Author:

Keywords:

alpha-msh, neuropeptides, melanophore-stimulating hormone, thyrotropin-releasing-hormone, frog melanotrope cells, background adaptation, median-eminence, immunocytochemical demonstration, depressed-patients, pars-intermedia, nerve-fibers, Science & Technology, Life Sciences & Biomedicine, Endocrinology & Metabolism, Neurosciences, Neurosciences & Neurology, alpha-MSH, MELANOPHORE-STIMULATING HORMONE, THYROTROPIN-RELEASING-HORMONE, FROG MELANOTROPE CELLS, BACKGROUND ADAPTATION, MEDIAN-EMINENCE, ALPHA-MSH, IMMUNOCYTOCHEMICAL DEMONSTRATION, DEPRESSED-PATIENTS, PARS-INTERMEDIA, NERVE-FIBERS, Animals, Brain-Derived Neurotrophic Factor, Immunohistochemistry, Median Eminence, Melanocytes, Microscopy, Immunoelectron, Neurotransmitter Agents, Oxytocin, Pituitary Gland, Presynaptic Terminals, Xenopus laevis, 1103 Clinical Sciences, 1109 Neurosciences, 3202 Clinical sciences, 3209 Neurosciences

Abstract:

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, occurs abundantly in the brain, where it exerts a variety of neural functions. We previously demonstrated that BDNF also exists in the endocrine melanotroph cells in the intermediate lobe of the pituitary gland of the amphibian Xenopus laevis, suggesting that BDNF, in addition to its neural actions within the brain, can act as a hormone. In the present study, we tested whether BDNF, in addition to its neural and hormonal roles, can be released as a neurohormone from the neural pituitary lobe of X. laevis. By light immunocytochemistry, we show that BDNF is present in perikarya, in ventrolaterally projecting axons of the hypothalamic magnocellular nucleus and in the neural lobe of the pituitary gland, and that it coexists in these structures with the amphibian neurohormone, mesotocin. The neural lobe was studied in detail at the ultrastructural level. Two types of neurohaemal axon terminals were observed, occurring intermingled and in similar numbers. Type A is filled with round, moderately electron-dense secretory granules with a mean diameter of approximately 145 nm. Type B terminals contain electron-dense and smaller, ellipsoid granules (long and short diameter approximately 140 and 100 nm, respectively). BDNF is exclusively present in secretory granules of type A axon terminals. Double gold-immunolabelling revealed that BDNF coexists in these granules with mesotocin. Furthermore, we demonstrate in an superfusion study performed in vitro that mesotocin stimulates peptide release from the endocrine melanotroph cells. On the basis of these data, we propose that BDNF can act on these cells as a neurohormone.