Enzymes of adenosine metabolism in the brain: diurnal rhythm and the effect of sleep deprivation

Adenosine plays a role in promoting sleep, an effect that is thought to be mediated in the basal forebrain. Adenosine levels vary in this region with prolonged wakefulness in a unique way. The basis for this is unknown. We examined, in rats, the activity of the major metabolic enzymes for adenosine - adenosine deaminase, adenosine kinase, ecto- and cytosolic 5'-nucleotidase - in sleep/wake regulatory regions as well as cerebral cortex, and how the activity varies across the day and with sleep deprivation. There were robust spatial differences for the activity of adenosine deaminase, adenosine kinase, and cytosolic and ecto-5'-nucleotidase. However, the basal forebrain was not different from other sleep/wake regulatory regions apart from the tuberomammillary nucleus. All adenosine metabolic enzymes exhibited diurnal variations in their activity, albeit not in all brain regions. Activity of adenosine deaminase increased during the active period in the ventrolateral pre-optic area but decreased significantly in the basal forebrain. Enzymatic activity of adenosine kinase and cytosolic-5'-nucleotidase was higher during the active period in all brain regions tested. However, the activity of ecto-5'-nucleotidase was augmented during the active period only in the cerebral cortex. This diurnal variation may play a role in the regulation of adenosine in relationship to sleep and wakefulness across the day. In contrast, we found no changes specifically with sleep deprivation in the activity of any enzyme in any brain region. Thus, changes in adenosine with sleep deprivation are not a consequence of alterations in adenosine enzyme activity.     

Abnormalities of leptin and ghrelin regulation in obesity-prone juvenile rats

Rats selectively bred to develop diet-induced obesity (DIO) spontaneously gain more body weight between 5 and 7 wk of age than do those bred to be diet resistant (DR). Here, chow-fed DIO rats ate 9% more and gained 19% more body weight from 5 to 6 wk of age than did DR rats but had comparable leptin and insulin levels. However, 6-wk-old DIO rats had 29% lower plasma ghrelin levels at dark onset but equivalent levels 6 h later compared with DR rats. When subsequently fed a high-energy (HE; 31% fat) diet for 10 days, DIO rats ate 70% more, gained more body and adipose depot weight, had higher leptin and insulin levels, and had 22% lower feed efficiency than DR rats fed HE diet. In DIO rats on HE diet, leptin levels increased significantly at 3 days followed by increased insulin levels at 7 days. These altered DIO leptin and ghrelin responses were associated with 10% lower leptin receptor mRNA expression in the arcuate (ARC), dorsomedial (DMN), and ventromedial hypothalamic nuclei and 13 and 15% lower ghrelin receptor (GHS-R) mRNA expression in the ARC and DMN than in the DR rats. These data suggest that increased ghrelin signaling is not a proximate cause of DIO, whereas reduced leptin sensitivity might play a causal role.     

睡眠剥夺对大鼠心肌损伤效应和抗氧化指标的影响

目的：探讨睡眠剥夺对大鼠心肌和抗氧化指标的影响。方法：大鼠随机分为睡眠剥夺2 d组（SD 2 d）、睡眠剥夺4 d组（SD 4 d）、睡眠剥夺6 d组（SD 6 d）、大平台对照组（TC）、正常对照组（CC）,利用＂小平台水环境法＂建立大鼠睡眠剥夺模型,利用BL-410机能实验系统描记体表心电图,采用光镜及透射电镜观察心肌形态学改变,测定心肌线粒体丙二醛含量、超氧化物歧化酶活性。结果：睡眠剥夺组大鼠心率加快,心电图出现缺血性改变;心肌细胞染色质、肌浆网、线粒体、闰盘等亚细胞结构出现损伤性改变,部分心肌纤维溶解、坏死,心肌间质水肿、出血、炎性细胞浸润;心肌线粒体MDA水平升高,SOD活性随睡眠剥夺时间延长有降低趋势。结论：睡眠剥夺能够引起大鼠心肌损伤,其引起的氧化应激可能是心肌损伤的机制。     

The effects of meal-feeding and the diurnal cycle on lipogenesis in brown adipose tissue of rats

A significant diurnal variation in the rates of lipogenesisin vivo in brown adipose tissue occurred in both virgin and lactating rats. On a meal-feeding regime of either a chow, high-sucrose, or high-lipid diet, there was a very large increase in BAT lipogenesis following the meal. The rates observed after the sucrose meal are the highest so far reported. There was no significant difference in BAT lipogenesis between lactating and virgin rats, contrary to previous reports by others. The pattern of stimulation of BAT lipogenesis by these feeding regimes was different from that for white adipose tissue and liver and was not correlated with plasma insulin levels.     

The effects of paradoxical sleep deprivation on estrous cycles of the female rats

The present purpose was to examine how sleep deprivation affects the estrous cycle of the female rat. Paradoxical sleep-deprived (PSD) adult female Wistar rats were compared to home-cage control (CTRL) on their estrous cyclicity. Forty-four PSD and forty-four CTRL female rats were distributed into 4 subgroups of 11 animals each according to the phase of estrous cycle and were subjected to sleep deprivation for 96 h by the multiple platform technique. After PSD period, vaginal estrous cycles were taken for an additional 9 days. Animals that were submitted to PSD in diestrus phase (PSD-diestrus) had their estrous cycles disrupted during the recovery period by showing a constant diestrus during the first week. As for hormone alterations, progesterone concentrations were statistically higher in PSD-diestrus compared to respective phase control and to PSD-proestrus and PSD-estrus rats while CTRL-metestrus had higher levels than CTRL-proestrus and estrus groups. Testosterone was significantly decreased in PSD-estrus in relation to PSD-proestrus and PSD-diestrus groups and was lower in CTRL-diestrus rats than in home-cage rats in proestrus. In addition, PSD-diestrus phase exhibited higher concentrations of corticosterone and lower estrogen than the respective control rats. These data indicate that PSD may modulate the ovarian hormone release through alterations in hormonal-neurochemical mechanisms.     

Rhythms in Fos expression in brain areas related to the sleep-wake cycle in the diurnal Arvicanthis niloticus

Most mammals show daily rhythms in sleep and wakefulness controlled by the primary circadian pacemaker, the suprachiasmatic nucleus (SCN). Regardless of whether a species is diurnal or nocturnal, neural activity in the SCN and expression of the immediate-early gene product Fos increases during the light phase of the cycle. This study investigated daily patterns of Fos expression in brain areas outside the SCN in the diurnal rodent Arvicanthis niloticus. We specifically focused on regions related to sleep and arousal in animals kept on a 12:12-h light-dark cycle and killed at 1 and 5 h after both lights-on and lights-off. The ventrolateral preoptic area (VLPO), which contained cells immunopositive for galanin, showed a rhythm in Fos expression with a peak at zeitgeber time (ZT) 17 (with lights-on at ZT 0). Fos expression in the paraventricular thalamic nucleus (PVT) increased during the morning (ZT 1) but not the evening activity peak of these animals. No rhythm in Fos expression was found in the centromedial thalamic nucleus (CMT), but Fos expression in the CMT and PVT was positively correlated. A rhythm in Fos expression in the ventral tuberomammillary nucleus (VTM) was 180 degrees out of phase with the rhythm in the VLPO. Furthermore, Fos production in histamine-immunoreactive neurons of the VTM cells increased at the light-dark transitions when A. niloticus show peaks of activity. The difference in the timing of the sleep-wake cycle in diurnal and nocturnal mammals may be due to changes in the daily pattern of activity in brain regions important in sleep and wakefulness such as the VLPO and the VTM.     

Glucocorticoid effects on the diurnal rhythm of circulating leptin levels

It is known that circulating leptin shows diurnal variation with a nocturnal rise; however, the mechanisms generating this rhythm have not been fully elucidated. Glucocorticoids are a potent stimulator of leptin secretion, and there is a reciprocal relationship between circulating leptin and glucocorticoid levels. We hypothesized that glucocorticoids could modulate the diurnal rhythm of circulating leptin. We therefore explored the diurnal variation of leptin under situations in which subjects showed no or some shift of glucocorticoid diurnal rhythm, such as prednisolone-administered humans, and adrenalectomized and corticosterone-replaced (ADX+B) rats. The peak level of plasma cortisol immunoreactivity was shifted from early morning to noon by prednisolone administration. The nocturnal increment of plasma leptin in prednisolone-administered patients (71.2 +/- 14.2% from 08:00 h value) was significantly greater than that in normal volunteers (12.2 +/- 7.5% from 08:00 h value), but the timing of nadir and the peak of plasma leptin was not shifted. In normal rats, the plasma concentration of leptin showed the diurnal rhythm with the bottom at 16:00 h and the top between midnight and early morning. The amplitude of leptin diurnal rhythm was significantly reduced in ADX+B rats (08:00 h: 3.0 +/- 0.2, 16:00 h: 2.7 +/- 0.2, 00:00 h; 3.7 +/- 0.2 ng/ml) compared with sham operated rats (08:00 h: 3.0 +/- 0.2, 16:00 h 2.2 +/- 0.2, 00:00 h: 4.7 +/- 0.4 ng/ml); but ADX+B rats still retained similar timing of nadir and the peak of plasma leptin as observed in sham rats. These results indicate that glucocorticoids enhance the amplitude of leptin diurnal rhythm, and are consistent with previous findings showing that glucocorticoids increase leptin secretion. Glucocorticoids appear to play modulatory, but not essential roles in generating leptin diurnal rhythm.     

Daily rhythms of serum leptin in ewes: effects of feeding, pregnancy and lactation

The aim of the present study was to test whether serum concentrations of leptin in ewes vary with a daily rhythm. For this purpose, we examined 24 h serum leptin profiles of ewes exposed to natural photoperiodic conditions and subjected to two different feeding schedules (regular feeding and fasting). The results show for the first time the existence of daily rhythm of plasma leptin in regularly fed ewes, with a minimum during the light phase and a peak during the dark phase. Daily rhythms of serum leptin persisted after 50 h of fasting, although fasting shifted the peak of the rhythm to the beginning of the light phase and significantly reduced daily leptin production. To gain a better understanding of the role of leptin in the temporal organization of physiological events related to pregnancy and lactation, we measured serum leptin profiles throughout 24 h in ewes either during pregnancy or lactation. Daily leptin rhythms were found to persist during pregnancy and lactation, but both physiological conditions altered leptin concentrations. Maternal serum leptin concentration rose between early and mid pregnancy, then decreased in the late pregnancy and during lactation. Daily serum leptin concentration was significantly lower in nonpregnant, nonlactating ewes, compared either to lactating or to early pregnant ewes.     

Chronic leptin infusion advances, and immunoneutralization of leptin postpones puberty onset in normally fed and feed restricted female rats

Does leptin play a vital role in initiating puberty in female rats and can it overrule a nutrionally imposed (i.e. a 30% feed restriction, FR) delay in puberty onset? Prepubertal female rats were chronically infused for 14 days with leptin (icv or sc) or leptin-antiserum (icv) while puberty onset was monitored by means of scoring the moment of vaginal opening (VO). Median VO age was higher (35 days versus 27 days) in FR animals but leptin levels at VO were significantly decreased (1.44 +/- 0.17 ng/ml versus 2.79 +/- 0.31 ng/ml). Centrally (icv) and peripherally (sc) infused leptin (1 microg/day) advanced VO age compared to FR controls (30 days versus 35 days and 31 days versus 41 days, respectively). Congruently, centrally (icv) administered leptin-antiserum (0.6 microg/day) delayed puberty onset. In normally fed rats median VO age was only marginally advanced (26 days versus 27 days) but only if leptin was applied centrally. The effects of FR on puberty onset are counteracted or even normalized by the infusion of leptin, whereas immunoneutralization of central leptin postpones puberty onset. We therefore conclude that central leptin is crucial for initiating puberty in female rats.     

The effect of high-fat diet on plasma ghrelin and leptin levels in rats

Ghrelin and leptin regulate appetite and energy homeostasis in humans and rodents. The effects of different nutritional factors on ghrelin and leptin secretion are not well documented in rats. Therefore, the aim of our study was to investigate the effect of a high-fat diet on plasma ghrelin and leptin levels and on adiposity. Twenty male Wistar rats, body weight220–260 g, were used in the study. Rats were randomized either on a standard chow diet (n=10) or on a high-fat diet (a mixture of nuts) forad libitum 11-week period. Body weight was measured once per week. At the end of the nutritional period, rats were sacrificed. Blood was collected for determination of lipids and glucose, as well as plasma ghrelin and leptin levels by ELISA method. The weight of different organs was determined. Rats fed on a high-fat diet showed significant increase in total body weight compared to control group. The long-term intake of high-fat diet caused hyperleptinemia and hypoghrelinemia. There was a significant positive correlation between plasma leptin levels and epididymal fat mass, liver and heart. In contrast, ghrelin levels showed inverse correlation with epididymal fat mass and liver weight. In conclusion, long-term intake of high-fat diet induced changes in plasma ghrelin and leptin in male rats, as well as in epididymal fat mass, liver and heart weights.     

Long-term effects of ghrelin and ghrelin receptor agonists on energy balance in rats

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), is the only circulating agent to powerfully promote a positive energy balance. Such action is mediated predominantly by central nervous system pathways controlling food intake, energy expenditure, and nutrient partitioning. The ghrelin pathway may therefore offer therapeutic potential for the treatment of catabolic states. However, the potency of the endogenous hormone ghrelin is limited due to a short half-life and the fragility of its bioactivity ensuring acylation at serine 3. Therefore, we tested the metabolic effects of two recently generated GHS-R agonists, BIM-28125 and BIM-28131, compared with ghrelin. All agents were administered continuously for 1 mo in doses of 50 and 500 nmol x kg(-1) x day(-1) using implanted subcutaneous minipumps in rats. High-dose treatment with single agonists or ghrelin increased body weight gain by promoting fat mass, whereas BIM-28131 was the only one also increasing lean mass significantly. Food intake increased during treatment with BIM-28131 or ghrelin, whereas no effects on energy expenditure were detected. With the lower dose, only BIM-28131 had a significant effect on body weight. This also held true when the compound was administered by subcutaneous injection three times/day. No symptoms or signs of undesired effects were observed in any of the studies or treated groups. These results characterize BIM-28131 as a promising GHS-R agonist with an attractive action profile for the treatment of catabolic disease states such as cachexia.     

Rhabdomeric membrane and smooth endoplasmic reticulum in photoreceptors of Manduca sexta: modulations associated with the diurnal light/dark cycle and effects of chromophore deprivation

Summary Aberrations of photoreceptor ultrastructure resulting from carotenoid/retinoid (vitamin A) deprivation were studied in the retina of Manduca sexta. The syndrome of chromophore deficiency included hypertrophy of smooth endoplasmic reticulum, variable dilation of rhabdomeric microvilli, the insertion of endomembrane fingers into such enlarged microvilli, and the formation of rhabdomeric vacuoles, intracellular compartments containing microvilli similar to those of the rhabdomere. Retinas were processed either with conventional procedures employing preliminary aldehyde fixation followed by heavy metal postfixation, or by fixation and incubation in unbuffered OsO₄. The latter method deposits osmium throughout the endomembrane system, within the rhabdomeric vacuoles, and in the extracellular space of the rhabdom. However, the intravillous fingers were rarely impregnated with osmium, despite their continuity with densely stained cisternae of the smooth endoplasmic reticulum. We suggest that the insertion of endomembrane fingers into dilated microvilli results from a cytoskeleton-mediated link between cisternae of the smooth endoplasmic reticulum and the rhabdomeric membrane, an association that may be important in the turnover of photoreceptor membrane. We interpret endomembrane hypertrophy and development of rhabdomeric vacuoles as symptoms of disturbance in the pathway leading to the assembly of the rhabdomere resulting from reduced synthesis of visual pigment.     

Gender-dependent differences in serum profiles of insulin and leptin in caloric restricted rats

In the present study, we have investigated whether differences between male and female rats described in response to 40% caloric restriction (CR) were influenced by circulating level variations of sex hormones and/or insulin and leptin. Body weights (BW), organ weights, and adipose depot weights (ADW) were also measured. The most affected tissues by CR were the fat depots. Metabolically active organs were the least affected, especially more in females than in males (male weight lost: 24.3% vs. female: 17.3%). Testosterone and estradiol circulating levels did not show changes by CR. Insulin levels were decreased by CR in both genders, but was more evident in female rats than males. Leptin serum levels were higher in male rats than in females, and CR caused a circulating leptin level reduction only in males. In conclusion, our results indicate that leptin and insulin could be one of the keys of the different hormonal control of energy homeostasis in response to CR between female and male rats. In this sense, leptin serum levels correlated statistically with BW and with individual ADW only in male rats, whereas insulin serum levels correlated statistically with BW and with any of the ADW studied only in females.     

Electroacupuncture suppresses expression of gastric ghrelin and hypothalamic NPY in chronic food restricted rats

Electroacupuncture (EA) has been reported to reduce body weight in overweight subjects in clinical practice, as well as in rats and mice with diet-induced obesity. In the present study, this effect of EA was tested in lean rats subjected to long-term food restriction (FR, food was offered only 1 h/day). Two hertz EA administered once every other day produced a further reduction in body weight in FR rats. Exploration of the mechanism involved revealed significant downregulation of the orexigenic peptides: ghrelin in the stomach, and neuropeptide Y (NPY) but not Agouti-related peptide (AgRP) in the hypothalamus, which was in line with the reduction in food intake in rats receiving EA stimulation as compared with those receiving restraint only. Uncoupling protein 3 (UCP3), involved in accelerating energy expenditure, was not significantly altered. These results suggest that the EA-induced body weight reduction was due mainly to a decrease in food intake rather than an increase in energy expenditure. A reduction in the orexigenic peptides ghrelin and NPY may be involved in the underlying mechanism.