Doctors in the United States may soon be using tissue from testicles to treat brain diseases such as Parkinson's and Alzheimer's. The idea is to transplant cells of an animal testis directly into the brains of patients.

The latest research was one of the more surprising topics of discussion at the annual meeting of the American Association for the Advancement of Science (AAAS) in Anaheim, California.

Testicle to brain transplants may sound like an improbable concept but the latest experiments on laboratory rats suggest they may offer a new way to treat several serious brain conditions.

Rats with a form of Parkinson's disease have shown considerable improvement in their symptoms after surgical implants of a certain kind of testicle cell in their heads. These cells are called sertoli cells.

Their normal role is to nourish developing sperm. According to Dr Paul Sanberg of the University of South Florida, this involves the secretion of chemicals called growth factors, which are very similar to those made in the brain.

"It's quite interesting that in fact the brain and testes have some relationship as far as the chemicals that are in there, and yes, it's funny but it's true in a number of ways," he said.

Cell repair

Some of these testicular chemicals encourage diseased or damaged brain cells to repair and reconnect with each other.

Dr Sanberg: Clinical trials are two years away

In human patients, Dr Sanberg is hoping to use testicular cells from pigs or rats - first of all in an attempt to treat Parkinson's disease. But Huntingdon's disease and Alzheimer's disease are other possible targets.

And although foreign to the human body, the cells have a way of protecting themselves from rejection once they have been transplanted.

"The other thing that they do is provide an immunological barrier. They secrete a substance called FAS-L which induces lymphocytes - which are the white blood cells that attack the body - to die. They induce what we call apoptosis in them, so that these lymphocytes won't attack the testes."

He believes his first clinical trials are at least two years away. However, at a press conference in Anaheim, Paul Sanberg revealed that another team based in San Francisco had recently started using another form of testicular tissue to treat the victims of strokes.

"They're in the clinic in phase one, looking at stroke patients to re-grow connections that are lost in stroke patients. And they have done nine patients as of this month," he said.