Neuronal glutamate transporter EAAT3 regulates hippocampal GABAergic plasticity and reversal learning

Long-term depression (LTD) is a form of synaptic plasticity implicated in tasks involving the modification or elimination of previously learned information. While glial glutamate transporters can control the strength of synaptic plasticity, much less is known about the contribution of the neuronal glutamate transporter EAAT3 in controlling hippocampal LTD and learning processes. Here, we report that overexpression of EAAT3 in principal neurons, but not in GABAergic interneurons, impairs heterosynaptic GABAergic synaptic plasticity (iLTD) and homosynaptic excitatory LTD in the hippocampus. LTD impairments can be reversed by inhibiting EAAT3 or by a brief exogenous activation of mGluR during LTD induction, suggesting that, by limiting glutamate spillover between neighboring synapses, EAAT3 contributes to setting the strength of different forms of hippocampal LTD. Moreover, mice overexpressing EAAT3 in principal neurons, but not in GABAergic interneurons, display impaired reversal learning, a phenotype that can be rescued by blocking EAAT3 in vivo. Together, these findings reveal that, by controlling the strength of hippocampal LTD, EAAT3 contributes to cognitive flexibility required for processing new information.