The action of acetylcholine in the supraoptic nucleus of the chloralosed dog

In an earlier paper (Pickford, 1939) experiments were described in which it was shown that acetylcholine (ACh.) given intravenously to the normal unanaesthetized dog during the course of a water diuresis resulted in a temporary inhibition of the diuresis. It was also demonstrated that this inhibitory effect could not be produced after the removal of the posterior lobe of the pituitary gland, and that the inhibition was unlike that caused. by intravenously administered adrenaline, or by the lowering of the blood pressure due to inhalation of amyl nitrite. It was concluded, therefore, that this inhibition was caused by the action of ACh. on the central nervous system, inducing a liberation into the circulation of the antidiuretic hormone of the posterior pituitary body. If ACh. takes part in transmitting the impulse in the hypothalamus, the cells of the supraoptic nucleus at once come to mind as a likely place for the ACh. to be effective (Fisher, Ingram & Ranson, 1938). In order to test this suggestion the following experiments were performed.