Disruption of hippocampus‐regulated behavioural and cognitive processes by heterozygous constitutive deletion of SynGAP

Abstract

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.