Influence of cerebral cortex in inhibition of oxytocin release induced by stressful stimuli

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Abstract
Weight increase of a litter of rats during the course of 1 hr of suckling, after a 9-hr separation from their mothers, was taken as a measure of the amount of oxytocin released. The opening in the mother of an orifice in the cranium, on each side of the midline (bilateral trauma), or the fracture of one femur (unilateral trauma) caused a marked decrease in the litter's weight gain. Milk ejection so depressed was restored to the normal level by administration of oxytocin (20 mU/100 g). Stimuli arising from the traumatized area, therefore, exert a central inhibition on oxytocin release. In hemimammectomized animals, femoral fracture on the side with intact mammary glands has a greater inhibitory effect than the fracture on the opposite side. Topical application of 25% KCl on the cerebral cortex, in order to induce cortical spreading depression, caused the disappearance of the inhibition of oxytocin secretion. The influence of corticofugal systems on the reticular formation as a possible mechanism responsible for the suppression of the inhibitory action of stimuli on the release of oxytocin is discussed.