[Asymmetric changes of the muscle tonus of the hindlimbs of rats subjected to administration of extracts from the left and right brain hemispheres].

Suboccipital administration to rats of the solutions of substances extracted from the left and right halves of the brain with 1 M hot acetic acid gives rise to humping, restricts animals' mobility and induces asymmetric changes in the muscle tone of the hind limbs. The hind limb may be extended back or aside at the same side where brain extraction was performed and may retain this position for 25-30 sec. Proteolysis of the extracts or preliminary administration of nalorphine to the animals abolished the occurrence of, while suboccipital administration of naloxon removed the extract-evoked changes in the muscle tone. After application of the extracts to the spinal cord of the hordotomized (Th5-Th7) rats the electrical activity rose at the same side where brain extraction was performed, primarily in the m. quadriceps. It is assumed that active factors extracted from the left and right halves of the brain are different; they are endogenous opioid peptides or else their effects on the activity of spinal motoneurons are mediated via the opiate systems.