PROGRESSION OF KAOLIN-INDUCED HYDROCEPHALUS AND CHANGES IN PERFORMANCE OF OPERANT TASKS BY RATS

The behavior of rats with progressive hydrocephalus was examined to de tect early neurological deterioration. Kaolin solution was injected in to the cisterna magna of 10 of 17 anesthetized 8-week-old male rats (d ay 0), and saline in the other 7 rats (control group). Reaction time ( RT, sec) and error ratio (ER, %) of unanesthetized rats escaping from electrical stimuli toward a nonstimulated sheet within a box were reco rded daily from day 4 until autopsy after 4 weeks. Three rats in the k aolin group died in acute stage. Rats were assigned to either severe ( S) (n = 4) or moderate (M) (n = 4) group according to the degree of ve ntricular dilatation at autopsy. The RTs prolonged and ERs increased i n the kaolin group and they reached their minimum values. Values after the minimum RT value on day 12 in the M-group and 22 in the S-group d uring the chronic stage were compared with those in the controls, whic h decreased throughout the experiments (P < 0.03). In all animals in t he S-group RT was prolonged each day with a linear regression (P < 0.0 05), although ER was decreased (0.69 > P > 0.23). In 3 rats and in ano ther rat in the: M-group RT was prolonged (P < 0.04 and P = 0.19) and ER was decreased in 3 rats (two: P = 0.41; one: P = 0.01) and increase d in one (P = 0.55). In conclusion, deteriorated motor function is mor e important for early diagnosis in progressive hydrocephalus than beha vioral symptoms.