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Internal Clock (internal + clock)
Selected AbstractsRestoration of body mass in King Penguins after egg abandonment at a critical energy depletion stage: early vs late breedersJOURNAL OF AVIAN BIOLOGY, Issue 4 2001Jean-Patrice Robin In fasting-incubating seabirds, it has been proposed that egg abandonment and refeeding should be induced when a low body mass (BM) threshold is attained, thus ensuring adult survival at the expense of immediate breeding. In the context of life-history trade-offs in long-lived birds, we have tested this hypothesis by comparing short-term survival and restoration of BM in King Penguins Aptenodytes patagonicus that abandoned their egg to those that were relieved normally by their mate at the end of the first incubation shift. Since King Penguins have an extended laying period, the possible influence of seasonal factors was also examined by comparing early and late breeders. Forty incubating males were experimentally forced to fast until egg abandonment by preventing relief by the female. At egg abandonment of both early and late breeding males, BM was below the BM threshold, fasting duration was eight days (about 30%) longer than for relieved birds, and plasma uric acid level was elevated (signature of increased body protein catabolism, phase III of fasting). All abandoning birds survived and came back from sea at a BM similar to that of relieved penguins. The duration of the foraging trip of abandoning early breeders was the same as that of relieved birds, and some abandoning birds engaged in a new breeding attempt. Abandoning late breeders, however, made foraging trips twice as long as those of relieved males. This difference can be explained by time constraints rather than nutritional constraints, abandoning early breeders having enough time left in the breeding season to engage in a new breeding attempt in contrast to abandoning late breeders. These observations lend support to the suggestion that not only BM but also an internal clock intervene in the decision to engage in breeding or not. By preventing a lethal energy depletion ashore and by acting at a fasting stage where the capacity to restore BM at sea is unaffected, abandonment at a low body condition threshold plays a major role in the trade-off between adult penguin survival and reproduction. [source] Acute Ethanol Potentiates the Clock-Speed Enhancing Effects of Nicotine on Timing and Temporal MemoryALCOHOLISM, Issue 12 2007Warren H. Meck Background:, Acute ethanol administration potentiates some of the behavioral effects of nicotine, although the extent of this effect is unknown. The present investigation assessed the ability of ethanol to potentiate nicotine's effect on the overestimation of multisecond durations as a result of an increase in the speed of an internal clock. Methods:, Adult male rats were exposed to the acute effects of ethanol (0.0, 0.5, 1.5, and 3.0 g/kg; IG) which was given 10 minutes prior to the administration of nicotine (0.0, 0.3, 0.6, and 1.0 mg/kg; IP). The effects of these combined treatments on timing and temporal memory were assessed using 18- and 36-second peak-interval procedures with separate visual/spatial cues for responding. Results:, When administered alone, ethanol had no consistent effect on peak time, but decreased peak rate, and increased peak spread as a function of dose. In contrast, nicotine alone shifted the peak times of the response distributions leftward in a proportional manner as a function of dose. When administered after pretreatment with ethanol, nicotine's effect on the horizontal placement of the peak functions was potentiated. Conclusions:, The observation that ethanol pretreatment potentiates the clock-speed enhancing effects of subsequently administered nicotine is discussed in terms of the role of ,7-nicotinic acetylcholine receptors and dopamine,glutamate interactions in cortico-striatal circuits thought to subserve interval timing. [source] Alcohol Consumption and the Body's Biological ClockALCOHOLISM, Issue 8 2005Rainer Spanagel This review summarizes new findings on the bidirectional interactions between alcohol and the clock genes, underlying the generation of circadian rhythmicity. At the behavioral level, both adult and perinatal ethanol treatments alter the free-running period and light response of the circadian clock in rodents; genetic ethanol preference in alcohol-preferring rat lines is also associated with alterations in circadian pacemaker function. At the neuronal level, it has been shown that ethanol consumption alters the circadian expression patterns of period (per) genes in various brain regions, including the suprachiasmatic nucleus. Notably, circadian functions of ,-endorphin,containing neurons that participate in the control of alcohol reinforcement become disturbed after chronic alcohol intake. In turn, per2 gene activity regulates alcohol intake through its effects on the glutamatergic system through glutamate reuptake mechanisms and thereby may affect a variety of physiological processes that are governed by our internal clock. In summary, a new pathologic chain has been identified that contributes to the negative health consequences of chronic alcohol intake. Thus, chronic alcohol intake alters the expression of per genes, and, as a consequence, a variety of neurochemical and neuroendocrine functions become disturbed. Further steps in this pathologic chain are alterations in physiological and immune functions that are under circadian control, and, as a final consequence, addictive behavior might be triggered or sustained by this cascade. [source] Anhydrobiosis in tardigrades and its effects on longevity traitsJOURNAL OF ZOOLOGY, Issue 3 2008S. Hengherr Abstract Living in harsh and variable environments that are prone to periodic desiccation, tardigrades exhibit remarkable tolerance against physical extremes through a state known as anhydrobiosis. To study the effect of this state on the longevity and hence the lifecycle in the taxon Tardigrada for the first time, we exposed a tardigrade species, Milnesium tardigradum, to alternating periods of drying and active feeding periods in a hydrated state. Compared with a hydrated control, the periodically dried animals showed a similar longevity, indicating that the time spent in anhydrobiosis was ignored by the internal clock. Thus, desiccation can produce a time shift in the age of tardigrades similar to the model described for rotifers that has been termed ,Sleeping Beauty'. [source] Ageing mechanisms: the role of telomere lossCLINICAL & EXPERIMENTAL DERMATOLOGY, Issue 7 2001P. Boukamp The ends of the chromosomes are capped by specialized structures, the telomeres. These are comprised of tracts of hexanucleotid sequences and, in combination with specific proteins, protect the chromosome against degradation, fusion events and as being recognized as 'damaged' DNA; thus, they guarantee chromosomal integrity. Due to deficiencies during DNA replication, the telomeres continuously loose part of their sequences and it has been proposed that this loss is the liming factor for the replicative capacity of a cell, i.e. telomeric loss is the counting mechanism - the internal clock of ageing. In order to proliferate indefinitely, the cells must prevent telomere erosion and this is mostly achieved by upregulation or de novo expression of the ribonucleoprotein complex telomerase. This enzyme, which has a reverse-transcriptase activity, is able to add telomeric sequences to the outer most ends off the telomeres and thereby stabilize or even elongate the telomeres. As telomerase is expressed in about 90% of all tumours while expression is absent in many somatic tissues, it is not surprising that the causal role of telomere erosion is presently the most favoured hypothesis of cellular ageing. [source] | |||||||||||||