TY - JOUR
T1 - Evidence that urocortin I acts as a neurohormone to stimulate αMSH release in the toad Xenopus laevis
AU - Calle, Marinella
AU - Corstens, Geert J.H.
AU - Wang, Liangchun
AU - Kozicz, Tamas
AU - Denver, Robert J.
AU - Barendregt, Henk P.
AU - Roubos, Eric W.
N1 - Funding Information:
The authors are very grateful to Jean Rivier and Wylie W. Vale of the Salk Institute, La Jolla, for supplying the synthetic X. laevis CRF and the rat UCN1 antiserum, to Will J.A.J. Smeets of the Vrije Universiteit Amsterdam for anatomical advise, to Frouwke J. Kuijpers-Kwant and Kari H.A. Meijer for technical assistance, and to Ron J.C. Engels for animal care. Partial support for this project was provided by a grant from National Science Foundation of the USA IBN 0235401 to R.J.D., and a grant from the Netherlands Organization of Scientific Research.
PY - 2005/4/8
Y1 - 2005/4/8
N2 - We have raised the hypothesis that in the South African clawed toad Xenopus laevis, urocortin 1 (UCN1), a member of the corticotropin-releasing factor (CRF) peptide family, functions not only within the brain as a neurotransmitter/neuromodulator but also as a neurohormone, promoting the release of α-melanophore-stimulating hormone (αMSH) from the neuroendocrine melanotrope cells in the intermediate lobe of the pituitary gland. This hypothesis has been investigated by (1) assessing the distribution of UCN1 and CRF by light immunocytochemistry, (2) determining the subcellular presence of UCN1 in the neural lobe of the pituitary gland by immuno-electron microscopy applying high-pressure freezing and cryosubstitution, and (3) testing the effect of UCN1 on MSH release from toad melanotrope cells using in vitro superfusion. In the X. laevis brain, the main site of UCN1-positive somata was found to be the Edinger-Westphal nucleus. UCN1 immunoreactivity (ir) also occurs in the nucleus posteroventralis tegmenti, central gray, nucleus reticularis medius, nucleus motorius nervi facialis, and nucleus motorius nervi vagi. UCN1 occurs together with CRF in the nucleus motorius nervi trigemini, and in the magnocellular nucleus, which send a UCN1- and CRF-containing fiber tract to the median eminence. Strong UCN1-ir and CRF-ir were found in the external zone of the median eminence. From the internal zone of the median eminence, UCN1-ir fibers, but few CRF-ir fibers, were found to project to the pituitary neural lobe, where they form numerous neurohemal axon terminals. Ultrastructurally, two types of terminal containing UCN1-ir secretory granules were distinguished: type A contains large, moderately electron-dense, round secretory granules and type B is filled with smaller, strongly electron-dense, ellipsoid secretory granules. In vitro superfusion studies showed that UCN1 stimulated the release of αMSH from melanotrope cells in a dose-dependent manner. Our results support the hypothesis that in X. laevis, UCN1 released from neurohemal axon terminals in the pituitary neural lobe functions as a stimulatory neurohormone for αMSH release from melanotrope cells of the pituitary intermediate lobe.
AB - We have raised the hypothesis that in the South African clawed toad Xenopus laevis, urocortin 1 (UCN1), a member of the corticotropin-releasing factor (CRF) peptide family, functions not only within the brain as a neurotransmitter/neuromodulator but also as a neurohormone, promoting the release of α-melanophore-stimulating hormone (αMSH) from the neuroendocrine melanotrope cells in the intermediate lobe of the pituitary gland. This hypothesis has been investigated by (1) assessing the distribution of UCN1 and CRF by light immunocytochemistry, (2) determining the subcellular presence of UCN1 in the neural lobe of the pituitary gland by immuno-electron microscopy applying high-pressure freezing and cryosubstitution, and (3) testing the effect of UCN1 on MSH release from toad melanotrope cells using in vitro superfusion. In the X. laevis brain, the main site of UCN1-positive somata was found to be the Edinger-Westphal nucleus. UCN1 immunoreactivity (ir) also occurs in the nucleus posteroventralis tegmenti, central gray, nucleus reticularis medius, nucleus motorius nervi facialis, and nucleus motorius nervi vagi. UCN1 occurs together with CRF in the nucleus motorius nervi trigemini, and in the magnocellular nucleus, which send a UCN1- and CRF-containing fiber tract to the median eminence. Strong UCN1-ir and CRF-ir were found in the external zone of the median eminence. From the internal zone of the median eminence, UCN1-ir fibers, but few CRF-ir fibers, were found to project to the pituitary neural lobe, where they form numerous neurohemal axon terminals. Ultrastructurally, two types of terminal containing UCN1-ir secretory granules were distinguished: type A contains large, moderately electron-dense, round secretory granules and type B is filled with smaller, strongly electron-dense, ellipsoid secretory granules. In vitro superfusion studies showed that UCN1 stimulated the release of αMSH from melanotrope cells in a dose-dependent manner. Our results support the hypothesis that in X. laevis, UCN1 released from neurohemal axon terminals in the pituitary neural lobe functions as a stimulatory neurohormone for αMSH release from melanotrope cells of the pituitary intermediate lobe.
KW - Corticotropin-releasing factor
KW - Cryosubstitution
KW - High-pressure freezing
KW - Immuno-electron microscopy
KW - Magnocellular nucleus
KW - Melanotrope cells
KW - Neural pituitary lobe
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U2 - 10.1016/j.brainres.2004.12.056
DO - 10.1016/j.brainres.2004.12.056
M3 - Article
C2 - 15804422
AN - SCOPUS:16244416884
SN - 0006-8993
VL - 1040
SP - 14
EP - 28
JO - Brain Research
JF - Brain Research
IS - 1-2
ER -