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Bertolesi GE, Debnath N, Malik HR, Man LLH, McFarlane S. Type II Opsins in the Eye, the Pineal Complex and the Skin of Xenopus laevis: Using Changes in Skin Pigmentation as a Readout of Visual and Circadian Activity. Front Neuroanat 2022; 15:784478. [PMID: 35126061 PMCID: PMC8814574 DOI: 10.3389/fnana.2021.784478] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 12/13/2021] [Indexed: 01/17/2023] Open
Abstract
The eye, the pineal complex and the skin are important photosensitive organs. The African clawed frog, Xenopus laevis, senses light from the environment and adjusts skin color accordingly. For example, light reflected from the surface induces camouflage through background adaptation while light from above produces circadian variation in skin pigmentation. During embryogenesis, background adaptation, and circadian skin variation are segregated responses regulated by the secretion of α-melanocyte-stimulating hormone (α-MSH) and melatonin through the photosensitivity of the eye and pineal complex, respectively. Changes in the color of skin pigmentation have been used as a readout of biochemical and physiological processes since the initial purification of pineal melatonin from pigs, and more recently have been employed to better understand the neuroendocrine circuit that regulates background adaptation. The identification of 37 type II opsin genes in the genome of the allotetraploid X. laevis, combined with analysis of their expression in the eye, pineal complex and skin, is contributing to the elucidation of the role of opsins in the different photosensitive organs, but also brings new questions and challenges. In this review, we analyze new findings regarding the anatomical localization and functions of type II opsins in sensing light. The contribution of X. laevis in revealing the neuroendocrine circuits that regulate background adaptation and circadian light variation through changes in skin pigmentation is discussed. Finally, the presence of opsins in X. laevis skin melanophores is presented and compared with the secretory melanocytes of birds and mammals.
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Affiliation(s)
- Gabriel E. Bertolesi
- Department of Cell Biology and Anatomy, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, University of Calgary, Calgary, AB, Canada
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Movsisyan AB, Oganezova ZG, Egorov EA. [Use and outcomes of antioxidant therapy in ophthalmic practice]. Vestn Oftalmol 2022; 138:126-132. [PMID: 36288427 DOI: 10.17116/oftalma2022138051126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Advances in medical diagnostic technologies, particularly in ophthalmology, help researchers understand histological characteristics of the human eye and study vision at the cellular level. In addition to its role in the ocular function associated with the control of movements, senses and protective responses, the nervous system plays a key role in regulation of the visual process. Neurodegenerative disorders hold a special place among systemic diseases. Presently, the development of such pathologies are associated with neuroinflammation, which has been proven to also contribute to the glaucomatous process. For this reason, achieving target intraocular pressure does not always guarantee stabilization of the degenerative process. In this context, neuroprotective agents are recommended for glaucoma management to all patients taking into consideration pathogenetic characteristics of the disease. Based on its antioxidative and neuroprotective effects, ethylmethylhydroxypyridine succinate (Mexidol) is commonly used in ophthalmic practice, specifically in the treatment of patients with glaucomatous optic neuropathy and retinal diseases. The results of studies demonstrate that Mexidol is effective in slowing down neurodegeneration and stabilizing visual functions in patients with primary open-angle glaucoma due to its antihypoxic, antioxidant and membrane-stabilizing properties, as well as its positive impact on the neuromediator balance and ocular blood flow.
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Affiliation(s)
- A B Movsisyan
- Hospital for War Veterans No. 2, Moscow, Russia
- Pirogov Russian National Research Medical University, Moscow, Russia
| | - Zh G Oganezova
- Pirogov Russian National Research Medical University, Moscow, Russia
- N.P. Bochkov Research Centre for Medical Genetics, Moscow, Russia
| | - E A Egorov
- Pirogov Russian National Research Medical University, Moscow, Russia
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Wiechmann AF, Martin TA, Horb ME. CRISPR/Cas9 mediated mutation of the mtnr1a melatonin receptor gene causes rod photoreceptor degeneration in developing Xenopus tropicalis. Sci Rep 2020; 10:13757. [PMID: 32792587 PMCID: PMC7426423 DOI: 10.1038/s41598-020-70735-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2019] [Accepted: 08/03/2020] [Indexed: 11/21/2022] Open
Abstract
Nighttime surges in melatonin levels activate melatonin receptors, which synchronize cellular activities with the natural light/dark cycle. Melatonin receptors are expressed in several cell types in the retina, including the photon-sensitive rods and cones. Previous studies suggest that long-term photoreceptor survival and retinal health is in part reliant on melatonin orchestration of circadian homeostatic activities. This scenario would accordingly envisage that disruption of melatonin receptor signaling is detrimental to photoreceptor health. Using in vivo CRISPR/Cas9 genomic editing, we discovered that a small deletion mutation of the Mel1a melatonin receptor (mtnr1a) gene causes a loss of rod photoreceptors in retinas of developing Xenopus tropicalis heterozygous, but not homozygous mutant tadpoles. Cones were relatively spared from degeneration, and the rod loss phenotype was not obvious after metamorphosis. Localization of Mel1a receptor protein appeared to be about the same in wild type and mutant retinas, suggesting that the mutant protein is expressed at some level in mutant retinal cells. The severe impact on early rod photoreceptor viability may signify a previously underestimated critical role in circadian influences on long-term retinal health and preservation of sight. These data offer evidence that disturbance of homeostatic, circadian signaling, conveyed through a mutated melatonin receptor, is incompatible with rod photoreceptor survival.
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Affiliation(s)
- Allan F Wiechmann
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
- Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
| | - Teryn A Martin
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Marko E Horb
- Marine Biological laboratory, Woods Hole, MA, USA
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Sheng W, Jin M, Pan G, Weng S, Sik A, Han L, Liu K. Cellular localization of melatonin receptor Mel1b in pigeon retina. Neuropeptides 2019; 78:101974. [PMID: 31645269 DOI: 10.1016/j.npep.2019.101974] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 08/10/2019] [Accepted: 09/22/2019] [Indexed: 12/15/2022]
Abstract
Melatonin, an important neuromodulator involved in circadian rhythms, modulates a series of physiological processes via activating its specific receptors, namely Mel1a (MT1), Mel1b (MT2) and Mel1c receptors. In this work, the localization of Mel1b receptor was studied in pigeon retina using double immunohistochemistry staining and confocal scanning microscopy. Our results showed that Mel1b receptor widely existed in the outer segment of photoreceptors and in the somata of dopaminergic amacrine cells, cholinergic amacrine cells, glycinergic AII amacrine cells, conventional ganglion cells and intrinsically photosensitive retinal ganglion cells, while horizontal cells, bipolar cells and Müller glial cells seemed to lack immunoreactivity of Mel1b receptor. That multiple types of retinal cells expressing Mel1b receptor suggests melatonin may directly modulate the activities of retina via activating Mel1b receptor.
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Affiliation(s)
- Wenlong Sheng
- Biology Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China.
| | - Meng Jin
- Biology Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China
| | - Ge Pan
- Biology Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China
| | - Shijun Weng
- State Key Laboratory of Medical Neurobiology, Institutes of Brain Science, Department of Ophthalmology, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Attila Sik
- Institute of Transdisciplinary Discoveries, University of Pecs, Pecs, Hungary; Institute of Physiology, Medical School, University of Pecs, Pecs, Hungary; Szentagothai Research Centre, University of Pecs, Pecs, Hungary; Medical School, University of Birmingham, Birmingham, UK
| | - Liwen Han
- Biology Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China
| | - Kechun Liu
- Biology Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan, China.
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Alkozi HA, Navarro G, Franco R, Pintor J. Melatonin and the control of intraocular pressure. Prog Retin Eye Res 2019; 75:100798. [PMID: 31560946 DOI: 10.1016/j.preteyeres.2019.100798] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 09/13/2019] [Accepted: 09/18/2019] [Indexed: 12/15/2022]
Abstract
Melatonin is not only synthesized by the pineal gland but by several ocular structures. This natural indoleamine is of great importance for regulating several eye processes, among which pressure homeostasis is included. Glaucoma, the most prevalent eye disease, also known as the silent thief of vision, is a multifactorial pathology that is associated to age and, often, to intraocular hypertension (IOP). Indeed IOP is the only modifiable risk factor and as such medications are available to control it; however, novel medications are sought to minimize undesirable side effects. Melatonin and analogues decrease IOP in both normotensive and hypertensive eyes. Melatonin activates its cognate membrane receptors, MT1 and MT2, which are present in numerous ocular tissues, including the aqueous-humor-producing ciliary processes. Melatonin receptors belong to the superfamily of G-protein-coupled receptors and their activation would lead to different signalling pathways depending on the tissue. This review describes the molecular mechanisms underlying differential functionalities that are attributed to melatonin receptors. Accordingly, the current work highlights the important role of melatonin and its analogues in the healthy and in the glaucomatous eyes, with special attention to the control of intraocular pressure.
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Affiliation(s)
- Hanan Awad Alkozi
- Department of Biochemistry and Molecular Biology, Faculty of Optics and Optometry, University Complutense of Madrid, Madrid, Spain
| | - Gemma Navarro
- Centro de Investigación en Red, Enfermedades Neurodegeneratives (CiberNed), Instituto de Salud Carlos III, Sinesio Delgado 6, 28029, Madrid, Spain; Department of Biochemistry and Physiology, School of Pharmacy and Food Sciences, Universitat de Barcelona, Avda. Juan XXIII, 27, 08027, Barcelona, Spain
| | - Rafael Franco
- Centro de Investigación en Red, Enfermedades Neurodegeneratives (CiberNed), Instituto de Salud Carlos III, Sinesio Delgado 6, 28029, Madrid, Spain; Department of Biochemistry and Molecular Biomedicine, School of Biology, Universitat de Barcelona, Diagonal 643, 08028, Barcelona, Barcelona, Spain.
| | - Jesus Pintor
- Department of Biochemistry and Molecular Biology, Faculty of Optics and Optometry, University Complutense of Madrid, Madrid, Spain; Real Academia Nacional de Farmacia, Calle Farmacia 11, 28004, Madrid, Spain.
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Bertolesi GE, Hehr CL, Munn H, McFarlane S. Two light-activated neuroendocrine circuits arising in the eye trigger physiological and morphological pigmentation. Pigment Cell Melanoma Res 2016; 29:688-701. [DOI: 10.1111/pcmr.12531] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Accepted: 08/22/2016] [Indexed: 01/08/2023]
Affiliation(s)
- Gabriel E. Bertolesi
- Department of Cell Biology and Anatomy; Hotchkiss Brain Institute; Alberta Children's Hospital Research Institute; University of Calgary; Calgary AB Canada
| | - Carrie L. Hehr
- Department of Cell Biology and Anatomy; Hotchkiss Brain Institute; Alberta Children's Hospital Research Institute; University of Calgary; Calgary AB Canada
| | - Hayden Munn
- Department of Cell Biology and Anatomy; Hotchkiss Brain Institute; Alberta Children's Hospital Research Institute; University of Calgary; Calgary AB Canada
| | - Sarah McFarlane
- Department of Cell Biology and Anatomy; Hotchkiss Brain Institute; Alberta Children's Hospital Research Institute; University of Calgary; Calgary AB Canada
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Pei H, Du J, Song X, He L, Zhang Y, Li X, Qiu C, Zhang Y, Hou J, Feng J, Gao E, Li D, Yang Y. Melatonin prevents adverse myocardial infarction remodeling via Notch1/Mfn2 pathway. Free Radic Biol Med 2016; 97:408-417. [PMID: 27387769 DOI: 10.1016/j.freeradbiomed.2016.06.015] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Revised: 06/04/2016] [Accepted: 06/16/2016] [Indexed: 01/17/2023]
Abstract
Mitochondrial dysfunction is linked with myocardial infarction (MI), a disorder in which Notch1 has attracted increasing attention. However, the involvement of Notch1 in mitochondrial impairment after an MI is poorly understood, as is the role of mitochondrial fusion-associated protein 2 (Mfn2). Moreover, whether melatonin potentiates the Notch1/Mfn2 pathway in post-MI cardiac damage remains unclear. In our study, small interfering RNAs against Notch1 or Mfn2 and Jagged1 peptide were delivered via intramyocardial injection. At 3 days after these treatments, MI was induced by ligation of the anterior descending branch. We found that this ablation of Notch1 or Mfn2 aggravated post-MI injury, including worsened mitochondrial damage and increased generation of reactive oxygen species (ROS). In contrast, Jagged1 improved mitochondrial structure and function, decreased ROS production and attenuated post-MI injury. Interestingly, though Mfn2 expression was mildly regulated by Notch1 signaling in myocardium, Mfn2 deficiency nearly eliminated the cardioprotection by Jagged1, as evidenced by suppressed cardiac function, aggravated myocardial fibrosis, increased cell apoptosis, worsened mitochondrial impairment and enhanced oxidative stress. These observations revealed that Mfn2 plays an indispensable role in protection against MI-induced injury by Notch1. The mechanism might involve disrupting a damaging cycle of mitochondrial damage and ROS generation. Furthermore, melatonin activated Notch1 signaling and increased Mfn2 expression were reversed by luzindole, a nonselective antagonist of the melatonin receptor. Notably, melatonin attenuated post-MI injury in normal mice, but not in mice deficient in Notch1 or Mfn2. These results demonstrate that melatonin attenuates post-MI injury via the Notch1/Mfn2 pathway in a receptor-dependent manner.
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Affiliation(s)
- Haifeng Pei
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China; Third Military Medical University, Chongqing 400042, China
| | - Jin Du
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Xiaofeng Song
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Lei He
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Yufei Zhang
- Department of Medical Genetics and Developmental Biology, School of Basic Medicine, Fourth Military Medical University, Xi'an 710032, China
| | - Xiuchuan Li
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Chenming Qiu
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Yangyang Zhang
- Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, China
| | - Juanni Hou
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Juan Feng
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Erhe Gao
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - De Li
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China
| | - Yongjian Yang
- Department of Cardiology, Chengdu Military General Hospital, Chengdu 610083, China; Third Military Medical University, Chongqing 400042, China.
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Yu L, Liang H, Dong X, Zhao G, Jin Z, Zhai M, Yang Y, Chen W, Liu J, Yi W, Yang J, Yi D, Duan W, Yu S. Reduced silent information regulator 1 signaling exacerbates myocardial ischemia-reperfusion injury in type 2 diabetic rats and the protective effect of melatonin. J Pineal Res 2015; 59:376-90. [PMID: 26327197 DOI: 10.1111/jpi.12269] [Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/05/2015] [Accepted: 08/14/2015] [Indexed: 01/06/2023]
Abstract
Diabetes mellitus (DM) increases myocardial oxidative stress and endoplasmic reticulum (ER) stress. Melatonin confers cardioprotective effect by suppressing oxidative damage. However, the effect and mechanism of melatonin on myocardial ischemia-reperfusion (MI/R) injury in type 2 diabetic state are still unknown. In this study, we developed high-fat diet-fed streptozotocin (HFD-STZ) rat, a well-known type 2 diabetic model, to evaluate the effect of melatonin on MI/R injury with a focus on silent information regulator 1 (SIRT1) signaling, oxidative stress, and PERK/eIF2α/ATF4-mediated ER stress. HFD-STZ treated rats were exposed to melatonin treatment in the presence or the absence of sirtinol (a SIRT1 inhibitor) and subjected to MI/R surgery. Compared with nondiabetic animals, type 2 diabetic rats exhibited significantly decreased myocardial SIRT1 signaling, increased apoptosis, enhanced oxidative stress, and ER stress. Additionally, further reduced SIRT1 signaling, aggravated oxidative damage, and ER stress were found in diabetic animals subjected to MI/R surgery. Melatonin markedly reduced MI/R injury by improving cardiac functional recovery and decreasing myocardial apoptosis in type 2 diabetic animals. Melatonin treatment up-regulated SIRT1 expression, reduced oxidative damage, and suppressed PERK/eIF2α/ATF4 signaling. However, these effects were all attenuated by SIRT1 inhibition. Melatonin also protected high glucose/high fat cultured H9C2 cardiomyocytes against simulated ischemia-reperfusion injury-induced ER stress by activating SIRT1 signaling while SIRT1 siRNA blunted this action. Taken together, our study demonstrates that reduced cardiac SIRT1 signaling in type 2 diabetic state aggravates MI/R injury. Melatonin ameliorates reperfusion-induced oxidative stress and ER stress via activation of SIRT1 signaling, thus reducing MI/R damage and improving cardiac function.
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Affiliation(s)
- Liming Yu
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Hongliang Liang
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Xiaochao Dong
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Guolong Zhao
- Department of Cardiovascular Surgery, General Hospital, Ningxia Medical University, Yinchuan, China
| | - Zhenxiao Jin
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Mengen Zhai
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Yang Yang
- Department of Biomedical Engineering, The Fourth Military Medical University, Xi'an, China
| | - Wensheng Chen
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Jincheng Liu
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Wei Yi
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Jian Yang
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Dinghua Yi
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Weixun Duan
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Shiqiang Yu
- Department of Cardiovascular Surgery, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
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Esposti F, Johnston J, Rosa JM, Leung KM, Lagnado L. Olfactory stimulation selectively modulates the OFF pathway in the retina of zebrafish. Neuron 2013; 79:97-110. [PMID: 23849198 PMCID: PMC3710973 DOI: 10.1016/j.neuron.2013.05.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/01/2013] [Indexed: 01/11/2023]
Abstract
Cross-modal regulation of visual performance by olfactory stimuli begins in the retina, where dopaminergic interneurons receive projections from the olfactory bulb. However, we do not understand how olfactory stimuli alter the processing of visual signals within the retina. We investigated this question by in vivo imaging activity in transgenic zebrafish expressing SyGCaMP2 in bipolar cell terminals and GCaMP3.5 in ganglion cells. The food-related amino acid methionine reduced the gain and increased sensitivity of responses to luminance and contrast transmitted through OFF bipolar cells but not ON. The effects of olfactory stimulus were blocked by inhibiting dopamine uptake and release. Activation of dopamine receptors increased the gain of synaptic transmission in vivo and potentiated synaptic calcium currents in isolated bipolar cells. These results indicate that olfactory stimuli alter the sensitivity of the retina through the dopaminergic regulation of presynaptic calcium channels that control the gain of synaptic transmission through OFF bipolar cells. Olfactory stimuli regulate transmission of signals through retinal bipolar cells Modulation of synaptic gain and sensitivity occur in OFF bipolar cells but not ON An inhibitor of dopamine uptake blocks odor-induced changes in synaptic gain Dopamine potentiates presynaptic calcium channels in isolated bipolar cells
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Affiliation(s)
- Federico Esposti
- Laboratory of Molecular Biology, Medical Research Council, Cambridge CB2 0QH, UK
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Huang H, Wang Z, Weng SJ, Sun XH, Yang XL. Neuromodulatory role of melatonin in retinal information processing. Prog Retin Eye Res 2013; 32:64-87. [PMID: 22986412 DOI: 10.1016/j.preteyeres.2012.07.003] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Revised: 07/24/2012] [Accepted: 07/25/2012] [Indexed: 12/15/2022]
Affiliation(s)
- Hai Huang
- Institute of Neurobiology, Institutes of Brain Science, Fudan University, Shanghai, PR China
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Role of melatonin and its receptors in the vertebrate retina. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 300:211-42. [PMID: 23273863 DOI: 10.1016/b978-0-12-405210-9.00006-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Melatonin is a chemical signal of darkness that is produced by retinal photoreceptors and pinealocytes. In the retina, melatonin diffuses from the photoreceptors to bind to specific receptors on a variety of inner retinal neurons to modify their activity. Potential target cells for melatonin in the inner retina are amacrine cells, bipolar cells, horizontal cells, and ganglion cells. Melatonin inhibits the release of dopamine from amacrine cells and increases the light sensitivity of horizontal cells. Melatonin receptor subtypes show differential, cell-specific patterns of expression that are likely to underlie differential functional modulation of specific retinal pathways. Melatonin potentiates rod signals to ON-type bipolar cells, via activation of the melatonin MT2 (Mel1b) receptor, suggesting that melatonin modulates the function of specific retinal circuits based on the differential distribution of its receptors. The selective and differential expression of melatonin receptor subtypes in cone circuits suggest a conserved function for melatonin in enhancing transmission from rods to second-order neurons and thus promote dark adaptation.
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