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Targeting of gonadotropin‐releasing hormone axons from preoptic area grafts to the median eminence
Author(s) -
Saitoh Y.,
Gibson M. J.,
Silverman A.J.
Publication year - 1992
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490330304
Subject(s) - median eminence , ganglionic eminence , immunocytochemistry , biology , pituitary gland , anatomy , gonadotropin releasing hormone , basal (medicine) , preoptic area , basal plate (neural tube) , medicine , hypothalamus , hormone , endocrinology , fetus , central nervous system , luteinizing hormone , pregnancy , placenta , genetics , cerebrum , insulin
Implantation of normal GnRH neurons can reverse many of the reproductive deficiencies that characterize hypogonadal (hpg) mice. Since the GnRH axons follow a stereotyped trajectory to their target we investigated the possibility that host brain regions adjacent to the graft might provide signals that induced this directional growth. The role of the adenohypophysis in GnRH axonal outgrowth was studied in mice with co‐grafts of fetal preoptic area (POA) and pituitary and in hypophysectomized hosts. When fetal pituitaries were grafted together with the POA, immunoreactive GnRH fibers did enter the glandular tissue but they also grew into the host median eminence. Surgical removal of the pituitary of hpg hosts prior to POA graft placement was also compatible with GnRH innervation of the host median eminence although in some individuals that innervation pattern was confined to the more caudal aspects. The results of these two experiments suggest that the anterior pituitary gland may be an attractive target for GnRH axons but that this tissue is not essential for directed GnRH axonal outgrowth to its target. To determine if the median eminence itself could direct the growth of GnRH axons, co‐grafts of POA and a fetal medial basal hypothalamic (MBH) block, which was predominantly median eminence, were made. Immunocytochemistry showed that an intragraft mini‐median eminence was formed with a highly organized and robust GnRH innervation. Ultrastructural analysis indicated that these axons terminated near fenestrated capillaries. However, even under these conditions some GnRH axons exited into the host median eminence. It now seems likely that a cellular component of the median eminence can provide a signal to attract GnRH axons. Whether this signal is produced by the specialized ependymal cells, by the endothelia, or by meningeal (pial) components must now be tested. © 1992 Wiley‐Liss, Inc.