title: Mediation of vagal cardioinhibitory responses by glutamatergic receptors in the caudal medulla of turtles.
abstract: Our previous studies showed that electrical stimulation of the nuclei ambiguous (NA) or dorsomotor nuclei of the vagus (DMV) complex in the brain stem of spontaneously breathing pond turtles (Cyclemys fiavomarginata), anesthetized with chloralose (4 mg/100 g) and urethane (40 mg/100 g), produced a marked slowing or even cessation of the heart rate, and resulted in an immediate fall of blood pressure. Results of the present study further demonstrated that the cardioinhibitory responses could also be elicited by microinjection of monosodium glutamate (0.2-20 nl, 50 mM) into the NA/DMV complex in turtles. A two-barrel glass micropipette held in a manipulator was connected to a pneumatic pressure pump for microinjection. The glutamate-induced cardioinhibitory responses could be significantly reduced in a dose-dependent manner by pretreatment with AP-5 (a NMDA receptor antagonist, at 1-8 nmole) or CNQX (a non-NMDA receptor antagonist; at 0.1-0.8 nmole) 20 min before glutamate administration. Histochemical verification by injecting horseradish peroxidase into the cervical vagus nerves revealed that retrogradely labeled glutamatergic neurons in the NA/DMV complex were observed. These results suggest that glutamatergic receptors in the caudal medulla may mediate vagal cardioinhibitory responses in the turtle.
authors.affiliation: Institute of Biomedical Engineering, Chung Yuan Christian University, Chung Li, Taiwan.
authors.forename: Yi-Chang
authors.initials: YC
authors.lastname: Hsieh
authors.forename: Ruei-Feng
authors.initials: RF
authors.lastname: Chen
authors.forename: Chun-Kuei
authors.initials: CK
authors.lastname: Su
authors.forename: Sheng-Hsien
authors.initials: SH
authors.lastname: Chen
authors.forename: Jui-Hsiang
authors.initials: JH
authors.lastname: Hsieh
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D001919:Bradycardia / Q000139:chemically induced / Q000503:physiopathology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D006321:Heart / Q000294:innervation; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D056325:Neuronal Tract-Tracers / Q000494:pharmacology; D009474:Neurons / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D012970:Sodium Glutamate / Q000494:pharmacology; D013268:Stimulation, Chemical; D014426:Turtles / Q000502:physiology*; D014630:Vagus Nerve / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
chemical_list: D018691:Excitatory Amino Acid Antagonists; D056325:Neuronal Tract-Tracers; D016194:Receptors, N-Methyl-D-Aspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D012970:Sodium Glutamate