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Bhoi JD, Goel M, Ribelayga CP, Mangel SC. Circadian clock organization in the retina: From clock components to rod and cone pathways and visual function. Prog Retin Eye Res 2023; 94:101119. [PMID: 36503722 PMCID: PMC10164718 DOI: 10.1016/j.preteyeres.2022.101119] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 08/22/2022] [Accepted: 08/25/2022] [Indexed: 12/13/2022]
Abstract
Circadian (24-h) clocks are cell-autonomous biological oscillators that orchestrate many aspects of our physiology on a daily basis. Numerous circadian rhythms in mammalian and non-mammalian retinas have been observed and the presence of an endogenous circadian clock has been demonstrated. However, how the clock and associated rhythms assemble into pathways that support and control retina function remains largely unknown. Our goal here is to review the current status of our knowledge and evaluate recent advances. We describe many previously-observed retinal rhythms, including circadian rhythms of morphology, biochemistry, physiology, and gene expression. We evaluate evidence concerning the location and molecular machinery of the retinal circadian clock, as well as consider findings that suggest the presence of multiple clocks. Our primary focus though is to describe in depth circadian rhythms in the light responses of retinal neurons with an emphasis on clock control of rod and cone pathways. We examine evidence that specific biochemical mechanisms produce these daily light response changes. We also discuss evidence for the presence of multiple circadian retinal pathways involving rhythms in neurotransmitter activity, transmitter receptors, metabolism, and pH. We focus on distinct actions of two dopamine receptor systems in the outer retina, a dopamine D4 receptor system that mediates circadian control of rod/cone gap junction coupling and a dopamine D1 receptor system that mediates non-circadian, light/dark adaptive regulation of gap junction coupling between horizontal cells. Finally, we evaluate the role of circadian rhythmicity in retinal degeneration and suggest future directions for the field of retinal circadian biology.
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Affiliation(s)
- Jacob D Bhoi
- Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, UTHEALTH-The University of Texas Health Science Center at Houston, Houston, TX, USA; Neuroscience Honors Research Program, William Marsh Rice University, Houston, TX, USA
| | - Manvi Goel
- Department of Neuroscience, Wexner Medical Center, College of Medicine, The Ohio State University, Columbus, OH, USA
| | - Christophe P Ribelayga
- Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, UTHEALTH-The University of Texas Health Science Center at Houston, Houston, TX, USA; Neuroscience Honors Research Program, William Marsh Rice University, Houston, TX, USA.
| | - Stuart C Mangel
- Department of Neuroscience, Wexner Medical Center, College of Medicine, The Ohio State University, Columbus, OH, USA.
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2
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Karamichos D, Escandon P, Vasini B, Nicholas SE, Van L, Dang DH, Cunningham RL, Riaz KM. Anterior pituitary, sex hormones, and keratoconus: Beyond traditional targets. Prog Retin Eye Res 2021; 88:101016. [PMID: 34740824 PMCID: PMC9058044 DOI: 10.1016/j.preteyeres.2021.101016] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Revised: 10/15/2021] [Accepted: 10/18/2021] [Indexed: 12/13/2022]
Abstract
"The Diseases of the Horny-coat of The Eye", known today as keratoconus, is a progressive, multifactorial, non-inflammatory ectatic corneal disorder that is characterized by steepening (bulging) and thinning of the cornea, irregular astigmatism, myopia, and scarring that can cause devastating vision loss. The significant socioeconomic impact of the disease is immeasurable, as patients with keratoconus can have difficulties securing certain jobs or even joining the military. Despite the introduction of corneal crosslinking and improvements in scleral contact lens designs, corneal transplants remain the main surgical intervention for treating keratoconus refractory to medical therapy and visual rehabilitation. To-date, the etiology and pathogenesis of keratoconus remains unclear. Research studies have increased exponentially over the years, highlighting the clinical significance and international interest in this disease. Hormonal imbalances have been linked to keratoconus, both clinically and experimentally, with both sexes affected. However, it is unclear how (molecular/cellular signaling) or when (age/disease stage(s)) those hormones affect the keratoconic cornea. Previous studies have categorized the human cornea as an extragonadal tissue, showing modulation of the gonadotropins, specifically luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Studies herein provide new data (both in vitro and in vivo) to further delineate the role of hormones/gonadotropins in the keratoconus pathobiology, and propose the existence of a new axis named the Hypothalamic-Pituitary-Adrenal-Corneal (HPAC) axis.
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Affiliation(s)
- Dimitrios Karamichos
- North Texas Eye Research Institute, University of North Texas Health Science Center, 3430 Camp Bowie Blvd, Fort Worth, TX, 76107, USA; Department of Pharmaceutical Sciences, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX, 76107, USA; Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX, 76107, USA.
| | - Paulina Escandon
- North Texas Eye Research Institute, University of North Texas Health Science Center, 3430 Camp Bowie Blvd, Fort Worth, TX, 76107, USA; Department of Pharmaceutical Sciences, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX, 76107, USA
| | - Brenda Vasini
- North Texas Eye Research Institute, University of North Texas Health Science Center, 3430 Camp Bowie Blvd, Fort Worth, TX, 76107, USA; Department of Pharmaceutical Sciences, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX, 76107, USA
| | - Sarah E Nicholas
- North Texas Eye Research Institute, University of North Texas Health Science Center, 3430 Camp Bowie Blvd, Fort Worth, TX, 76107, USA; Department of Pharmaceutical Sciences, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX, 76107, USA
| | - Lyly Van
- University of Oklahoma Health Sciences Center, 940 Stanton L Young, Oklahoma City, OK, USA; Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Deanna H Dang
- College of Medicine, University of Oklahoma Health Sciences Center, 940 Stanton L Young, Oklahoma City, OK, USA
| | - Rebecca L Cunningham
- Department of Pharmaceutical Sciences, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX, 76107, USA
| | - Kamran M Riaz
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
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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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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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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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7
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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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Wiechmann AF, Sherry DM. Melatonin receptors are anatomically organized to modulate transmission specifically to cone pathways in the retina of Xenopus laevis. J Comp Neurol 2012; 520:1115-27. [PMID: 22020534 DOI: 10.1002/cne.22783] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Melatonin receptors have been identified in several retinal cell types, including photoreceptors, horizontal cells, amacrine cells, and ganglion cells. Recent reports suggest that melatonin potentiates signaling from rods to inner retinal neurons. However, the organization of the melatonin receptors mediating this action in the outer plexiform layer (OPL) is not clear. To assess melatonin receptor localization in the OPL, double-label confocal immunohistochemistry for Mel1a or Mel1b melatonin receptors was performed in combination with markers for cone photoreceptors (calbindin, XAP-1) and ON bipolar cells (guanine nucleotide binding protein alpha, Goα) on the retina of Xenopus laevis. Both Mel1a and Mel1b receptors were specifically associated with processes contacting the pedicles of cones, but localized to processes from different sets of second-order neurons. Mel1a receptors localized to the large axonal processes of horizontal cells, while Mel1b receptors localized to the dendrites of OFF bipolar cells. Both receptors also localized to third-order amacrine and ganglion cells and their processes in the inner plexiform layer. This study indicates that Mel1a and Mel1b melatonin receptors are expressed specifically in the Xenopus OPL to modulate transmission from cones to horizontal cells and OFF bipolar cells, respectively; they are second-order neurons that predominantly contact ribbon synapses and display OFF responses to light. When combined with results from recent physiological studies, the current results suggest a conserved function for melatonin in enhancing transmission from rods to second-order neurons across species, although the precise mechanisms by which melatonin enhances this transmission are likely to vary in a species-dependent manner.
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Affiliation(s)
- Allan F Wiechmann
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
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Yang XF, Miao Y, Ping Y, Wu HJ, Yang XL, Wang Z. Melatonin inhibits tetraethylammonium-sensitive potassium channels of rod ON type bipolar cells via MT2 receptors in rat retina. Neuroscience 2010; 173:19-29. [PMID: 21094224 DOI: 10.1016/j.neuroscience.2010.11.028] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2010] [Revised: 10/29/2010] [Accepted: 11/13/2010] [Indexed: 11/16/2022]
Abstract
By challenging specific receptors, melatonin synthesized and released by photoreceptors regulates various physiological functions in the vertebrate retina. Here, we studied modulatory effects of melatonin on K+ currents of rod-dominant ON type bipolar cells (Rod-ON-BCs) in rat retinal slices by patch-clamp techniques. Double immunofluorescence experiments conducted in isolated cell and retinal section preparations showed that the melatonin MT₂ receptor was expressed in somata, dendrites and axon terminals of rat Rod-ON-BCs. Electrophysiologically, application of melatonin selectively inhibited the tetraethylammonium (TEA)-sensitive K+ current component, but did not show any effect on the 4-aminopyridine (4-AP)-sensitive component. Consistent with the immunocytochemical result, the melatonin effect was blocked by co-application of 4-phenyl-2-propionamidotetralin (4-P-PDOT), a specific MT₂ receptor antagonist. Neither protein kinase A (PKA) nor protein kinase G (PKG) seemed to be involved because both the PKA inhibitor Rp-cAMP and the PKG inhibitor KT5823 did not block the melatonin-induced suppression of the K+ currents. In contrast, application of the phospholipase C (PLC) inhibitor U73122 or the protein kinase C (PKC) inhibitor bisindolylmaleimide IV (Bis IV) eliminated the melatonin effect, and when the Ca²+ chelator BAPTA-containing pipette was used, melatonin failed to inhibit the K+ currents. These results suggest that suppression of the TEA-sensitive K+ current component via activation of MT₂ receptors expressed on rat Rod-ON-BCs may be mediated by a Ca²+-dependent PLC/inositol 1,4,5-trisphosphate (IP₃/PKC signaling pathway.
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Affiliation(s)
- X-F Yang
- Institutes of Brain Science, Institute of Neurobiology and State Key Laboratory of Medical Neurobiology, Fudan University, 138 Yixueyuan Road, Shanghai 200032, PR China
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Zhao WJ, Zhang M, Miao Y, Yang XL, Wang Z. Melatonin potentiates glycine currents through a PLC/PKC signalling pathway in rat retinal ganglion cells. J Physiol 2010; 588:2605-19. [PMID: 20519319 PMCID: PMC2916991 DOI: 10.1113/jphysiol.2010.187641] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2010] [Accepted: 05/24/2010] [Indexed: 12/15/2022] Open
Abstract
In vertebrate retina, melatonin regulates various physiological functions. In this work we investigated the mechanisms underlying melatonin-induced potentiation of glycine currents in rat retinal ganglion cells (RGCs). Immunofluorescence double labelling showed that rat RGCs were solely immunoreactive to melatonin MT(2) receptors. Melatonin potentiated glycine currents of RGCs, which was reversed by the MT(2) receptor antagonist 4-P-PDOT. The melatonin effect was blocked by intracellular dialysis of GDP-beta-S. Either preincubation with pertussis toxin or application of the phosphatidylcholine (PC)-specific phospholipase C (PLC) inhibitor D609, but not the phosphatidylinositol (PI)-PLC inhibitor U73122, blocked the melatonin effect. The protein kinase C (PKC) activator PMA potentiated the glycine currents and in the presence of PMA melatonin failed to cause further potentiation of the currents, whereas application of the PKC inhibitor bisindolylmaleimide IV abolished the melatonin-induced potentiation. The melatonin effect persisted when [Ca(2+)](i) was chelated by BAPTA, and melatonin induced no increase in [Ca(2+)](i). Neither cAMP-PKA nor cGMP-PKG signalling pathways seemed to be involved because 8-Br-cAMP or 8-Br-cGMP failed to cause potentiation of the glycine currents and both the PKA inhibitor H-89 and the PKG inhibitor KT5823 did not block the melatonin-induced potentiation. In consequence, a distinct PC-PLC/PKC signalling pathway, following the activation of G(i/o)-coupled MT(2) receptors, is most likely responsible for the melatonin-induced potentiation of glycine currents of rat RGCs. Furthermore, in rat retinal slices melatonin potentiated light-evoked glycine receptor-mediated inhibitory postsynaptic currents in RGCs. These results suggest that melatonin, being at higher levels at night, may help animals to detect positive or negative contrast in night vision by modulating inhibitory signals largely mediated by glycinergic amacrine cells in the inner retina.
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Affiliation(s)
- Wen-Jie Zhao
- Institutes of Brain Science and Institute of Neurobiology, State Key Laboratory of Medical Neurobiology, Fudan University, 138 Yixueyuan Road, Shanghai 200032, China
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Wiechmann AF, Summers JA. Circadian rhythms in the eye: The physiological significance of melatonin receptors in ocular tissues. Prog Retin Eye Res 2008; 27:137-60. [DOI: 10.1016/j.preteyeres.2007.10.001] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Huang H, Lee SC, Yang XL. Modulation by melatonin of glutamatergic synaptic transmission in the carp retina. J Physiol 2005; 569:857-71. [PMID: 16239269 PMCID: PMC1464261 DOI: 10.1113/jphysiol.2005.098798] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Melatonin is involved in a variety of physiological functions through activating specific receptors coupled to GTP-binding protein. Melatonin and its receptors are abundant in the retina. Here we show for the first time that melatonin modulates glutamatergic synaptic transmission from cones to horizontal cells (HCs) in carp retina. Immunocytochemical data revealed the expression of the MT1 receptor on carp HCs. Whole-cell recordings further showed that melatonin of physiological concentrations potentiated glutamate-induced currents from isolated cone-driven HCs (H1 cells) in a dose-dependent manner, by increasing the efficacy and apparent affinity of the glutamate receptor. The effects of melatonin were reversed by luzindole, but not by K 185, indicating the involvement of the MT1 receptor. Like melatonin, methylene blue (MB), a guanylate cyclase inhibitor, also potentiated the glutamate currents, but internal infusion of cGMP suppressed them. The effects of melatonin were not observed in cGMP-filled and MB-incubated HCs. These results suggest that the melatonin effects may be mediated by decreasing the intracellular concentration of cGMP. Consistent with these observations, melatonin depolarized the membrane potential of H1 cells and reduced their light responses, which could also be blocked by luzindole. These effects of melatonin persisted in the presence of the antagonists of receptors for dopamine, GABA and glycine, indicating a direct action of melatonin on H1 cells. Such modulation by melatonin of glutamatergic transmission from cones to HCs is thought to be in part responsible for circadian changes in light responsiveness of cone HCs in teleost retina.
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Affiliation(s)
- Hai Huang
- Institute of Neurobiology, Fudan University, 220 Handan Road, Shanghai, 200433, China
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Abstract
Dissimilarities in ocular physiopathology exist between human males and females. These differences can be observed in the lacrimal and other eye-associated glands, the ocular surface, the crystalline lens, and the retinochoroid complexes. Literature on the subject revealed that because of sex steroid hormone (estrogen, progesterone, and androgen) actions, various physiological conditions, such as age, menstrual cycles, pregnancy, and menopause or andropause, where the hormone milieu changes, affect vision. Well-designed scientific studies are lacking on the subject, although such studies hold much potential value. This review analyzes the relatively new area of hormones and vision.
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Affiliation(s)
- P D Gupta
- Iladevi Cataract and IOL Research Centre, Gurukul Road, Memnagar, Ahmedabad, India
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15
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Isorna E, Guijarro AI, Delgado MJ, López-Patiño MA, Pedro ND, Luis Alonso-Gómez A. Ontogeny of central melatonin receptors in tadpoles of the anuran Rana perezi: modulation of dopamine release. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2005; 191:1099-105. [PMID: 16075267 DOI: 10.1007/s00359-005-0032-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2005] [Revised: 06/22/2005] [Accepted: 06/26/2005] [Indexed: 10/25/2022]
Abstract
The objective of this work was to study melatonin receptors in the eye and the brain and their possible functionality in the ontogeny of Rana perezi. The binding of 2-[(125)I]melatonin increases throughout embryonic larval development in both tissues. The most pronounced increase takes place at the end of premetamorphosis and during early prometamorphosis. This rise coincides temporarily with the appearance of the rhythmic melatonin-synthesizing capacity in the retina. In the three studied developmental stages (32G, 40G and 49-50G), melatonin-binding sites are coupled to G proteins and become functional. Moreover, melatonin inhibits dopamine (DA) release by the eyecups and brain of R. perezi tadpoles in vitro (stage 40G). Thus, the modulation of DA release could be one mechanism by which melatonin interacts with hormones, like prolactin and thyroxine that are involved in the regulation of anuran development and metamorphosis. Finally, we show that melatonin decreases K(+)-evoked cAMP content in the frog retina in vitro, suggesting that the effect of melatonin on DA release in the frog retina is mediated by the inhibition of this intracellular messenger.
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Affiliation(s)
- Esther Isorna
- Departamento de Fisiología (Fisiología Animal II). Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain
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Wiechmann AF, Udin SB, Summers Rada JA. Localization of Mel1b melatonin receptor-like immunoreactivity in ocular tissues of Xenopus laevis. Exp Eye Res 2004; 79:585-94. [PMID: 15381042 DOI: 10.1016/j.exer.2004.07.004] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2004] [Accepted: 07/09/2004] [Indexed: 11/18/2022]
Abstract
The circadian signaling molecule, melatonin, is produced by pinealocytes and retinal photoreceptors. In the retina, melatonin is thought to diffuse into the inner retina to act as a paracrine signal of darkness by binding to specific receptors in retinal neurons. The retinal cell locations of the Mel1a and Mel1c melatonin receptor types have been reported, but the localization of the Mel1b receptor, which is the most highly expressed melatonin receptor type in the retina, is unknown. To determine the cellular distribution of Mel1b melatonin receptor protein in the Xenopus laevis retina and other ocular tissues, polyclonal antibodies were raised against a peptide fragment of the X. laevis Mel1b receptor. Western blot analysis of several ocular tissues revealed the presence of one or more immunoreactive bands in the sclera, cornea, lens, retinal pigment epithelium (RPE)/choroid, and neural retina. In the neural retina, the major immunoreactive bands displayed electrophoretic mobilities corresponding to approximately 35, 42, 45, and 80 Kd. Sections of X. laevis eyes were analyzed by immunocytochemistry and confocal microscopy, in combination with antibodies against the Mel1a melatonin receptor, a rod photoreceptor-specific protein, opsin, and two amacrine cell-specific markers, tyrosine hydroxylase (TOH; dopaminergic cells) and glutamic acid decarboxylase (GAD; GABA-ergic cells). Mel1b immunoreactivity was localized to the apical membranes of RPE cells, and punctate Mel1b immunoreactivity was observed in both rod and cone photoreceptor inner segments. Presumptive horizontal cells that ramify in the outer plexiform layer (OPL) were immunoreactive for Mel1b, and were exclusive of the Mel1a immunoreactivity present in the OPL. Neither TOH nor GAD co-localized with the Mel1b immunoreactivity that was present in the inner plexiform layer (IPL), suggesting that Mel1b is not expressed in dopaminergic or GABA-ergic amacrine cells. Mel1b immunoreactivity was observed in ganglion cells of the retina, a population of cells covering the outer surface of the outer fibrous layer of the sclera, and in lens fibers located in the outer regions of the lens. These results suggest that melatonin may influence retinal function by binding to receptors on RPE and photoreceptor cells, and by acting on neurons of the inner retina that do not use dopamine or GABA as a neurotransmitter. Furthermore, melatonin may bind to receptors on cells located in the sclera and lens, perhaps to modify the growth or function of these ocular tissues.
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Affiliation(s)
- Allan F Wiechmann
- Department of Cell Biology, University of Oklahoma Health Sciences Center, P.O. Box 26901, Oklahoma City, OK 73190, USA.
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Abstract
The scornea and sclera have been shown to exhibit circadian rhythms in cellular proliferation, wound healing and extracellular matrix synthesis. The distribution of melatonin Mel1a and Mel1c receptors was examined in the cornea and sclera of the Xenopus laevis eye in order to determine whether melatonin may potentially influence the growth and/or development of these ocular tissues. Sections of adult X. laevis eyes were analyzed by immunocytochemistry and confocal microscopy, using antibodies prepared against specific peptide sequences of the Xenopus Mel1a and Mel1c receptor proteins. Antibodies were pre- incubated with their appropriate antigenic peptides to control for non-specific labelling. Analysis of the distribution of Mel1a and Mel1c receptor immunoreactivity in the Xenopus eye revealed that both the Mel1a and Mel1c receptors were located in the outer fibrous layer (OFL) of the sclera, with Mel1c labelling being the most prominent. Similarly, Mel1a and Mel1c (Mel1c mostly) were also located in cells of the inner fibrous layer (IFL) with Mel1c being most abundant. The chondrocytes of the cartilaginous layer also appeared to express Mel1a, Mel1c, or both receptors. Both Mel1a and Mel1c receptor immunoreactivity were observed in the corneal epithelium and endothelium. Whereas the Mel1a antibody labelled the entire corneal epithelial layer, the Mel1c antibody labelled only the most superficial layer of epithelial cells. Cell processes of fibroblasts of the corneal stroma were immunoreactive for either Mel1a or Mel1c receptors. The identification of Mel1a and Mel1c receptors in restricted distributions in the cornea and sclera suggests that melatonin may play a role in the cellular physiology of these ocular tissues.
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Affiliation(s)
- Allan F Wiechmann
- Department of Cell Biology, Health Sciences Center, University of Oklahoma, PO Box 26901, Oklahoma City, OK 73190, USA.
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