Learning and MemoryState-dependent impairment in object recognition after hippocampal NOS inhibitionBlokland, Arjan1,3; Prickaerts, Jos2; Honig, Wiel2; de Vente, Jan2Author Information 1Department of Psychology, Maastricht Brain and Behavior Institute, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands 2Department of Psychiatry and Neuropsychology, Maastricht Brain and Behavior Institute, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands 3Corresponding Author: Arjan Blokland ACKNOWLEDGEMENTS: The research of A.B. has been made possible by a fellowship of the Royal Netherlands Academy of Arts and Sciences. Received 16 September 1998; accepted 14 October 1998 NeuroReport: December 21st, 1998 - Volume 9 - Issue 18 - p 4205-4208 Buy Abstract IN the present study we investigated the consequences of hippocampal nitric oxide synthase (NOS) inhibition on the performance in an object recognition task in rats. In a first study we injected Nω-nitro-L-arginine (LNA) into the hippocampus directly after the first trial. One hour later the discrimination performance of the animals was assessed. It was found that 1 μ g and 3 O°g, but not 3 μg, L-NA impaired the performance of the rats. In a second study in which we injected L-NA 45 min before the first trial no effects of treatment (10 μg and 3 Oμg) were observed. Since treatment with 30 μg has been found to inhibit hippocampal NOS almost completely and lasts longer than 2 h, it was concluded that hippocampal NOS inhibition induced a state-dependent performance deficit. Consequently, studies that examine the effects of NOS inhibition on cognitive functions should take this confounding effect into account. © 1998 Lippincott Williams & Wilkins, Inc.