Int. J. Devl Neuroscience 30 (2012) 545–553 Contents lists available at SciVerse ScienceDirect International Journal of Developmental Neuroscience j our na l ho me p age: www.elsevier.com/locate/ijdevneu The development of sensorimotor reflexes in albino mice; albino rats and black-hooded rats Ahmed A. Allam a,b,∗ , Rasha E. Abo-Eleneen b a King Saud University, College of Science, Zoology Department, P.O. Box 2455, Riyadh 11451, Saudi Arabia b Beni-Suef University, Faculty of Science, Zoology Department, Beni-Suef 65211, Egypt a r t i c l e i n f o Article history: Received 12 May 2012 Received in revised form 12 August 2012 Accepted 12 August 2012 Keywords: Sensorimotor reflexes Spinal cord Cerebrum Cerebellum Rodent newborns a b s t r a c t The present investigation aimed to show the differences in the development of sensorimotor reflexes and their relationship to the structural changes in spinal cord, cerebellum and cerebral cortex in three rodent species. The three species are albino rats (A-Rats), black-hooded rats (B-Rats) and albino mice. The development of selected reflexes was examined from day (D1) to D21. The structural changes were investigated at D7, D14, and D21. The following reflexes were analyzed: fore-limb/hind-limb grasp, sur- face body righting, fore-limb hopping, chin tactile placing, visual placing and body righting in the air. The developmental pattern of the reflexes was different in three rodent species. Although the black-hooded rats and albino rats belong to the same species, they are different in their appearance and developmental pattern. The development of external features and sensorimotor reflexes appeared earlier in mice than in A-Rats and B-Rats. At D7, differentiation of neurons was observed in the spinal cord while in cerebellum and cerebrum the neurons were found to be undifferentiated. At D14 and D21, the differentiated neu- rons were observed in spinal cord, cerebellum and cerebrum. Our data indicate that the developmental pattern of the reflexes in rodents may not be species specific but may be related to the animal strain. © 2012 ISDN. Published by Elsevier Ltd. All rights reserved. 1. Introduction A reflex is a stereotyped motor response of the central nervous system (CNS) to internal or external stimuli (Rossignol, 1996; Zehr and Stein, 1999). Nicholls et al. (1992) has shown that the simplest motor actions of reflexes are mediated by relatively straightfor- ward circuitry in the spinal cord. Reflexes may be unconscious responses to stress and danger that serve as the protective or sur- vival mechanisms (Swerdlow and Mark, 1998). Fully integrated reflexes become part of an internal skill (Lebedev et al., 2008). The sensorimotor connection may be too strong resulting in excessive motor reactivity or too weak resulting in low muscle tone. Negative response is present when a reflex fails to occur (Masgutova et al., 2010). The ontogeny of sensorimotor reflexes evaluation in albino rats (e.g., visual and tactile orientation, forelimb and hindlimb hopping, righting reflexes) from birth through adulthood are elaborated to achieve mature characteristics at various ages during ontogeny with a rostralcaudal developmental pattern (Almli and Fisher, ∗ Correspondence address: King Saud University, College of Science, Zoology Department, P.O. Box 2455, Riyadh11451, Saudi Arabia. Tel.: +966 544265061; fax: +966 4678514. E-mail address: allam1081981@yahoo.com (A.A. Allam). 1977). The neurobehavioral evolution of the normally growing rat may be investigated by examining a series of motor and sensory tests (reflexes) from birth up to weaning. The second week after the birth represents an important step in the neurobehavioral matura- tion of the rat. These tests may be useful to evaluate changes that may be induced by pharmacological and toxicological agents in the developing rats and mice (Ten et al., 2003). The reflex ontogeny is a sensitive indicator for the adaptation of the neonate to extra- uterine life during development. The reflexes maturation might herald the CNS maturation (Vaglenova et al., 2008; Khalki et al., 2012). The rate of development of each sensorimotor reflex might be related to the developmental rate of specific CNS regions medi- ating the reflex (Allam, 2008). It is therefore essential to study both the postnatal development of the CNS regions and sensorimotor reflexes during CNS development (Cassidy et al., 1994). The spinal motorneurons are the final output of motor systems, therefore a detailed developmental study is important for a greater understanding of the development of motor reflexes (Takahashi et al., 1999). The grasp, hopping and body righting on the surface reflexes are mediated by spinal cord neurons. It is well known that at birth the cerebellum of mice and rats is in a state of immaturity and its histogenesis and morphogenesis mainly occurs postnatally (Jacobson, 1970). The mature cerebellar cortex of all vertebrates is divided into 3 regions: a deep granular layer (stratum granulosum), middle Purkinje cell layer (ganglionic), and a superficial molecular 0736-5748/$36.00 © 2012 ISDN. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijdevneu.2012.08.005