Anxiety responses and neurochemical changes in a kaolin-induced rat model of hydrocephalus

Hydrocephalus is a pathological enlargement of the ventricles of the brain, which can result from various diseases of the central nervous system. Patients with hydrocephalus frequently show motor abnormalities, such as abnormal gait and posture, as well as intellectual and emotional impairment. The present study was designed to investigate anxiety responses in rats with kaolin-induced hydrocephalus.

A total of 26 Sprague-Dawley rats were used for this study. Hydrocephalus was induced in 14 Sprague-Dawley rats by injecting 0.1 ml of 20% kaolin solution into the cisterna magna; 12 rats were administered the same volume of saline in the same fashion and served as controls. Seven of the rats that were injected with kaolin and 6 of the rats injected with saline were killed 3 days after injection (Group 1); the remaining rats were killed 4 weeks after injection (Group 2) to evaluate effects related to acute and chronic hydrocephalus. The rats were tested in an elevated plus maze after induction of hydrocephalus by kaolin injection. After the animals were killed, brain sections were immunostained for cholecystokinin and neuropeptide Y. In addition, tyrosine hydroxylase immunoreactivity in the ventral tegmental area was evaluated by immunohistological staining.

The rats with acute hydrocephalus showed decreased entry into and spent less time in the open arms of the elevated plus maze as compared with the control rats. The hydrocephalic rats had significantly more cholecystokinin-immunoreactive neurons and fewer neuropeptide Y-immunoreactive neurons in their brains. In addition, hydrocephalus progress in this model was positively correlated with the anxiety response. The numbers of tyrosine hydroxylase-immunoreactive neurons were decreased significantly in the hydrocephalic rats as compared with the control rats.

These results suggest that the rat model of hydrocephalus is characterized by increased anxiety response and is associated with the functional impairment of the central dopamine system.