NMDA receptors in NTS are involved in bradycardic but not in pressor response of chemoreflex

Authors:
  • JCJoão H. Costa-Silva
    João H. Costa-Silva
  • DZDaniel B. Zoccal
    Daniel B. Zoccal
  • BMBenedito H. Machado
    Benedito H. Machado
  • DMDavi J. A. Moraes
    Davi J. A. Moraes
  • LBLeni G. H. Bonagamba
    Leni G. H. Bonagamba
  • VBValdir A. Braga
    Valdir A. Braga
  • MBMelissa A. Burmeister
    Melissa A. Burmeister
  • RSRam V. Sharma
    Ram V. Sharma
  • RDRobin L. Davisson
    Robin L. Davisson
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Abstract
Activation of carotid chemoreceptors with intravenous potassium cyanide (KCN) produces increases in arterial pressure, bradycardia, and tachypnea. In the present study, we activated carotid chemoreceptors with KCN and the neurotransmission of the chemoreceptor reflex into the commissural nucleus tractus solitarii (NTS) was blocked with phosphonovaleric acid (AP-5), an N-methyl-D-aspartate (NMDA)-selective antagonist. The aim of this study was to evaluate the involvement of NMDA receptors in the cardiovascular and respiratory responses produced by chemoreceptor activation in unanesthetized rats. The pressor response to KCN was not changed after microinjection of three different doses of AP-5 into the NTS, whereas the bradycardic response was reduced in a dose-dependent manner. The increase in respiratory frequency in response to carotid chemoreceptor activation was also not affected by AP-5 microinjected into the NTS. The data indicate that the activation of the cardiovagal component of the chemoreflex in the commissural NTS is mediated by NMDA receptors, whereas pressor and ventilatory responses are not.