Journal article
The GnRH System of Seasonal Breeders: Anatomy and Plasticity
Brain research bulletin, Vol.44(4), pp.445-457
1997
Handle:
https://hdl.handle.net/2376/110190
PMID: 9370210
Abstract
Seasonal breeders, such as sheep and hamsters, by virtue of their annual cycles of reproduction, represent valuable models for the study of plasticity in the adult mammalian neuroendocrine brain. A major factor responsible for the occurrence of seasonal reproductive transitions is a striking change in the responsiveness of gonadotropin-releasing hormone (GnRH) neurons to the inhibitory effects of gonadal steroids. However, the neural circuitry mediating these seasonal changes is still relatively unexplored. In this article, we review recent findings that have begun to define that circuitry and its plasticity in a well-studied seasonal breeder, the ewe. Tract tracing studies and immunocytochemical analyses using Fos and FRAs as markers of activation point to a subset of neuroendocrine GnRH neurons in the MBH as potential mediators of pulsatile GnRH secretion. Because the vast majority of GnRH neurons lack estrogen receptors, seasonal changes in responsiveness to estradiol are most probably conveyed by afferents. Two possible mediators of this influence are dopaminergic cells in the A14/A15 cell groups of the hypothalamus, and estrogen receptor-containing cells in the arcuate nucleus that project to the median eminence. The importance of GnRH afferents in the regulation of season breeding is underscored by observations of seasonal changes in the density of synaptic inputs onto GnRH neurons. Thyroid hormones may participate in this remodeling, because they are important in seasonal reproduction, influence the morphology of other brain systems, and thyroid hormone receptors are expressed within GnRH neurons. Finally, in the hamster, neonatal hypothyroidism affects the number of caudally placed GnRH neurons in the adult brain, suggesting that thyroid hormones may influence development of the GnRH system as well as its reproductive functions in the adult brain.
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Details
- Title
- The GnRH System of Seasonal Breeders: Anatomy and Plasticity
- Creators
- Michael N Lehman - Department of Cell Biology, Department of Neurobiology and Department of Anatomy, University of Cincinnati College of Medicine, 231 Bethesda Avenue, Cincinnati, OH 45267-0521, USARobert L Goodman - Department of Physiology, West Virginia University, Morgantown, West Virginia 26506, USAFred J Karsch - Reproductive Sciences Program, University of Michigan, Ann Arbor, Michigan 49109, USAGary L Jackson - Department of Veterinary Biosciences, University of Illinois at Urbana/Champaign, Urbana, Illinois 61801, USASandra J Berriman - Department of Cell Biology, Department of Neurobiology and Department of Anatomy, University of Cincinnati College of Medicine, 231 Bethesda Avenue, Cincinnati, OH 45267-0521, USAHeiko T Jansen - Department of Cell Biology, Department of Neurobiology and Department of Anatomy, University of Cincinnati College of Medicine, 231 Bethesda Avenue, Cincinnati, OH 45267-0521, USA
- Publication Details
- Brain research bulletin, Vol.44(4), pp.445-457
- Academic Unit
- Integrative Physiology and Neuroscience, Department of
- Publisher
- Elsevier Inc
- Identifiers
- 99900547138801842
- Language
- English
- Resource Type
- Journal article