Sciatic nerve transection in neonatal rats induces apoptotic neuronal death in L5 dorsal root ganglion.

Transection of a peripheral nerve in neonatal rats induces death of the axotomized neurons which may be due to either necrosis or apoptosis. In the present investigation, neuronal cell death in L5 dorsal root ganglion was evaluated after unilateral sciatic nerve transection in rats at 1, 3, 5, 7 and 10 days age. After 5 days, right (experimental) and left (control) dorsal root ganglia in all groups were removed, fixed, processed and embedded for either light or electron microscopy. Normal nucleoli were counted in paraffin embedded serial sections, and correction factors for split and multiple nucleoli were applied as well as the physical disector. The number of neurons in the right dorsal root ganglia, as compared with the controls, was significantly lower in all groups, and the percentage of the reduction at 1, 3, 5, 7 and 10 days was 32.4, 27.2, 23.8, 22.8 and 21.8% respectively. On the other hand, the results of neuronal counts using the disector method showed 34.0, 25.7, 20.2, 20.0 and 14.2% reduction in the number of neurons at 1, 3, 5, 7 and 10 days, respectively. The microscopic and ultrastructural results indicated that there were typical morphological changes similar to those of apoptosis, including condensed basophilic nuclei, formation of nuclear caps, cell shrinkage and apoptotic body formation. We concluded that there is an increase in apoptosis in dorsal root ganglia following sciatic nerve axotomy with the greatest neuronal loss on postnatal day 1.

Ultrastructure of apoptotic oligodendrocytes in the spinal cord of adult rat with long-standing axotomised sciatic nerve.

The apoptosis in the oligodendrocytes was evaluated in adult rat which were axotomised and sacrificed three months aftersurgery. The apoptotic cell had electron dense organelles with condensed cytoplasm, the nucleus showed chromatin condensation with formation of band-like structure of clumped chromatin, and subsequently the cell underwent progressive shrinkage. The advanced stage of apoptosis showed electron lucency in the chromatin band, followed by disintegration of the nucleus, while the cytoplasm was replaced with high electron dense granular substance forming round electron dense apoptotic cells. The autophagy was also noticed in the cytoplasm of these cells, consisting of membrane bounded cytoplasmic organelles. Because the autophagy was seen in the apoptotic cell, this indicates that the autophagy is not limited to autophagic type programmed cell death.