Brain lesions and water-maze learning deficits after systemic administration of kainic acid to adult rats

The relationship between hippocampal damage and spatial learning deficiencies was studied in rats injected with kainic acid (10 mg/kg i.p.). A single injection was given either before or after the acquisition phase of the Morris water-maze task. In this acquisition phase, the animals were required to find a hidden underwater platform starting from four different points. The task was repeated twice a day for 10 days. In the retention phase after 10 days rest, the rats repeated the same task. The damage caused by the treatment occurred in several prosencephalic areas, including the piriform and enthorhinal cortices, the thalamus and the hippocampus. In the latter, greatest damage was seen in CA1 followed by CA3 while CA2 and the gyrus dentatus appeared almost unaffected. The behavioural results indicated that kainic acid impaired but did not preclude the acquisition of the water-maze task. During the retention phase, no significant differences in latencies were found between animals that were treated before and after acquisition, thus, indicating that pretraining does not play an important role in the recovery of these spatial abilities following hippocampal lesions.