Synaptic connections in the mammalian nervous system are established during development but are refined during adult life. In the CNS, synaptic plasticity is partly regulated by recycling postsynaptic neurotransmitter receptors. Bruneau and Akaaboune now describe the dynamics of acetylcholine receptor(AChR) recycling at the neuromuscular junction (NMJ) in mice and reveal that tyrosine dephosphorylation controls the insertion and maintenance of recycled AChR at this accessible synapse (see ). Previously,the researchers had shown, by using biotin-bungarotoxin and labelled streptavidin, that many AChRs reappear in the postsynaptic membrane after internalization and intermingle with AChRs that have not been internalized -so-called pre-existing AChRs. Now they show that recycled AChRs are removed from functional synapses much faster than pre-existing receptors. Denervation of the NMJ increases their removal rate; conversely, muscle stimulation prevents their loss. These findings shed light on how receptors at less accessible synapses are recycled and thus how synaptic plasticity is regulated in the CNS.
