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651.
Halobacteria are aerobic chemo-organotroph archaea that grow optimally between pH 8 and 9 using a wide range of carbon sources.
These archaea have developed alternative processes of energy provision for conditions of high cell densities and the reduced
solubility of molecular oxygen in concentrated brines. The halobacteria can switch to anaerobic metabolism by using an alternative
final acceptor in the respiratory chain or by fermentation, or alternatively, they can employ photophosphorylation. Light
energy is converted by several retinal-containing membrane proteins that, in addition to generating a proton gradient across
the cell membrane, also make phototaxis possible in order to approach optimal light conditions. The structural and functional
features of ATP synthesis in archaea are discussed, and similarities to F-ATPases (functional aspects) or vacuolar ATPases
(structural aspects) are presented.
Received: 18 December 1995 / Accepted: 3 April 1996 相似文献
652.
To understand the developmental regulation of acetylcholine (ACh) synthesis in the Xenopus retina, the properties of choline acetyltransferase (CAT) and cholinesterase (ChE), as well as histochemical localization of ChE in the retina, were studied during development. CAT activity first became detectable in the developing eyecup at stages 35/36. This was followed by a rapid, 50-fold rise in specific activity between stages 35/36 and 44. Since this rapid rise coincided with an almost identical increase in total ACh synthesis in whole retinae found in previous studies, it is suggested that this increase was sufficient to account for the rapid increase in total ACh synthesis. Moreover, it also correlated with increased rates of synaptogenesis in both the inner and the outer plexiform layers. Total ChE was resolved into specific and nonspecific ChE by the use of tetraisopropylpyrophosphoramide. Total ChE activities first became detectable at stages 35/36. Specific ChE [acetylcholinesterase (AChE)] increased from 50% at stage 39 to 95% of total ChE activities at stage 66. Again, the most rapid increase in both total ChE and AChE activities occurred between stages 35/36 and 44. Histochemical studies showed that AChE was localized predominantly in the two plexiform layers, with the inner plexiform layer more heavily stained at all stages. Moreover, a stratified staining pattern, clearly discerned in the inner plexiform layer, also correlated with synaptogenesis during this early period of retinal development. 相似文献
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654.
T. Hariyama A. Terakita M. Sakayori Y. Katsukura K. Ozaki Y. Tsukahara 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,183(2):165-170
Based on electroretinogram measurements, fireflies are reported to possess two spectral-sensitivity peaks: one in the near-ultraviolet
and the other in the green region. This suggests that at least two kinds of visual pigment should be present (Lall and Lloyd
1989). Analyses by high pressure liquid chromatography revealed that there are two kinds of chromophores, i.e., retinal (A1)
and 3-hydroxyretinal (A3), in the compound eye of Japanese fireflies of the genus Luciola (Gleadall et␣al. 1989). Through selective light-adaptation experiments and in vitro analyses by high pressure liquid chromatography,
it is demonstrated that the A1 is the chromophore of an ultraviolet-sensitive visual pigment and the A3 is the chromophore
of a green-sensitive pigment. The absolute amounts of A1 and A3 were, respectively, 32.1 ± 3.9 and 111.1 ± 35.2 pmol in male,
and 26.9 ± 6.9 and 63.4 ± 18.2 pmol in female (mean ± SD per animal). These results indicate that the amount of green-sensitive
visual pigment in males is significantly higher than in females. A difference in the distribution of these chromophores is
demonstrated in the eyes of female (but not male) fireflies: in the dorsal region of the female eye, the A1:A3 ratio is higher
than that for the rest of the eye.
Accepted: 28 February 1998 相似文献
655.
Feature detection in biomedical signals is crucial for deepening our knowledge about the involved physiological processes. To achieve this aim, many analytic approaches can be applied but only few are able to deal with signals whose time dependent features provide useful clinical information. Among the biomedical signals, the electroretinogram (ERG), that records the retinal response to a light flash, can improve our comprehension of the complex photoreceptoral activities.The present study is focused on the analysis of the early response of the photoreceptoral human system, known as a-wave ERG-component. This wave reflects the functional integrity of the photoreceptors, rods and cones, whose activation dynamics are not yet completely understood. Moreover, since in incipient photoreceptoral pathologies eventual anomalies in a-wave are not always detectable with a “naked eye” analysis of the traces, the possibility to discriminate pathologic from healthy traces, by means of appropriate analytical techniques, could help in clinical diagnosis.In the present paper, we discuss and compare the efficiency of various techniques of signal processing, such as Fourier analysis (FA), Principal Component Analysis (PCA), Wavelet Analysis (WA) in recognising pathological traces from the healthy ones. The investigated retinal pathologies are Achromatopsia, a cone disease and Congenital Stationary Night Blindness, affecting the photoreceptoral signal transmission. Our findings prove that both PCA and FA of conventional ERGs, don't add clinical information useful for the diagnosis of ocular pathologies, whereas the use of a more sophisticated analysis, based on the wavelet transform, provides a powerful tool for routine clinical examinations of patients. 相似文献
656.
Amino Acid Neurotransmitters in Nucleus Tractus Solitarius: An In Vivo Microdialysis Study 总被引:3,自引:0,他引:3
Amino acid neurotransmitters in the nucleus tractus solitarius (NTS) are thought to play a key role in the mediation of visceral reflexes and glutamate has been proposed as the neurotransmitter of visceral afferent nerves projecting to this region. The present studies sought to characterize the use of in vivo microdialysis to examine extracellular fluid levels of amino acids in the NTS of anesthetized rats. Using a microdialysis probe that was 450 μm in length and a sensitive HPLC assay for amino acids, amino acids could be measured in dialysate samples collected from the NTS. Perfusion of the microdialysis probe with 60 mM K±, to elicit depolarization of nerve terminals in the vicinity of the probe, resulted in increased dialysate fluid levels of aspartate, glutamate, glycine, taurine, and GABA. In contrast, glutamine and tyrosine were decreased and other amino acids were not significantly affected. Prior removal of the ipsilateral nodose ganglion did not alter the K±-evoked changes in dialysate levels of any of these amino acids. Electrical stimulation of the vagus nerves, using a variety of stimulus parameters, did not significantly alter dialysate levels of glutamate or any of the other amino acids that were measured. Blockade of glutamate uptake with dihydrokainate increased dialysate levels of glutamate, aspartate, and GABA, but in the presence of dihydrokainate vagal stimulation did not alter dialysate levels of these amino acids. The results show that in vivo microdialysis can be used to examine amino acid efflux in the rat NTS and provide further evidence for amino acidergic neural transmission in the NTS. However, these studies fail to support the hypothesis that vagal afferents release glutamate or aspartate. 相似文献
657.
Pamela S. Lagali David J. Picketts 《Journal of ocular biology, diseases, and informatics》2011,4(3):111-120
Retinal neurons are highly vulnerable to a diverse array of neurotoxic stimuli that leads to their degeneration, which is
a major contributor to blindness. This review summarizes the role of epigenetic factors in mediating neuronal homeostasis
and survival to protect against cell death and neurodegenerative conditions. Studies in human patients and mouse models implicate
numerous chromatin modifications in neuroprotective processes including histone protein acetylation and methylation, DNA methylation,
and ATP-dependent nucleosome remodeling. Recent research has begun to uncover specific epigenetic mechanisms invoked by neurotoxic
stimuli. Continued investigation in this area will be the key to the generation of therapeutic strategies for the intervention
of retinal neurodegenerative diseases. 相似文献
658.
659.
660.
Insulin-like growth factor-1 regulation of retinal progenitor cell proliferation and differentiation
Yuyao Wang Dandan Zhang Yi Zhang Ni Ni Zhimin Tang Zhisha Bai 《Cell cycle (Georgetown, Tex.)》2018,17(4):515-526
Strategies to improve retinal progenitor cell (RPC) capacity to yield proliferative and multipotent pools of cells that can efficiently differentiate into retinal neurons, including photoreceptors, could be vital for cell therapy in retinal degenerative diseases. In this study, we found that insulin-like growth factor-1 (IGF-1) plays a role in the regulation of proliferation and differentiation of RPCs. Our results show that IGF-1 promotes RPC proliferation via IGF-1 receptors (IGF-1Rs), stimulating increased phosphorylation in the PI3K/Akt and MAPK/Erk pathways. An inhibitor experiment revealed that IGF-1-induced RPC proliferation was inhibited when the PI3K/Akt and MAPK/Erk pathways were blocked. Furthermore, under the condition of differentiation, IGF-1-pretreated RPCs prefer to differentiate into retinal neurons, including photoreceptors, in vitro, which is crucial for visual formation and visual restoration. These results demonstrate that IGF-1 accelerates the proliferation of RPCs and IGF-1 pretreated RPCs may have shown an increased potential for retinal neuron differentiation, providing a novel strategy for regulating the proliferation and differentiation of retinal progenitors in vitro and shedding light upon the application of RPCs in retinal cell therapy. 相似文献