Activation of tuberoinfundibular and tuberohypophysial dopamine neurons following intracerebroventricular administration of bombesin.
The effect of bombesin on the activity of dopamine (DA) neurons comprising the nigrostriatal, mesolimbic, tuberoinfundibular and tuberohypophysial systems in the male rat was determined by measuring: (1) the accumulation of 3,4-dihydroxyphenylalanine (DOPA) after administration of a decarboxylase inhibitor, and (2) the concentration of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in brain (striatum, nucleus accumbens, median eminence) and pituitary regions (intermediate and neural lobes) containing terminals of these neurons. Intracerebroventricular (i.c.v.) injection of bombesin caused a dose- and time-related increase in the activity of DA neurons projecting to the median eminence and intermediate lobe of the pituitary, and a corresponding decrease in the concentrations of prolactin and alpha-melanocyte-stimulating hormone (alpha MSH) in the plasma. In contrast, doses of bombesin up to 10 ng i.c.v. failed to alter the activity of DA neurons terminating in the striatum, nucleus accumbens or neural lobe of the pituitary gland. Equimolar doses of bombesin and gastrin-releasing peptide (GRP), a bombesin-like peptide, increased the concentrations of DOPAC in the median eminence and intermediate lobe of the pituitary, suggesting that GRP-preferring receptors may be responsible for the stimulatory effects of bombesin on DA neuronal activity in these regions. The results of these studies suggest that bombesin increases the activity of tuberoinfundibular and tuberohypophysial DA neurons projecting to the median eminence and intermediate lobe of the pituitary, respectively, and thereby inhibits the secretion of prolactin and alpha MSH.
Manzanares
J
J
Department of Pharmacology and Toxicology, Michigan State University, East Lansing 48824.
Toney
T W
TW
Lookingland
K J
KJ
Moore
K E
KE
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D001839:Bombesin / Q000008:administration & dosage / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology*; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007276:Injections, Intraventricular; D008473:Median Eminence / Q000187:drug effects / Q000378:metabolism; D009074:Melanocyte-Stimulating Hormones / Q000097:blood / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009928:Organ Specificity; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000097:blood / Q000378:metabolism; D012016:Reference Values
D015102:3,4-Dihydroxyphenylacetic Acid; D011388:Prolactin; D009074:Melanocyte-Stimulating Hormones; D001839:Bombesin; D004298:Dopamine