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Searching for cognitive enhancement in the Morris water maze: better and worse performance in D‐amino acid oxidase knockout ( Dao −/− ) mice
Author(s) -
Pritchett David,
Taylor Amy M,
Barkus Christopher,
Engle Sandra J,
Brandon Nicholas J,
Sharp Trevor,
Foster Russell G,
Harrison Paul J,
Peirson Stuart N,
Bannerman David M
Publication year - 2016
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/ejn.13192
Subject(s) - morris water navigation task , neuroscience , long term potentiation , synaptic plasticity , knockout mouse , water maze , hippocampus , hippocampal formation , nmda receptor , elevated plus maze , psychology , t maze , chemistry , pharmacology , biochemistry , receptor , biology , anxiety , psychiatry
Abstract A common strategy when searching for cognitive‐enhancing drugs has been to target the N ‐methyl‐ d ‐aspartate receptor (NMDAR), given its putative role in synaptic plasticity and learning. Evidence in favour of this approach has come primarily from studies with rodents using behavioural assays like the Morris water maze. D‐amino acid oxidase (DAO) degrades neutral D‐amino acids such as D‐serine, the primary endogenous co‐agonist acting at the glycine site of the synaptic NMDAR. Inhibiting DAO could therefore provide an effective and viable means of enhancing cognition, particularly in disorders like schizophrenia, in which NMDAR hypofunction is implicated. Indirect support for this notion comes from the enhanced hippocampal long‐term potentiation and facilitated water maze acquisition of ddY/ Dao − mice, which lack DAO activity due to a point mutation in the gene. Here, in Dao knockout ( Dao −/− ) mice, we report both better and worse water maze performance, depending on the radial distance of the hidden platform from the side wall of the pool. Dao −/− mice displayed an increased innate preference for swimming in the periphery of the maze (possibly due to heightened anxiety), which facilitated the discovery of a peripherally located platform, but delayed the discovery of a centrally located platform. By contrast, Dao −/− mice exhibited normal performance in two alternative assays of long‐term spatial memory: the appetitive and aversive Y‐maze reference memory tasks. Taken together, these results question the proposed relationship between DAO inactivation and enhanced long‐term associative spatial memory. They also have generic implications for how Morris water maze studies are performed and interpreted.