Excitatory amino acid receptors in the nucleus tractus solitarius mediate the responses to the stimulation of cardio-pulmonary vagal afferent C fiber endings.
Stimulation of cardio-pulmonary vagal afferent C fiber endings by right atrial injections of phenylbiguanide (PBG, 40 micrograms/kg) elicited apnea, bradycardia and hypotension. These responses were abolished by bilateral vagotomy low in the neck. Stimulation of neurons in a specific nucleus tractus solitarius site (0.5 mm rostral, 0.5 mm lateral and 0.5 mm deep with reference to the calamus scriptorius) by injections of L-glutamate produced responses similar to those following the stimulation of cardio-pulmonary vagal afferent C fiber endings by PBG. Inhibition of neurons in this NTS site by injections of muscimol abolished the responses to PBG. Specific blockade of NMDA receptors by microinjections of AP-7 (100 pmol) or non-NMDA receptors (KA and AMPA) by injections of DNQX (10-25 pmol) into this NTS site did not block the responses to PBG. Microinjections of kynurenic acid (1-4 nmol) into this NTS site blocked the responses to right atrial injections of PBG. These results indicate that: (1) blockade of either NMDA receptors or non-NMDA receptors (KA and AMPA) alone in the above-mentioned NTS site does not abolish the responses to the stimulation of cardio-pulmonary vagal afferent C fiber endings; (2) it is necessary to block NMDA as well as non-NMDA receptors in this NTS site for abolishing the responses to the stimulation of these nerve endings.
Vardhan
A
A
Section of Neurological Surgery, UMDNJ-New Jersey Medical School, Newark 07103.
Kachroo
A
A
Sapru
H N
HN
D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D006321:Heart / Q000294:innervation; D008168:Lung / Q000294:innervation; D008297:Male; D008845:Microinjections; D009118:Muscimol / Q000008:administration & dosage; D009411:Nerve Endings / Q000187:drug effects*; D009412:Nerve Fibers / Q000187:drug effects*; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017459:Receptors, Amino Acid / Q000502:physiology*; D017552:Solitary Nucleus / Q000187:drug effects / Q000502:physiology*; D014630:Vagus Nerve / Q000187:drug effects*
D001645:Biguanides; D011810:Quinoxalines; D017459:Receptors, Amino Acid; D009118:Muscimol; C056723:FG 9041; C008846:phenyl biguanide