[Characteristics of the development of postural asymmetry in rats as affected by the opioids met-enkephalin and the kappa-agonist bremazocine].

It has been found that bremazocine and met-enkephalin induce postural asymmetry in spinal rats under subarachnoidal and intravenous administration. Intravenous administration of bremazocine to intact animals--even if after it (an hour later) their spinal cord is sectioned--produces no asymmetry, i. e. the spinal cord section is necessary for asymmetry development. The magnitude of postural asymmetry and the side of limb flexion are not constant for each animal, but they change in time. Though, on the average, the percent of asymmetric animals and the ratio of left and right flexions in each group of animals are practically constant. When the spinal cord is sectioned at the T1-T4 level, the bremazocine and metenkephalin induce mainly the right-leg flexion: when the section is made at the T5-T9 level, the left-leg is bent, i. e. the flexion side depends on the level of the section. It is suggested that the ability of opioids to induce postural asymmetry is based on lateralization of opioid receptors in the rat spinal cord.