Reorganization of neural peptidergic systems in the median eminence after hypophysectomy

Abstract

Earlier studies have shown the formation of a novel neural lobe after hypophysectomy, an experimental manipulation that causes transection of neurohypophyseal nerve fibers and removal of pituitary hormones. The mechanisms that underly this regenerative process are poorly understood. The localization and number of peptide-immunoreactive (-IR) fibers in the median eminence were studied in normal rats and in rats at different times of survival after hypophysectomy using indirect immunofluorescence histochemistry. The number of vasopressin (VP)-IR fibers increased in the external layer of the median eminence in 5 d hypophysectomized rats. Oxytocin (OXY)-IR fibers decreased in the internal layer and progressively extended into the external layer. At long survival times (9 and 16 months) both VP- and OXY-IR fibers had a bilayered distribution occupying both the external and internal layers. Double-labeling experiments combining VP and tyrosine hydroxylase antisera as well as OXY and growth hormone-releasing factor antisera showed that injured neurosecretory fibers growing into the external layer displaced fibers from parvocellular cells originally located there. As a result, there was essentially an inversion in the distribution of these fibers within the median eminence. Galanin (GAL)- and cholecystokinin (CCK)-IR fibers exhibited a similar pattern of distribution after the lesion. 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 GAL- and CCK-IR fibers progressively decreased, but after longer survivals (9 and 16 months) there was a dramatic reappearance. Dynorphin (DYN)-LI showed a dramatic increase at all levels of the median eminence at short survival times after hypophysectomy, followed by a subsequent decrease to a final stage of a few, strongly immunoreactive fibers in the external layer at longer survival times. Vasoactive intestinal polypeptide (VIP)- and peptide histidine-isoleucine (PHI)-IR fibers in hypophysectomized animals had already contacted portal vessels 5 d after hypophysectomy, and from then on progressively increased in numbers. Finally, most of the peptide fibers described above formed dense innervation patterns around the large blood vessels along the lateral borders of the median eminence. The present results show that hypophysectomy induces a wide variety of changes in hypothalamic neurosecretory fibers. Not only is the expression of several peptides in these fibers modified following different survival times, but a reorganization of the distribution of immunoreactive fibers within the median eminence is demonstrated. The hypothesis is raised that regeneration of injured neurosecretory fibers may be dependent on changes in the expression of peptides possessing trophic actions.

Vasopressin-Containing Neurons of the Hypothalamic Parvocellular Paraventricular Nucleus of the Jerboa: Plasticity Related to Immobilization Stress

“…A less dense plexus of VP-immunoreactive fibers is visible in the external zone of the ME. Consequently, the pattern of distribution of VP-containing nerve endings in the jerboa ME is similar to the one of the rat [42, 43]. Such a pattern suggests an eventual hypophysiotropic effect of VP in jerboas.…”

Ectopic galanin expression and normal galanin receptor 2 and galanin receptor 3 mRNA levels in the forebrain of galanin transgenic mice

“…To accomplish these diverse biological functions, GAL gene expression is highly plastic. GAL is dramatically up-regulated in rat anterior pituitary by estrogen (Kaplan et al, 1988), in the rat basal forebrain by nerve growth factor (Planas et al, 1997) and following experimental injury to the rat central and peripheral nervous systems, including olfactory bulbectomy (Holmes and Crawley, 1996), hypophysectomy (Villar et al, 1994), neurochemical dorsal raphe lesions (Gabriel et al, 1995), immunotoxic basal forebrain lesions (Hartonian et al, 2002), potassium chloride (KCl)-mediated cortical spreading depression (Shen et al, 2003), and sciatic nerve transection (Villar et al, 1989).…”

Localization of vasopressin mRNA and immunoreactivity in pituicytes of pituitary stalk-transected rats after osmotic stimulation.

“…(Bar = 1 ,um.) alterations in AVP biosynthesis (27) and complete degeneration of the severed nerve terminals in the NL by 6 days after transection (22). In contrast, the electrical procedure carried out by Mohr et (28,29).…”