These multiple forms (isoforms or subtypes) of phosphodiesterase were isolated from rat brain using polyacrylamide gel electrophoresis in the early 1970s by Weiss and coworkers, and were soon afterward shown to be selectively inhibited by a variety of drugs in brain and other tissues, also by Weiss and coworkers.
The potential for selective phosphodiesterase inhibitors to be used as therapeutic agents was predicted in the 1970s by Weiss  and coworkers. This prediction has now come to pass in a variety of fields (e.g. sildenafil as a PDE5 inhibitor and Rolipram as a PDE4 inhibitor).