Introduction 1 2 3 4 5 3 6 3 6 7 8 9 10 11 13 14 15 13 16 18 19 20 21 22 24 24 25 26 27 28 29 28 32 5 33 34 35 36 37 Materials and methods Animals Adult female Wistar rats (280–300 g body weight, Charles River) were maintained in a temperature-controlled vivarium on a 12:12-h light-dark cycle with food and tap water freely available. Rats were handled daily for 2 weeks before surgery. Spinal cord injury induction and experimental design 5 38 2 5 38 40 n 38 5 Motor and sensory functional recovery assessment 5 41 42 38 40 38 40 43 38 44 45 46 5 38 38 40 43 38 40 40 43 44 46 46 Recovery of lower urinary tract function 47 48 49 After SCI the rats were not capable initially of spontaneous micturition, and their bladders were manually expressed twice daily. The volume of expressed urine was measured each time, and the data were used to estimate the initiation of LUT function after SCI. Histological analysis Tissue processing and immunohistochemical staining 38 5 38 Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling assays and quantification n 5 Quantification n Statistical analysis t Results Guanosine improves neurological function 1 1 P Fig. 1 n n P  38 40 2 2 P 3 3 P Fig. 2 n n P  Fig. 3 n n P  4 P Fig. 4 n n P  P 5 Fig. 5 n n P  Guanosine accelerated LUT functional recovery following SCI 48 6 6 P 6 Fig. 6 n n P P  Guanosine attenuates macrophage and microglia activation, but not astrogliosis 50 51 7 P 7 Fig. 7 a b b e a e P c d d c Scale bar  Guanosine attenuates apoptotic cell death in lesion site of spinal cord 8 P Fig. 8 a c b c P Scale bar a b  Guanosine increases axon and myelin sparing 9 9 9 9 9 9 Fig. 9 a b c d a b NF c d c e f red green Scale bar  Discussion 32 52 28 34 35 53 41 54 55 56 57 58 59 40 60 47 48 49 21 61 34 35 15 62 67 63 67 68 69 70 71 72 73 74 75 34 35 36 37 26 27 28 67 This study is important not only because it is the first to demonstrate the neuroprotective effect of systemically administered guanosine in acute spinal cord injury, but also because it indicates some of the potential mechanisms whereby guanosine may exert its neuroprotective effects in vivo. This work provides a basis for further exploration of the purinergic mechanisms underlying the neuroprotective effects of exogenous guanosine. Furthermore, and of potential clinical importance, is that guanosine was effective when it was administered 4 h after the injury—a realistic time frame in which to initiate treatment after spinal cord injury in humans.