Scientists said Thursday that experimental drugs protected rats against a substance that kills brain cells, suggesting a possible approach to fighting Parkinson's disease.

The toxic substance produces Parkinsonlike symptoms in humans, and it kills the same brain cell circuitry that is affected by Parkinson's disease.But scientists cautioned that the link between those effects and natural Parkinson's is unclear, so the usefulness of the toxin-blocking drugs in treating Parkinson's is unknown.

Parkinson's disease is a potentially disabling condition that can include tremor, rigidity and gradual loss of spontaneous movement. It is caused by the death of specific brain cells, but in most cases, the trigger for that cell death is not known.

Scientists at the Schering AG corporation said they injected the brains of rats with electrically charged particles called MPP-plus, which the body manufactures from a substance called MPTP, the chemical that produces the Parkinsonlike effects.

They found that brain damage largely could be prevented if the animals were given drugs called NMDA antagonists, either before or with the MPP-plus injection.