Figure 4. Time-effect curves for a 1:3 fixed ratio of morphine to clonidine administered to L5/L6 ligated rats are shown. Circles, squares, triangles, and diamonds represent 1 micro gram morphine + 3 micro gram clonidine, 3 micro gram morphine + 10 micro gram clonidine, 10 micro gram morphine + 30 micro gram clonidine, and 30 micro gram morphine + 100 micro gram clonidine, respectively. Error bars represent +/- SEM.