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Biological and Anatomical Evidence for Kisspeptin Regulation of the Hypothalamic-Pituitary-Gonadal Axis of Estrous Horse Mares

Animal Reproduction and Biotechnology Laboratory (C.M., J.A.A.-A., C.M.C.), Department of Biomedical Sciences; Departments of Animal Sciences (J.E.B.) and Clinical Sciences (P.M.M.), Equine Reproduction Laboratory, Colorado State University, Fort Collins, Colorado 80523; Department of Basic Medical Sciences (C.D.F., R.J.H.), University of Arizona College of Medicine, Phoenix, Arizona 85004; Maxwell H. Gluck Equine Research Center (E.L.S.), University of Kentucky, Lexington, Kentucky 40536

Address all correspondence and requests for reprints to: Dr. Colin M. Clay, Animal Reproduction and Biotechnology Laboratory, Foothills Campus, Colorado State University, Fort Collins, Colorado 80523. E-mail: colin.clay{at}colostate.edu.

The purpose of the present study was to evaluate the effects of kisspeptin (KiSS) on LH and FSH secretion in the seasonally estrous mare and to examine the distribution and connectivity of GnRH and KiSS neurons in the equine preoptic area (POA) and hypothalamus. The diestrous mare has a threshold serum gonadotropin response to iv rodent KiSS decapeptide (rKP-10) administration between 1.0 and 500 µg. Administration of 500 µg and 1.0 mg rKP-10 elicited peak, mean, and area under the curve LH and FSH responses indistinguishable to that of 25 µg GnRH iv, although a single iv injection of 1.0 mg rKP-10 was insufficient to induce ovulation in the estrous mare. GnRH and KiSS-immunoreactive (ir) cells were identified in the POA and hypothalamus of the diestrous mare. In addition, KiSS-ir fibers were identified in close association with 33.7% of GnRH-ir soma, suggesting a direct action of KiSS on GnRH neurons in the mare. In conclusion, we are the first to reveal a physiological role for KiSS in the diestrous mare with direct anatomic evidence by demonstrating a threshold-like gonadotropin response to KiSS administration and characterizing KiSS and GnRH-ir in the POA and hypothalamus of the diestrous horse mare.

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				A. E. Oakley, D. K. Clifton, and R. A. Steiner Kisspeptin Signaling in the Brain Endocr. Rev., October 1, 2009; 30(6): 713 - 743. [Abstract] [Full Text] [PDF]