Effects of microinjection of dopamine (DA) intracisterna magna (ICM) or into caudal nucleus of tractus solitarii (cNTS) on the cardiovascular responses to chemoreflex activation in awake rats

Abstract

There is evidence that DA is a neuromodulator in the brainstem areas involved with the autonomic activity to the cardiovascular system. In present study we evaluated the effect of microinjection of DA ICM or into cNTS on the cardiovascular and respiratory responses to chemoreflex activation in awake rats. Guide cannulas were implanted in the direction of ICM or cNTS and femoral artery and vein catheterized. On the day of the experiments chemoreflex was activated with KCN (iv) before and after microinjection of DA ICM (n=9) or into NTS bilaterally (n=8) and mean arterial pressure (MAP) and heart rate (HR) were recorded. Microinjection of DA ICM, but not in the cNTS, produced a significant reduction in baseline MAP (98±2 vs 84±1 mmHg) and HR (374±10 vs 326±8 bpm). Microinjection of DA ICM or into cNTS produced no significant changes in the magnitude of the pressor and bradycardic responses to chemoreflex activation. Microinjection of DA into cNTS also produced no effect on the tachypneic response to chemoreflex activation. The data obtained with ICM microinjection shows that dopamine receptors in the brainstem are involved in the basal autonomic modulation to the cardiovascular system. However, DA in the cNTS does not modulate the basal autonomic activity to the cardiovascular system neither cardiovascular and respiratory responses to chemoreflex activation. Financial support: CNPq and FAPESP.