Optogenetic Control of Synaptic AMPA Receptor Endocytosis Reveals Roles of LTD in Motor Learning

Long-term depression (LTD) of AMPA-type glutamate receptor (AMPA receptor)-mediated synaptic transmission has been proposed as a cellular substrate for learning and memory. Although activity-induced AMPA receptor endocytosis is believed to underlie LTD, it remains largely unclear whether LTD and AMPA receptor endocytosis at specific synapses are causally linked to learning and memory in vivo. Here we developed a new optogenetic tool, termed PhotonSABER, which enabled the temporal, spatial, and cell-type-specific control of AMPA receptor endocytosis at active synapses, while the basal synaptic properties and other forms of synaptic plasticity were unaffected. We found that fiberoptic illumination to Purkinje cells expressing PhotonSABER in vivo inhibited cerebellar motor learning during adaptation of the horizontal optokinetic response and vestibulo-ocular reflex, as well as synaptic AMPA receptor decrease in the flocculus. Our results demonstrate that LTD and AMPA receptor endocytosis at specific neuronal circuits were directly responsible for motor learning in vivo. VIDEO ABSTRACT.