Fig. 2. Effect of yohimbine on clonidine-induced inhibition of norepinephrine release from rat spinal cord dorsal horn synaptosomes. The first value on the left is norepinephrine release induced by KCl, 10 mm, with all subsequent values in which there is both KCl and clonidine, 1 μm. Values shown represent the mean ± SEM of four to six observations. *P < 0.05 compared with KCl plus clonidine alone.