The regulated secretion of bioactive peptides requires the coordinated actions of a variety of gene products ranging from peptide precursors to post-translational processing enzymes and the cytosolic machinery involved in vesicle exocytosis. To evaluate the role of plasticity of peptidergic processes in the clinical response to electroconvulsive treatment, we monitored expression of a peptide (neuropeptide Y, NPY), a post-translational processing enzyme (peptidylglycine alpha-amidating monooxygenase, PAM) and a cytosolic component involved in peptide secretion and neurite extension (kalirin) in the hippocampus. Adult male rats were subjected to single or repeated electroconvulsive shock. In general, levels of NPY, PAM and kalirin mRNA showed similar transient increases after acute and repeated electroconvulsive shock. In contrast, repeated, but not acute, electroconvulsive shock brought about widespread changes in protein expression. Increased amounts of NPY and PAM accumulated in mossy fibers, and dentate granule cell dendrites contained increased amounts of NPY, PAM and kalirin. CA1 pyramidal neurons expressed increased amounts of PAM and kalirin, with an accumulation of both proteins in their dendrites. Scattered interneurons contained increased levels of NPY and PAM after acute and repeated shocks. However, scattered interneurons contained increased levels of kalirin only after repeated shocks. The distinctly different effects of repeated vs. acute electroconvulsive shock support an important role for peptidergic plasticity in the therapeutic effects observed following electroconvulsive treatment.