Repeated electroconvulsive shock downregulates the opioid receptors in rat brain

Ten consecutive daily electroconvulsive shocks (ECSs), which produce maximal tonic and clonic convulsions, caused reductions of mu- and delta-opioid receptor binding in the hypothalamus, hippocampus and caudate nucleus, but not in the frontal cortex and brainstem. These changes of opioid receptor binding were not observed in rats receiving a single ECS. Scatchard analysis revealed that ECS-induced reduction of mu- and delta-receptor binding was due to a decrease in the binding sites but not to a change in the binding affinity. Time course studies showed that 7 days after the end of 10 consecutive daily ECSs, both mu- and delta-receptor binding remained lower than those of sham controls. However, the effects of ECS on the opioid receptor binding disappeared in 2-3 weeks. These observations are consistent with the hypothesis that ECS treatments increase the release of opioid peptides in certain brain regions which in turn down-regulate the opioid receptors.