66 Purinergic Signalling (2008) 4:61–71 Fig. 2 Quantitative assessment of immunostaining shows that systemic treatment with guanosine stimulates endogenous oligoden- droglial progenitors (NG2+ cells) to proliferate and mature in rats with stable chronic spinal cord injury. a, b Bromodeoxyuridine (BrdU) was used to label proliferating cells after treatment. BrdU immunostaining in cross sections from vehicle- (a) and guanosine- (b) treated animals at the lesion 14 days after treatment shows increased BrdU+ nuclei in b compared to the vehicle-treated control group in a. Scale bar = 50 μm. c Quantitative analysis shows that 7 or 14 days after guanosine treatment there was a significant increase in the number of BrdU+ cells compared with vehicle-treated controls. d, e Demonstrate examples of double-fluorescent immunostaining using antibodies against BrdU (in green) and a marker (NG2) for oligodendroglial progenitors (in red) in cross sections from vehicle- (d) and guanosine- (e) treated animals at the lesion 14 days after treatment. Scale bar = 50 μm. f–h Show quantification of proliferating progenitors (NG2+/ BrdU+ double-labelled cells; f) and total number of NG2 cells (g). Data indicate that after 7 or 14 days administration guanosine significantly stimulates proliferation of oligodendroglial progenitors (f, g). Concurrently, guanosine also significantly increases the number of mature oligodendroglia shown in i and j compared to vehicle- treated controls (h, j) using fluorescent immunostaining with a specific marker (Rip) to label the mature oligodendroglia. Scale bar = 50 μm Results and discussion After SCI, motor function in the legs partially recovered over 3–4 weeks, after which there was no further improvement (Fig. 1a). Daily guanosine for 14 days (8 mg/kg intraperitoneally beginning 35 days after injury) produced improvement in locomotor performance over the next 2 weeks; control rats showed no improvement (Fig. 1b). This treatment regimen was associated with significantly increased amounts of myelin in the penumbra of the cord lesions shown by Luxol fast blue staining (Fig. 1c–e). The extent of Luxol fast blue staining in the