has start location has end location process has causal agent peptide zwitterion presynapse postsynapse retrograde trans-synaptic signaling retrograde trans-synaptic signaling by neuropeptide biological_process GO:0099082 Cell-cell signaling from postsynapse to presynapse, across the synaptic cleft, mediated by a neuropeptide. trans-synaptic signaling trans-synaptic signaling by neuropeptide