Rostral ventrolateral medullary (RVLM) but not medullary lateral tegmental field (LTF) neurons are in the pathway mediating sympathoexcitatory (SE) responses elicited by activation of cardiac and splanchnic sympathetic afferents

Abstract

The LTF is involved in mediating sympathetic responses to activation of baroreceptor, arterial chemoreceptor, and vagal afferents but not trigeminal or sciatic afferents (Orer et al, Am J Physiol 286: R451‐64, 2004). In the current study, we tested the hypothesis that the LTF is an element of the sympatho‐sympathetic reflex pathway. We studied the effects of blockade of NMDA or non‐NMDA receptors bilaterally in the LTF on the area under the curve of the computer‐averaged SE potential in the right inferior cardiac nerve elicited by trains of stimuli applied at 0.5 Hz to afferents in left inferior cardiac and splanchnic nerves (lCN, lSN) of Dial‐urethane anesthetized cats. SE responses to lCN stimulation were unchanged by microinjection of either D‐AP5 (101±5% of control; n = 5) or NBQX (98±8% of control; n = 5). Responses to lSN stimulation were similarly unaffected: 92 ± 4 (n = 6) and 90 ± 5 (n = 4) % of control after D‐AP5 and NBQX. Thus, LTF is not a part of these reflex pathways. However, microinjection of NBQX into RVLM significantly (P ≤ 0.05) reduced SE responses to stimulation of lCN (37± 11% of control; n = 6) and lSN (35 ± 11 % of control; n = 5). D‐AP5 microinjection into RVLM did not significantly effect SE responses to stimulation of lCN or lSN (79 ± 13 and 72 ± 17 % of control; n = 5 each). These data show that activation of non‐NMDA receptors in RVLM contribute to SE responses to activation of sympathetic afferents. (Supported by HL33266)