Sirtuins and the circadian clock interplay in cardioprotection: focus on sirtuin 1.

Chronic disruption of circadian rhythms which include intricate molecular transcription-translation feedback loops of evolutionarily conserved clock genes has serious health consequences and negatively affects cardiovascular physiology. Sirtuins (SIRTs) are nuclear, cytoplasmic and mitochondrial histone deacetylases that influence the circadian clock with clock-controlled oscillatory protein, NAMPT, and its metabolite NAD. Sirtuins are linked to the multi-organ protective role of melatonin, particularly in acute kidney injury and in cardiovascular diseases, where melatonin, via upregulation of SIRT1 expression, inhibits the apoptotic pathway.

The cholinergic forebrain arousal system acts directly on the circadian pacemaker.

Sleep and wake states are regulated by a variety of mechanisms. One such important system is the circadian clock, which provides temporal structure to sleep and wake. Conversely, changes in behavioral state, such as sleep deprivation (SD) or arousal, can phase shift the circadian clock.

Phase shifts to light are altered by antagonists to neuropeptide receptors.

The mammalian circadian clock in the suprachiasmatic nucleus (SCN) is a heterogeneous structure. Two key populations of cells that receive retinal input and are believed to participate in circadian responses to light are cells that contain vasoactive intestinal polypeptide (VIP) and gastrin-releasing peptide (GRP). VIP acts primarily through the VPAC2 receptor, while GRP works primarily through the BB2 receptor.

Variability of behavioral chronotypes of 16 mammalian species under controlled conditions.

Human chronotypes (differences in preference for early or late rising each day) have been extensively studied in recent years, but no attempt has been made to compare human chronotypes with the chronotypes of other animal species. We evaluated behavioral chronotypes in 16 mammalian species along a body size gradient of five orders of magnitude (from mice to cattle). Individuals of all species were studied under a 12L:12D photoperiod in a thermoneutral environment with food and water available at all times.

Activation of M1/4 receptors phase advances the hamster circadian clock during the day.

The mammalian circadian clock in the suprachiasmatic nucleus (SCN) can be reset by the cholinergic agonist carbachol. In hamsters, intraSCN carbachol produces phase advances during the day. This phenomenon has previously been attributed to the muscarinic receptors, as carbachol-induced phase shifts are blocked by pretreatment with the muscarinic antagonist atropine.

Triptans attenuate circadian responses to light.

Daily exposure to light synchronizes the circadian clock, located in the suprachiasmatic nucleus (SCN), to external day/night cycles. These responses to light can be modified by serotonergic drugs, such as serotonin 5HT1B receptor agonists. Triptans are specific 5HT1B agonists prescribed to treat migraines.

Effects of lighting condition on circadian behavior in 5-HT1A receptor knockout mice.

Serotonin (5-HT) is an important regulator of the mammalian circadian system, and has been implicated in modulating entrained and free-running rhythms, as well as photic and non-photic phase shifting. In general, 5-HT appears to oppose the actions of light on the circadian system of nocturnal rodents. As well, 5-HT mediates, at least in part, some non-photic responses.

Daily variation in melatonin level, antioxidant activity and general immune response of peripheral blood mononuclear cells and lymphoid tissues of Indian goat Capra hircus during summer and winter.

Daily variation in circulatory melatonin level, during different seasons, has been reported to influence immune system and free-radical scavenging capacity in mammals, including human beings. Similar studies have not been carried out on small ruminant viz. goats that are susceptible to opportunistic infections, increased oxidative load and sickness during free-grazing activity and frequent exposure to agro-chemicals.

Slow and fast orthodromic and antidromic variants in acute 9-h jet-lagged pygmy field mice.

Biological clocks help organism to adapt temporally to a variety of rhythmic environmental cues. Acute changes in the rhythmicity of entraining cues causes short- to long-term physiological distress in individuals, for example, those occurring during jet-lag after long-haul transmeridial flights, or shift work. Variations in the rate of re-entrainment to a 9 h advanced schedule (simulation of acute Jet-lag/shift work) in the Indian pygmy field mouse, Mus terricolor are reported.

L-5-hydroxytryptophan resets the circadian locomotor activity rhythm of the nocturnal Indian pygmy field mouse, Mus terricolor.

We report that L-5-hydroxytryptophan (5-HTP), a serotonin precursor, resets the overt circadian rhythm in the Indian pygmy field mouse, Mus terricolor, in a phase- and dose-dependent manner. We used wheel running to assess phase shifts in the free-running locomotor activity rhythm. Following entrainment to a 12:12 h light-dark cycle, 5-HTP (100 mg/kg in saline) was intraperitoneally administered in complete darkness at circadian time (CT)s 0, 3, 6, 9, 12, 15, 18, and 21, and the ensuing phase shifts in the locomotor activity rhythm were calculated.