COMMISSURAL NTS CONTRIBUTES TO PRESSOR-RESPONSES TO GLUTAMATE INJECTED INTO THE MEDIAL NTS OF AWAKE RATS

In the present study we investigated whether interruption of the chemo receptor reflex by an electrolytic lesion of the commissural subnucleu s of the nucleus tractus solitarii (commNTS) influenced presser and br adycardic responses induced by microinjection of L-glutamate (L-Glu) i nto the medial NTS (mNTS) of conscious rats. Seven days after sham les ions, seven rats demonstrated significant presser [change in mean arte rial pressure (MAP) = +33 +/- 3 mmHg] and bradycardic [change in heart rate (HR) = -74 +/- 8 beats/min (bpm)] responses to chemoreceptor ref lex activation by intravenous injection of KCN. Likewise, L-Glu (1 nmo l in 100 nl) injected into the mNTS in sham rats induced presser (+29 +/- 2 mmHg) and bradycardic responses (-90 +/- 8 bpm). However, in 11 rats with lesions in commNTS, presser and bradycardic chemoreceptor re flex responses were abolished, and injection of L-Glu into the mNTS de creased MAP (-14 +/- 6 mmHg) and HR (-59 +/- 16 bpm) as is reported in anesthetized control rats. We conclude that presser responses induced by L-Glu microinjected into the baroreceptor reflex region of mNTS in conscious rats depend on the integrity of the commNTS, which plays an important role in central chemoreceptor reflex pathways.