Miwa Toyoda, Hiroshi Saito and Norio Matsuki (*)
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan (*) To whom correspondence should be addressed.
Abstract: The aim of the present study was to elucidate the role of carbon monoxide (CO) in learning and to compare it with that of nitric oxide (NO). Effects of an inhibitor of heme oxygenase which produces CO, Zn-protoporphyrin IX, on passive avoidance learning and spatial learning in mice were examined using step through, step down and water maze tests. Zn-protoporphyrin IX (10, 20 nmol, i.c.v.) affected neither type of learning. In contrast, N-omega-nitro-L-arginine (40 nmol, i.c.v.), an inhibitor of NO synthase, impaired spatial learning, but not passive avoidance learning. These results suggest that NO but not CO is involved in spatial learning.
Carbon monoxide, Zn-protoporphyrin IX, Spatial learning, Passive avoidance learning, Nitric oxide
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