الفهرس 
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Abstract
It is well known that, the newborn mammals demonstrate variable degrees of locomotor ability. The newborn of precocial animals, such as guinea pig (order Rodentia, family Cavidae) can support their weight and locomote soon after birth, whereas the newborn of non¬precocial species, such as rats (order Rodentia, family Muridae) and rabbit, (order Lagomorpha, family Leporidae) can not support their weights. The interaction between the developmental rate of some regions of the nervous system (cerebral hemisphere, cerebellum, brachial and lumber regions of spinal cord) and the pattern of locomotion was investigated in R. norvegicus and O. cuniculus at birth, one, two and three weeks old, while in C. porcellus was studied at birth and also at three weeks old. So, the present parameters were used to follow these interactions:1. The changes in the relative lengths of the brain regions in the present mammals were variable among them. The large brains refer to the high proportion of body metabolism to maintain their brains. 2. The histological structures of the cerebral cortex show that there is no obvious lamination can be detectable in the cortical plate at different investigated ages of rat, while in both rabbit and guinea pig it is present at day 21. On the other hand, the pyramidal cells appeared in guinea pig since the day of birth, while in rabbits and rats, these neurons first recognized in the cerebral cortex at 7 and 14 days old respectively. These results may refer to the growth of guinea pig cerebral cortex precedes that of rabbit which in turn precedes the development of rat cerebral cortex. It is known that the pyramidal cells initiate the contraction of voluntary muscles and the cerebral cortex associate many stimuli before the performance of motor activity. The present observations said that the early development of the cerebral cortex affects on the locomotion pattern of guinea pig which can walk soon after birth, while both rat and rabbit can not and need 2 weeks or more. 3. The cerebellar cortex is differ among the present mammals: firstly, the thickness of the external granular layer decreased significantly with age until it disappeared completely at day 21 of guinea pig, while it still present in rat and rabbit. This decrease in thickness is due to migration of the cells of this layer to the neighboring molecular layer. This may reveal that the present molecular layer in guinea pig is fully formed at day 21 while in rat and rabbit it still in the developmental process. Secondly, the stellate and basket cells of the molecular layer started to appear since day one in guinea pig, day 7 in rabbits and day 14 in rats. The length of basket cells differs significantly among the present mammals. Thirdly, the Purkinje cells of the cerebellar cortex were arranged in a single row since day 14 in rat and rabbit and since the day of birth in guinea pig. The change in the length and diameter of these cells is significant among the present mammals and increased significantly by time except the length of these cells in guinea pig which has insignificant increase. Fourthly, the internal granular layer is difficult to be differentiated from the deep white matter till 14 days old in both rat and rabbit, while in guinea pig this layer is clearly differentiated since the day of birth. The thickness of this layer is variable by time and among the present mammals. These results confined that impulses produced from the cerebellum influence the contraction of skeletal muscles, so equilibrium maintained. On the other hand, the cerebellum is also important for the refinement of movement. So, the development of guinea pig cerebellar cortex precedes that of rat and rabbit and this may indicate why the guinea pig can walk since the day of birth while both rat and rabbit can not.4. For the spinal cord in rats, the neurons and astrocytes of the brachial spinal cord can be recognized since the day of birth, while in the lumber spinal cord these cells appeared at day 7. The diameter of the brachial motoneurons is significantly larger than the diameter of the lumber motoneurons at different ages. On the other hand, in rabbit and guinea pig, the lumber motoneurons have larger diameter than the brachial motoneurons at different investigated ages. Both astrocytes and motoneurons of the lumber spinal cord appeared with a high dendritic arborization and more developed than the comparable cells of the brachial spinal cord. Generally, the present work confined the rostrocaudal gradient in the development of the spinal cord in rat while in rabbit and guinea pig there is a caudorostral gradient. The astrocytes at day one in both regions of spinal cord were detected in guinea pig while they were absent in the lumber spinal cord of rat and in both types of spinal cord in rabbit. These astrocytes provide both structural and metabolic support for the neurons and increase the speed of impulse conduction. So, the spinal cord of guinea pig at day one has both structural and metabolic support more than those of rat and rabbit and this may be one of the reasons which help guinea pig to walk soon after birth. In the present mammals, the density of Nissl granules were investigated in the neurons of the cerebral cortex, cerebellar cortex and the 2 regions of the spinal cord. High density of these granules refer to the high metabolic activity of the neurons.5. For the development of the myogenic pattern, semithin sections of gastrocnemius muscle were made in the present mammals at day 1 and day 21. At birth, the gastrocnemius muscle of guinea pig has well developed structure and more obvious cross striations than in rat and rabbit. Regular cross striations are being arranged more obviously by time due to the arrangement of contractile proteins which being laid down in the myotube. Again, this study confined that the precocial animals locomote soon after birth than non¬precocial one.6. The ontogenic myological changes were investigated at the superficial muscles in the fore and hind limbs. Also, the identification of these muscles and the anatomical nomenclature were performed in the present study. These muscles appear differ in their relative lengths among the present mammals. The brachial muscles in the present mammals are characterized by long fibers and short tendons. The opposite is true in the antebrachial muscles. This difference was clearly explained as the two types of muscles have distinct main functions, the long¬fibered muscles are for acceleration and jumping, while the short¬fibered ones to save energy. However, the insertion pattern of the present muscles tendons differ among the present mammals. The tendons might function as strain energy stores in the locomotion and the long tendons in mammalian muscles have an important role in running and implications for the control of movements.7. The activity of ATPase was measured in six different muscles in the fore limb (Triceps Brach| Longum, Extensor Carpi Radialis and Biceps Brach|)and hind limb (Gastrocnemius, Tibialis Cranialis and Gracilis) of the present mammals at day 1 and day 21. At birth, the activity of this enzyme in guinea pig is significantly higher than in rat and rabbit. The activity of ATPase decreases by time in guinea pig, while the opposite is true in the other investigated animals. Fibers containing high ATPase activity are classified as fast fibers, and those containing lower ATPase activity are slow fibers, so they both differ in the maximal shortening velocity. According to this report, the muscle fibers in guinea pig at birth have a higher shortening velocity and higher ability to perform their functions than rat and rabbit, whose their muscle fibers ability to perform its function increases by time.8. The locomotion pattern of the present mammals were investigated by using high speed video camera from day 1 to 3 weeks old each 7 days in both rat and rabbit and at birth and 3 weeks old in guinea pig. The newborns rat and rabbit are hardly able to move on the ground. They are loosing balance during locomotion until the body weight is supported on the four limbs. In guinea pig, the pups can walk soon after birth and they never loose balance. According to the present study, the development of the cerebellum in guinea pig preceding that of rat and rabbit. Other studies refer to the importance of the cerebellum to control muscle activity and maintain the gait balance and this may explain why guinea pig obtaining balance before rat and rabbit.9. The development of sensorimotor reflexes were investigated in the youngs of rat and rabbit each week from day 1 to day 21, while in guinea pig these tests were made at birth and at 3 weeks old. These reflexes are rooting, grasping, body righting on a surface, body righting in the air, chin tactile placing, visual placing, limb tactile placing and hopping. These reflexes differ in their developmental degree among the present mammals and by time, this is because the appearance and maturation of the previous reflexes correlated with the neural maturation. Statistical and regression analyses were performed for the neurons of cerebral cortex, cerebellar cortex and the two regions of spinal cord and also for myological pattern in the present animals. All these data were compared by using analysis of variance test (Anova) for comparing these measured data among the present mammals at different ages.