Innervation of the pars intermedia and control of alpha-melanotropin secretion in the newt.
In this study we have investigated the presence of nerve fibers containing dopamine, thyrotropin-releasing hormone (TRH) and neuropeptide Y (NPY) in the pars intermedia of the crested newt and we have examined the possible effect of these neurohormones on the release of alpha-melanotropin (alpha-MSH) by neurointermediate lobes in vitro. By means of immunohistochemistry, we observed the presence of tyrosine hydroxylase (TH)-immunoreactive fibers in the pars intermedia of the crested newt. Using a specific antiserum to dopamine, these fibers appeared to be mainly dopaminergic in nature. Unlike anurans, urodele amphibians do not exhibit TRH or NPY-like immunoreactivity in the pars intermedia. A perifusion system technique for newt pituitaries was developed to investigate the effect of dopamine, TRH and NPY on alpha-MSH secretion. Administration of increasing concentrations of dopamine (from 10(-9) to 10(-5)M) induced a dose-related inhibition of alpha-MSH release. This inhibitory effect was mimicked by the dopamine agonist apomorphine (10(-6)M). In contrast, the secretory activity of the newt pars intermedia was not affected by administration of synthetic TRH or NPY (up to 10(-7) and 10(-6)M, respectively). These results indicate that the neurotransmitter dopamine likely plays a pivotal role in the regulation of melanotropin secretion in urodele amphibians.
Danger
J M
JM
Groupe de Recherche en Endocrinologie Moléculaire, CNRS URA 650, Unité Alliée à l'INSERM, Université de Rouen, Mont-Saint-Aignan, France.
Perroteau
I
I
Franzoni
M F
MF
Saint-Pierre
S
S
Fasolo
A
A
Vaudry
H
H
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D007150:Immunohistochemistry; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D009478:Neuropeptide Y / Q000494:pharmacology; D010477:Perfusion; D010902:Pituitary Gland / Q000294:innervation*; D012455:Salamandridae; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D009478:Neuropeptide Y; D013973:Thyrotropin-Releasing Hormone; D009074:Melanocyte-Stimulating Hormones; D001058:Apomorphine; D004298:Dopamine