This is very interesting thanks butterfly. I didnt know GDNF could be delivered via a tube in the abdomen! Because it is much clearer than i could explain I have taken the liberty of copying what Jon Stamford wrote in May 2011 on another site ( Health Unlocked). Hope you find it interesting.
"In the early part of this decade Stephen Gill at Frenchay Hospital in Bristol conducted a small clinical trial that should have changed the face of pharmacotherapy for Parkinson's. The drug in question was GDNF (Glial Derived Neurotrophic Factor), a naturally occurring brain constituent, administered by pump into the brains of half a dozen patients.
The results were remarkable and, even accounting for journalistic hyperbole, make compelling viewing http://youtu.be/gnDHMveS9_M
Patients that could barely walk before GDNF, strode purposefully afterwards. Words like "miracle" and "cure" were bandied about. And this is not normally part of the dispassionate vocabulary of science.
So what went wrong? Why is GDNF not part of the treatment arsenal available to neurologists?
Shortly after this pilot study was completed, the manufacturers of GDNF (Amgen) pulled the plug and GDNF was no longer available for human use. The reasons for this decision have been debated long and hard over many years and for much of that time the company's position has not changed. Time went by and the Frenchay study gathered dust, an interesting research curio.
But suddenly it is back in the limelight. Amgen have relented and GDNF is being manufactured again. And Prof Gill has a new improved delivery system -- more targeted on the areas of need. "