The Journal of Neuroscience, October 1994, 14(10): 59966012 Reorganization of Neural Peptidergic Systems Median Eminence after Hypophysectomy Marcel0 J. Villar, Bjiirn Meister, and Tomas Hiikfelt Department of Neuroscience, The Berzelius Laboratory, Karolinska Institutet, Stockholm, 171 77 Sweden Earlier studies have shown the formation of a novel neural crease to a final stage of a few, strongly immunoreactive lobe after hypophysectomy, an experimental manipulation fibers in the external layer at longer survival times. Vaso- that causes transection of neurohypophyseal nerve fibers active intestinal polypeptide (VIP)- and peptide histidine- and removal of pituitary hormones. The mechanisms that isoleucine (PHI)-IR fibers in hypophysectomized animals had underly this regenerative process are poorly understood. already contacted portal vessels 5 d after hypophysectomy, The localization and number of peptide-immunoreactive and from then on progressively increased in numbers. Fi- (-IR) fibers in the median eminence were studied in normal nally, most of the peptide fibers described above formed rats and in rats at different times of survival after hypophy- dense innervation patterns around the large blood vessels sectomy using indirect immunofluorescence histochemistry. along the lateral borders of the median eminence. The number of vasopressin (VP)-IR fibers increased in the The present results show that hypophysectomy induces external layer of the median eminence in 5 d hypophysec- a wide variety of changes in hypothalamic neurosecretory tomized rats. Oxytocin (OXY)-IR fibers decreased in the in- fibers. Not only is the expression of several peptides in these ternal layer and progressively extended into the external fibers modified following different survival times, but a re- layer. At long survival times (9 and 16 months) both VP- and organization of the distribution of immunoreactive fibers OXY-IR fibers had a bilayered distribution occupying both within the median eminence is demonstrated. The hypoth- the external and internal layers. Double-labeling experi- esis is raised that regeneration of injured neurosecretory ments combining VP and tyrosine hydroxylase antisera as fibers may be dependent on changes in the expression of well as OXY and growth hormone-releasing factor antisera peptides possessing trophic actions. showed that injured neurosecretory fibers growing into the [Key words: regeneration, neurohypophysis, neuropep- external layer displaced fibers from parvocellular cells orig- tide, plasticity, trophic factor, supraoptic nucleus, paraven- inally located there. As a result, there was essentially an tricular nucleus, hypophysectomy, galanin, cholecystokinin, inversion in the distribution of these fibers within the median dynorphin, vasopressin, oxytocin, vasoactive intestinalpoly- eminence. Galanin (GAL)- and cholecystokinin (CCK)-IR fi- peptide, peptide histidine-isoleucine] bers exhibited a similar pattern of distribution after the le- sion. Thus, after 5 d there was an increase in GAL- and CCK- IR fibers in the internal layer. At 14 and 30 d, the number of The hypothalamic magnocellular neurosecretory system con- GAL- and CCK-IR fibers progressively decreased, but after sistsof a group of peptidergic neurons distributed in the para- longer survivals (9 and 16 months) there was a dramatic ventricular (PVN) and supraoptic (SON) nuclei and somebasal reappearance. Dynorphin (DYN)-LI showed a dramatic in- accessory cells, all of which project to the neural lobe of the crease at all levels of the median eminence at short survival hypophysis (for review, seeBrownstein et al., 1980; Silverman times after hypophysectomy, followed by a subsequent de- and Zimmerman, 1983; Swansonand Sawchenko, 1983). The most important peptides in this system are vasopressin(VP) and oxytocin (OXY), which are releasedinto blood vesselsto exert a wide variety of actions, the best-establishedones being Received Jan. 12, 1994; revised Mar. 16, 1994; accepted Mar. 29, 1994. related to water balancethrough VP and milk ejection and uter- This work was supported by the Swedish MRC (04X-10358, 04X-2887), the ine contraction induced by OXY (for review, see Sawchenko National Institute of Ageing (AG 10491), Marianne and Marcus Wallenbergs and Swanson, 1985; Leng and Bicknell, 1986; Cunningham and Stiftelse, Fredrik and Ingrid Thuring Stiftelse, Ake Wibergs Stiftelse, the Swedish Tercentenary Bank Foundation, Konung Gustav V:s and Drottning Victorias Stif- Sawchenko, 1991; Reeves and Andreoli, 1992; Young, 1992). telse, Magnus Bergvalls Stiftelse, Tore Nilsons Stiftelse, the Wenner Gren Center The magnocellular hypothalamic cells show a remarkable ca- Foundation (M.J.V.), and research funds of the Karolinska Institute. M.J.V. is an pacity for regeneration even in adult animals. Although many established investigator of the National Research Council in Argentina. For the generous supply of antisera we express sincere gratitude to Professors R. Elde, of these neurons both in the PVN and SON are known to de- Minnesota University, MN (VP); J. Fahrenkrug, Bispebjerg Hospital, Copenhagen, generateafter hypophysectomy or stalk transection (Rasmussen, Denmark (VIP, PHI); P. Frey, Sandoz Research Institute, Bern, Switzerland (CCK); 1940; Frykman, 1942; Bodian and Marsen, 195 1; Billenstein M. Goldstein, New York University Medical Center, NY (TH); M. Morris, Wake Forest University, Winston-Salem, NC (OXY); L. Terenius, Karolinska Institute, and Leveque, 1955; Moll and De Wied, 1962; Raisman, 1973; Stockholm. Sweden (DYN): J. Walsh. Universitv of California. Los Aneeles. CA Antunes et al., 1980; Burlet et al., 1983; Herman et al., 1986, (monoclonal CCK); and HIGainer, GIH, Bethesda, MD (mondclonal O%Yli\lP). Correspondence should be addressed to Bjbm Meister, M.D., Ph.D., at the 1987), surviving neurons may, under certain conditions, gen- above address. erate a “new” neural lobe by sprouting of their projections at Copyright 0 1994 Society for Neuroscience 0270-6474/94/145996-17$05.00/O the level of the external layer of the median eminence and the The Journal of Neuroscience, October 1994, 14(10) 5997 proximal stump ofthe pituitary stalk (Stutinsky, 195 1; Dellman, Materials and Methods 1973; Raisman, 1973). The mechanisms by which injured mag- The experimentswere carried out with the approval ofSto&holms norru nocellular cells undergo degenerative or regenerative processes djurf6rsiiksetiska niimnd, the local animal experimentation and ethics remain unknown. However, there are results suggesting that committee. very little axonal regeneration occurs at the lesion site, when Surgicalprocedures. Male Sprague-Dawley rats (150-l 80 gm; ALAB, Stockholm, Sweden) were anesthetized with chloral hydrate (350 mg/ transection of the axons are performed within the hypothalamus kg), placed in a stereotaxic instrument, and hypophysectomized by as- (Danilova and Polenov, 1977; Scott and Knigge, 198 1; Nagy et piration through an intra-auricular approach (see Waynforth, 1980). al., 1983; Dellman et al., 1987; Dellman and Carithers, 1992). The animals were allowed to survive for different periods (5, 14, 30 d; These results have led to the idea that fibers and terminals from 2, 3, 9, and 16 months), during which they were maintained with food and 5% glucose in a 0.9% NaCl solution to drink ad libitum. Once the magnocellular cells need a special microenvironment in order survival period was completed, the animals were sacrificed and pro- to regenerate after lesion, and this may be in part provided by cessed for immunohistochemistry. A parallel group of animals with all fenestrated blood vessels and pituicytes (Dellman et al., 1988; the surgical procedures performed, but without the aspiration, as well Carithers and Dellman, 1992; Dellman and Carithers, 1992). as normal animals were added as controls. In this way, it has been hypothesized that a so far unknown Immunohistochemicalprocedure. Lesioned animals and controls were reanesthetized with sodium pentobarbital (Mebumal; 60 mg/kg, i.p.) trophic factor(s) could promote regenerative processes (Dellman and perfused via the ascending aorta with 50 ml of Ca*+-free Tyrode’s and Carithers, 1992). A complementary hypothesis could be solution (37°C) followed by 50 ml (37°C) of a mixture of 4% parafor- that after injury neurosecretory neurons may also activate in- maldehyde and 0.4% picric acid in 0.16 M phosphate buffer at pH 6.9 ternal mechanisms in order to produce trophic molecules that (Zamboni and de Martino, 1967), followed by ice-cold fixative (as above) for 6 min. The brains were dissected out, and the completeness of the will promote their survival. One possible group of compounds hypophysectomy was confirmed. The tissue was then immersed for 90 involved in such processes may be not only classic growth fac- min in the same fixative and rinsed for at least 48 hr in 0.1 M phosphate tors but also neuropeptides (see Strand et al., 1992). In addition, buffer (pH 7.0) containing 10% sucrose, 0.02% Bacitracin (Sigma, St. it is also possible that the synthesis of substances not necessary Louis, MO), and 0.01% sodium azide (Merck, Darmstadt, Germany). during these stages could be turned off. Cryostat sections (14 pm thick) of the hypothalamic region containing the median eminence were processed for the indirect immunofluores- In addition to VP and OXY, magnocellular cells also co-store cence technique of Coons and collaborators (see Coons, 1958). Briefly, a number of bioactive substances, although their functional sig- sections