Elfn1 Regulates Target-Specific Release Probability at CA1-Interneuron Synapses

On the Receiving End One type of neuron, the hippocampal pyramidal neuron, forms two different types of synapses with two different downstream partners. When the partner is an oriens-lacunosum moleculare (O-LM) interneuron, the pyramidal neuron only releases its synaptic vesicles with a low probability. When the cell on the receiving end is a parvalbumin (PV)-positive interneuron, the likelihood of synaptic vesicle release is high. How can the postsynaptic cell change the release characteristics of the presynaptic cell? Sylwestrak and Ghosh (p. 536 , published online 4 October; see the Perspective by McBain ) describe how the extracellular leucine-rich repeat fibronectin containing 1 (Elfn1) protein in the postsynaptic OLM interneurons affects vesicle release probability in the presynaptic pyramidal neuron. Misexpression of Elfn1 in PV interneurons converted vesicle release to the OLM pattern. Thus, a regulator located in the postsynaptic cell can modulate the function of the synapse.