Acute peripheral nociceptor sensitization drives spinal sensitization and activates spino-supraspinal-spinal loops leading to descending inhibitory and facilitatory controls of spinal neuronal activity that further modify the extent and degree of the pain state.  Injection of complete Freund's adjuvant resulted in inflammation and swelling of hairy hind foot skin in rats, a transient thermal hyperalgesia lasting <2 h, and longlasting primary mechanical hyperalgesia (≥7 days).  Much longer lasting thermal hyperalgesia was apparent in glabrous skin (1 h to >72 h).  In hairy skin, transient hyperalgesia was associated with sensitization of withdrawal reflexes to thermal activation of either A- or C-nociceptors.  In glabrous skin, yohimbine had no effect on an equivalent thermal inflammatory hyperalgesia. 
THERM