Activation of the CA2-vCA1 pathway reverses social discrimination dysfunction in Shank3B knockout mice

Social memory dysfunction is a feature of several neuropsychiatric and neurodevelopmental disorders. Mutation or deletion of the SHANK3 gene, which codes for a synaptic scaffolding protein, has been linked to autism spectrum disorder (ASD) and Phelan-McDermid syndrome, conditions associated with impairments in social memory. Shank3B knockout (KO) mice exhibit several behavioral abnormalities that may be analogous to symptoms of ASD, including social discrimination deficits. The CA2 region of the hippocampus integrates numerous afferents and sends a major output to the ventral CA1 (vCA1), circuitry that plays an important role in social memory. Despite finding few differences in excitatory afferents to the CA2 in Shank3B KO mice, chemogenetic activation of CA2 excitatory neurons restored social recognition function to wildtype (WT) levels. Specific activation of the CA2-vCA1 circuitry had a similar effect. Neuronal oscillations in the theta, gamma and, sharp wave ripple ranges have been linked to social memory, but we observed no differences in these measures between WT and Shank3B KO mice in the vCA1 in response to social stimuli. However, activation of CA2 excitatory neurons enhanced vCA1 theta power in Shank3B KO mice, concurrent with behavioral improvements. These findings suggest that stimulating adult circuitry in a mouse model with neurodevelopmental impairments can be sufficient to invoke latent function, particularly with respect to social memory dysfunction. The extent to which vCA1 network oscillations in the theta range are responsible for rescued behavioral function remains unknown.