Ionotropic glutamate receptors in the rostral ventrolateral medulla mediate sympathetic responses to acute stress in conscious rabbits

In conscious, chronically instrumented rabbits (n=7), airjet stress evoked increases in arterial pressure (AP) and renal sympathetic nerve activity (RSNA), which were greatest in the first 2 min (+10 mm Hg and +127%, respectively), but then rapidly reached a stable level (+7 mm Hg and +37%, respectively). Bilateral microinjection into the rostral ventrolateral medulla (RVLM) of an ionotropic excitatory amino acid (EAA) receptor antagonist kynurenate (10 nmol/200 nl) did not affect resting AP and RSNA, but reduced their initial peak responses to airjet by 80% and 52%, respectively, without altering the stable levels of these responses. By contrast, bilateral microinfusion of glutamate (2 nmol/20 nl/min) into the RVLM increased resting AP by 13 mm Hg, but did not alter the RSNA and AP responses to airjet stress. These results suggest that the RVLM is an essential site for conveying excitatory environmental influences to the sympathetic nervous system in conscious rabbits. The EAA receptors are critically important in initiating the pressor and sympathoexcitatory responses to acute emotional stress, but play relatively little role in the maintenance of these responses.