Zonisamide-induced long-lasting recovery of dopaminergic neurons from MPTP-toxicity

Zonisamide is an antiepileptic drug that also improves the cardinal symptoms of Parkinson's disease. This study investigated the effects of zonisamide on dopaminergic neuronal degeneration in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. Six groups of mice were treated as follows: 1) normal saline; 2) MPTP, 15 mg/kg×4 every 2h; 3) MPTP and zonisamide, 40 mg/kg×1, 1h after the last MPTP dose; 4) MPTP and zonisamide, 1 day after the last dose of MPTP; 5) MPTP and zonisamide, 1h before the first MPTP dose; and 6) zonisamide, 40 mg/kg. MPTP-treatment decreased the contents of dopamine as well as the number and area of tyrosine hydroxylase (TH)-positive neurons. Concurrent treatment of mice with zonisamide and MPTP did not show any inhibition of the toxic effect of MPTP towards dopamine contents at 1 week after treatment but it increased the number and area of TH-positive neurons compared to the MPTP-treated group. Surviving TH-positive neurons had recovery of dopamine production after several weeks. Moreover, zonisamide increased the number of S100β-positive and glial fibrillary acidic protein (GFAP)-positive astrocytes and dopamine turnover. These results suggest that zonisamide acts as a neuro-protectant against MPTP-induced dopaminergic neuronal degeneration as shown by an increase of TH-positive neurons and this may be mediated by increased S100β secretion.