Preface

Circadian clocks are endogenous and temperature-compensating timekeepers that provide temporal organization of biological processes in living organisms including cyanobacteria, plants, animals and humans. Circadian rhythms allow living organisms to adapt to the daily light cycles associated with Earth's rotation and to anticipate and prepare for precise and regular environmental changes. The endogenous circadian rhythms are adjusted to the envi‐ ronment by different surrounding cues, such as temperature, light and redox cycles. Biologi‐ cal clocks regulate several biological functions, including hormone levels, body temperature, cell regeneration, metabolism, photoperiodism and other biological activities.

This book discusses the fundamental advances of how the circadian clock regulates critical biological functions as well as the cellular and molecular mechanisms controlling circadian rhythm in living organisms. It also provides new insights into and sheds new light on the current research trends and future research directions related to circadian rhythm. This book provokes interest in many readers, researchers and scientists, who can find this infor‐ mation useful for the advancement of their research works towards a better understanding of circadian rhythm regulatory mechanisms.

The book includes eight chapters. The first introductory chapter "Circadian Rhythms and Their Molecular Mechanisms" presents an introduction to the history, importance and mo‐ lecular mechanisms of circadian rhythms in living organisms. The second chapter "Circadi‐ an Rhythm and Chronobiology" discusses the recent progresses related to circadian biological research as well as understanding how biological clocks govern the human me‐ tabolism. The third chapter "Circadian Clock Gene Expression and Drug/Toxicant Interac‐ tions as Novel Targets of Chronopharmacology and Chronotoxicology" discusses the interactions of circadian clock genes with drugs and/or toxicants to better understand the importance of circadian clock gene expression as novel targets in pharmacology and toxicol‐ ogy. The fourth chapter "Quantification of Irregular Rhythms in Chronobiology: A Time Series Perspective" compares wavelets and SSA analysis for the quantification of irregular rhythms at different frequency scales and discusses their respective advantages and disad‐ vantages for application in chronobiology. The fifth chapter "Jet Lag" describes the phenom‐ enon of jet lag and its associated symptoms. The sixth chapter "Features of Circadian Rhythms in Patients with Cerebrovascular Diseases" describes in detail the pathogenetic role of desynchronosis in the development of cerebrovascular diseases (CVD). The seventh chapter "The Chronobiology of Acid-Base Balance under General Anaesthesia in Rat Mod‐ el" reviews the status of acid-base balance and ion concentration in arterial blood under commonly used anaesthesias in experiments in dependence on the light-dark cycle in breathing rats. The eighth chapter "Sudden Death of Circadian Rhythm in Chagasic Patients Compared to Non-Chagasic Patients" compares the circadian rhythm of sudden death in Ch versus non-Ch patients.

The book editor would like to thank Ms. Romina Skomersic, Publishing Process Manager, for her wholehearted cooperation in the publication of this book.

#### **Mohamed Ahmed El-Esawi, PhD**

**Chapter 1**

Provisional chapter

**Introductory Chapter: Circadian Rhythms and Their**

DOI: 10.5772/intechopen.78756

A circadian rhythm is a biological process which shows an endogenous and entrainable oscillation of about 24 h. These 24-h rhythms are regulated by a circadian clock and are widely displayed in different organisms, including plants, fungi, animals, and cyanobacteria [1]. The endogenous circadian rhythms are adjusted to the environment by different surrounding cues, such as temperature, light, and redox cycles. In 2017, Jeffrey C. Hall and his colleagues have awarded the Nobel Prize in Physiology or Medicine for their discoveries of molecular mechanisms controlling the circadian rhythm. Circadian system runs as a result of four main components: (i) photosensitive retinal neurons and retinohypothalamic tract through which light signals come from the environment, (ii) internal circadian oscillator, generating rhythms and synchronizing them with the environment, (iii) signal paths transmitting information from the central regulator to peripheral rhythm generators, and (iv) peripheral rhythm generators

In 1729, the French scientist Jean-Jacques d'Ortous de Mairan reported the first observation of an endogenous circadian oscillation and found that 24-h patterns in the movement of the leaves of the plant species Mimosa pudica continued even when the plants were kept in constant darkness [2, 3]. In 1896, Patrick and Gilbert reported that during a prolonged sleep deprivation period, sleepiness can increase and decrease within a period of approximately 24 h [4]. Furthermore, in 1918, J.S. Szymanski reported that the animals have shown their capability of maintaining 24-h activity patterns even in the absence or changes of external factors such as light and temperature. Circadian rhythms were also reported in the bees rhythmic feeding times in the early twentieth century. In 1935, circadian rhythms were also noticed in the fruit fly Drosophila melanogaster [5, 6]. In 1954, Colin Pittendrigh reported that temperature played a crucial role in eclosion rhythm, and the eclosion period was delayed without stopping when the temperature decreased, indicating that circadian rhythm is controlled by an internal

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Introductory Chapter: Circadian Rhythms and Their

**Molecular Mechanisms**

Molecular Mechanisms

http://dx.doi.org/10.5772/intechopen.78756

(clock genes and proteins in peripheral cells).

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Mohamed A. El-Esawi

Mohamed A. El-Esawi

1. Introduction

Sainsbury Laboratory, University of Cambridge, Cambridge, United Kingdom Botany Department, Faculty of Science, Tanta University, Egypt

#### **Introductory Chapter: Circadian Rhythms and Their Molecular Mechanisms** Introductory Chapter: Circadian Rhythms and Their Molecular Mechanisms

DOI: 10.5772/intechopen.78756

Mohamed A. El-Esawi Mohamed A. El-Esawi

Compared to Non-Chagasic Patients" compares the circadian rhythm of sudden death in Ch

The book editor would like to thank Ms. Romina Skomersic, Publishing Process Manager,

Sainsbury Laboratory, University of Cambridge, Cambridge, United Kingdom

Botany Department, Faculty of Science, Tanta University, Egypt

**Mohamed Ahmed El-Esawi, PhD**

for her wholehearted cooperation in the publication of this book.

versus non-Ch patients.

VIII Preface

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.78756
