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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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Baba K, Tosini G. Assessing the Role of Melatonin in the Modulation of Visual Functions in the Mouse. Methods Mol Biol 2022; 2550:377-389. [PMID: 36180707 DOI: 10.1007/978-1-0716-2593-4_38] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The electroretinogram (ERG) is a noninvasive method to evaluate retinal function. It can be applied to patients to be diagnosed a variety of retinal pathologies such as photoreceptor dystrophy, diabetic retinopathy, macular degeneration, and glaucoma. ERG has also been a reliable tool to assess retinal functions in animal studies that range from fish to humans. Melatonin is a neurohormone that regulates several retinal functions within the retina, and previous studies have shown that melatonin plays an important role in the modulation of the ERG in humans and other vertebrates. This chapter describes experimental methods to evaluate retinal function using ERG in the mouse and how to assess the contribution of melatonin. An introduction is provided for materials, environmental settings, recording procedures, and analysis necessary for ERG measurements.
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Affiliation(s)
- Kenkichi Baba
- Department of Pharmacology & Toxicology, Morehouse School of Medicine, Atlanta, GA, USA.
| | - Gianluca Tosini
- Department of Pharmacology & Toxicology, Morehouse School of Medicine, Atlanta, GA, USA
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3
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Ko GYP. Circadian regulation in the retina: From molecules to network. Eur J Neurosci 2020; 51:194-216. [PMID: 30270466 PMCID: PMC6441387 DOI: 10.1111/ejn.14185] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Revised: 08/16/2018] [Accepted: 08/20/2018] [Indexed: 12/14/2022]
Abstract
The mammalian retina is the most unique tissue among those that display robust circadian/diurnal oscillations. The retina is not only a light sensing tissue that relays light information to the brain, it has its own circadian "system" independent from any influence from other circadian oscillators. While all retinal cells and retinal pigment epithelium (RPE) possess circadian oscillators, these oscillators integrate by means of neural synapses, electrical coupling (gap junctions), and released neurochemicals (such as dopamine, melatonin, adenosine, and ATP), so the whole retina functions as an integrated circadian system. Dysregulation of retinal clocks not only causes retinal or ocular diseases, it also impacts the circadian rhythm of the whole body, as the light information transmitted from the retina entrains the brain clock that governs the body circadian rhythms. In this review, how circadian oscillations in various retinal cells are integrated, and how retinal diseases affect daily rhythms.
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Affiliation(s)
- Gladys Y-P Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas
- Texas A&M Institute for Neuroscience, Texas A&M University, College Station, Texas
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4
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Osier ND, Pham L, Pugh BJ, Puccio A, Ren D, Conley YP, Alexander S, Dixon CE. Brain injury results in lower levels of melatonin receptors subtypes MT1 and MT2. Neurosci Lett 2017; 650:18-24. [PMID: 28377323 DOI: 10.1016/j.neulet.2017.03.053] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 03/29/2017] [Accepted: 03/31/2017] [Indexed: 02/09/2023]
Abstract
BACKGROUND Traumatic brain injury (TBI) is a devastating and costly acquired condition that affects individuals of all ages, races, and geographies via a number of mechanisms. The effects of TBI on melatonin receptors remain unknown. PURPOSE The purpose of this study is to explore whether endogenous changes in two melatonin receptor subtypes (MT1 and MT2) occur after experimental TBI. SAMPLE A total of 25 adult male Sprague Dawley rats were used with 6 or 7 rats per group. METHODS Rats were randomly assigned to receive either TBI modeled using controlled cortical impact or sham surgery and to be sacrificed at either 6- or 24-h post-operatively. Brains were harvested, dissected, and flash frozen until whole cell lysates were prepared, and the supernatant fluid aliquoted and used for western blotting. Primary antibodies were used to probe for melatonin receptors (MT1 and MT2), and beta actin, used for a loading control. ImageJ and Image Lab software were used to quantify the data which was analyzed using t-tests to compare means. RESULTS Melatonin receptor levels were reduced in a brain region- and time point- dependent manner. Both MT1 and MT2 were reduced in the frontal cortex at 24h and in the hippocampus at both 6h and 24h. DISCUSSION MT1 and MT2 are less abundant after injury, which may alter response to MEL therapy. Studies characterizing MT1 and MT2 after TBI are needed, including exploration of the time course and regional patterns, replication in diverse samples, and use of additional variables, especially sleep-related outcomes. CONCLUSION TBI in rats resulted in lower levels of MT1 and MT2; replication of these findings is necessary as is evaluation of the consequences of lower receptor levels.
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Affiliation(s)
- Nicole D Osier
- University of Pittsburgh School of Nursing, Victoria Building, 3500 Victoria Street, Pittsburgh, PA, 15213, USA; Safar Center for Resuscitation Research, Children's Hospital of Pittsburgh of UPMC, John G. Rangos Research, Center - 6th floor, 4401 Penn Avenue, Pittsburgh, PA, 15224, USA.
| | - Lan Pham
- University of Pittsburgh School of Nursing, Victoria Building, 3500 Victoria Street, Pittsburgh, PA, 15213, USA.
| | - Bunny J Pugh
- Safar Center for Resuscitation Research, Children's Hospital of Pittsburgh of UPMC, John G. Rangos Research, Center - 6th floor, 4401 Penn Avenue, Pittsburgh, PA, 15224, USA.
| | - Ava Puccio
- University of Pittsburgh School of Nursing, Victoria Building, 3500 Victoria Street, Pittsburgh, PA, 15213, USA; University of Pittsburgh Department of Neurological Surgery, Brain Trauma Research Center, UPMC Presbyterian, Suite B-400, 200 Lothrop Street, Pittsburgh, PA, 15213, USA.
| | - Dianxu Ren
- University of Pittsburgh School of Nursing, Victoria Building, 3500 Victoria Street, Pittsburgh, PA, 15213, USA.
| | - Yvette P Conley
- University of Pittsburgh School of Nursing, Victoria Building, 3500 Victoria Street, Pittsburgh, PA, 15213, USA; University of Pittsburgh Department of Human Genetics, Crabtree Hall, 130 De Soto Street, Pittsburgh, PA, 15261, USA.
| | - Sheila Alexander
- University of Pittsburgh School of Nursing, Victoria Building, 3500 Victoria Street, Pittsburgh, PA, 15213, USA; University of Pittsburgh School of Medicine, M240 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA, 15261, USA.
| | - C Edward Dixon
- Safar Center for Resuscitation Research, Children's Hospital of Pittsburgh of UPMC, John G. Rangos Research, Center - 6th floor, 4401 Penn Avenue, Pittsburgh, PA, 15224, USA; University of Pittsburgh Department of Neurological Surgery, Brain Trauma Research Center, UPMC Presbyterian, Suite B-400, 200 Lothrop Street, Pittsburgh, PA, 15213, USA; VA Pittsburgh Healthcare System, 4100 Allequippa St, Pittsburgh, PA, 15261, USA.
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5
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Abstract
Retinas of all classes of vertebrates contain endogenous circadian clocks that control many aspects of retinal physiology, including retinal sensitivity to light, neurohormone synthesis, and cellular events such as rod disk shedding, intracellular signaling pathways, and gene expression. The vertebrate retina is an example of a “peripheral” oscillator that is particularly amenable to study because this tissue is well characterized, the relationships between the various cell types are extensively studied, and many local clock-controlled rhythms are known. Although the existence of a photoreceptor clock is well established in several species, emerging data are consistent with multiple or dual oscillators within the retina that interact to control local physiology. Aprominent example is the antiphasic regulation of melaton in and dopamine in photoreceptors and inner retina, respectively. This review focuses on the similarities and differences in the molecular mechanisms of the retinal versus the SCN oscillators, as well as on the expression of core components of the circadian clockwork in retina. Finally, the interactions between the retinal clock(s) and the master clock in the SCN are examined.
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Affiliation(s)
- Carla B Green
- Department of Biology, University of Virginia, Charlottesville, VA 22904, USA.
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6
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Tian N, Xu HP, Wang P. Dopamine D2 receptors preferentially regulate the development of light responses of the inner retina. Eur J Neurosci 2014; 41:17-30. [PMID: 25393815 DOI: 10.1111/ejn.12783] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 09/25/2014] [Accepted: 10/13/2014] [Indexed: 01/14/2023]
Abstract
Retinal light responsiveness measured via electroretinography undergoes developmental modulation, and is thought to be critically regulated by both visual experience and dopamine. The primary goal of this study was to determine whether dopamine D2 receptors regulate the visual experience-dependent functional development of the retina. Accordingly, we recorded electroretinograms from wild-type mice and mice with a genetic deletion of the gene that encodes the D2 receptor raised under normal cyclic light conditions and constant darkness. Our results demonstrate that D2 receptor mutation preferentially increases the amplitude of the inner retinal light responses evoked by high-intensity light measured as oscillatory potentials in adult mice. During postnatal development, all three major components of electroretinograms, i.e. a-waves, b-waves, and oscillatory potentials, increase with age. Comparatively, D2 receptor mutation preferentially reduces the age-dependent increase in b-waves evoked by low-intensity light. Light deprivation from birth reduces b-wave amplitudes and completely abolishes the increased amplitude of oscillatory potentials of D2 receptor mutants. Taken together, these results demonstrate that D2 receptors play an important role in the activity-dependent functional development of the mouse retina.
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Affiliation(s)
- Ning Tian
- Department of Ophthalmology and Visual Science, University of Utah School of Medicine, Salt Lake City, UT, 84132, USA
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7
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Popova E. Role of dopamine in distal retina. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2014; 200:333-58. [PMID: 24728309 DOI: 10.1007/s00359-014-0906-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 03/24/2014] [Accepted: 03/25/2014] [Indexed: 01/11/2023]
Abstract
Dopamine is the most abundant catecholamine in the vertebrate retina. Despite the description of retinal dopaminergic cells three decades ago, many aspects of their function in the retina remain unclear. There is no consensus among the authors about the stimulus conditions for dopamine release (darkness, steady or flickering light) as well as about its action upon the various types of retinal cells. Many contradictory results exist concerning the dopamine effect on the gross electrical activity of the retina [reflected in electroretinogram (ERG)] and the receptors involved in its action. This review summarized current knowledge about the types of the dopaminergic neurons and receptors in the retina as well as the effects of dopamine receptor agonists and antagonists on the light responses of photoreceptors, horizontal and bipolar cells in both nonmammalian and mammalian retina. Special focus of interest concerns their effects upon the diffuse ERG as a useful tool for assessment of the overall function of the distal retina. An attempt is made to reveal some differences between the dopamine actions upon the activity of the ON versus OFF channel in the distal retina. The author has included her own results demonstrating such differences.
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Affiliation(s)
- E Popova
- Department of Physiology, Medical Faculty, Medical University, 1431, Sofia, Bulgaria,
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8
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He Q, Xu HP, Wang P, Tian N. Dopamine D1 receptors regulate the light dependent development of retinal synaptic responses. PLoS One 2013; 8:e79625. [PMID: 24260267 PMCID: PMC3834122 DOI: 10.1371/journal.pone.0079625] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Accepted: 10/02/2013] [Indexed: 12/30/2022] Open
Abstract
Retinal synaptic connections and function are developmentally regulated. Retinal synaptic activity plays critical roles in the development of retinal synaptic circuitry. Dopamine receptors have been thought to play important roles in the activity-dependent synaptic plasticity in central nervous system. The primary goal of this study is to determine whether dopamine D1 receptor regulates the activity-dependent development of retinal light responsiveness. Accordingly, we recorded electroretinogram from wild type mice and mice with genetic deletion of D1 dopamine receptor (D1-/- mice) raised under cyclic light conditions and constant darkness. Our results demonstrated that D1-/- mice have reduced amplitudes of all three major components of electroretinogram in adulthood. When the relative strength of the responses is considered, the D1-/- mice have selective reduction of the amplitudes of a-wave and oscillatory potentials evoked by low-intermediate intensities of lights. During postnatal development, D1-/- mice have increased amplitude of b-wave at the time of eye-opening but reduced developmental increase of the amplitude of b-wave after eye opening. Light deprivation from birth significantly reduced the amplitudes of b-wave and oscillatory potentials, increased the outer retinal light response gain and altered the light response kinetics of both a- and b-waves of wild type mice. In D1-/- mice, the effect of dark rearing on the amplitude of oscillatory potentials was diminished and dark rearing induced effects on the response gain of outer retina and the kinetics of a-wave were reversed. These results demonstrated roles of dopamine D1 receptor in the activity-dependent functional development of mouse retina.
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Affiliation(s)
- Quanhua He
- College of Pharmacy, The Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio, United States of America
| | - Hong-ping Xu
- Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Ping Wang
- Department of Ophthalmology and Visual Science, University of Utah School of Medicine, Salt Lake City, Utah, United States of America
| | - Ning Tian
- Department of Ophthalmology and Visual Science, University of Utah School of Medicine, Salt Lake City, Utah, United States of America
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9
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Kovacic P, Somanathan R. Cell signaling, receptors, electrical effects and therapy in circadian rhythm. J Recept Signal Transduct Res 2013; 33:267-75. [PMID: 23914781 DOI: 10.3109/10799893.2013.822890] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Circadian rhythm has been the object of much attention. This review addresses the aspects of cell signaling, receptors, therapy and electrical effects in a multifaceted fashion. The pineal gland, which produces the important hormones melatonin and serotonin, exerts a prominent influence, in addition to the supraschiasmatic nucleus. Many aspects involve free radicals which have played a widespread role in biochemistry.
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Affiliation(s)
- Peter Kovacic
- Department of Chemistry and Biochemistry, San Diego State University, San Diego , CA , USA and
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10
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Lavoie J, Rosolen SG, Chalier C, Hébert M. Negative impact of melatonin ingestion on the photopic electroretinogram of dogs. Neurosci Lett 2013; 543:78-83. [PMID: 23562505 DOI: 10.1016/j.neulet.2013.02.070] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Revised: 01/22/2013] [Accepted: 02/19/2013] [Indexed: 10/27/2022]
Abstract
Melatonin follows a circadian rhythm entrained by the light/dark cycle and plays a role in promoting light sensitivity at night. It has been suggested that melatonin and dopamine reciprocal inhibition may contribute to the switch between day and night vision. The purpose of this study was to investigate the impact of a high dose of melatonin administration on the photopic and scotopic electroretinogram (ERG) of dogs in the daytime, when it is not thought to be present. Photopic and scotopic ERG luminance response functions were obtained from 7 anaesthetized beagle dogs (3 males and 4 females), once without melatonin (control) and once after oral administration of melatonin (90 mg/dog). Vmax (maximal b-wave amplitude achieved) and logK (retinal sensitivity) were calculated from the derived luminance response function. Photopic flicker ERG was also recorded. In photopic condition, a-wave amplitude (control: -126.90 μV; with melatonin: -49.64 μV; p<0.001) and Vmax (control: 252.50 μV; with melatonin: 115.40 μV; p<0.001) were decreased. A significant reduction of the photopic flicker ERG amplitude was observed after melatonin ingestion. In scotopic condition, an overall difference was reported before and after melatonin ingestion for the a- and b-wave amplitude, but no change was significant for Vmax. Melatonin ingestion at a high dose during the day decreases the photopic amplitude of a- and b-wave, but has no impact on implicit time. This negative impact of melatonin on photopic system may serve to promote night vision.
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Affiliation(s)
- Joëlle Lavoie
- Centre de recherche de l'Institut Universitaire en santé mentale de Québec, Quebec City, 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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12
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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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Martins J, Castelo-Branco M, Batista A, Oliveiros B, Santiago AR, Galvão J, Fernandes E, Carvalho F, Cavadas C, Ambrósio AF. Effects of 3,4-methylenedioxymethamphetamine administration on retinal physiology in the rat. PLoS One 2011; 6:e29583. [PMID: 22216322 PMCID: PMC3246479 DOI: 10.1371/journal.pone.0029583] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Accepted: 11/30/2011] [Indexed: 01/28/2023] Open
Abstract
3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is known to produce euphoric states, but may also cause adverse consequences in humans, such as hyperthermia and neurocognitive deficits. Although MDMA consumption has been associated with visual problems, the effects of this recreational drug in retinal physiology have not been addressed hitherto. In this work, we evaluated the effect of a single MDMA administration in the rat electroretinogram (ERG). Wistar rats were administered MDMA (15 mg/kg) or saline and ERGs were recorded before (Baseline ERG), and 3 h, 24 h, and 7 days after treatment. A high temperature (HT) saline-treated control group was also included. Overall, significantly augmented and shorter latency ERG responses were found in MDMA and HT groups 3 h after treatment when compared to Baseline. Twenty-four hours after treatment some of the alterations found at 3 h, mainly characterized by shorter latency, tended to return to Baseline values. However, MDMA-treated animals still presented increased scotopic a-wave and b-wave amplitudes compared to Baseline ERGs, which were independent of temperature elevation though the latter might underlie the acute ERG alterations observed 3 h after MDMA administration. Seven days after MDMA administration recovery from these effects had occurred. The effects seem to stem from specific changes observed at the a-wave level, which indicates that MDMA affects subacutely (at 24 h) retinal physiology at the outer retinal (photoreceptor/bipolar) layers. In conclusion, we have found direct evidence that MDMA causes subacute enhancement of the outer retinal responses (most prominent in the a-wave), though ERG alterations resume within one week. These changes in photoreceptor/bipolar cell physiology may have implications for the understanding of the subacute visual manifestations induced by MDMA in humans.
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Affiliation(s)
- João Martins
- Centre of Ophthalmology and Vision Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
- Centre for Neuroscience and Cell Biology (CNC), University of Coimbra, Coimbra, Portugal
| | - Miguel Castelo-Branco
- Centre of Ophthalmology and Vision Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
| | - Ana Batista
- Centre of Ophthalmology and Vision Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
| | - Bárbara Oliveiros
- Centre of Ophthalmology and Vision Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
| | - Ana Raquel Santiago
- Centre of Ophthalmology and Vision Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
| | - Joana Galvão
- Centre of Ophthalmology and Vision Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
| | - Eduarda Fernandes
- REQUIMTE - Laboratory of Toxicology, Department of Biological Sciences, Faculty of Pharmacy, University of Porto, Porto, Portugal
| | - Félix Carvalho
- REQUIMTE - Department of Chemical Sciences, Faculty of Pharmacy, University of Porto, Porto, Portugal
| | - Cláudia Cavadas
- Centre for Neuroscience and Cell Biology (CNC), University of Coimbra, Coimbra, Portugal
- Faculty of Pharmacy, University of Coimbra, Coimbra, Portugal
| | - António F. Ambrósio
- Centre of Ophthalmology and Vision Sciences, IBILI, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
- Centre for Neuroscience and Cell Biology (CNC), University of Coimbra, Coimbra, Portugal
- AIBILI, Coimbra, Portugal
- * E-mail:
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Fornaro M, Bandini F, Ogliastro C, Cordano C, Martino M, Cestari L, Escelsior A, Rocchi G, Colicchio S, Perugi G. Electroretinographic assessment in major depressed patients receiving duloxetine: might differences between responders and non-responders indicate a differential biological background? J Affect Disord 2011; 135:154-9. [PMID: 21820182 DOI: 10.1016/j.jad.2011.07.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Revised: 07/13/2011] [Accepted: 07/14/2011] [Indexed: 11/19/2022]
Abstract
INTRODUCTION Despite intense research efforts, still too little is known about the biological determinants of depression, thus soliciting diverse study approaches. Among others, the electroretinography (ERG) has been proposed even as a putative proxy (retinal) measurement of central dopaminergic activity for Major Depressive Disorder (MDD) both in drug-naïve patients and subjects receiving antidepressant treatments. Nonetheless, current evidences are merely preliminary, essentially considering just older classes of antidepressants, thus requiring confirmation studies even with newer agents as duloxetine. METHOD Twenty MDD subjects and 20 matched controls received duloxetine 60 mg/day for 12 weeks, being monitored both by standard ERG recording and by administration of the Hamilton scales for Depression and Anxiety and the Young Mania Rating Scale at baseline and week 12 (end of the study). RESULTS ERG mean rod b-wave amplitude significantly reduced from baseline to week 12 in those depressed subjects achieving final response (p=.024), decreasing from the highest rank values to the ones, substantially unmodified, seen among non-responders and controls. LIMITATIONS Small sample size and lack of multiple assessments. CONCLUSIONS At least some MDD patients responding to duloxetine might exhibit a peculiar ERG pattern, hypothetically indicating a specific biological background. If confirmed by larger-sampled studies, these results might shed further light in the understanding of the biological determinants of different subtypes of depression, ideally showing alternative patterns of response upon different treatment interventions.
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Affiliation(s)
- Michele Fornaro
- Department of Neurosciences, Ophthalmology and Genetics - Section of Psychiatry, University of Genova, Italy.
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15
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Danilenko KV, Plisov IL, Cooper HM, Wirz-Justice A, Hébert M. Human Cone Light Sensitivity and Melatonin Rhythms Following 24-hour Continuous Illumination. Chronobiol Int 2011; 28:407-14. [DOI: 10.3109/07420528.2011.567425] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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16
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Circadian variation in the electroretinogram and the presence of central melatonin. Doc Ophthalmol 2010; 120:265-72. [DOI: 10.1007/s10633-010-9221-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Accepted: 01/31/2010] [Indexed: 10/19/2022]
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17
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MT2-like melatonin receptor modulates amplitude receptor potential in visual cells of crayfish during a 24-hour cycle. Comp Biochem Physiol A Mol Integr Physiol 2009; 154:486-92. [DOI: 10.1016/j.cbpa.2009.07.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2009] [Revised: 07/29/2009] [Accepted: 07/30/2009] [Indexed: 11/17/2022]
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Gagné AM, Danilenko KV, Rosolen SG, Hébert M. Impact of oral melatonin on the electroretinogram cone response. J Circadian Rhythms 2009; 7:14. [PMID: 19922677 PMCID: PMC2785757 DOI: 10.1186/1740-3391-7-14] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Accepted: 11/19/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In the eye, melatonin plays a role in promoting light sensitivity at night and modulating many aspects of circadian retinal physiology. It is also an inhibitor of retinal dopamine, which is a promoter of day vision through the cone system. Consequently, it is possible that oral melatonin (an inhibitor of retinal dopamine) taken to alleviate circadian disorders may affect cone functioning. Our aim was to assess the impact of melatonin on the cone response of the human retina using electroretinography (ERG). METHODS Twelve healthy participants aged between 18 to 52 years old were submitted to a placebo-controlled, double-blind, crossover, and counterbalanced-order design. The subjects were tested on 2 sessions beginning first with a baseline ERG, followed by the administration of the placebo or melatonin condition and then, 30 min later, a second ERG to test the effect. RESULTS Following oral melatonin administration, a significant decrease of about 8% of the cone maximal response was observed (mean 6.9 muV +/- SEM 2.0; P = 0.0065) along with a prolonged b-wave implicit time of 0.4 ms +/- 0.1, 50 minutes after ingestion. CONCLUSION Oral melatonin appears to reach the eye through the circulation. When it is administered at a time of day when it is not usually present, melatonin appears to reduce input to retinal cones. We believe that the impact of melatonin on retinal function should be taken into consideration when used without supervision in chronic self-medication for sleep or circadian disorder treatment.
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Affiliation(s)
- Anne-Marie Gagné
- Centre de Recherche Université Laval Robert-Giffard, Faculty of Medicine, Université Laval, Québec, Canada.
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19
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Baba K, Pozdeyev N, Mazzoni F, Contreras-Alcantara S, Liu C, Kasamatsu M, Martinez-Merlos T, Strettoi E, Iuvone PM, Tosini G. Melatonin modulates visual function and cell viability in the mouse retina via the MT1 melatonin receptor. Proc Natl Acad Sci U S A 2009; 106:15043-8. [PMID: 19706469 PMCID: PMC2736407 DOI: 10.1073/pnas.0904400106] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2009] [Indexed: 11/18/2022] Open
Abstract
A clear demonstration of the role of melatonin and its receptors in specific retinal functions is lacking. The present study investigated the distribution of MT1 receptors within the retina, and the scotopic and photopic electroretinograms (ERG) and retinal morphology in wild-type (WT) and MT1 receptor-deficient mice. MT1 receptor transcripts were localized in photoreceptor cells and in some inner retinal neurons. A diurnal rhythm in the dark-adapted ERG responses was observed in WT mice, with higher a- and b-wave amplitudes at night, but this rhythm was absent in mice lacking MT1 receptors. Injection of melatonin during the day decreased the scotopic response threshold and the amplitude of the a- and b-waves in the WT mice, but not in the MT1(-/-) mice. The effects of MT1 receptor deficiency on retinal morphology was investigated at three different ages (3, 12, and 18 months). No differences between MT1(-/-) and WT mice were observed at 3 months of age, whereas at 12 months MT1(-/-) mice have a significant reduction in the number of photoreceptor nuclei in the outer nuclear layer compared with WT controls. No differences were observed in the number of cells in inner nuclear layer or in ganglion cells at 12 months of age. At 18 months, the loss of photoreceptor nuclei in the outer nuclear layer was further accentuated and the number of ganglion cells was also significantly lower than that of controls. These data demonstrate the functional significance of melatonin and MT1 receptors in the mammalian retina and create the basis for future studies on the therapeutic use of melatonin in retinal degeneration.
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MESH Headings
- Adaptation, Biological
- Aging
- Animals
- Cell Survival
- Darkness
- Electroretinography
- Gene Expression Regulation
- Melatonin/metabolism
- Mice
- Mice, Knockout
- RNA, Messenger/genetics
- Receptor, Melatonin, MT1/deficiency
- Receptor, Melatonin, MT1/genetics
- Receptor, Melatonin, MT1/metabolism
- Retina/cytology
- Retina/metabolism
- Retinal Degeneration/metabolism
- Retinal Degeneration/therapy
- Vision, Ocular
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Affiliation(s)
- Kenkichi Baba
- Neuroscience Institute, Morehouse School of Medicine, Atlanta, GA 30310
| | - Nikita Pozdeyev
- Departments of Ophthalmology and Pharmacology, Emory University School of Medicine, Atlanta, GA 30322; and
| | - Francesca Mazzoni
- Istituto di Neuroscience, Consiglio Nazionale delle Ricerche, Pisa 56100, Italy
| | | | - Cuimei Liu
- Neuroscience Institute, Morehouse School of Medicine, Atlanta, GA 30310
| | - Manami Kasamatsu
- Neuroscience Institute, Morehouse School of Medicine, Atlanta, GA 30310
| | | | - Enrica Strettoi
- Istituto di Neuroscience, Consiglio Nazionale delle Ricerche, Pisa 56100, Italy
| | - P. Michael Iuvone
- Departments of Ophthalmology and Pharmacology, Emory University School of Medicine, Atlanta, GA 30322; and
| | - Gianluca Tosini
- Neuroscience Institute, Morehouse School of Medicine, Atlanta, GA 30310
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20
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Danilenko KV, Plisov IL, Wirz‐Justice A, Hébert M. Human Retinal Light Sensitivity and Melatonin Rhythms Following Four Days in Near Darkness. Chronobiol Int 2009; 26:93-107. [DOI: 10.1080/07420520802689814] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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21
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Abstract
Ion channels are the gatekeepers to neuronal excitability. Retinal neurons of vertebrates and invertebrates, neurons of the suprachiasmatic nucleus (SCN) of vertebrates, and pinealocytes of non-mammalian vertebrates display daily rhythms in their activities. The interlocking transcription-translation feedback loops with specific post-translational modulations within individual cells form the molecular clock, the basic mechanism that maintains the autonomic approximately 24-h rhythm. The molecular clock regulates downstream output signaling pathways that further modulate activities of various ion channels. Ultimately, it is the circadian regulation of ion channel properties that govern excitability and behavior output of these neurons. In this review, we focus on the recent development of research in circadian neurobiology mainly from 1980 forward. We will emphasize the circadian regulation of various ion channels, including cGMP-gated cation channels, various voltage-gated calcium and potassium channels, Na(+)/K(+)-ATPase, and a long-opening cation channel. The cellular mechanisms underlying the circadian regulation of these ion channels and their functions in various tissues and organisms will also be discussed. Despite the magnitude of chronobiological studies in recent years, the circadian regulation of ion channels still remains largely unexplored. Through more investigation and understanding of the circadian regulation of ion channels, the future development of therapeutic strategies for the treatment of sleep disorders, cardiovascular diseases, and other illnesses linked to circadian misalignment will benefit.
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Affiliation(s)
- Gladys Y-P Ko
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77843-4458, USA.
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22
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Ko ML, Jian K, Shi L, Ko GYP. Phosphatidylinositol 3 kinase-Akt signaling serves as a circadian output in the retina. J Neurochem 2009; 108:1607-20. [PMID: 19166512 DOI: 10.1111/j.1471-4159.2009.05931.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The daily rhythm of L-type voltage-gated calcium channels (L-VGCCs) is part of the cellular mechanism underlying the circadian regulation of retina physiology and function. However, it is not completely understood how the circadian clock regulates L-VGCC current amplitudes without affecting channel gating properties. The phosphatidylinositol 3 kinase-protein kinase B (PI3K-Akt) signaling pathway has been implicated in many vital cellular functions especially in trophic factor-induced ion channel trafficking and membrane insertion. Here, we report that PI3K-Akt signaling participates in the circadian phase-dependent modulation of L-VGCCs. We found that there was a circadian regulation of Akt phosphorylation on Thr308 that peaked at night. Inhibition of PI3K or Akt significantly decreased L-VGCC current amplitudes and the expression of membrane-bound L-VGCCalpha1D subunit only at night but not during the subjective day. Photoreceptors transfected with a dominant negative Ras had significantly less expression of phosphorylated Akt and L-VGCCalpha1D subunit compared with non-transfected photoreceptors. Interestingly, both PI3K-Akt and extracellular signal-related kinase were downstream of Ras, and they appeared to be parallel and equally important pathways to regulate L-VGCC rhythms. Inhibition of either pathway abolished the L-VGCC rhythm indicating that there were multiple mechanisms involved in the circadian regulation of L-VGCC rhythms in retina photoreceptors.
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Affiliation(s)
- Michael L Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA
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23
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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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24
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Bartell PA, Miranda-Anaya M, McIvor W, Menaker M. Interactions between dopamine and melatonin organize circadian rhythmicity in the retina of the green iguana. J Biol Rhythms 2008; 22:515-23. [PMID: 18057326 DOI: 10.1177/0748730407308167] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Circadian physiology in the vertebrate retina is regulated by several neurotransmitters. In the lateral eyes of the green iguana the circadian rhythm of melatonin content peaks during the night while the rhythm of dopamine peaks during the day. In the present work, the authors explore the interaction of these 2 neurotransmitters during the circadian cycle. They depleted retinal dopamine with intravitreal injections of 6-hydroxydopamine (6-OHDA) and measured ocular melatonin content in vivo throughout 1 circadian cycle. The circadian rhythm of ocular melatonin not only persisted but increased 10-fold in amplitude. This increase was substantially reduced by the intraocular administration of dopamine. 6-OHDA-treated retinas, unlike those from untreated animals, did not express a circadian rhythm of melatonin synthesis in vitro. To deplete retinal melatonin, the authors pinealectomized iguanas and blocked retinal melatonin synthesis by depleting serotonin with intraocular injections of 5,6-dihydroxytryptamine. In animals so treated, they found that the circadian rhythm of retinal dopamine content was abolished, the levels of dopamine were lowered, and the levels of dopamine metabolites were greatly increased. The data suggest that in iguanas, the amplitude of the circadian rhythm of melatonin synthesis in the eye is suppressed by dopamine while the rhythm of dopamine depends, at least in part, on the presence of melatonin.
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Affiliation(s)
- Paul A Bartell
- Department of Biology, University of Virginia, Charlottesville, VA 22903, USA.
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25
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Storch KF, Paz C, Signorovitch J, Raviola E, Pawlyk B, Li T, Weitz CJ. Intrinsic circadian clock of the mammalian retina: importance for retinal processing of visual information. Cell 2007; 130:730-741. [PMID: 17719549 PMCID: PMC2040024 DOI: 10.1016/j.cell.2007.06.045] [Citation(s) in RCA: 342] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2007] [Revised: 04/27/2007] [Accepted: 06/18/2007] [Indexed: 10/22/2022]
Abstract
Circadian clocks are widely distributed in mammalian tissues, but little is known about the physiological functions of clocks outside the suprachiasmatic nucleus of the brain. The retina has an intrinsic circadian clock, but its importance for vision is unknown. Here we show that mice lacking Bmal1, a gene required for clock function, had abnormal retinal transcriptional responses to light and defective inner retinal electrical responses to light, but normal photoreceptor responses to light and retinas that appeared structurally normal by light and electron microscopy. We generated mice with a retina-specific genetic deletion of Bmal1, and they had defects of retinal visual physiology essentially identical to those of mice lacking Bmal1 in all tissues and lacked a circadian rhythm of inner retinal electrical responses to light. Our findings indicate that the intrinsic circadian clock of the retina regulates retinal visual processing in vivo.
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Affiliation(s)
- Kai-Florian Storch
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Carlos Paz
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - James Signorovitch
- Department of Biostatistics, Harvard School of Public Health, Boston, MA 02115, USA
| | - Elio Raviola
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Basil Pawlyk
- Massachusetts Eye & Ear Infirmary, Berman-Gund Laboratory, Department of Ophthalmology, Harvard Medical School, Boston MA 02114, USA
| | - Tiansen Li
- Massachusetts Eye & Ear Infirmary, Berman-Gund Laboratory, Department of Ophthalmology, Harvard Medical School, Boston MA 02114, USA
| | - Charles J Weitz
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
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26
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Ko ML, Liu Y, Dryer SE, Ko GYP. The expression of L-type voltage-gated calcium channels in retinal photoreceptors is under circadian control. J Neurochem 2007; 103:784-92. [PMID: 17683482 DOI: 10.1111/j.1471-4159.2007.04816.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Photoreceptors are non-spiking neurons, and their synapses mediate the continuous release of neurotransmitters under the control of L-type voltage-gated calcium channels (VGCCs). Photoreceptors express endogenous circadian oscillators that play important roles in regulating photoreceptor physiology and function. Here, we report that the L-type VGCCs in chick cone photoreceptors are under circadian control. The L-type VGCC currents are greater when measured during the subjective night than during the subjective day. Using antibodies against the VGCCalpha1C and VGCCalpha1D subunits, we found that the immunofluorescence intensities of both VGCCalpha1C and VGCCalpha1D in photoreceptors are higher during the subjective night. However, the mRNA levels of VGCCalpha1D, but not VGCCalpha1C, are rhythmic. Nocturnal increases in L-type VGCCs are blocked by manumycin A, PD98059, and KN93, which suggest that the circadian output pathway includes Ras, Erk, and calcium-calmodulin dependent kinase II. In summary, four independent lines of evidence show that the L-VGCCs in cone photoreceptors are under circadian control.
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Affiliation(s)
- Michael L Ko
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas 77843, USA
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27
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Storch KF, Paz C, Signorovitch J, Raviola E, Pawlyk B, Li T, Weitz CJ. Physiological importance of a circadian clock outside the suprachiasmatic nucleus. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2007; 72:307-18. [PMID: 18419288 DOI: 10.1101/sqb.2007.72.053] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Circadian clocks are widely distributed in mammalian tissues, but little is known about the physiological functions of clocks outside the suprachiasmatic nucleus of the brain. The retina has an intrinsic circadian clock, but its importance for vision is unknown. Here, we show that mice lacking Bmal1, a gene required for clock function, had abnormal retinal transcriptional responses to light and defective inner retinal electrical responses to light, but normal photoreceptor responses to light and retinas that appeared structurally normal as observed by light and electron microscopy. We generated mice with a retina-specific genetic deletion of Bmal1, and they had defects of retinal visual physiology essentially identical to those of mice lacking Bmal1 in all tissues and lacked a circadian rhythm of inner retinal electrical responses to light. Our findings indicate that the intrinsic circadian clock of the retina regulates retinal visual processing in vivo.
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Affiliation(s)
- K-F Storch
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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28
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Turgut M, Kaplan S, Metin K, Koca YB, Soylu E, Sahin B, Ateşlier ZBB, Başaloğlu HK. Effects of Constant Lightness, Darkness and Parachlorophenylalanine Treatment on Tail Regeneration in the Lizard Ophisops elegans macrodactylus: Macroscopic, Biochemical and Histological Changes. Anat Histol Embryol 2006; 35:155-61. [PMID: 16677209 DOI: 10.1111/j.1439-0264.2005.00653.x] [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] [Indexed: 11/27/2022]
Abstract
A better understanding of regenerative growth is very important for the development of new potential strategies. Recently, the pineal secretory product melatonin was shown to stimulate the regeneration process. In this study, we carried out an experimental investigation of tail regeneration in young adult lizards, Ophisops elegans macrodactylus Berthold, 1842, addressing the role of melatonin on the regeneration process. Lizards were divided into three groups: constant light-exposed control group (n = 13), constant dark-exposed group (n = 15) and parachlorophenylalanine (p-CPA) treatment group exposed to constant light (n = 15). Using a tail autotomy procedure, the effects of p-CPA treatment on connective tissue together with neural tissue and vascular tissue in regenerating tail in lizards were investigated. p-CPA (400 microg/kg body mass) was injected from day 0 to 30 days after autotomy. p-CPA treatment produced a significant increase in the length of the regenerated tail compared with light-exposed control and dark-exposed lizards. Total collagen content was found to be higher in p-CPA-treated animals in comparison with other groups. Histologically, a higher percentage of connective tissue and vascular tissue and a lower percentage of neural tissue were found in the regenerated tails of the p-CPA-treated lizards. Importantly, the percentage of neural tissue in lizards in the dark-exposed animals was higher than that in animals of both light-exposed and p-CPA treatment groups. Thus, it is clear that p-CPA has a stimulatory influence on fibroblast collagen production and vascularization of the regenerated tail in the lizards. Furthermore, it seems that the neural regeneration process was markedly enhanced in lizards exposed to continuous darkness. Based on the results of our study, it is suggested that melatonin may be an active factor that speeds up the rate of tail regeneration in lacertilians.
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Affiliation(s)
- M Turgut
- Department of Neurosurgery, Adnan Menderes University Medical Faculty, 09100 Aydin, Turkey
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29
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Abstract
The circadian rhythm of the chick electroretinogram (ERG) is regulated by the indoleamine hormone melatonin. To determine if the concentration of melatonin or the time at which it was administered would have differential effects on ERG parameters, we conducted experiments analyzing the effects of melatonin at different times of the day. Circadian rhythms of a- and b-wave implicit times and amplitudes were observed in both light:dark (LD) and in continuous darkness (DD). Intramuscular melatonin administration of 1 mg/kg and 100 ng/kg decreased a- and b-wave amplitudes and increased a- and b-wave implicit times. This effect was significantly greater than that observed for 1 ng/kg melatonin, which had little to no effect over the saline controls. The effect of 1 mg/kg and 100 ng/kg melatonin on a- and b-wave amplitude in LD and on b-wave amplitude in DD was greater during the night (ZT/CT 17) than during the day (ZT/CT 5). The fold change in b-wave implicit time over that of controls was greater during the day (ZT/CT 5) than during the night (ZT/CT 17). These data indicate that melatonin may play a role in regulating a day and night functional shift in the retina, and that it does so via regulation of a retinal clock.
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Affiliation(s)
- Jennifer L Peters
- Department of Biology and Center for Biological Clocks Research, Texas A&M University, College Station, TX, USA
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