Biomedical subjects

Nathalie Loos

Publications and source records attributed to Nathalie Loos.

4 recordsLinked to original sources

PubMed2006

Spontaneous motor activity in fat-fed, streptozotocin-treated rats: a nonobese model of type 2 diabetes.

We investigated the effects of diabetes on the spontaneous motor activities (SMA) of streptozotocin-treated rats fed a high-fat diet (HFD), a new nonobese model of type 2 diabetes. The daily changes in the duration of SMA were assessed via infrared cells, which detected all movements of rats that had been fed for 3 weeks with a standard or HFD and then injected with vehicle or 50 mg/kg of streptozotocin. Five to six days after streptozotocin injection, the daily body weight and the levels of duration of SMA of the diabetic rats were depressed, manifest by a substantial decline in the frequency of occurrence of nocturnal SMA episodes. The dramatic depression of daily duration of SMA levels observed in the rats given a HFD and treated with streptozotocin appears to be related solely to the diabetic state and not to body weight and/or HFD consumption, since the HFD (and/or related metabolic effects) remained ineffective in altering this feature in rats that grow normally. By thoroughly separating the prediabetic and the diabetic phases, we have been able to more readily explore the deleterious effects of the stages of both of these phases on changes in daily SMA levels.

Animal Feed↗

PubMed2006

Effect of high-fat diet and metformin treatment on ventilation and sleep apnea in non-obese rats.

We investigated the effect of insulin resistance on ventilation and the incidence of sleep apnea in non-obese rats and determined whether metformin could change ventilation and occurrence of sleep apneas. Five groups of rats were studied: (1) standard chow; (2) high-fat groups, with 1 with metformin; (2) had type 2 diabetes induced by streptozotocin, with 1 with metformin. Compared to standard rats, ventilatory parameters remained unchanged in the high-fat fed diet as well as in diabetic rats. However, their oxygen consumption was reduced (p<or=0.01). They had a lower ventilatory response to CO2 challenge (p<or=0.01), and their sleep apnea scores increased markedly (p<or=0.001). These results suggest that insulin resistance could impair the ventilation control. Metformin treatment, known to reduce insulin resistance, got sleep apnea scores back to their basic levels, reinforcing the idea that insulin resistance is a major factor in the occurrence of apneas in this rat model.

Analysis of Variance↗

PubMed2005

Sympathetic nervous control of the cerebral circulation in sleep.

Cerebral vessels are extensively innervated by sympathetic nerves arising from superior cervical ganglia, and these nerves might play a protective role during the large arterial pressure surges of active sleep (AS). We studied lambs (n=10) undergoing spontaneous sleep-wake cycles before and after bilateral removal of the superior cervical ganglia (SCGx, n=5) or sham ganglionectomy (n=5). Lambs were instrumented to record cerebral blood flow (CBF, flow probe on the superior sagittal sinus), carotid arterial pressure (P(ca)), intra-cranial pressure (P(ic)), cerebral perfusion pressure (Pcp=Pca-Pic) and cerebral vascular resistance (CVR). Prior to SCGx, CBF (mL min-1) was significantly higher in AS than in Quiet Sleep (QS) and Quiet Wakefulness (QW) (17+/-2, 13+/-3, and 14+/-3 respectively, mean+/-SD, P<0.05). Following SCGx, baseline CBF increased by 34, 31, and 29% respectively (P<0.05). CVR also decreased in all states by approximately 25% (P<0.05). During phasic AS, surges of Pca were associated with transient increases in Pcp, Pic and CBF. Following SCGx, peak CBF and Pic during surges became higher and more prolonged (P<0.05). Our study is the first to reveal that tonic sympathetic nerve activity (SNA) constricts the cerebral circulation and restrains baseline CBF in sleep. SNA is further incremented during arterial pressure surges of AS, limiting rises in CBF and Pic, possibly by opposing vascular distension as well as by constricting resistance vessels. Thus, SNA may protect cerebral microvessels from excessive distension during AS, when large arterial blood pressure surges are common.

Animals↗

PubMed2003

Liver temperature during sleep.

STUDY OBJECTIVE: The liver, like brown adipose tissue, is an important source of nonshivering thermogenesis. We tested the hypothesis that the thermal state of the liver is preserved during slow wave sleep but deteriorates during paradoxical sleep. METHODS: Twelve adult male Wistar rats were equipped with electrodes and thermistor probes--which measured cortical (Tco), interscapular brown adipose tissue (Tibat), and liver (Tl) temperatures--for thermal and sleep studies. Six rats were exposed to thermoneutral (24 degrees C) and 6 to low (9 degrees C) ambient temperature. Isolated paradoxical sleep episodes preceded and followed by more than 3 minutes of wakefulness or slow wave sleep were analyzed. The Tco, Tibat, and Tl levels were also assessed during the slow wave sleep that preceded each isolated paradoxical sleep episode. RESULTS: During slow wave sleep, the Tibat and Tl were clearly higher in rats exposed to the cold than in those exposed to the thermoneutral condition (< 1 degrees C). During paradoxical sleep, however, these 2 temperatures decreased in rats exposed to the cold condition, and the changes observed for Tco were completely inversed. CONCLUSIONS: These results support the hypothesis that the thermal state in the liver of rats deteriorates during paradoxical sleep and suggest that nonshivering thermogenesis in the liver contributes to the defense of global thermal homeostasis in the sleeping endothermic organism, especially during slow wave sleep.

Animals↗