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1

Centralny zegar biologiczny ptaków

100%
Prusik M.
Medycyna Weterynaryjna
|
2018
|
tom 74
|
nr 04
In birds many life processes runs in diurnal (e.g. locomotor activity, feeding, melatonin secretion) and seasonal rhythms (e.g. reproduction, song, feathering, migration) depending on the environmental light and the activity of their central clock system (CCS). The structure and mechanisms of the activity of the avian CCS are the most complex among vertebrates. CCS consists of three oscillators (in the retina, SCN and pineal gland) possessing their own sensory input system (photopigments) and effective output system (products for direct biological effects). So far, 14 forms of photopigments (Opn1, Opn2, Opn3, TMT, Opn4x, Opn4m, Opn5, RGR, RRH, VA-opsins, pinopsin, Cry1, Cry2 i Cry4) and 12 clock genes making up oscillators (Bmal1, Bmal2, Clock, NPas2 called also Mop4 and Rorα – positive genes and Cry1, Cry2, Cry4, Per2, Per3, E4bp4 and Rev-erbα – negative genes) have been described in the CCS in birds. Photopigments are placed in all layers of the retina; in the brain – mainly in regions of nuclei: septalis lateralis, premammillaris, habenularis and paraventricularis; in the pineal gland – in all kinds of pinealocytes. Most photopigments belonging to the opsin family are linked with the nucleotide phototransduction path, typical for vertebrates, but, in avian CCS, also the phosphoinositol phototransduction path, characteristic for invertebrates, exists and concerns Opn4x and Opn5. Oscilators are placed in nuclei of cells of all layers of the retina, in mSCN and vSCN (with great species variability) and in pinealocytes. It is supposed that all nonvisual photopigments have a direct role in the synchronization of the oscillator activity with the environmental light, but molecular the mechanisms of the interaction between photopigments and the oscillator remain unknown. The impact of each of the three oscillators of the CCS in the generation of biological rhythms in birds show great species differentiation. The differences concern both the domination of one of the oscillators over the others and the assignation of biological processes which the individual oscillator synchronizes rhythmically with the environmental light.
2

Regulacja sekrecji melatoniny w szyszynce ptakow

80%
Prusik M., Lewczuk B.
Medycyna Weterynaryjna
|
2008
|
tom 64
|
nr 05
639-645
The avian pineal gland releases melatonin in a cyclic manner, with the highest level at night and the lowest level during the daytime. Mechanisms regulating melatonin secretion in birds are very complex, probably due to the phylogenetic position of the avian pineal gland as an intermediate form between the pineals of lower vertebrates and mammals. Avian pinealocytes possess an endogenous oscillator, formed by a self-regulated system of cock genes, that controls the transcription of several enzymes, among them arylalkylamine N-acetyltransferase (AA-NAT), the enzyme limiting melatonin synthesis. These cells are also directly photosensitive due to the presence of photopigments, pinopsin and melanopsin, as well as corresponding signal transduction systems. Light acting via pinopsin induces a cascade of events that leads to the decrease in cGMP and cAMP levels, AA-NAT activity and melatonin secretion. Melanopsin is probably involved in an entrainment of the circadian oscillator to the environmental light conditions. The function of the avian pineal gland is also regulated by light acting indirectly via the retina as well as by the extrapineal oscillator located in the suprachiasmatic nucleus. Both structures influence the pinealocyte activity via a common multisynaptic pathway, which ends in the gland as the sympathetic nerve fibers. Norepinephrine released from these fibers stimulates α₂-adrenoreceptors in pinealocyte plasmalemma and inhibits adenylate cyclase activity and melatonin secretion. The significance of direct and indirect routes of light perception as well as intra- and extra-pineal oscillators in the regulation of melatonin secretion may differ between species, but this problem is poorly recognized.
3

Cytogeniczne podłoże zegara biologicznego

80%
Pszczolkowski M., Cymborowski B.
Kosmos
|
1991
|
tom 40
|
nr 1
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