Reducing expression of GluN1OXX subunit splice variants of the NMDA receptor interferes with spatial reference memory

This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/behavioural-brain-research/.The GluN1 subunit of the NMDA receptor shows age-related changes in its\ud expression pattern, some of which correlate with spatial memory performance in mice.\ud Aged C57BL/6 mice show an age-related increase in mRNA expression of GluN1\ud subunit splice variants that lack the N terminal splice cassette, GluN1ₒₓₓ (GluN1-a). This\ud increase in expression is associated with good performance in reference and working\ud memory tasks. The present study was undertaken to determine if GluN1ₒₓₓ splice\ud variants are required for good performance in reference memory tasks in young mice.\ud Mice were bilaterally injected with either siRNA specific for GluN1ₒₓₓ splice variants,\ud control siRNA or vehicle alone into ventro-lateral orbital cortices. A fourth group of mice\ud did not receive any injections. Starting five days post-injection, mice were tested for their\ud performance in spatial reference memory, associative memory and cognitive flexibility\ud tasks over 4 days in the Morris water maze. There was a 10 -19% reduction in mRNA\ud expression for GluN1ₒₓₓ splice variants within the ventro-lateral orbital cortices in mice\ud following GluN1ₒₓₓ siRNA treatment. Declines in performance within the first half of\ud reference memory testing were seen in the mice receiving siRNA against the GluN1ₒₓₓ\ud splice variants, as compared to the mice injected with control siRNA, vehicle and/or no\ud treatment. These results suggest a role for the GluN1ₒₓₓ splice variants in orbital regions\ud for early acquisition and/or consolidation of spatial reference memory