By Jens Hannibal
Rhythmic alterations in body structure and behavior inside a 24 h interval ensue in residing organisms on the earth to satisfy the demanding situations linked to the day-by-day adjustments within the exterior atmosphere. The circadian pacemaker liable for the temporal inner agency and the new release of endogenous rhythms of roughly 24 h is found within the hypothalamic suprachiasmatic nucleus (SCN) in mammals. The endogenous interval generated by means of the pacemaker is on the subject of, yet mostly no longer equivalent to 24 h and the organic clock as a result should be day-by-day adjusted (entrained) via exterior cues. The day-by-day alteration of sunshine and darkness a result of rotation of our planet by itself axis relating to the sunlight is the main sought after "zeitgeber" which adjusts the section of the circadian rhythms to the astronomical day size, a approach referred to as photoentrainment. In mammals, mild is perceived merely via photoreceptors situated within the retina. gentle details is mediated to the SCN through the retinohypothalamic tract (RHT) through activation of the classical photoreceptor procedure of rods and cones and a extra lately pointed out approach of intrinsic photosensitive retinal ganglion cells (ipRGCs) utilizing melanopsin as a photopigment.
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Additional info for Neuronal Input Pathways to the Brains Biological Clock and their Functional Significance
In rats, but not in hamsters, some studies have shown that also the 5-HT2A/2C receptor plays a role in the interaction between 5-HT and light (Kennaway 2004). Electrical stimulation of the optic nerves attached to a brain slice preparation produces excitatory postsynaptic currents (EPSCs) in voltage-clamped SCN neurons. Stimulation-produced short-latency EPSCs are inhibited by application of 8-OH-DPAT, consistent with activation of 5-HT7 receptors in the SCN (Pickard et al. 1999). In cultured SCN neurons, glutamate-induced calcium increase is markedly attenuated after application of 5-HT and/or 8-OH-DPAT, and this effect is blocked by the 5-HT7/2 receptor antagonist ritanserin (Quintero and McMahon 1999a).
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From Sangaard et al. 2003) 52 Figures Fig. 22 Effects of NPY on light-induced phase shift and Per gene expression. Upper panel shows that NPY applied in vitro blocks the in vivo light induced phase shifts on the electrical activity of the hamster SCN as recorded in vitro (Yannielli and Harrington 2000). Lower panel shows that NPY applied to the hypothalamic slice preparation suppresses in vivo light induced expression of Per1 and Per2 mRNA in hamster SCN. (Adapted from Brewer et al. 2002) References Abrahamson EE, Leak RK, Moore RY (2001) The suprachiasmatic nucleus projects to posterior hypothalamic arousal systems.