Acute and subacute hydrocephalus in a rat neonatal model: correlation with functional injury of neurotransmitter...

The evolution and severity of hydrocephalus in animal models varies in the species and mode of induction. This makes comparisons of the physiological system under investigation difficult between models. We noted that injection of kaolin into neonatal rats results in a dichotomous outcome into either an acute or subacute form. We investigated the clinical and functional transmitter system changes to compare these two types of hydrocephalus evolution.

Hydrocephalus was induced in Wistar neonatal rats (within a week after their birth) by intracisternal injection of 0.02 ml volume of 25% kaolin solution under microscopic guidance. The same volume of sterile saline was injected into 12 neonatal rats as control group. The animals were assigned to either the acute or subacute group according to their head size, and sacrificed at 2, 4 and 8 weeks after injection. Biparietal diameter, ventricular size, cholinergic interneurons in the neostriatum and dopaminergic projection neurons in the substantia nigra were analyzed at each stage.

Animals affected with the acute type of hydrocephalus had obvious head enlargement, rapid ventricular enlargement, and all died at about 4 weeks. Animals with subacute type had slowly progressive ventricular enlargement, and all survived until 8 weeks. There appeared to be more kaolin ventral to the brainstem in the acute type. The number of cholinergic neostriatal neurons was significantly reduced at 2 and 4 weeks in the acute type, but only at 8 weeks in the subacute type. The number of dopaminergic nigral neurons was decreased at 4 weeks in the acute type, but unaffected in the subacute type.

The severity of onset of hydrocephalus in this animal model also correlates with the clinical outcome and changes in functional transmitter systems.