Intracellular recording from neurones of the rat subfornical organ in vitro.

1. Intracellular recordings from neurones in the subfornical organ in vitro showed that there were two classes of neurones. One class lay within 55 micron of the ventricular surface and was synaptically excited but not inhibited by stimulation of the body or columns of the fornix. These neurones could not be excited antidromically. The other class lay more deeply and was antidromically and synaptically excited and inhibited by stimulation of the body and columns of the fornix. 2. The neurones of the subfornical organ appeared to have the characteristics of neurosecretory neurones. Their action potentials were prolonged and their antidromic spike was easily broken down into components by repetitive stimulation. 3. The organization of the subfornical organ inferred from extracellular recording was confirmed by the results of intracellular recording.