No evidence for involvement of angiotensin II in spatial learning in water maze in rats

There is increasing evidence suggesting angiotensin II (AII) may inhibit memory formation in a range of conditioned avoidance and habituation learning tasks in rodents. We were interested to determine if AII might also play an inhibitory role in spatial learning. Angiotensin-converting enzyme (ACE) inhibitors, which block the formation of AII from AI, improve acquisition and/or retention of basal performance inhibited by the muscarinic receptor antagonist, scopolamine, in conditioned avoidance and habituation tasks. In hooded Wistar rats, over 5 days of training in a water maze neither the ACE inhibitor, ceranapril 5 and 50 micrograms/kg/day, nor the ACE inhibitor, ramipril 2 and 10 mg/kg/day, altered the increase in path length produced by administration of scopolamine 0.75 mg/kg/day. In probe trails (without platform), on the last day of training, ceranapril 50 micrograms/kg produced a 35% further deterioration in performance in the scopolamine-treated rats (P < 0.02). Administration of the substrate, renin, that leads to AII formation, did not alter water maze performance over 5 days of training. The angiotensin receptor antagonist, losartan, has been shown to improve basal and scopolamine-impaired performance in a habituation task and reverse the inhibition in long-term potentiation produced by diazepam. However, neither losartan 10 and 30 mg/kg/day nor ramipril 2 and 10 mg/kg/day reversed diazepam-impaired (3 mg/kg/day) acquisition of the spatial memory task over 5 days of training. These studies suggest AII does not inhibit spatial learning in rats in the constant platform position water maze task nor does it mediate the inhibitory effects of scopolamine or diazepam in this task.