ULTRASTRUCTURAL-CHANGES IN THE DEEP CORTICAL PYRAMIDAL CELLS OF INFANT RATS WITH INHERITED HYDROCEPHALUS AND THE EFFECT OF SHUNT TREATMENT

Pathological changes in the cortical gray matter in infantile hydrocep halus vary with the age at onset and may not be reversible with shunt treatment, We have used electron microscopy to investigate the sequenc e of pathological change and the effect of shunt treatment on layer VI pyramidal cells from infant II-Tx rats with inherited early-onset hyd rocephalus. Tissue was prepared from the frontal and visual cortex of control and hydrocephalic rats at 4, 11, and 21 days after birth, toge ther with al-day rats previously treated with ventriculosubcutaneous s hunts at 4-5 or 10-11 days after birth. Both cortical regions gave sim ilar results but the effects were more severe in the visual cortex. In the early stages of hydrocephalus, the pyramidal cells were in cluste rs with fewer mature dendrites and less cytoplasmic organization than those in control rats, and some neuronal processes were vacuolated. In intermediate hydrocephalus the changes were more severe, with vacuola ted cytoplasm, fewer cytoplasmic organelles, frequent swollen processe s, and infrequent synapses. In advanced hydrocephalus at 21 days, many neurons showed degenerative changes, with edematous Golgi and dilated endoplasmic reticulum, distorted mitochondria, and single ribosomes. The neuropil contained many spongy areas with distended profiles. Shun t treatment prevented most of the changes if carried out at 4 days. Sh unt treatment at 11 days also gave a dramatic recovery at the cellular level, but there were more immature pyramidal cells and edematous pro cesses in the neuropil than in the 4-day-treated rats. The changes in hydrocephalus are consistent with progressive neuronal damage, which i s largely prevented by early shunt treatment. (C) 1997 Academic Press.