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.
PIP: The effect of selective lesioning of brain serotonin or catecholamine-containing neurons on the activity of oral steroid contraceptives was examined in rats. Dosage combinations of lynestrenol and mestranol were administered orally to the animals. The midbrain raphe (MR) lesion or the intraventricular injection of 6-hydroxydopamine (6-OHDA) produced, respectively, a marked decrease of serotonin and catecholamines in the forebrain. In the sham-operated or MR-lesioned animals, the estrous, cycle, fertility, and activity of the steroids studied were not affected. In pargyline plus 6-OHDA-treated rats the estrous cycle was irregular in 4 out of 17 animals (p less than .05). No marked differences in the number of pregnant rats were found between MR-lesioned or 6-OHDA treated rats. These negative results obtained with the MR lesion or with the 6-OHDA treatment indicate that neither serotonin nor catecholamines play an important role in fertility or contraceptive action of the steroids studied.