http://if-pan.krakow.pl/pjp/pdf/2009/3_383.pdf

Physiology and pharmacology of melatonin in relation to biological rhythms.

Circadian rhythmicity in vertebrate retinas: Regulation by a photoreceptor oscillator

Inner retinal circadian clocks and non-visual photoreceptors: novel players in the circadian system.

Circadian rhythm and photic control of cAMP level in chick retinal cell cultures: a mechanism for coupling the circadian oscillator to the melatonin-synthesizing enzyme, arylalkylamine N-acetyltransferase, in photoreceptor cells.

Melatonin is a hormone produced mainly by the pineal gland in most vertebrate species, including humans. Recent metabolic, receptor and functional studies created a picture of the melatoninergic system(s) in living organisms, its organization, physiology and a role in some pathologic conditions. The melatonin-generating system is characterized by three basic features: (1) photosensitivity, (2) diurnal (or circadian) rhythmicity (with highest levels of melatonin production occurring at night in darkness), and (3) age-related decline in its activity. Cyclic nocturnal increases of melatonin levels are proportional to the length of nights (or dark periods of an imposed light-dark cycle); the hormone thus conveys a photoperiodic message, and functions in an organism as an internal biochemical clock and calendar. Biological actions of melatonin are mediated via specific melatonin receptors, whose distribution in the body is uneven, yet with decisively highest density in the suprachiasmatic nuclei of the hypothalamus, pars tuberalis of the pituitary, and the retina (particularly in birds and lower vertebrates). Such a distribution of melatonin receptors suggests that the principal physiological role of the hormone is related to both chronobiology and modulation of the body hormonal milieu. This review surveys recent developments in the melatonin field, and summarizes current knowledge on the melatoninergic mechanisms, including the therapeutic aspect related to the hormone.

Melatonin and its physiological and therapeutic properties.

Chick retina and pineal gland differentially respond to constant light and darkness: in vivo studies on serotoninN-acetyltransferase (NAT) activity and melatonin content

The molecular mechanism underlying the role of calcium influx in the regulation of retinal serotonin N-acetyltransferase (NAT) activity was studied in vivo in chickens. Systemic administration of organic antagonists of voltage-sensitive calcium channels (VSCC), i.e., nimodipine and nifedipine, resulted in a marked suppression of the nocturnal increase of NAT activity in chicken retina. In contrast, NAT activity stimulated by nonhydrolysable analogs of cyclic AMP (dibutyryl-cyclic AMP and 8-bromo-cyclic AMP), forskolin, a direct activator of adenylate cyclase, and by phosphodiesterase inhibitors (aminophylline and 3-isobutyl-1-methylxanthine), was not significantly affected by various tested VSCC antagonists. The inhibitory effect of nimodipine on the dark-dependent increase in NAT activity of chicken retina was abolished by Bay K 8644, a selective VSCC agonist. The results presented in this paper indicate an important role of calcium influx through L-type of VSCC in the induction of NAT activity in chicken retina, and suggest that a requirement of calcium ions in the process of NAT induction in the retina may be primarily at the level of cyclic AMP production.

Calcium channel blockers in vivo inhibit serotonin N‐acetyltransferase (NAT) activity in chicken retina stimulated by darkness and not by agents elevating intracellular cyclic AMP level

Intravitreal application of membrane-permeable analogs of cyclic GMP increases serotonin N-acetyltransferase (NAT) activity in retinas of light-exposed chicks: comparison with the effect of cyclic AMP analogs and darkness.

Marlena Wawrocka

Papers

Chick retina and pineal gland differentially respond to constant light and darkness: in vivo studies on serotoninN-acetyltransferase (NAT) activity and melatonin content

Calcium channel blockers in vivo inhibit serotonin N‐acetyltransferase (NAT) activity in chicken retina stimulated by darkness and not by agents elevating intracellular cyclic AMP level

Intravitreal application of membrane-permeable analogs of cyclic GMP increases serotonin N-acetyltransferase (NAT) activity in retinas of light-exposed chicks: comparison with the effect of cyclic AMP analogs and darkness.