of white adipose tissue in rats induces preadipocyte proliferation without noticeable changes in metabolism.

The direct influence of the sympathetic nervous system on white adipose tissue was studied by performing a unilateral surgical denervation of the retroperitoneal fat pad in rats, the contralateral pad being used as a control. One week after surgery, the weight of the denervated pad was significantly higher than that of the intact pad. In vivo, glucose utilization was not altered by denervation.

Increased GDP binding and thermogenic activity in brown adipose tissue mitochondria during arousal of the hibernating garden dormouse (Eliomys quercinus L.).

1. The thermogenic activity of brown adipose tissue in hibernating garden dormice during hypothermic torpor and at different states of arousal were studied. High levels of GDP binding were observed on isolated brown fat mitochondria, indicating that the thermogenic proton conductance pathway is very active in brown fat during arousal.

Sympathoadrenal activity and hypoglycemia in the hibernating garden dormouse.

The hibernating garden dormouse is spontaneously hypophagic during the prehibernating period at which time we found a low peripheral sympathetic activity (S.A.).

Liver and brown fat mitochondrial response to cold in the garden dormouse (Eliomys quercinus).

The involvement of two organs, i.e. the liver and the brown adipose tissue (BAT) in response to cold in a hibernating species such as the garden dormouse has been studied.

[Lethargic hypothermia induced by a protein free diet in a hibernating rodent, the dormouse (Eliomys quercinus L.)].

In garden dormouse protein deficiency leads to reversible hypothermic torpor, comparable with that provoked by starvation or occuring naturally during hibernation, whether the diet consists wholly of apples or of synthetic protein-free food. Torpor induced by protein deficiency occurs even though the energy requirements of the animal are amply satisfied. These phases of lethargy occur after a certain delay and with a variable frequency, both of which vary with the ambient temperature.

[Annual cycle of oxygen consumption (QO 2) in a hibernating animalthe garden dormouse: reduction of the QO 2 and hypothermia following fasting].

A circannual cycle of oxygen consumption (QO2) was observed in active garden dormice maintained during 19 months under external conditions for temperature and lighting. QO2 was minimum in october and maximum in may. In the same animals deprivation of food induced hypothermia and a 23% decrease in QO2 which always preceeded hypothermia.

[Role of the season and of the nutritonnal state on the distribution of tissular fatty acids in the hibernating dormouse (Eliomys quercinus L.)].

Seasonal changes were observed in fatty acid composition of plasma, liver and cardiac muscle. During hibernation unsaturated fatty acids levels increase in plasma cholesterol esters (CE), glycerides (GL) and phospholipids. After spring arousal, the oleic acid content decreases in total fatty acids of liver and cardiac muscle.

[Tissue lactates, pH and blood gasses in hibernating dormouse: changes during periodic arousals].

Periodic arousal in the garden dormouse is accompagnied by a rise in plasma and muscle lactate levels and a diminution of muscle glycogen. In addition, the decrease of arterial blood pH and O2 concentration agrees well with these results. All of which are in good agreement with the general stimulation of adrenergic activity observed at the onset of rewarming.