Zonisamide Attenuates MPTP Neurotoxicity in Marmosets

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induces parkinsonism in humans and animals. The effects of zonisamide on dopamine neurons were studied in MPTP-treated common marmosets (Callithrix jacchus). Groups of animals (n = 3) were treated with MPTP (2.5 mg/kg, every 24 h x 3); MPTP plus zonisamide (40 mg/kg administered 1 h before each MPTP dose); MPTP plus selegiline (a known MAO-B inhibitor) (2 mg/kg administered 1 h before each MPTP dose); and saline controls. An immunohistochemical study of the substantia nigra was performed 14 days after MPTP treatment in each group. MPTP reduced the mean number of tyrosine hydroxylase (TH)-positive neurons to 10% of the normal control group and mean cell size was significantly (P < 0.001) reduced from 424 to 159 mu m(2). In the group pre-treated with zonisamide, the mean number of TH-positive neurons was reduced to 26% of that in the normal control group and the mean neuron size was significantly (P < 0.05) increased from 159 to 273 mu m(2) compared with the group treated with MPTP alone. Moreover, in the group pre-treated with selegiline, the mean number of TH-positive neurons was 47% of that in the normal control group and the mean neuron size was increased significantly (P < 0.01) from 159 to 319 mu m(2) compared to the group treated with MPTP alone. This observation suggests that zonisamide reduces MPTP toxicity.