Peptide and acetylcholine action on neurones of the cat subfornical organ.

Angiotensin II, related oligopeptides and acetylcholine were tested on neurones of the cat subfornical organ (SFO). Angiotensin II activates SFO-neurones by local administration onto the surface, by i.v. injection or with the aid of microiontophoretic techniques. Application of related oligopeptides, bradykinin, physalaemin and eledoisin showed no comparable results. Activation of neurones similar to those observed after angiotensin II was obtained with acetylcholine. About 30% of the cells tested were excited by both substances, 56% of tested SFO-cells responded only to angiotensin II, but not to acetylcholine. Atropine sulphate prevents specifically the acetylcholine excitation. Since angiotensin II is involved in regulatory mechanism of thirst, these results suggest the possibility that the SFO is one of the sites, where dipsogenic receptors for this circulating peptide are located.