"Pre-treatment of SH-SY5Y cells with guanosine decreases MPP + -induced DNA fragmentation. SH-SY5Y cells were exposed to MPP + (500 μM) for 48 h to induce DNA fragmentation. Some cells were pre-treated with guanosine (1–300 μM) for 1 h prior to MPP + . Guanosine and MPP + remained in the cultures for the duration of the experiment. DNA fragmentation was determined after 48 h by oligonucleosomal ELISA as described in the "" Materials and methods "" section and is expressed as the percentage of the positive control ( n > 3). MPP + increased DNA fragmentation significantly at 48 h compared to that of untreated controls (* p"