WE found NADPH-diaphorase (presumably identical with nitric oxide synt
hase) in pyramidal neurones of the hippocampus in slices that stayed i
n a chamber for 30 min or longer. In some instances parallel slices sh
owed normal membrane properties when studied electrophysiologically. I
n freshly made slices the pyramidal neurones were not stained. Thus, a
fter induction of the enzyme, the hippocampal pyramidal neurones can s
ynthesize nitric oxide which may serve as a retrograde messenger in lo
ng-term potentiation. The enzyme may also play a role in cell loss see
n in slices which stayed in a chamber for 9-22 h before fixation.