Involvement of the parabrachial nucleus in the pressor response to chemoreflex activation in awake rats.
Activation of the chemoreflex with potassium cyanide (KCN, 40 microg/rat, i.v.) in awake rats produces pressor and bradycardic responses as well as a tachypneic response. In the present study, we evaluated the involvement of the periaqueductal gray matter (PAG) and the parabrachial nucleus (PBN) in the neural pathways of the cardiovascular responses to chemoreflex activation. The cardiovascular responses to chemoreflex activation were evaluated before and after bilateral microinjection of 2% lidocaine, a local anesthetic, into the PBN or PAG in order to block in a reversible manner the neuronal activity and axonal conduction of fibers of passage in these areas. The data show that the pressor response to chemoreflex activation 3 min after bilateral microinjection of lidocaine into the dorsolateral aspect of the PBN was significantly reduced in comparison to the control response (32 +/- 5 vs. 48 +/- 4 mm Hg, n = 7), with no significant changes in the bradycardic responses. The effect of lidocaine was reversible since the pressor response was back to control levels 15 min after microinjection of this anesthetic. Bilateral microinjections of lidocaine into the dorsolateral (n = 11) or lateral (n = 8) columns of the PAG in distinct groups of rats produced no significant changes in the pressor or bradycardic responses of the chemoreflex. These data indicate that the PBN is part of the neuronal pathways involved in the sympathoexcitatory component of the chemoreflex while the PAG is not.
Haibara
Andréa S
AS
Department of Physiology and Biophysics, Institute of Biological Sciences, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
Tamashiro
Edwin
E
Olivan
Marcelo V
MV
Bonagamba
Leni G H
LG
Machado
Benedito H
BH
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D011149:Pons / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D013997:Time Factors; D014851:Wakefulness
D000889:Anti-Arrhythmia Agents; D004791:Enzyme Inhibitors; D008012:Lidocaine; D011190:Potassium Cyanide