INVOLVEMENT OF NON-NMDA AND NMDA RECEPTORS IN GLUTAMATE-INDUCED PRESSOR OR DEPRESSOR RESPONSES OF THE PONS AND MEDULLA

1. Fifty-five intact and six baroreceptor denervated and vagotomized c ats of either sex were anaesthetized intraperitoneally with urethane ( 400 mg/kg) and alpha-chloralose (40 mg/kg). Responses of the systemic arterial pressure (SAP), mean SAP (MSAP) and sympathetic vertebral ner ve (VNA) and renal nerve activities (RNA) were recorded. 2. In intact animals, monosodium L-glutamate (Glu, 0.1 mol/L, 50 nL) was microinjec ted into presser areas of the locus coeruleus (LC), gigantocellular te gmental field (GTF), rostral ventrolateral medulla (RVLM) and dorsomed ial medulla (DM), and the depressor areas of caudal ventrolateral medu lla (CVLM). The induced actions were compared before anal after microi njection of either glutamate antagonists, glutamate diethylester (GDEE , 0.5 mol/L, 50-100 nL), a competitive AMPA receptor blocker, or 2-ami no-5-phosphonovaleric acid (D-AP5, 0.025 mol/L, 50-100 nL), a competit ive N-methyl-D-aspartate (NMDA) receptor blocker. GDEE completely bloc ked the increases of SAP and VNA elicited from all presser areas. D-AP 5 only partially blacked the presser but slightly blocked VNA and RNA responses from LC, GTF and DM, particularly those from RVLM. Neither G DEE nor D-AP5 blocked the depressor responses of SAP and two nerve act ivities elicited from CVLM. 3. In baroreceptor denervated animals, NMD A (2 mmol/L, 50-100 nL) and AMPA (0.2 mmol/L, 50-100 nL) were microinj ected into the same presser areas of GTF, RVLM and DM and the depresso r area of CVLM responsive to Glu activation (0.1 mol/L, 30 nL). In RVL M, DM and CVLM, the results of either NMDA or AMPA were similar to tho se induced by Glu. However, in GTF, microinjection of either NMDA or A MPA did not induce similar responses to Glu. This suggests that the na ture of GTF may differ from RVLM and DM. 4. The above results suggest that the Glu-induced presser responses from LC, GTF, DM and especially RVLM, are primarily mediated through AMPA receptors. The Glu-induced depressor responses from CVLM may not be predominantly mediated by eit her AMPA or NMDA receptors. 5. In both baroreceptor-intact and -denerv ated cats stimulation of the presser areas often produced an increase of VNA and a decrease of RNA, while in the depressor CVLM decreased bo th VNA and RNA. The VNA, but not RNA were positively correlated with t he presser responses, while both VNA and RNA were positively correlate d with the depressor responses. This may suggest that neurons of the s ympathetic vertebral and renal nerves are topographically organized in the brain.