Bilateral behavioral and regional cerebral blood flow changes during painful peripheral mononeuropathy in the rat.

A unilateral chronic constriction injury (CCI) of the sciatic nerve produced bilateral effects in both pain related behaviors and in the pattern of forebrain activation. All CCI animals exhibited spontaneous pain-related behaviors as well as bilateral hyperalgesia and allodynia after CCI. Further, we identified changes in baseline (unstimulated) forebrain activation patterns 2 weeks following CCI by measuring regional cerebral blood flow (rCBF). Compared to controls, CCI consistently produced detectable, well-localized and typically bilateral increases in rCBF within multiple forebrain structures in unstimulated animals. For example, the hindlimb region of somatosensory cortex was significantly activated (22%) as well as multiple thalamc nuclei, including the ventral medial (8%), ventral posterior lateral (10%) and the posterior (9%) nuclear groups. In addition, several forebrain regions considered to be part of the limbic system showed pain-induced changes in rCBF, including the anterior dorsal nucleus of the thalamus (23%), cingulate cortex (18%), retrosplenial cortex (30%), habenular complex (53%), interpeduncular nucleus (45%) and the paraventricular nucleus of the hypothalamus (30%). Our results suggest that bilateral somatosensory and limbic forebrain structures participate in the neural mechanisms of prolonged persistent pain produced by a unilateral injury.