Search results for "Chiasma"
showing 10 items of 27 documents
Circadian Rhythm Variations and Nutrition in Children
2018
AbstractCircadian rhythms are the changes in biological processes that occur on a daily basis. Among these processes are reactions involved in metabolic homeostasis. Circadian rhythms are structured by the central clock in the suprachiasmatic nucleus of the hypothalamus via the control of melatonin expression. Circadian rhythms are also controlled by the peripheral clocks, which are intracellular mechanisms composed of the clock genes, whose expression follows a circadian pattern. Circadian rhythms are impacted by signals from the environment called zeitgebers, or time givers, which include light exposure, feeding schedule and composition, sleeping schedule and pattern, temperature, and phy…
Microsporogenesis in three wild species of the genusAntirrhinumL. (A. litigiosumPau,A. pulverulenthumLazaro andA. subbaeticumGüemes, Sánchez and Mate…
2010
The diploid chromosome number (2n = 2x = 16) in three wild species A. litigiosum Pau, A. pul- verulenthum Lazaro and A. subbaeticum Guemes, Sanchez & Mateu, belonging to the genus Antirrhinum was cytologically observed. Genetic stability of the simultaneous meiotic division type was found in these natural growing snapdragons. The synchronicity at the initial meiotic stages and at tetrad and pollen creation was high and disappeared with the diakinesis initiation. Refl ecting the systematic position of the studied species into Antirrhinum, the performed investigation mani- fested similarity: in the presence of univalents and quadrivalent confi gurations parallel with bivalents at the early me…
Anterograde tracing of retinal afferents to the tree shrew hypothalamus and raphe
2000
The anterograde neuronal transport of Cholera toxin B subunit (CTB) was used in this study to label the termination of retinal afferents in the hypothalamus of the tree shrew Tupaia belangeri. Upon pressure-injection of the substance into the vitreous body of one eye, a major projection of the retinohypothalamic tract (RHT) was found to the hypothalamic suprachiasmatic nuclei (SCN). Although the innervation pattern was bilateral, the ipsilateral SCN received a somewhat stronger projection. Labeling was also found in the supraoptic nucleus and its perinuclear zone, respectively, mainly ipsilaterally as well as in the bilateral para- and periventricular hypothalamic regions without lateral pr…
Meiosis in translocation heterozygotes in the mosquito Culex pipiens.
1971
Adult Culex pipiens males irradiated with both X-rays and neutrons were crossed to untreated females and F1-egg rafts were checked for dominant lethality. F1-progenies were outcrossed with normal individuals in order to obtain lines with inherited semisterility. From a total of 120 lines that showed a certain amount of sterility 12 lines were studied cytologically. 10 lines showed reciprocal chromosome exchanges.—At late pachytene and diplotene cross configurations with large asynaptic regions at the center of the cross are obligatory. Bivalents, chains of three, chains of four, and ring configurations are present at metaphase and anaphase I. The different frequencies of the occurrence of s…
Photoperiod effects on bombesin- and cholecystokinin-like immunoreactivity in the suprachiasmatic nuclei of the Djungarian hamster (Phodopus sungorus)
1991
The immunocytochemical distribution of the putative satiety peptides bombesin (BBS) and cholecystokinin (CCK) were studied in the hypothalamic suprachiasmatic nuclei (SCN) of male and female Djungarian hamsters (Phodopus sungorus) held under either long (light/dark, LD 16:8 h) or short (LD 8:16) photoperiod. The animals were killed by perfusion with a fixative at the middle of the light period and the tissue was processed by routine immunohistochemical methods. Perikarya exhibiting BBS- or CCK-like immunoreactivity (LI) were found in the SCN of animals of all groups. Sex-related differences were not observed. In contrast, long-term exposure to short days decreased the number of neurons exhi…
Anterograde tracing of retinohypothalamic afferents with Fluoro-Gold
1997
The anterograde neuronal tracing properties of Fluoro-Gold (FG) were characterized in this study by its ability to label the retinohypothalamic tract (RHT) upon pressure injection of the substance into the vitrous body of the eye in the Djungarian hamster, Phodopus sungorus. Tracing was compared to the anterograde neuronal transport of cholera toxin B subunit (CTB), Fast blue (FB), Phaseolous vulgaris leucoagglutinin (PHA-L) and biocytin. After survival times that ranged from 24 h to 4 weeks, a major projection was found to the bilateral hypothalamic suprachiasmatic nuclei (SCN). Labeling was also found in the anterior medial preoptic nucleus and, in relatively sparse amounts, in the latera…
Rat pineal arylalkylamine-N-acetyltransferase: cyclic AMP inducibility of its gene depends on prior entrained photoperiod.
2003
The nocturnal biosynthesis of melatonin in the rat pineal depends on strongly enhanced expression of the enzyme N-acetyltransferase [arylalkylamine N-acetyltransferase (AA-NAT); EC 2.3.1.87]. AA-NAT transcription is stimulated during darkness by adrenergic inputs to the pineal from the suprachiasmatic nucleus (SCN). Nocturnal activation of the AA-NAT promotor following stimulation of pinealocyte adrenoceptors involves cAMP-dependent stimulation of protein kinase A (PKA). The nocturnal rise in AA-NAT depends on the lighting conditions. As compared with light/dark (LD) 12:12, the delay between dark onset and the nocturnal rise in AA-NAT is shortened under long photoperiods and prolonged under…
Melatonin binding sites in brain of the 2-day-old chicken: An autoradiographic localisation
1990
Melatonin, released in a circadian manner from the avian pineal gland into the circulation, is concentrated in distinct brain areas, possibly by receptor-mediated uptake mechanisms. For anatomical localisation of putative melatonin receptors in birds, cryostat-cut, coronal 15 microns brain sections of 2-day-old chicken were investigated by means of in vitro receptorautoradiography, using 125I-melatonin as a ligand. Binding occurred in brain structures receiving or mediating visual or auditory sensory input. Binding characteristics were investigated in homogenates of a brain region labelled by 125I-melatonin and showed to be specific and saturable (Kd: 87.2 pM; Bmax: 16.1 fmol/mg protein). R…
Daily oscillation of gene expression in the retina is phase-advanced with respect to the pineal gland
2007
Abstract The photoreceptive retina and the non-photoreceptive pineal gland are components of the circadian and the melatonin forming system in mammals. To contribute to our understanding of the functional integrity of the circadian system and the melatonin forming system we have compared the daily oscillation of the two tissues under various seasonal lighting conditions. For this purpose, the 24-h profiles of the expression of the genes coding for arylalkylamine N-acetyltransferase (AA-NAT), nerve growth factor inducible gene-A (NGFI-A), nerve growth factor inducible gene-B (NGFI-B), retinoic acid related orphan receptor β (RORβ), dopamine D4 receptor, and period2 (Per2) have been simultane…
Neuropeptide Y (NPY)-like immunoreactivity in peripheral and central nerve fibres of the golden hamster (Mesocricetus auratus) with special respect t…
1986
Inforimation on the ambient lighting conditions is conveyed from the retina to the pineal organ by a neuronal pathway involving the suprachiasmatic nucleus (SCN) which acts as a circadian pacemaker. In the hamster, circadian rhythms have been shown to be influenced by injection of neuropeptide Y (NPY) into the SCN. Since NPY-immunoreactive nerve fibres are present in the rat and guinea-pig pineal glands it appeared of interest to investigate the hamster pineal as part of the circadian rhythm generating/regulating system. For comparison kidney, small intestine and cerebral cortex were studied. Like in the other rodent species so far investigated only a few of the abundant sympathetic nerve f…