Effects of estrogens and progesterone on the synaptic organization of the hypothalamic ventromedial nucleus

• Published in: Neuroscience Vol. 162; no. 2; pp. 307 - 316
• Main Authors: Sá, S.I, Lukoyanova, E, Madeira, M.D
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 18.08.2009; Elsevier
• Subjects: Animals; Biological and medical sciences; Cell Count; diarylpropionitrile; Dose-Response Relationship, Drug; Estradiol - analogs & derivatives; Estradiol - pharmacology; estrogen receptor; Estrogen Receptor alpha - agonists; Estrogen Receptor beta - agonists; Estrogens - administration & dosage; Estrogens - pharmacology; Female; Fundamental and applied biological sciences. Psychology; Ligands; mifepristone; Neurology; Neurons - cytology; Neurons - drug effects; Neurons - ultrastructure; Nitriles - pharmacology; Phenols; Posture; Progesterone - administration & dosage; Progesterone - pharmacology; Progestins - pharmacology; Propionates - pharmacology; propyl-pyrazole-triol; Pyrazoles - pharmacology; Rats; Rats, Wistar; Sexual Behavior, Animal - drug effects; synapses; Synapses - drug effects; Synapses - ultrastructure; Ventromedial Hypothalamic Nucleus - cytology; Ventromedial Hypothalamic Nucleus - drug effects; Ventromedial Hypothalamic Nucleus - ultrastructure; ventromedial nucleus; Vertebrates: nervous system and sense organs; PR; DPN; N V; ventrolateral part of the ventromedial nucleus of the hypothalamus; progesterone; VCS; estrogen receptor-β; mifepristone; estrogen receptor-α; VMNvl; O; P; oil; analysis of variance; ANOVA; PPT; ventromedial nucleus; EB; estradiol benzoate; numerical density; ERβ; estrogen receptor; ERα; progestin receptors; RU486; propyl-pyrazole-triol; ventromedial nucleus of the hypothalamus; diarylpropionitrile; ER; synapses; VMN; vaginocervical stimulation; Estrogen receptor; Central nervous system; Estrogen; Hypothalamus; Ovarian hormone; Encephalon; Synapse; Ventromedial nucleus; Mifepristone; Progesterone; Sex steroid hormone
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2009.04.066

Abstract The majority of the studies on the actions of estrogens in the ventrolateral part of the hypothalamic ventromedial nucleus (VMNvl) concern the factors that modulate the receptive component of the feminine sexual behavior and the expression of molecular markers of neuronal activation. To further our understanding of the factors that regulate synaptic plasticity in the female VMNvl, we have examined the effects of estradiol and progesterone, and of estrogen receptor (ER) subtype selective ligands on the number of dendritic and spine synapses established by individual VMNvl neurons and on sexual behavior. In contrast to earlier studies that analyzed synapse densities, our results show that exogenous estradiol increases the number of spine as well as of dendritic synapses, irrespective of the dose and regimen of administration. They also reveal that an effective dose of estradiol administered as one single pulse induces the formation of more synapses than the same dose administered as two pulses on consecutive days. Our results further show that both ER subtypes are involved in the mediation of the synaptogenic effects of estrogens on VMNvl neurons since the administration of the selective ERα, propyl-pyrazole-triol (PPT), and ERβ, diarylpropionitrile (DPN), agonists induced a significant increase in the number of synapses that, however, was more exuberant for PPT. Despite its relevant role in feminine sexual behavior, progesterone had no synaptogenic effect in the VMNvl as no changes in synapse numbers were noticed in rats treated with progesterone alone, with estradiol followed by progesterone or with the antiprogestin mifepristone (RU486). Except for the sequential administration of estradiol and progesterone, none of the regimens was associated with lordosis response to vaginocervical stimulation. Therefore, from the sex steroids that undergo cyclic variations over the estrous cycle, only estrogens, acting through both ERα and ERβ, play a key role in the activation of the neural circuits involving the ventromedial nucleus of the hypothalamus.