Estradiol Increases Multiunit Electrical Activity in the A15 Area of Ewes Exposed to Inhibitory Photoperiods

Seasonal anestrus in ewes results from an increase in response to the negative feedback action of estradiol (E 2 ). This increase in the inhibitory effects of E 2 is controlled by photoperiod and appears to be mediated, in part, by dopaminergic neurons in the retrochiasmatic area of the hypothalamus...

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Bibliographic Details
Published in:Biology of reproduction 2000-11, Vol.63 (5), p.1352-1357
Main Authors: GOODMAN, Robert L, THIERY, Jean-Claude, DELALEU, Bernadette, MALPAUX, Benoit
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Computer Science
Electrodes, Implanted
Electrophysiology
Estradiol - pharmacology
Female
Fundamental and applied biological sciences. Psychology
Hypothalamus - cytology
Hypothalamus - drug effects
Hypothalamus - physiology
Life Sciences
Luteinizing Hormone - metabolism
Neurons - drug effects
Neurons - physiology
Photoperiod
Sheep
Thermoregulation. Hibernation. Estivation. Ecophysiology and environmental effects
Vertebrates: anatomy and physiology, studies on body, several organs or systems
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Summary:Seasonal anestrus in ewes results from an increase in response to the negative feedback action of estradiol (E 2 ). This increase in the inhibitory effects of E 2 is controlled by photoperiod and appears to be mediated, in part, by dopaminergic neurons in the retrochiasmatic area of the hypothalamus (A15 group). This study was designed to test the hypothesis that E 2 increases multiunit electrical activity (MUA) in the A15 during inhibitory long days. MUA was monitored in the retrochiasmatic area of 14 ovariectomized ewes from 4 h before to 24 h after insertion of an E 2 -containing implant subcutaneously. In six of these ewes, MUA activity was also monitored before and after insertion of blank implants. Three of the 14 ewes were excluded from analysis because E 2 failed to inhibit LH. When MUA was recorded within the A15, E 2 produced a gradual increase in MUA that was sustained for 24 h. Blank implants failed to increase MUA in the A15 area, and E 2 did not alter MUA if recording electrodes were outside the A15. These data demonstrate that E 2 increases MUA in the A15 region of ewes and are consistent with the hypothesis that these neurons mediate E 2 negative feedback during long photoperiods.
ISSN:0006-3363
1529-7268
DOI:10.1095/biolreprod63.5.1352