Katsuo Seto

Effects of estrogen on the excitability of neurons projecting from the noradrenergic A1 region to the preoptic and anterior hypothalamic area

Estradiol benzoate administered to ovariectomized female rats significantly elevated the mean spontaneous firing rate and frequency of successful antidromic propagation into the somatodendritic spike and significantly reduced the strength of post-stimulus inhibition in presumed A1 noradrenergic neurons projecting directly to the preoptic and anterior hypothalamic area. The occurrence of both antidromic spikes and post-stimulus inhibition of the majority of these neurons was completely abolished by the injection of 6-hydroxydopamine but not by 5, 7-dihydroxytryptamine directly into the medial forebrain bundle.

Mechanisms in the Limbic System Controlling Reproductive Functions of the Ovary with Special Reference to the Positive Feedback of Progestin to the Hippocampus

Publisher Summary The purpose of this chapter is to discuss mechanisms in the limbic system controlling reproductive functions of the ovary with special reference to the positive feedback of progestin to the hippocampus. The mechanism by which limbic structures modulate the function of the hypothalamo-hypophysial system is undoubtedly neural in character. On the other hand, it is inferred that the sex hormone and gonadotrophin act on the excitabilities of the limbic structures. The experiments are given in the chapter is designed to demonstrate the existence of positive feedback control of the hippocampus on ovarian progesterone formation and its output, as well as the existence of negative feedback control of the amygdala on ovarian progesterone formation and its output. In conclusion, the results of these experiments support the presumption that the hippocampus and the amygdala are the critical areas of feedback control of progesterone: the hippocampo-hypothalamo-pituitary-gonad axis is a loop of the positive feedback of progesterone and the medial amygdaloid complex a loop of the negative feedback of progesterone.

Influence of Repeated Immobilization Stress upon the Circadian Rhythmicity of Adrenocorticoid Biosynthesis

Experiments were carried out to elucidate the influence of stress on the diurnal change in adrenal biosynthetic activity during controlled 24 h light-dark cycles. stress Groups of 10 rabbits were deca

Biosynthesis of Ovarian Steroids in the Rabbit: Influence of Progesterone or Estradiol Implantation into the Hypothalamus and Limbic Structures

The feedback action of progesterone and estradiol implants in the hippocampus amygdala and hypothalamus was investigated and their influence on the incorporation of acetate-1-carbon-14 into ovarian steroids by ovarian homogenate in rabbits was estimated. Progesterone implants in the alverus of the hippocampus markedly increased carbon-14 progestin formation. This region may be part of a positive feedback mechanism that regulates progestin production. Carbon-14-estrogen formation was markedly suppressed by estradiol implants in the medial nucleus of the amygadala which implies that the site is related to the negative feedback control of estrogen formation. Estradiol implants in various sites of the amygdala resulted in a decrease in progestin labeling. Progesterone implants in the medial preoptic area suppressed carbon-14-estrogen formation and those placed in the periventricular arcuate nucleus and the ventromedial hypothalamus nucleus encouraged carbon-14-estrogen formation. It is suggested that the periventricular arcuate nucleus and ventromedial hypothalamus nucleus are involved in different feedback mechanisms for progestin and estrogen formaton and that the medial preoptic area is involved in the reciprocal feedback control of estrogen formation. Estrogen implants inhibited estrogen formation in the medial preoptic area anterior hypothalamic area ventromedial hypothalamic nucleus and periventricular arcuate nucleus and facilitated estrogen formation in the supraoptic nucleus. Estradiol implants in the medial preoptic area anterior hypothalamic area and ventromedial hypothalamic nucleus facilitated progestin periventricular arcuate nucleus.