Effect of L-DOPA on nitric oxide production in striatum of freely mobile mice.

In Parkinson's disease, nitric oxide (NO) and other free radicals are thought to be involved in neuronal degeneration. Furthermore, L-DOPA is suggested to have a cytotoxic action on dopaminergic neurons. We studied 24-h NO production and the effect of L-DOPA on this in freely mobile mice using in vivo microdialysis. A microdialysis probe was implanted into the right striatum 12 h before the experiment. This dialysis probe was perfused with Ringer solution for 100 min, then with 20, 50, or 100 nM L-DOPA for 20 min, and finally with Ringer solution. Dialysate fractions were collected every 20 min for 4 h. Production of nitrite and total NO were significantly higher during daytime than during nighttime. Nitrate production was increased significantly by L-DOPA. NO production in the striatum appears to exhibit a diurnal rhythm and to increase with exposure to L-DOPA.