The Role Of Cortico-striatal Circuit In Decreased Motivation In Rats With Neuropathic Pain

A lot of previous research on chronic pain has focused on the abnormal sensory signal transduction in the spinal cord. With the emergence of new research tools and methods, increasingly more research began to notice that the higher function in the brain was not only involved in pain cognition and pain perception but also involved in the occurrence and development of chronic pain. However, there were few research if ever documented about how chronic pain influenced higher function and how related circuit mediated abnormal pain perception under such disease state. Therefore, in order to further explore the relationship between motivational change and brain activity under chronic pain state, we trained rats to perform a motivation related T maze task. And we found that nerved injured animals were more inclined to choose the arm which had less food and needed small effort(LR) thus had significantly lower rate for choosing the arm which had more food while needed large effort(HR) compared with sham animals. During the task, we simultaneously recorded the local field potential of the prefrontal cortex and the nucleus accumbens. We found that the task related theta coherence and gamma coherence of the two brain was lower in the nerve injuried animals than that in the sham animals. Furthermore, nerve injured animals had lower task related gamma power in the nucleus accumbens than sham animals. Thus, we concluded that:(1) animals had decreased motivation after nerve injury represented by its decreased choices toward HR arms. (2) such motivation change is correlated with theta coherence and gamma coherence between the prefrontal cortex and the nucleus accumbens. To be specific, decreased gamma coherence indicating overall decreased motivational state while decreased theta coherence indicating motivational choice is observed in nerve injuried animals thus might lead to their impaired motivation. (3) decreased coherence was task-dependent and might be accounted by decreased theta and gamma power in the nucleus accumbens which further suggested that the projection from the prefrontal cortex to the nucleus accumbens might mediate the motivational behavior change in the animal model of chronic pain.