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Local inhibition of hippocampal nitric oxide synthase does not impair place learning in the Morris water escape task in rats

Authors

  • Arjan Blokland,

    1. Faculty of Psychology and
    2. European Graduate School of Neuroscience (EURON) Department of Psychiatry and Neuropsychology, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
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  • Jan De Vente,

    1. European Graduate School of Neuroscience (EURON) Department of Psychiatry and Neuropsychology, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
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  • Jos Prickaerts,

    1. European Graduate School of Neuroscience (EURON) Department of Psychiatry and Neuropsychology, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
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  • Wiel Honig,

    1. European Graduate School of Neuroscience (EURON) Department of Psychiatry and Neuropsychology, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
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  • Marjanne Markerink- Van Ittersum,

    1. European Graduate School of Neuroscience (EURON) Department of Psychiatry and Neuropsychology, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
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  • Harry Steinbusch

    1. European Graduate School of Neuroscience (EURON) Department of Psychiatry and Neuropsychology, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
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A. Blokland, Faculty of Psychology, Section Biological Psychology, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands. E-mail: a.blokland@psychology.unimaas.nl

Abstract

Recent studies have provided evidence that nitric oxide (NO) has a role in certain forms of memory formation. Spatial learning is one of the cognitive abilities that has been found to be impaired after systemic administration of an NO-synthase inhibitor. As the hippocampus has a pivotal role in spatial orientation, the present study examined the role of hippocampal NO in spatial learning and reversal learning in a Morris task in adult rats. It was found that Nω-nitro-l-arginine infusions into the dorsal hippocampus affected the manner in which the rats were searching the submerged platform during training, but did not affect the efficiency to find the spatial location of the escape platform. Hippocampal NO-synthase inhibition did not affect the learning of a new platform position in the same water tank (i.e. reversal learning). Moreover, no treatment effects were observed in the probe trials (i.e. after acquisition and after reversal learning), indicating that the rats treated with Nω-nitro-l-arginine had learned the spatial location of the platform. These findings were obtained under conditions where the NO synthesis in the dorsal hippocampus was completely inhibited. On the basis of the present data it was concluded that hippocampal NO is not critically involved in place learning in rats.

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