Single and repeated electroconvulsive shock differentially affects the prodynorphin and pro-opiomelanocortin system in the rat

Abstract

The effects of single and repeated maximal electroconvulsive shock (ECS, 150 mA, 50 Hz, 0.5 s) on the immunoreactive (ir-)dynorphin and β-endorphin level in the rat brain, spinal cord and pituitary were studied. A single ECS induced a transient decrease in the hypothalamic ir-dynorphin, but did not influence the peptide content in the spinal cord, hippocampus and neurointermediate lobe of the pituitary. In contrast, the single ECS only slightly decreased the ir-β-endorphin level in the hypothalamus, but caused a considerable fall in the peptide content in both lobes of the pituitary. A repeated ECS (every day for 9 days and 3 times a week for 3 weeks) markedly increased the ir-dynorphin content in the hypothalamus by 28 and 56%, respectively. Irrespective of the paradigm used, the repeated ECS strongly influenced spinal dynorphin neurons. At the beginning of our experiment (ECS applied 3 times) a fall in the peptide levels could be observed, but a longer treatment (ECS applied 9 times) led to its enhancement. The repeated ECS also induced a gradual decrease in the hippocampal ir-dynorphin level, followed by a long-term, rebound increase. In contrast to those numerous changes evoked in the dynorphin system, the repeated ECS did not evoke any changes in the hypothalamic and pituitary ir-β-endorphin levels. As shown in the behavioral experiment, an acute ECS treatment resulted in a moderate increase in the pain threshold, measured by tail-flick and hot-plate tests. A prolonged ECS administration (3, 6 and 9 times) markedly enhanced the ECS-induced analgesia and catalepsy. We suggest that the prodynorphin system, but not the pro-opiomelanocortin one, can be involved in behavioral effects observed after the repeated ECS.