Repeated electroconvulsive shocks alter the biosynthesis of enkephalin and concentration of dynorphin in the rat brain

Ten daily electroconvulsive shocks (ECSs) caused a two-fold increase in (Met5)-enkephalin-like immunoreactivity (ME-LI) and an 80% increase in the level of mRNA coding for preproenkephalin A in the hypothalamus. These observations suggest that repeated ECSs increase the biosynthesis of hypothalamic ME. Ten daily ECSs also increased dynorphin A (1-8)-like immunoreactivity (DN-LI) in hypothalamus (45%) but not in frontal cortex. Unlike other brain regions, a 64% decrease of DN-LI was found in the hippocampus after 10 daily ECSs whereas a significant increase of ME-LI (40%) was observed. Furthermore, immunocytochemical studies revealed an increase of (Leu5)-enkephalin-like immunoreactivity in the perforant pathway and a decrease of DN-LI in the mossy fiber system of the hippocampus after 10 daily ECSs. These studies suggest that alterations in enkephalin and dynorphin in the limbic system may contribute to the behavioral changes observed after repeated ECSs.