The microstructure of cortical neuropil before and after decompression in experimental infantile hydrocephalus.

Hydrocephalus is a common clinical disorder and responsible for many pediatric neurological deficits. Relatively little is known about the cellular mechanisms of this disorder and less is known about reconstitution of connectivity following ventricular shunt procedures. In the present studies experimental infantile hydrocephalus produced by kaolin injection was studied in a neonate kitten model. The neuropil of the cerebral cortex was examined in hydrocephalic animals and animals which received a ventriculoperitoneal shunt to reduce ventriculomegaly. The brains were processed for Golgi silver impregnation and electron microscopy to study the detailed dendritic and synaptic architecture. The periventricular region of the hydrocephalic animals exhibited increased extracellular space and signs of neuronal degeneration. Components of the deep neuropil (laminae V-VI) were in disarray and surrounded by edematous extracellular spaces. The superficial neuropil (laminae I-IV), in contrast, appeared intact, but detailed examination showed indications of dendritic degeneration. Shunt procedures successfully restored the cortical mantle to near normal thickness. However, Golgi light microscopy and electron microscopy revealed that dendritic appendage morphology was altered. The results are discussed in regard to development of neuronal connectivity following shunt procedures.