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Keywords:

  • activity;
  • anxiety;
  • NMDA receptor;
  • reference memory;
  • working memory

Abstract

The brain-specific Ras/Rap-GTPase activating protein (SynGAP) is a prime candidate linking N-methyl-d-aspartate receptors to the regulation of the ERK/MAP kinase signalling cascade, suggested to be essential for experience-dependent synaptic plasticity. Here, we evaluated the behavioural phenotype of SynGAP heterozygous knockout mice (SG+/−), expressing roughly half the normal levels of SynGAP. In the cognitive domain, SG+/− mice demonstrated severe working and reference memory deficits in the radial arm maze task, a mild impairment early in the transfer test of the water maze task, and a deficiency in spontaneous alternation in an elevated T-maze. In the non-cognitive domain, SG+/− mice were hyperactive in the open field and appeared less anxious in the elevated plus maze test. In contrast, object recognition memory performance was not impaired in SG+/− mice. The reduction in SynGAP thus resulted in multiple behavioural traits suggestive of aberrant cognitive and non-cognitive processes normally mediated by the hippocampus. Immunohistochemical evaluation further revealed a significant reduction in calbindin-positive interneurons in the hippocampus and doublecortin-positive neurons in the dentate gyrus of adult SG+/− mice. Heterozygous constitutive deletion of SynGAP is therefore associated with notable behavioural as well as morphological phenotypes indicative of hippocampal dysfunction. Any suggestion of a possible causal link between them however remains a matter for further investigation.