These might be relevant citations:

"CNS animal fMRI in pain and analgesia."

"fMRI of pain processing in the brain: a within-animal comparative study of BOLD vs. CBV and noxious electrical vs. noxious mechanical stimulation in rat."

"Pain fMRI response in anesthetized rats correlates with behavioral response to pain in awake rats "

["New animal model for objective pain research: noninvasive functional imaging in anesthetized animals by BOLD fMRI to study initial processes of chronic pain