title: A1 neurons and excitatory amino acid receptors in rat caudal medulla mediate vagal excitation of supraoptic vasopressin cells.
abstract: Extracellular recordings from the supraoptic nucleus of the rat established that vasopressinergic neurosecretory cells were excited by stimulation of cervical but not abdominal vagal afferents. This response was absent or significantly attenuated after microinjection of gamma-aminobutyric acid into a region of the caudal medulla known to contain the A1 noradrenaline cell group. Consistent with the possible involvement of the A1 group, vagal stimulation approximately doubled the frequency of proto-oncogene expression in A1 noradrenaline neurons, as indicated by the occurrence of nuclear Fos-like immunoreactivity in tyrosine hydroxylase-positive neurons of the caudal ventrolateral medulla. Finally, A1 region microinjection of either the N-methyl-D-aspartic acid (NMDA) receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV), or the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), significantly reduced vasopressin cell responses to vagal stimulation. These findings suggest that: (i) the A1 group is an essential component in a pathway which relays facilitatory vagal input of cardiopulmonary origin to neurosecretory vasopressin cells, and (ii) the activation of A1 neurons in this pathway involves both NMDA and non-NMDA excitatory amino acid receptors, an observation consistent with an input to A1 cells which generates 'mixed' excitatory postsynaptic potentials.
authors.affiliation: Department of Physiology and Pharmacology, University of Queensland, Australia.
authors.forename: T A
authors.initials: TA
authors.lastname: Day
authors.forename: J R
authors.initials: JR
authors.lastname: Sibbald
authors.forename: D W
authors.initials: DW
authors.lastname: Smith
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism*; D015415:Biomarkers / Q000737:chemistry; D004558:Electric Stimulation; D007031:Hypothalamus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009490:Neurosecretory Systems / Q000166:cytology / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017459:Receptors, Amino Acid / Q000502:physiology; D013495:Supraoptic Nucleus / Q000166:cytology* / Q000187:drug effects; D014630:Vagus Nerve / Q000502:physiology*
chemical_list: D015415:Biomarkers; D016760:Proto-Oncogene Proteins c-fos; D017459:Receptors, Amino Acid; D001127:Arginine Vasopressin