“…The effect of different dosage combinations of lynoestrenol and mestranol were studied in rats that have been subjected to selective lesioning of brain serotonin or catecholamine-containing neurons.Lesions of the midbrain raphe, which cause a marked decrease of serotonin in the forebrain, were without any effect on the estrus cycle, fertility and activity of the steroids under study.An intraventricular injection of 6-hydroxydopamine, which causes a selective decrease of noradrenaline and dopamine in the forebrain, produced a transient effect only on the estrus cycle but did not significantly change the fertility or the activity of the substances investigated.The data indicate that the integrity of monoaminergic neurons in the brain is not an essential condition for the aspects investigated in the present study.Oral contraceptives, containing an estrogen and a progestational agent, are considered to prevent contraception mainly by inhibiting ovulation through an interference with gonadotrophin secretion at either hypothalamic or anterior pituitary level (Diczfalusy, 1968;Tyler, 1967;Eisenfeld, 1972). The exact mechanism by which they exert this effect is still unknown.…”