Dopaminergic mechanisms in the nucleus tractus solitarius and effects on blood pressure.

The actions of dopamine (DA) agonists and antagonists upon spontaneously active neurons in the nucleus tractus solitarius (NTS), dorsal motor nucleus of the vagus (nX), and the nucleus nervi hypoglossi (nXII) were studied. DA was applied microiontophoretically to 42 neurons within the NTS and nX. Sixteen of these cells were stimulated by DA and 9 neurons were depressed. In neurons localized in the nXII nucleus, DA inhibited 19 cells out of 23. Noradrenaline (NA) excited 11 out of 30 cells in the NTS and nX. In the area of nXII nucleus, NA inhibited 6 out of 19 cells and did not modify 11 cells. Acetylcholine (ACh) stimulated the firing of 18 out of 22 neurons. The effects on NA and DA were directly compared on 21 neurons in the NTS. On 16 cells of this group the responses to DA were quantitatively or qualitatively different from those to NA. The DA receptor blockers sulpiride and fluphenazine antagonized the effects of DA but not those due to NA or ACh. Bilateral microinjections of DA (50 nmole) in the area of the NTS induced an increase in systemic blood pressure and heart rate. ACh induced similar effects. NA in the NTS decreased blood pressure and produced bradycardia. The effects of DA on heart rate and blood pressure were blocked by sulpiride or fluphenazine. The cardiovascular role played by DA in the NTS is discussed.