Rhythms physiological

Naturally Occurring Compounds. Many derivatives of iadole are found ia plants and animals where they are derived from the amino acid tryptophan. Several of these have important biological function or activity. Serotonin [50-67-9] (12) functions as a neurotransmitter and vasoconstrictor (35). Melatonin [73-31-4] (13) production is controlled daily by the circadian cycle and its physiological level iafluences, and seasonal rhythms ia humans and other species (36). Indole-3-acetic acid [87-51-4] (14) is a plant growth stimulant used ia several horticultural appHcations (37). 

The major drawback of these models, however, is their lack of a clear reference between model components and constituent parts of the biological system (e.g. structures like ion channels, transporter proteins, receptors, etc.). These models, therefore, do not permit the simulation of patho-physiological detail, such as the series of events that follows a reduction in oxygen supply to the cardiac muscle and, ultimately, causes serious disturbances in heart rhythm. 

Circadian rhythm 24-Hour cycles of behavior and physiology that are generated by endogenous biological clocks (pacemakers). 

Bland, B. H. (1986). The physiology and pharmacology of hippocampal formation theta rhythms. Prog. Neurobiol. 26, 1-54. 

Perturbation of the 5-HT system can elicit changes in a wide variety of behaviors. Furthermore, drugs that act on serotonergic neurons and their receptors are used to treat diseases such as depression, anxiety disorders and schizophrenia. Thus, 5-HT has been implicated in the regulation of many behaviors and physiological processes. The involvement of 5-HT in three areas - neuroendocrine function, circadian rhythms and feeding behavior - will be highlighted for illustrative purposes. 

Hormones circulate as signaling substances in the blood at very low concentrations (10 to between 10 mol L ). These values change periodically in rhythms that depend on the time of day, month, or year, or on physiological cycles. 

Sinus rhythm with a rate of less than 60/min is defined as sinus bradycardia. This bradycardia is usually a physiological response. Pathological and/or symptomatic sinus bradycardia may suggest sinus node dysfunction (see sick sinus syndrome). Vagally induced sinus bradycardia may be responsive to atropine, but only needs to be treated if symptomatic. Atropine doses of less than 0.5 mg may cause a paradoxical increase in vagal bradycardia. 

Circadian clock-controlled rhythms provide most organisms with an orchestrated temporal programme that allows for appropriate timing of physiology (i.e. blood pressure, hormonal levels) and behaviour (i.e. alertness, sleep-wake cycle). The mammalian central circadian pacemaker resides in the suprachiasmatic nucleus (SCN) of the brain (Weaver 1998). At the molecular level, the core oscillator driving the mammahan clock consists of interconnected autoregulatory... 

In mammalian tissue culture cells, robust circadian gene expression can be entrained by 12 h temperature cycles with an amplitude of 4 °C (e.g. 37 °C versus 33 °C) (Brown et al 2002). We thus wondered whether physiological temperature rhythms, themselves circadian and with an amplitude of —4 °C in most mammals, could also sustain cyclic clock-gene transcription. To this end, we engineered a... 

Circadian clocks are molecular time-keeping mechanisms found in a broad range of cell types from a variety of organisms. The primary roles of these clocks are to maintain their own 24 hour molecular rhythm and to drive the rhythmic expression of genes that control output processes in physiology, metabohsm and behaviour. Core features of the clock are its ability to synchronize to daily environmental speitgehers (e.g. hght—dark or temperature cycles), and then maintain rhythmic function when placed in constant conditions. 

Studies of mammals subjected to SCN destruction and transplantation have revealed that the hypothalamic SCN contains a master circadian oscillator which is involved in a number of behaviours and hormonal secretions. The circadian oscillatory activity of SCN neurons is directly demonstrated by the measurement of [ " C] glucose metabolic activity and field potentials assessed by electro-physiological devices. The clock oscillatory genes mPer1 and mPer2 are expressed rhythmically in most neurons in the SCN. Thus, thousands of clock cells in the SCN might generate the rhythm. 

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