Atrial natriuretic polypeptide depresses angiotensin II induced excitation of neurons in the rat subfornical organ in vitro

The effects of atrial natriuretic polypeptide (ANP) on the extracellularly recorded activity of neurons in the subfornical organ (SFO) were investigated in rat brain slice preparations by adding the peptide to the perfusion medium. Eight (14%) of 56 SFO neurons were inhibited and none of the cells were excited by ANP at 10(-7) M. Of 42 SFO neurons tested with both ANP and angiotensin II (AII) at 10(-7) M, 4 (10%) cells were inhibited by ANP and excited by AII, the remainder responded to either one or other of the peptides but not both or were unresponsive. In 13 (87%) of 15 SFO neurons, ANP at 10(-7) M depressed by more than 40% the excitation induced by AII at 10(-7) M, while ANP did not always depress the excitation induced by raising the extracellular potassium concentrations in 6 SFO cells tested. We conclude that ANP strongly depresses AII-induced excitation in all SFO neurons, although it has very weak inhibitory effects on spontaneous activity, thus ANP may act as a neuromodulator in the SFO.