Available online at http://www.ajol.info/index.php/njbas/index Nigerian Journal of Basic and Applied Science (December, 2015), 23(2): 179-184 DOI: http://dx.doi.org/10.4314/njbas.v23i2.13 ISSN 0794-5698 Ontogenetic Developmental Stages as Common Methods of Relating the Age of Wistar Rats with Human’s 1 A.B. El-ta’alu, 2 A.J. Alhassan and 3 Rabiu I. Fage 1 Department of Human Physiology, Faculty of Basic Medical Sciences, Bayero University, Kano, Nigeria 2 Department of Biochemistry, Faculty of Basic Medical Sciences, Bayero University, Kano, Nigeria 3 Department of Anatomy, Faculty of Basic Medical Sciences, Bayero University, Kano, Nigeria [*Corresponding author E-mail: abbassido@yahoo.com; .: +2348109716223] 179 Review Article ABSTRACT: The precise correlation between the age of laboratory rats and humans is still a subject of debate. A number of researchers have tried to detect these correlations in various ways but failed to successfully provide any proper association. Like human beings, the Wistar rats go through the ontogenetic developmental stages «Prenatal → Birth → Infancy → Childhood → Adolescence → Adulthood → Death». Therefore, the stages of ontogenesis, from post-natal up to post-senescence can be used as surrogate markers to relate the ages of rats with those of human beings. The aim of this review was to compare and relate rat and human ages at different phases of their ontogenetic development. Rats grow rapidly during their childhood and both sexes become sexually mature 50-60 days after birth but attain social maturity 5-6 months later. It was also observed that, in adulthood, every day of the animal is approximately equivalent to 34.8 human days, which means one rat’s month can be likened to three human years. The differences herein signify the variations in animals’ anatomy, physiology, and ontogenetic developmental processes. This review would solve the lingering issues of rats’ human age correlation and allow for making reasonable conclusions in researches that involve humans and experimental animals. Keywords: Human age, laboratory rat, ontogenesis, physiology, puberty, rat age. INTRODUCTION Rats have a long history in medical research. They were the first mammalian species specifically domesticated to be used in the laboratory. They are thought to have originated in some parts of Asia; Rattus rattus was well established in Europe by 1100 A.D., with Rattus norvegicus commonly found in Europe in the 1700s. By the 1800s, these animals were used for neuro-anatomy studies in the United States and in Europe. It was in the late 1800s and early 1900s that individual stocks and strains had their beginnings (Animals in research, 2013; Sengupta, 2013). The success of the rat in research today has been linked to the Wistar Institute in the United States of America, when in 1906, the institute developed the Wistar albino strain (Rattus norvegicus) (The Wistar Institute: History, 2007). Currently, there are 117 albino strains of the laboratory rat, all of which can be traced genetically back to the one rat, likely to have arisen as a mutation from a hooded (piebald) rat strain (Animals in research, 2013). Since their development as a laboratory species, rats have been used to answer a wide range of basic science questions ranging from physiology, anatomy, immunology, pharmacology, toxicology, nutrition, behaviour and learning, cancer studies, teratology, experimental oncology, gerontology, cardiovascular research, dental research, immunogenetics, and experimental parasitology (Sengupta, 2013). Consequently, a large amount of data has been collected that has translated into their extensive use as a model for human disease (Sengupta, 2013). According to Sengupta (2013), among the rodents, rats are the mostly widely used animals for experimental purposes (accounting for approximately 20% of the total number of mammals used for scientific purposes), followed by mouse, rabbit, dog, pig and primate, especially for in vivo studies (Sengupta, 2013). Numerous methods have been investigated in several studies to correlate the ages of small mammals with that of a human: using the weight of the eye lens, growth of molar teeth, counting of endosteal layers in the tibia, musculoskeletal growth along with the closure and thickening of the epiphyses (Sengupta, 2013), etc., but all of the techniques employed are relative methods and do not exactly define the absolute age thus, researchers generally use more than one method at a time to have a proper idea about the age of the experimental animal. It is, therefore, expedient to study this phenomenon, taking into account the different stages of the animals’ life; to have a correlation, which is easy, accurate, and does not require animals’