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| Titel: |
The Bird Clock: A Complex, Multi-Oscillatory and Highly Diversified System |
| Auteur: |
Kumar, Vinod Singh, Bhanu Pratap Rani, Sangeeta |
| Verschenen in: |
Biological rhythm research |
| Paginering: | Jaargang 35 (2004) nr. 1-2 pagina's 121-144 |
| Jaar: |
2004-02 |
| Inhoud: |
A clock is conceptualized as comprising an input-pacemaker-output system. An overtly measured output, such as the rhythm of activity, feeding or secretion of melatonin, is the consequence of underlying activity of genes at all three levels (input, pacemaker and output) of the clock system. Molecular biochemical studies suggest that the rhythmicity is generated intrinsically within specialized tissues (pacemaker cells) by autoregulatory feedback loops involving gene transcription and post-translational modifications of the 'clock proteins'. Each tissue that can generate oscillations and produce a stable rhythmic output in synchronization with external (environmental) signals is called a clock, and birds appear to have multiple clocks. Independent input-pacemaker-output systems are present at a minimum of three levels — the retina of the eyes, the pineal gland, and the hypothalamus. This is different from mammals in which input, pacemaker and output are localized in different structures. Further, in birds, each clock interacts with one or more other clocks, and, together, these clocks form a centralized clocking system (CCS). The degree of interdependence between the components of the CCS can vary greatly between species as well as between seasons within an individual. All these properties make the avian CCS a highly complex and diverse timing system. In this article, we will first summarize evidence for the possession of clocks at the three levels (the retina of the eye, the pineal gland, and the hypothalamus), and then present examples that show the complexity and diversity of the avian CCS. We will also analyze how the avian CCS is integrated to produce stable and yet highly adaptive short- and long-term periodic functions. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
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