Comparison of abstinence syndromes following chronic administration of mu and kappa opioid agonists in the rat.

Abstinent states were compared following chronic administration of mu and kappa opioid agonists, morphine and ethylketocyclazocine, respectively. Rats were prepared with chronic EEG and EMG electrodes and indwelling IV cannulae. One group of rats was chronically administered IV morphine, while a second group received chronic injections of IV ethylketocyclazocine. Morphine abstinence was associated with suppression of REM sleep occurrences, increases in number of wet-dog shakes, and a decline in EEG spectral power during slow-wave sleep episodes. In contrast, the ethylketocyclazocine abstinence syndrome included minor abstinence signs. Differences in abstinent states between morphine and ethylketocyclazocine indicate the involvement of separate receptor populations in the process of dependence on morphine and ethylketocyclazocine.