Hi Island Mike,
The dopamine-producing cells that are lost in Parkinson's also produce other chemical messengers, including GABA. Recent research has suggested that people with Parkinson's may not have enough of this messenger.
Gabapentin increases the amount of GABA in the brain, and you're right there have been some studies of gabapentin in people with Parkinson's. These studies have been relatively small so some more research is needed to know if gabapentin is beneficial, who it benefits the most, and if there are any side-effects.
We know that gabapentin does not interact with the GABA receptors in the brain. Recent research suggest that drugs that mimic the effects of GABA - by interacting with these receptors - may be more effective. We are currently funding a research project that is investigating whether chemicals that mimic the effects of GABA improve movement symptoms in mice.
Hope that helps,
Parkinson's UK Research Team