A [14C]iodoantipyrine study of inter-regional correlations of neural substrates following central post-stroke pain in rats

BACKGROUND Central pain syndrome is characterized by a combination of abnormal pain sensations, and pain medications often provide little or no relief. Accumulating animal and clinical studies have shown that impairments of the spinothalamic tract (STT) and thalamocingulate pathway causes somatosensory dysfunction in central post-stroke pain (CPSP), but the involvement of other neuronal circuitries in CPSP has not yet been systematically examined. The aim of the present study was to evaluate changes in brain activity and neuronal circuitry using [(14)C]iodoantipyrine (IAP) in an animal model of CPSP. RESULTS Rats were subjected to lateral thalamic hemorrhage to investigate the characteristics of CPSP. Thermal and mechanical hyperalgesia developed in rats that were subjected to thalamic hemorrhagic lesion. The medial prefrontal cortex (mPFC), anterior cingulate cortex (ACC), striatum, thalamus, hypothalamus, and amygdala were more active in the CPSP group compared with rats that were not subjected to lateral thalamic hemorrhage. The inter-regional correlation analysis showed that regional cerebral blood flow in the mPFC was highly correlated with the amygdala in the right brain, and the right brain showed complex connections among subregions of the ACC. Rats with CPSP exhibited strong activation of the thalamocingulate and mPFC-amygdala pathways. CONCLUSIONS These results corroborate previous findings that the STT and thalamocingulate pathway are involved in the pathophysiological mechanisms of CPSP symptoms. The mPFC, amygdala, and periaqueductal gray emerged as having important correlations in pain processing in CPSP. The present data provide a basis for a neural correlation hypothesis of CPSP, with implications for CPSP treatment.