Loss of CA1 cells following global ischaemia correlates with spatial deficits in the circular platform task

The effect of 15 min, four-vessel-occlusion (4-VO) ischaemia on performance by rats in the circular platform task (CPT) was investigated. Possible correlations between the extent of hippocampal cell loss and behavioural disruption were evaluated. Sham-operated controls (n=10) and 4-VO ischaemic animals (n=32) were required to escape from a 1.2 m diameter, brightly illuminated, white surface into a dark goal box located under one of 18 equally-spaced, 9 cm diameter holes arranged around the circumference (3 trials per day). The goal box was maintained in a single, fixed, rewarded location relative to the extramaze cues for 7 days (days 16-22 post-ischaemia). During the reversal test, the goal box was transferred to a new location 140 degrees from the initial point and kept in this new position from day 23 through day 25 post-ischaemia. Ischaemic rats were slower to find the goal box than sham-operated controls; this learning deficit correlated with the degree of neuronal loss in the CA1, but not in the CA2, CA3 and CA4 subfields and presubiculum of the hippocampal formation. During the reversal test, ischaemic rats persisted in searching for the goal box at the initially rewarded location. The circular platform task provides a good model for behavioural studies following transient forebrain ischaemia in the rat.