The neuroendocrine mechanism of reproductive photorefractoriness in the ewe
Kao, Chen Chih
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Permalink
https://hdl.handle.net/2142/23484
Description
Title
The neuroendocrine mechanism of reproductive photorefractoriness in the ewe
Author(s)
Kao, Chen Chih
Issue Date
1991
Doctoral Committee Chair(s)
Jackson, Gary L.
Department of Study
Physiology
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Neuroscience
Biology, Animal Physiology
Language
eng
Abstract
The objective of this study was to explore the possible neuroendocrine mechanisms of reproductive photorefractoriness using pharmacological and neurosurgical approaches. Ovary-intact (INTACT), ovariectomized (OVX) and ovariectomized estradiol-treated (OVX + E$\sb2$) ewes were subjected to 3 different photoperiodic regimens which resulted in reproductive quiescent: (1) exposure to long days (16L:8D), which caused photosuppression (LDPS); (2) prolonged exposure to short days (10L:14D); which caused photorefractoriness (SDPR); (3) exposure to natural photoperiod which induced seasonal anestrus. LH pulse pattern was monitored 8 h after cyproheptadine injection (3 mg/kg), and again 7 days later after injection of pimozide (0.25 mg/kg). Cyproheptadine did not change LH pulse parameters in any group of INTACT, OVX or OVX + E$\sb2$ ewes. Pimozide did not affect LH pulse frequency in LDPS ewes. However, pimozide increased LH pulse frequency (p $<$ 0.005) and mean concentrations (p $<$ 0.005) in SDPR OVX + E$\sb2$ ewes, whereas it suppressed LH frequency (p $<$ 0.05) and amplitude (p $<$ 0.03) in SDPR INTACT and SDPR OVX ewes. Further, two groups of ovary-intact ewes were subjected to frontal hypothalamic deafferentation (FHD) in the breeding season (FHD-B) or the anestrous season (FHD-NB). All ewes were placed under a 8L:16D photoperiod starting on 9 Sep 1987 to 21 Feb 1990. Progesterone data were analyzed. There was no significant difference in the proportion of animals showing refractoriness among the FHD-B, FHD-NB and sham FHD ewes. Spectral analysis showed that ewes in all three groups exhibited a 15-18 days progesterone cycle and more than 85% of the ewes exhibited a cyclicity with a 435 day period. All the knife cuts were located in the postsuprachiasmatic region between the suprachiasmatic and arcuate nuclei. These results suggest that (1) The role of the dopaminergic system differs in SDPR and LDPS, (2) the effect of pimozide in SDPR ewes is altered by ovarian steroids, (3) the serotonergic system has little observable role in regulation pulsatile LH secretion in any of the 3 different states of anestrus, and (4) damage to postsuprachiasmatic structures alone is not sufficient to alter the expression of SDPR.
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