Key result
While individual inhibition of the CVLM or NTS increased mean arterial pressure, simultaneous blockade reduced it below baseline (88-92 mmHg vs 105 mmHg control) in anesthetized rats.
Simultaneous blockade of the NTS and CVLM reveals that important pressor mechanisms arise from these regions to control vascular resistance and arterial pressure.
Challenges simplistic NTS/CVLM models in rats; leaves open relevance to human blood pressure control.
In the present study, we investigated the effects of inhibition of the caudal ventrolateral medulla (CVLM) with the GABA(A) agonist muscimol combined with the blockade of glutamatergic mechanism in the nucleus of the solitary tract (NTS) with kynurenic acid (kyn) on mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances. In male Holtzman rats anesthetized intravenously with urethane/chloralose, bilateral injections of muscimol (120 pmol) into the CVLM or bilateral injections of kyn (2.7 nmol) into the NTS alone increased MAP to 186 +/- 11 and to 142 +/- 6 mmHg, respectively, vs. control: 105 +/- 4 mmHg; HR to 407 +/- 15 and to 412 +/- 18 beats per minute (bpm), respectively, vs. control: 352 +/- 12 bpm; and renal, mesenteric and hindquarter vascular resistances. However, in rats with the CVLM bilaterally blocked by muscimol, additional injections of kyn into the NTS reduced MAP to 88 +/- 5 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Moreover, in rats with the glutamatergic mechanisms of the NTS blocked by bilateral injections of kyn, additional injections of muscimol into the CVLM also reduced MAP to 92 +/- 2 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Simultaneous blockade of NTS and CVLM did not modify the increase in HR but also abolished the increase in renal vascular resistance produced by each treatment alone. The results suggest that important pressor mechanisms arise from the NTS and CVLM to control vascular resistance and arterial pressure under the conditions of the present study.
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Moreira et al. (2005) studied Arterial pressure regulation. Muscimol into CVLM and kynurenic acid into NTS vs. Control baseline was evaluated on Mean arterial pressure (MAP). While individual inhibition of the CVLM or NTS increased mean arterial pressure, simultaneous blockade reduced it below baseline (88-92 mmHg vs 105 mmHg control) in anesthetized rats.
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