Daily rhythms

Lesions of serotonergic neurons in laboratory animals have been reported by some, but not all, investigators to disrupt locomotor rhythms or to result in the loss of the daily rhythm of corticosterone. There is evidence that, in the hamster, the median raphe nucleus projects to the SCN whereas the dorsal raphe nucleus innervates the IGL furthermore, the serotonergic innervation to the SCN and not the IGL is necessary for the photic entrainment of locomotor activity [22]. It appears then, that the SCN circadian pacemaker or clock is modulated by stimulation of serotonergic receptors in the SCN and that serotonergic projections to the SCN may modulate the phase of the SCN in intact animals. 

Haim, A. and Fluxman, S. (1996). Daily rhythms of metabolic rates role of chemical signals in coexistence of spiny mice of the genus Acomys. Journal of Chemical Ecology 22, 223-231. 

Lee C, Bae K, Edery I 1998 The Drosophila CLOCK protein undergoes daily rhythms in abundance, phosphorylation and interactions with the PER-TIM complex. Neuron 4 857-867... 

Kume K, Zylka MJ, Sriram S et al 1999 mCRYl and mCRY2 are essential components of the negative limb of the circadian clock feedback loop. Cell 98 193-205 Lee C, Bae K, Edery I 1998 The Drosophila CLOCK protein undergoes daily rhythms in abundance, phosphorylation, and interactions with the PER-TIM complex. Neuron 21 857-867... 

The photoperiod affects the daily metabolic rhythm by setting and adjusting the biological clock . Fish and other aquatic animals have been studied less in this connection than have terrestrial animals, probably because of the technical difficulties of observation in the wild. Many systematic observations must be made to establish the character of daily rhythms. Small numbers of irregular samplings are insufficient 12 evenly spaced samples per day would not be excessive. Such sampling must be repeated over many... 

The ratio of oxygen uptake to ammonia excretion in Black Sea mussels has been found to exhibit a distinct daily rhythm (Slatina, 1986). As a rule, the ammonia coefficient (O/N) tends to increase greatly at night. As this rise in energy metabolism does not result from an enhanced locomotor activity, it is difficult to explain or to find any analogue in fish. Farbridge and Leatherland (1987) demonstrated a strong effect of the lunar cycles on amino acid uptake by the scales, also on nucleic acids, metabolic reserves and plasma thyroid hormones in coho salmon. 

In the section devoted to daily rhythms, we introduced the idea of a biological clock . Here we deal with a biological calendar over the annual period. It is based on an ecological trigger which launches each stage, the key factor here being the photoperiod. Any population, be it of fish, birds or other... 

Van der Goes van Naters W. M., Den Otter C. J. and Maes F. W. (1998) Olfactory sensitivity in tsetse flies a daily rhythm. Chem. Senses 23, 351-357. 

Pineal serotonin fluctuates, rising and falling in a daily rhythm. 

Under resting conditions, CRH and AVP are released from the hypothalamus in a pulsatile fashion with a frequency of 2-3 episodes per hour (Engler et al., 1989). The amplitude of the neuropeptide pulses normally increases in the morning, resulting in a circadian fluctuation in ACTH and cortisol levels. This daily rhythm is modulated by feeding and activity schedules, but is particularly perturbed by stressful stimuli originating internally (e.g., anxiety or systemic infection) or externally (e.g., threatening situations). Thus, acute stressors lead to activation of the stress response. 

Many of our basic physiological functions exhibit a circadian (daily) rhythm. Most noticeably, we tend to sleep each night for about eight hours, but other functions - core temperature and production of pituitary hormones, for example - also exhibit such a rhythm. If sensory cues, most importantly light, are eliminated then our sleeping/waking cycle will elongate from 24 to about 30 hours. It is therefore clear that sensory inputs affect the basic circadian cycle, but what has been... 

Sulzman 1983 Murphy and Campbell 1996 Arendt 1998). Periodic changes are observed for most plasma hormones and reproductive cycle hormones in particular. These hormonal changes may be short-term pulsatile changes or daily rhythms or follow longer-term cycles (see Chapter 10 Wong et al. 1983 Kempainnen and Sartin 1981 Fukuda et al. 1988 Orth, Peterson, and Drucker 1988 Nigi and Torii 1991 Torii and Nigi 1994). 

---