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@Real Academia Nacional de Farmacia. Spain 49 Melatonin and melanopsin in the eye: friends or foes? Title in Spanish: Melatonina y melanopsina en el ojo: ¿amigos o enemigos? Hanan Awad Alkozi 1, * 1 Department of Biochemistry, Faculty of Optics and Optometry, University Complutense , Madrid, Spain * Corresponding Author: Hanan-q1@live.com An Real Acad Farm Vol. 85, Nº 1 (2019), pp. 49-59 Received: January 22, 2019 Accepted: April 8, 2019 Language of Manuscript: English Premio CINFA del Concurso Científico 2018 de la Real Academia Nacional de Farmacia 1. INTRODUCTION When someone mention the eye to a professional in this field, the first thing that comes to mind is vision, and ocular pathologies which can lead to blindness. All the possible ocular diseases starting from the tear-film until the retina, could result in either reversible or irreversible blindness. However, the ocular organ exceeds this very important function, and it is rather a window for both out- and inside of the body. It is the organ which permits us to capture the daylight and all the information about the time of the day, and it is the first vehicle for photo-entrainment. In order to accomplish the function of photo- entrainment, the ocular organ contains a small number of cells laying in the inner retina, which comprise a photopigment named melanopsin (1). This photopigment is responsible of capturing light and passing its signals through a series of chemical reactions to several brain regions, until it reaches the pineal gland, where it suppresses melatonin synthesis (2). With modern life, and the use of artificial light instead of depending on daylight, a serious debate was generated regarding the risk of light pollution. Melanopsin containing retinal ganglion cells receives confusing signals and it is activated when light is switched on at night; hence disrupting the circadian rhythm and leading to serious health issues as a consequence of suppressing melatonin synthesis (3). Melatonin (N-acetyl-5-methoxytryptamine) is a neurohormone classically known to be produced by the pineal gland (4). This hormone is considered the chemical expression of darkness, because of its role in regulating the circadian rhythm. Melatonin levels raise during the night and its levels are lower at daytime, hence, it is the natural sleep aid our body has (5). However, from the moment this hormone was discovered and characterized, numerous researchers investigated it, and they detected its presence not only by the blood stream, but also because it is synthesized in several organs and cells (6). ABSTRACT: Melatonin is a neurohormone synthesized in several ocular structures apart from its original source, the pineal gland. It is of great importance in several functions such as maintaining a healthy values of intraocular pressure. Moreover, it decreases intraocular pressure in the case of glaucoma. This nuerohormone is controlled by the activation of a photopigment responible for non-image forming tasks in the eye, this photopigment is Melanopsin, present in a subclass of retinal ganglion cells, and very recently, it was discovered in different ocular structures. When Melanopsin is activated by the short wavelength component of light, it supresses Melatonin synthesis. This action is controlled mainly by light could affect several functions including the regulation of intraocular pressure. In this sense, the present work highlights the history and importance of the relationship between both Melatonin and Melanopsin to maintain a healthy ocular homeostasis. RESUMEN: La Melatonina es una neurohormona sintetizada en varias estructuras oculares, aparte de su fuente original, la glándula pineal. Es de gran importancia por varias funciones, como el mantenimiento de valores saludables de presión intraocular. Además, disminuye la presión intraocular en el caso de glaucoma. Esta nuerohormona se controla mediante la activación de un fotopigmento responsable de las tareas no relacionada con la formación de imágenes en el ojo, este fotopigmento es la Melanopsina, presente en una subclase de células ganglionares de la retina y, muy recientemente, se descubrió en diferentes estructuras oculares. Cuando la melanopsina se activa por el componente de longitud de onda corta de la luz, suprime la síntesis de melatonina. Esta acción está controlada principalmente por la luz que podría afectar varias funciones, incluida la regulación de la presión intraocular. En este sentido, el presente trabajo destaca la historia y la importancia de la relación entre la melatonina y la melanopsina para mantener una homeostasis ocular saludable. ANALES DE
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