Kaolin-Induced Hydrocephalus in the Developing Rat Brain: Deficits of Visual Perception and Structural Changes in the Visual Cortex.

Abstract

BACKGROUND AND OBJECTIVES: Cortical visual deficits occur in hydrocephalus but the morphological changes in the visual cortex are not fully understood. This study assessed the population and cytoarchitecture of neurons in the cortex of neonatal and juvenile rats, in relation to the findings on assessment of visual perception. METHODS: Hydrocephalus was induced by injecting sterile kaolin (150 mg/l) into the cisterna magna of neonatal (7 days old) and juvenile (4 weeks old) rats. Vision was assessed using a dark chamber preference test prior to sacrifice at two and four weeks for the neonatal rats, and four and eight weeks for the juvenile rats following kaolin injection, at which time significant ventriculomegaly and cortical thinning were apparent in the parieto-occipital region. Tissue samples from the visual cortex were processed for modified Golgi, haematoxylin and eosin, and Nissl stains. RESULTS: The hydrocephalic rats failed the dark chamber tests of transition, peeping and preference and lacked a distinct horizontal layering of the visual cortex. There was neuronal degeneration as evidenced by increased pyknosis, and increased cytoplasmic eosinophilia. The size and dendritic branching of pyramidal neurons in layer 5 were reduced. This was especially notable in the juvenile group after four weeks of hydrocephalus. The density of layer 5 pyramidal neurons was reduced in both neonatal and juvenile hydrocephalic rats at the two time points of assessment. CONCLUSIONS: The results showed that hydrocephalus altered the morphology of the pyramidal neurons of the visual cortex, and suggest that these changes were associated with deficits in visual perception.