Efferent projections from the retrochiasmatic area to the median eminence and to the pars nervosa of the hypophysis with special reference to the A15 dopaminergic cell group in the sheep |
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Authors: | Véronique Gayrard Jean-Claude Thiéry Jean Thibault Yves Tillet |
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Institution: | (1) Laboratoire de Neuroendocrinologie Sexuelle, INRA Station de Physiologie de la Reproduction des Mammifères Domestiques, F-37380 Nouzilly, France;(2) Present address: Ecole Nationale Vétérinaire, 23 Chemin des Capelles, F-31076 Toulouse, France;(3) Present address: Laboratoire de Biochimie Cellulaire, Collège de France, F-75231 Paris, France |
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Abstract: | Anterograde tracers, viz. Phaseolus vulgaris leucoagglutinin and fluorescein dextran, were used in conjunction with tyrosine hydroxylase immunohisto-chemistry to study the projections of the A15 dopaminergic cell group towards the median eminence and pituitary in sheep. After injection of the tracers in the retrochiasmatic area, which contains the cell group A15, fibres containing anterograde tracer were observed in the internal zone of the median eminence and in the pars nervosa of the pituitary. Numerous tyrosine hydroxylase immunoreactive fibers were present in the external zone of the median eminence and in the pars intermedia and the pars nervosa of the pituitary, with characteristic patterns of organisation in each area. Most tyrosine hydroxylase-immunoreactive fibres containing fluorescein dextran were located in the pars nervosa, whereas only a few were observed in the internal zone of the median eminence. It was concluded that at least part of the dopaminergic innervation of the pars nervosa originated from the A15 group. These results provide morphological evidence for (1) the role of dopaminergic neurons of the A15 cell group in the seasonal control of prolactin secretion via the release of dopamine in the pars nervosa, and (2) putative physiological interactions between dopamine and the secretion of neurohypophysial hormones in sheep. |
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Keywords: | Anterograde tracers Immunohistochemistry Tyrosine hydroxylase A15 dopaminergic group Retrochiasmatic area Prolactin secretion Sheep |
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