IMPAIRED LEARNING AND MEMORY IN MATURE SPONTANEOUSLY HYPERTENSIVE RATS

In very old, normotensive rats, a disorganization occurs selectively in the retrosplenial cortex, and a similar disorganization occurs in this area in spontaneously hypertensive rats (SHR) at a much earlier age. Since this breakdown compromises a neural circuit involved in learning and memory, this study tests the hypotheses that these functions are disturbed in mature SHR and that they can be prevented or attenuated by long-term, anti-hypertensive therapy. SHR and Sprague Dawley rats (SD) at 3- and 12 months of age, and a group of SHR that had been normotensive from 3 to 12 months of age (CAP-SHR) were trained on an 8 arm radial maze task. Of the 12-month-old groups, SD reached criterion earliest (28+/-2 days) and made the least number of total errors. In comparison, 12-month-old SHR took significantly longer to reach criterion (39+/-2 days) and made nearly twice as many total errors. CAP-SHR were intermediate between the other two groups (32+/-2 days). Three-month-old SD learned the task at the same rate as the 12-month-old SD. In contrast, 3-month-old SHR learned the task significantly faster (21+/-1 days) and with fewer errors than any other group. These data indicate that, in SHR, learning and memory are compromised by 12 months of age, and that anti-hypertensive therapy with captopril partially prevents this decline.