Reduction in opiate activation after chronic electroconvulsive shock--possible role for endorphins in the behavioral effects of convulsive shock treatment.

Group-housed adult male Sprague-Dawley rats were given a series of 4 exposures to electroconvulsive shock therapy or equivalent handling without shock (sham treatment). Twenty-four hours after the final treatment the rats were given vehicle or one of two doses of morphine intraperitoneally, and motor activity was assessed by remote sensing for 60 min. A significant shift of the normal dose-response curve towards the right was seen after electroshock. This may point to cross-tolerance between electroshock and opiates upon this behavioral measure. The results are consistent with the hypothesis that endorphins may mediate certain aspects of electroshock.