title: Fos-determined distribution of neurons activated during the Bezold-Jarisch reflex in the medulla oblongata in conscious rabbits and rats.
abstract: Experiments were performed in unanaesthetized rabbits and rats to investigate the distribution, within the medulla oblongata, of neurons activated during the Bezold-Jarisch reflex. Repeated intravenous injections of phenylbiguanide evoked depressor and bradycardic responses in both rabbits and rats. Fos-positive neurons were present in the nucleus tractus solitarius and in the caudal ventrolateral medulla oblongata. Double-label tyrosine hydroxylase (TH) immunohistochemical studies in the ventrolateral medulla showed that most Fos-positive neurons in the caudal ventrolateral medulla were TH-negative neurons scattered between A1 noradrenaline cells, in the rabbit and in the rat. Approximately 20% of neurons in the caudal ventrolateral medulla in rabbits, and 50% in rats, were immunoreactive for both Fos and TH. Some Fos-positive, TH-negative neurons in the caudal ventrolateral medulla were retrogradely labelled with cholera toxin B-Gold after injection of this tracer into the sympathoexcitatory region of the rostral ventrolateral medulla. Our data suggests that neurons in the nucleus tractus solitarius, and rostrally projecting TH-negative neurons in the caudal ventrolateral medulla, are part of the pathway by which stimulation of cardiopulmonary receptors inhibits sympathetic vasomotor tone to decrease blood pressure during the Bezold-Jarisch reflex.
authors.affiliation: Centre for Neuroscience, Flinders University, Bedford Park, Australia.
authors.forename: Z J
authors.initials: ZJ
authors.lastname: Gieroba
authors.forename: L
authors.initials: L
authors.lastname: MacKenzie
authors.forename: J O
authors.initials: JO
authors.lastname: Willoughby
authors.forename: W W
authors.initials: WW
authors.lastname: Blessing
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology; D001645:Biguanides / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D016762:Genes, fos; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D001645:Biguanides; D007004:Hypoglycemic Agents; D014446:Tyrosine 3-Monooxygenase; C008846:phenyl biguanide