At excitatory and inhibitory synapses, an immediate transfer of additional neurotransmitter receptors from non-synaptic positions to the synapse mediates synaptic long-term potentiation (LTP). Different types of non-synaptic reserve pools permit the rapid supply of transmembrane neurotransmitter receptors. Recycling endosomes (REs) serve as an intracellular reservoir of receptors that is delivered to the plasma membrane on LTP induction. Furthermore, AMPA receptors at the non-synaptic plasma membrane provide an extrasynaptic reserve pool that is also important to potentiate synapse function. Finally, bidirectional synaptic versus extrasynaptic trapping of freely diffusing plasma membrane GABAA receptors (GABAARs) by scaffolding proteins modulates synaptic transmission. Here we discuss novel findings regarding neurotransmitter receptor reservoirs and potential reserve pool mechanisms for synaptic potentiation.
