Following unilateral CST transections, intracortical infusion of a purine nucleoside, inosine, induces a 10-fold increase in the number of intact CST axons in the spinal cord that cross the midline to enter the denervated dorsal funiculus(dDF) (Benowitz et al., PNAS 96: 13486-90). These collaterals form synapses that are identifiable by EM in the denervated synaptic neuropil, lamina IV (dIV), adjacent to dDF (Soni et al., SfN Abs 26,325.9). Here, we investigated whether the inosine-effect is also exhibited as the crossed, intact axons continue to grow through dDF and into dIV (axogenesis), then undergo synaptogenesis. Unilateral CST transection was performed as before in mature rats. One group (n=3) was treated with 50mM of inosine in PBS, delivered into the intact cortex (4 wks @ 0.25 ul/hr), while the second group (n=3) was infused with PBS, alone. BDA was injected into the intact cortex to identify their trajectory in the spinal cord. We observed that inosine increases the number of intact CST axons tha...