Morphological changes of lumbar spinal neurons after sciatic nerve transection in neonate rats

Axotomy of the sciatic nerve have been documented to cause neuronal loss, especially in newborn rats. Few works have focused on time course of neuronal loss and the type of cell death, which occurs after axotomy. Forty rat pups were anesthetized by hypothermia and the right sciatic nerve transected at five days of their age and the left side was used as control. The operated animals were sacrificed 3, 5, 7, 10 and 14 days after axotomy. The animal were anesthetized with ether and perfused and fixed with paraformaldehyde and glutaraldehyde followed by osmium tetroxide as a post fixative. Forth to sixth lumbar spinal segments were used for light and electron microscopic processing and embedding. Transverse serial sections was cut and stained with Hematoxylin and Eosin as well as cresyl violet. Semi-thin sections was cut from resin embedded block and stained with Toluidine blue. The number of motoneurons (MNs) from experimental and control sides of lumbar spinal cord was counted by superimposing eyepiece graticule on the microscopic image. The comparison between the operated and control sides was done by student’s t- test. The analysis of variance was also done to compare the variation among the groups. Ultrastructural features of dead MNs showed the classical features of apoptotic neurons. Other MNs showed the vacculation of cytoplasm. The conclusion of this study is that axotomy of sciatic nerve resulted in apoptotic cell death of motoneurons of spinal cord as well as a time-dependent reduction of cell number where the peak of the cell loss occurred at day 10.