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Potential for Polysialylated Form of Neural Cell Adhesion Molecule-Mediated Neuroplasticity within the Gonadotropin-Releasing Hormone Neurosecretory System of the Ewe¹

Department of Physiology (F.J.K.), Reproductive Sciences Program (C.V., H.J.B., F.J.K.), University of Michigan, Ann Arbor, Michigan 48109-0404; Department of Cell Biology, Neurobiology and Anatomy, University of Cincinnati College of Medicine (H.T.J., L.C., M.N.L.), Cincinnati, Ohio 45267-0521; Department of Biological Sciences, Kent State University (J.D.G.), Kent, Ohio 44240-0001; and Division of Pediatric Cardiology, Department of Pediatrics, Rainbow Babies and Childrens Hospital, Case Western Reserve University (M.W.), Cleveland, Ohio 44106-6011

Address all correspondence and request for reprints to: Dr. F. J. Karsch, Reproductive Science Program, University of Michigan, 300 North Ingalls Building, Room 1101 SW, Ann Arbor, Michigan 48109-0404. E-mail: fjkarsch{at}umich.edu

The GnRH neurosecretory system undergoes marked structural and functional changes throughout life. The initial goal of this study was to examine the neuroanatomical relationship between GnRH neurons and a glycoprotein implicated in neuroplasticity, the polysialylated form of neural cell adhesion molecule (PSA-NCAM). Using dual label immunocytochemistry in conjunction with confocal microscopy, we determined that fibers, terminals, and perikarya of GnRH neurons in adult ovariectomized ewes are intimately associated with PSA-NCAM. In the preoptic area, intense PSA-NCAM immunoreactivity was evident around the periphery of GnRH cell bodies. The second goal of this study was to determine whether PSA-NCAM expression associated with GnRH neurons varies in conjunction with seasonal changes in the activity of the GnRH neurosecretory system in ovariectomized ewes treated with constant release implants of estradiol. During the breeding season when reproductive neuroendocrine activity was enhanced, the expression of PSA-NCAM immunoreactivity associated with GnRH neurons was significantly greater than that during anestrus when GnRH secretion was reduced. This difference, which occurred despite an unchanging ovarian steroid milieu, was not observed in preoptic area structures devoid of GnRH immunoreactivity, suggesting that the seasonal change is at least partially specific to the GnRH system. The close association between PSA-NCAM and GnRH neurons and the change in this relationship in conjunction with seasonal alterations in GnRH secretion provide anatomical evidence that this molecule may contribute to seasonal remodeling of the GnRH neurosecretory system of the adult.

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