Synaptic scaling of corticostriatal circuits underlies hyperactivity in GABA Transporter-1 deficient mice

Homeostatic synaptic scaling entails adjustment of synaptic strength on a cell to prolonged changes of neuronal activity, which is postulated to participate in neuropsychiatric disorders in vivo. Here, we find that sustained elevation in ambient GABA levels, by either genetic deletion or pharmacological blockade of GABA transporter-1 (GAT1), leads to synaptic scaling up of corticostriatal pathways, which underlies locomotor hyperactivity. Meanwhile, medium spiny neurons of the dorsal striatum exhibit an aberrant increase in excitatory synaptic transmission and corresponding structural changes in dendritic spines. Mechanistically, GAT1 deficiency dampens the expression and function of metabotropic glutamate receptors (mGluRs) and endocannabinoid (eCB)-dependent long-term depression of excitatory transmission. Conversely, restoring mGluR function in GAT1 deficient mice rescues excitatory transmission. Lastly, pharmacological potentiation of mGluR-eCB signaling or inhibition of homomeric-GluA1 AMPA receptors eliminates locomotor hyperactivity in the GAT1 deficient mice. Together, these results reveal a synaptic scaling mechanism in corticostriatal pathways that regulate locomotor activity.