title: Involvement of the purinergic system in central cardiovascular modulation at the level of the nucleus ambiguus of anaesthetized rats.
abstract: Anatomical studies have demonstrated the existence of purinergic P2 receptors in the nucleus ambiguus (NA), a site containing cardiac vagal motoneurons. However, very little is known about the functional role of these receptors in central cardiac vagal regulation. The aims of our study were to evaluate the following: (1) the blood pressure and heart rate responses following purinoceptor activation within the NA; (2) the role of purinoceptors and excitatory amino acid (EAA) receptors in mediating the cardiovascular responses evoked by ATP and L-glutamate stimulation of NA; and (3) the role of NA purinoceptors in mediating the cardiovascular responses of the Bezold-Jarisch reflex. In anaesthetized rats, microinjection of L-glutamate (5.0 nmol/50 nl) into the NA induced a marked and immediate onset bradycardia with minimal change in arterial pressure. Microinjection of ATP into the NA induced a dose-dependent (0.31-6.0 nmol/50 nl) bradycardia and pressor responses. It is noteworthy that the bradycardia occurred either before or simultaneously with a pressor response (when present), indicating that it was not a baroreceptor reflex mediated response due to the rise in arterial pressure. The pressor response was prevented by α(1)-adrenergic blockade with prazosin, whereas muscarinic blockade with methyl-atropine abolished the evoked bradycardia. Ipsilateral microinjection of PPADS (a P2 receptor antagonist; 500 pmol/100 nl) into the NA significantly attenuated the ATP-induced bradycardia but spared the pressor response. In contrast, PPADS in the NA had no effect on the L-glutamate-evoked bradycardic response. Ipsilateral injection of kynurenic acid (a non-selective EAA receptor antagonist; 10 nmol/50 nl) into the NA totally blocked the bradycardia induced by l-glutamate and partly attenuated the ATP induced bradycardia. Finally, both the depressor and the bradycardic responses of the Bezold-Jarisch reflex were attenuated significantly (P < 0.01 and P < 0.05, respectively) following bilateral microinjection of PPADS into the NA. These results identify ATP and purinergic P2 receptors within the ventrolateral medulla as excitatory to cardiovagal neurons. Additionally, our data show that P2 receptors within the ventrolateral medulla are integral to the cardiovascular responses of the Bezold-Jarisch reflex.
authors.affiliation: Physiological Sciences, Health Sciences Center, Federal University of Espírito Santo, Vitória, Espírito Santo, Brazil.
authors.forename: Luciana M
authors.initials: LM
authors.lastname: Passamani
authors.forename: Diego França
authors.initials: DF
authors.lastname: Pedrosa
authors.forename: Hélder
authors.initials: H
authors.lastname: Mauad
authors.forename: Luiz Carlos
authors.initials: LC
authors.lastname: Schenberg
authors.forename: Julian F R
authors.initials: JF
authors.lastname: Paton
authors.forename: Karla N
authors.initials: KN
authors.lastname: Sampaio
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D058668:Adrenergic alpha-1 Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D001286:Atropine Derivatives / Q000494:pharmacology; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects / Q000294:innervation* / Q000378:metabolism; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D007736:Kynurenic Acid / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000378:metabolism / Q000502:physiology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D058919:Purinergic P2 Receptor Antagonists / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism / Q000502:physiology*; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology
chemical_list: D058668:Adrenergic alpha-1 Receptor Antagonists; D001286:Atropine Derivatives; D018691:Excitatory Amino Acid Antagonists; D018727:Muscarinic Antagonists; D058919:Purinergic P2 Receptor Antagonists; D017470:Receptors, Glutamate; D018048:Receptors, Purinergic P2; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D018698:Glutamic Acid; D011732:Pyridoxal Phosphate; C006649:methylatropine; D000255:Adenosine Triphosphate; D007736:Kynurenic Acid; D011224:Prazosin