['Alpha 2 adrenoceptor agonists produce antinociception in normal animals and alleviate mechanical allodynia in animals with nerve injury, although their mechanism of action may differ in these situations. The purpose of this study was to examine the location and number of cells in the spinal cord activated by intrathecal clonidine in these two circumstances and to test whether one class of interneurons, cholinergic, express alpha 2 adrenoceptors.', 'Intrathecal saline or clonidine, 10 and 30 microg, was injected in normal rats or those with mechanical allodynia following partial sciatic nerve section. Two hours later, animals were anesthetized and pericardially perfused. The number of cells in superficial and deep dorsal horn laminae at the L4-L5 level immunostained for phosphorylated cAMP response element binding protein (pCREB) were quantified. In separate studies, the authors colocalized alpha2C adrenoceptors with cholinergic neurons.', 'Intrathecal clonidine increased pCREB immunoreactive cells in both superficial and deep laminae by 50-100% in normal animals. The number of pCREB immunoreactive cells increased in nerve-injured compared to normal rats. Intrathecal clonidine decreased pCREB immunoreactive cells in the deep dorsal horn of injured animals. Alpha2C adrenoceptors colocalized with cholinergic neurons in both superficial and deep dorsal horn.'] Is clonidine-induced neuronal activation in the spinal cord altered after peripheral nerve injury?