Long-term MPTP-treated monkeys are resistant to GM1 systemic therapy.

GM1 has been reported to promote sprouting of dopaminergic mesencephalic neurons when administered at the time of MPTP treatment. Owing to its potential clinical significance, we evaluated behavioral effects of GM1 treatment in three Cebus apella monkeys with a persistent hemiparkinsonian syndrome after 20-22 mo of an intracarotid infusion of MPTP. MPTP monkeys compared with normal ones presented difficulty in solving motor cognitive tests and reversal of circling activity after apomorphine treatment. Monkeys were treated during 3 wk with daily saline, followed by 4 wk with GM1 (20 mg/kg, im). Neither during saline nor GM1 treatment, nor 30 d afterwards, did the animals improve their performances nor did the apomorphine tests reveal significant changes in circling behavior. These results are discussed in terms of their possible implications for Parkinson disease treatment.