Ovarian steroid hormones modulate circadian rhythms of neuroendocrine dopaminergic neuronal activity

• Published in: Brain research Vol. 1005; no. 1; pp. 164 - 181
• Main Authors: Sellix, Michael T., Egli, Marcel, Henderson, Ross P., Freeman, Marc E.
• Format: Journal Article
• Language: English
• Published: London Elsevier B.V 16.04.2004; Amsterdam Elsevier; New York, NY
• Subjects: Animals; Biological and medical sciences; Circadian Rhythm - drug effects; Circadian Rhythm - physiology; Corticosterone - blood; Dopamine - metabolism; Estradiol - metabolism; Estradiol - pharmacology; Female; Fundamental and applied biological sciences. Psychology; Gonadal Steroid Hormones - metabolism; Gonadal Steroid Hormones - pharmacology; Hormones and neuropeptides. Regulation; Hypothalamus; Hypothalamus. Hypophysis. Epiphysis. Urophysis; Neurons - drug effects; Neurons - metabolism; Neurosecretory Systems - drug effects; Neurosecretory Systems - metabolism; Ovariectomy; Ovary - drug effects; Ovary - metabolism; Pituitary; Progesterone - metabolism; Progesterone - pharmacology; Prolactin - blood; Rat; Rats; Rats, Sprague-Dawley; Steroid; Vertebrates: endocrinology; Steroid; Endocrine and autonomic regulation; Hypothalamus; Rat; Pituitary; Steroid hormone; Rodentia; Central nervous system; Neuroendocrine regulation; Biological rhythm; Circadian rhythm; Ovarian hormone; Encephalon; Vertebrata; Mammalia; Pituitary gland
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/j.brainres.2004.01.049

Dopamine (DA) is the primary inhibitor of prolactin (PRL) secretion. Three populations of neuroendocrine dopaminergic neurons (NDNs) designated tuberoinfundibular (TIDA), tuberohypophyseal (THDA) and periventricular hypophyseal DAergic (PHDA) neurons regulate PRL secretion. Given that ovarian steroids modulate both DA release and PRL secretion independently, we characterized the role of steroid hormones in coupling rhythmic NDN activity and PRL secretion. OVX rats under a standard 12:12 L:D cycle (L:D), constant dark (DD), or a 6-h phase-delayed L:D cycle (pdL:D) were treated with Estradiol-17β (E) or E and Progesterone (E+P). NDN activity, defined by DA:DOPAC ratio in nerve terminals, was determined by HPLC-EC. E or E+P stimulated PRL surges in L:D that persisted under DD. In TIDA neurons, E or E+P treatment reduced the amount of DA released under L:D and DD and advanced the rhythm of DA turnover. E and E+P treatment reduced THDA and PHDA neuron activity under L:D, but did not affect these rhythms under DD. Circadian rhythms of PRL, corticosterone and DA turnover in NDN terminals from steroid treated rats entrained to a pdL:D cycle within 7 days. Therefore, ovarian steroids differentially adjust the timing and magnitude of NDN activity to facilitate coupling of DA release and PRL secretion.