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Expression of Gonadotropin Releasing Hormone (GnRH) and gonadotropin inhibitory hormone (GnIH) in photoperiod responsive and nonresponsive morphs of Northern red-backed vole, Myodes rutilus

Status Complete
Seeking Researchers No
Start Date 07/01/2008
End Date 06/30/2009
Funding Source Undergraduate Research Grant
Funding Amount
Community Partner
Related Course
Last Updated 06/26/2009 09:39PM
Keywords vole, gonadotropin, reproduction

People

Faculty
  Ian van Tets

Student Researchers
  Tina Tran

Abstract

Arvicoline rodents living at high latitudes typically undergo a seasonal cessation in reproductive activity during the winter in response to short day lengths and environmental conditions. Although the inactivation of reproduction generally holds true, the phenomenon of winter breeding has been documented in most species and occurs sporadically. Photoperiod non-responsive morphs are individuals within small mammal populations that possess the ability to maintain a reproductively active condition under short days breed in winter during mild years. Responsiveness to photoperiod has many implications for seasonal and out-of season breeding, including an effect on populations of small mammals, predators, and secondary prey species. To date, there is not a clear understanding of the mechanism by which non-responsiveness to photoperiod occurs, but it is likely to be secretion of gonadotropin releasing hormone (GnRH) and gonadotropin inhibitory hormone (GnIH) in the hypothalamus, which then regulates other hormones downstream through hypothalamic-pituitary-gonad (H-P-G) axis. This study will determine whether photoperiod responsiveness in high-latitude voles is regulated at the hypothalamic level, and whether there is an associated downstream regulation of the pituitary and gonadal hormones. I will analyze sections of the pre-optic area (POA) and dorsal medial hypothalamus (DMH) that were collected from brains of male M. rutilus treated with either long (16L:8D, n=18) or short (8L:16D, n=76) day lengths. Short day animals were grouped by reproductive phenotype and were categorized as either non-responsive, intermediately responsive, or responsive to photoperiod. I will stain brain sections from each group using an established GnRH/GnIH immunohistochemical procedure. I will then catalog microscope images of these brain sections to establish a photographic database and use digital image analysis software to compare expression of each neuropeptide among the groups. I will compare this data with existing data for luteinizing hormone and testosterone in these study animals. This study will provide insight on the effects of day length on GnRH and GnIH hormone production in different photoperiod – responsive morphs. It will ultimately determine the mechanism by which reproduction is regulated via the H-P-G axis and thereby explain the physiological occurrence of winter breeding in small mammal populations.

Specific Aim: To test whether voles that regress their reproductive structures in response to short days exhibit higher levels of gonadotropin inhibiting hormone (GnIH) and lower levels of gonadotropin releasing hormone (GnRH) in the hypothalamus than voles that maintain large reproductive structures under short photoperiods.

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