Differential involvement of hippocampal angiotensin 1 receptors in learning and memory processes in bulbectomized rats

There is conflicting evidence regarding the effect of AT1 receptor antagonists on learning and memory processes. The effects of angiotensin II and losartan administration into CA1 hippocampal area on the avoidance performance in olfactory bulbectomized (OBX) rats using active avoidance (shuttle box) test and passive avoidance (step through) test were investigated. Rats were microinjected unilaterally through implanted guide cannulas into the CA1 area of the dorsal hippocampus and the drugs were administered separately, 5 minutes before each training session. The microinjections of losartan into the left, but not the right CA1 hippocampal area improved the acquisition and retention of active and passive avoidance learning, thus suggesting dependence on the side of injection. The unilateral (left or right) administration of angiotensin II did not significantly affect the performance of OBX rats in the avoidance tasks. A differential distribution of the AT1 receptors in the left and right hemisphere could contribute for the asymmetry in the behavioral effects of the AT receptor antagonist.