It has been widely accepted that the primary somatosensory cortex (SI) plays an essential role in the sensory-discriminative aspect of pain perception. However, it remains unclear whether the SI has a role in the descending modulation of pain. The present study was designed to test whether the cortical outputs influenced the nociceptive behaviors in rats, using behavioral, pharmacological, neuroelectrophysiological, as well as immunohistochemical methods. Microinjections of a GABAA agonist and GABAA antagonist into SI was used to investigate the functional role of SI in the descending pain modulation. In addition, we explored the effects of emotional and cognitive factors on the pain-related activity in rats. The results showed that there was a facilitatory influence of SI on the acute pain sensation, represented as the enhancement of the spontaneous pain behavior. By contrast,an inhibitory effect of SI output was observed in the chronic pain state by showing a reduction of the thermal hyperalgesia and allodynia of the CFA-inflamed and nerve-ligated hindpaws. The electrophysiological data demonstrated that the descending influence of cortical modulation from SI may be mediated by thalamic nociceptive relay neurons. These results suggested that the sensory thalamocotical pathway plays an important role in not onl
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