Sympatho - excitation during chemoreflex active expiration is mediated by L - 2 glutamate in the RVLM / Bötzinger complex of rats 3 4

29 The involvement of glutamatergic neurotransmission in the rostral ventrolateral 30 medulla/Bötzinger/pre-Bötzinger complexes (RVLM/BötC/pre-BötC) on the respiratory 31 modulation of sympatho-excitatory response to peripheral chemoreflex activation 32 (chemoreflex) was evaluated in the working heart-brainstem preparation of juvenile 33 rats. We identified different types of baroand chemosensitive pre-sympathetic and 34 respiratory neurons intermingled within the RVLM/BötC/pre-BötC. Bilateral 35 microinjections of Kynurenic acid (KYN) into the rostral aspect of RVLM 36 (RVLM/BötC) produced additional increase in frequency of phrenic nerve (PN: 0.38 ± 37 0.02 vs 1 ± 0.08 Hz; p<0.05; n=18) and hypoglossal (HN) inspiratory response (41 ± 2 38 vs 82 ± 2%; p<0.05; n=8), but decreased post-inspiratory (35 ± 3 vs 12 ± 2%; p<0.05) 39 and late-expiratory (24 ± 4 vs 2 ±1%; p<0.05; n=5) abdominal (AbN) responses to 40 chemoreflex. Likewise, expiratory vagal (cVN; 67 ± 6 vs 40 ± 2%; p<0.05; n=5) and 41 expiratory component of sympatho-excitatory (77 ± 8 vs 26 ± 5%; p<0.05; n=18) 42 responses to chemoreflex were reduced after KYN microinjections into RVLM/BötC. 43 KYN microinjected into the caudal aspect of the RVLM (RVLM/pre-BötC; n=16) 44 abolished inspiratory responses [PN (n=16) and HN (n=6)], and no changes in 45 magnitude of sympatho-excitatory (n=16) and expiratory (AbN and cVN; n=10) 46 responses to chemoreflex, producing similar and phase locked vagal, abdominal and 47 sympathetic responses. We conclude that in relation to chemoreflex activation a) 48 ionotropic glutamate receptors in RVLM/BötC and RVLM/pre-BötC are pivotal to 49 expiratory and inspiratory responses, respectively and b) activation of ionotropic 50 glutamate receptors in RVLM/BötC is essential to the coupling of active expiration and 51 sympatho-excitatory response. 52