Early synaptic deficits in GSK-3β overexpressing mice.

Synaptic dysfunction is the prominent feature of many neuropsychiatric and neurological diseases, in which glycogen synthase kinase 3β (GSK-3β) has been shown to play a role. Overexpression of constitutively active form of GSK-3β (GSK-3β[S9A]) in mice recapitulates the cognitive and structural brain deficits characteristic for manic phase of bipolar disorder (BD). Yet, the mechanisms underlying GSK-3β-induced synaptic dysfunction have not been fully elucidated. The aim of the present study was to dissect the effect of GSK-3β overactivity on synaptic function in adolescent (3-week-old) mice. We found that overactivity of GSK-3β in adolescent transgenic mice leads to an alteration in dendritic spines morphology of granule cells in dentate gyrus (DG) without changes in overall spine density. There was an increase in the number of thin, presumably immature dendritic spines in GSK-3β[S9A] mice. Subsequent electrophysiological analysis showed changes in excitatory synaptic transmission manifested by an increase of inter-event intervals of miniature excitatory postsynaptic currents (mEPSCs) in DG granule cells and an increase in the number of silent (unfunctional) synapses at the perforant path-DG pathway in GSK-3β[S9A] mice. Altogether, our data indicate that GSK-3β overactivity leads to synaptic deficits in adolescent, GSK-3β[S9A] mice. These data might provide potential mechanisms underlying GSK-3β-induced synaptic dysfunction in psychiatric disorders.