In order to elucidate the role played by the limbic structure for the regulation of pituitary-ovarian functioning, electrical stimulation was applied to the limbic structure and the hypothalamus through chronically implanted electrodes, and its influence on biosynthesis of various ovarian steroids was studied in the mature New Zealand white rabbit.
The implanted rabbits were primed with estradiol benzoate in oil (0.1 mg s. c.) for 2 days prior to stimulation to ensure anestrous state. Electrical stimulation, consisting of monophasic square wave pulses, was delivered unilaterally for 30min., 60 sec. on and 60 sec. off, 190-210μA, at 0.1 msec. duration, 60 cps. The experimental results as follows.
1. Ovulation was induced in 23 out of 27 cases by stimulating the alveus of the hippocampus. Facilitation of biosynthesis of various progestin fractions accompanied ovulation. Stimulation delivered to the cornus ammonis and the fascia dentata failed to induce ovulation in all of 17 cases. In these cases biosynthesis of progestin fractions was facilitated. Estrogen biosynthesis was little affected by brain stimulation regardless of whether ovulation was induced or not.
2. Ovulation was induced by stimulating the intermediate and medial nuclei of the amygdala in all of 13 cases. Progestin biosynthesis was markedlyf acilitated in these cases. Estrogen formation was slightly increased. Stimulation applied to the medial principal and lateral nuclei was ineffective in inducing ovulation, but progestin biosynthesis was considerably facilitated. Estrogen formation was not affected.
3. Stimulation of the periventricular arcuate nucleus of the hypothalamus was accompanied by ovulation and by facilitation of progestin biosynthesis. Supraoptic stimulation induced ovulation and facilitation of progestin formation in 5 out of 9 cases. Stimulation delivered to the centralgrey was ineffective in progestin formation.
4. Ovulation was induced by LH administration or copulation. Biosynthesis of progestin was remarkably facilitated, while estrogenwas moderately increased.
5. The influence of hippocampal or amygdalar stimulationon the progestin biosynthetic pattern was quite different from that of copulation, LH administration or stimulation of the periventricular arcuate nucleus.
6. The effects of hippocampal stimulation on ovarian functions were cancelled by destroying the fornix or periventricular arcuatenucleus but not by lesioning the stria terminalis.
7. Progesterone implants in the hippocampus facilitated progestin biosynthesis in the ovary. Thus hippocampus can be regarded as a focus concerned with positive feedback regulation of progesterone release.
8. Progesterone implants in the amygdala or supraoptic region or anterior hypothalamic area were almost ineffective for the steroid biosynthetic pattern of the ovary.
9. Thus the limbic system, above all the hippocampus, plays a significant role in the brain-pituitary-ovarian system.
View full abstract