Estrogen inhibits tuberoinfundibular dopaminergic neurons but does not cause irreversible damage

• Published in: Brain research bulletin Vol. 80; no. 6; pp. 347 - 352
• Main Authors: Morel, Gustavo R, Carón, Rubén W, Cónsole, Gloria M, Soaje, Marta, Sosa, Yolanda E, Rodríguez, Silvia S, Jahn, Graciela A, Goya, Rodolfo G
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16-12-2009
• Subjects: 17-β estradiol; Aging; Animals; Arcuate Nucleus of Hypothalamus - cytology; Arcuate Nucleus of Hypothalamus - drug effects; Arcuate Nucleus of Hypothalamus - physiology; Brain - cytology; Brain - drug effects; Brain - physiology; Cell Count; Cell Size - drug effects; Dopamine - metabolism; Estradiol - administration & dosage; Estradiol - adverse effects; Estradiol - pharmacology; Estrogens - administration & dosage; Estrogens - adverse effects; Estrogens - pharmacology; Female; Hyperprolactinemia - chemically induced; Hypothalamus; Hypothalamus - cytology; Hypothalamus - drug effects; Hypothalamus - physiology; Neurology; Neurons - cytology; Neurons - drug effects; Neurons - physiology; Ovariectomy; Paraventricular Hypothalamic Nucleus - cytology; Paraventricular Hypothalamic Nucleus - drug effects; Paraventricular Hypothalamic Nucleus - physiology; Pituitary Gland - cytology; Pituitary Gland - drug effects; Pituitary Gland - physiology; Prolactin; Prolactin - blood; Rats; Rats, Sprague-Dawley; Reversible inhibition; TIDA neurons; Tyrosine 3-Monooxygenase - metabolism; Reversible inhibition; Aging; Hypothalamus; 17-β estradiol; TIDA neurons; Prolactin
• ISSN: 0361-9230; 1873-2747
• DOI: 10.1016/j.brainresbull.2009.08.026

Abstract Dopaminergic neurons of the hypothalamic tuberoinfundibular dopaminergic (TIDA) system exert a tonic inhibitory control on prolactin (PRL) secretion whereas estrogen, known to inhibit TIDA neuron function, has been postulated to be toxic to TIDA neurons when it is chronically high. In order to determine whether estrogen in high doses can cause permanent damage to TIDA function, we submitted young female rats to continue high doses of estrogen administered, either centrally (intrahypothalamic estrogen implants) or peripherally (subcutaneous estrogen implants or weekly intramuscular (i.m.) injections for 7 weeks), subsequently withdrawing the steroid and observing the evolution of lactotrophes, serum PRL and TIDA neurons. Serum PRL was measured by radioimmunoassay whereas tyrosine hydroxylase positive (TH+) neurons and PRL cells were morphometrically assessed in sections of fixed hypothalami and pituitaries, respectively. After 30 days, hypothalamic estrogen implants induced a significant increase in serum PRL, whereas TH+ neurons were not detectable in the arcuate-periventricular hypothalamic (ARC) region of estrogen-implanted rats. Removal of implants on day 30 restored TH expression in the ARC and brought serum PRL back to basal levels 30 days after estrogen withdrawal. Subcutaneous or i.m. administration of estrogen for 7 weeks induced a marked hyperprolactinemia. However, 30 weeks after estrogen withdrawal, TH neuron numbers in the ARC were back to normal and serum PRL returned to basal levels. After peripheral but not central estrogen withdrawal, pituitary weight and lactotrophic cell numbers remained slightly increased. Our data suggest that estrogen even at high doses, does not cause permanent damage to TIDA neurons.