title: Sympathoexcitation during chemoreflex active expiration is mediated by L-glutamate in the RVLM/Bötzinger complex of rats.
abstract: The involvement of glutamatergic neurotransmission in the rostral ventrolateral medulla/Bötzinger/pre-Bötzinger complexes (RVLM/BötC/pre-BötC) on the respiratory modulation of sympathoexcitatory response to peripheral chemoreflex activation (chemoreflex) was evaluated in the working heart-brain stem preparation of juvenile rats. We identified different types of baro- and chemosensitive presympathetic and respiratory neurons intermingled within the RVLM/BötC/pre-BötC. Bilateral microinjections of kynurenic acid (KYN) into the rostral aspect of RVLM (RVLM/BötC) produced an additional increase in frequency of the phrenic nerve (PN: 0.38 ± 0.02 vs. 1 ± 0.08 Hz; P < 0.05; n = 18) and hypoglossal (HN) inspiratory response (41 ± 2 vs. 82 ± 2%; P < 0.05; n = 8), but decreased postinspiratory (35 ± 3 vs. 12 ± 2%; P < 0.05) and late-expiratory (24 ± 4 vs. 2 ±1%; P < 0.05; n = 5) abdominal (AbN) responses to chemoreflex. Likewise, expiratory vagal (cVN; 67 ± 6 vs. 40 ± 2%; P < 0.05; n = 5) and expiratory component of sympathoexcitatory (77 ± 8 vs. 26 ± 5%; P < 0.05; n = 18) responses to chemoreflex were reduced after KYN microinjections into RVLM/BötC. KYN microinjected into the caudal aspect of the RVLM (RVLM/pre-BötC; n = 16) abolished inspiratory responses [PN (n = 16) and HN (n = 6)], and no changes in magnitude of sympathoexcitatory (n = 16) and expiratory (AbN and cVN; n = 10) responses to chemoreflex, producing similar and phase-locked vagal, abdominal, and sympathetic responses. We conclude that in relation to chemoreflex activation 1) ionotropic glutamate receptors in RVLM/BötC and RVLM/pre-BötC are pivotal to expiratory and inspiratory responses, respectively; and 2) activation of ionotropic glutamate receptors in RVLM/BötC is essential to the coupling of active expiration and sympathoexcitatory response.
authors.affiliation: Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Davi J A
authors.initials: DJ
authors.lastname: Moraes
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Zoccal
authors.forename: Benedito H
authors.initials: BH
authors.lastname: Machado
mesh_terms: D000818:Animals; D002628:Chemoreceptor Cells / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D045853:Exhalation / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D018377:Neurotransmitter Agents; D018698:Glutamic Acid