Selective enhancement of chronic pain in 'smart' mice with NR2B overexpression in forebrains. a. Overexpression of NR2B mRNA in pain-related forebrain areas including the ACC and insular cortex (IC). No overexpression of NR2B was detected in the spinal cord. b. Enhancement of behavioral nociceptive licking responses to peripheral subcutaneous injection of formalin in NR2B transgenic mice. c. Summarized three different phases of behavioral nociceptive licking responses in wild-type and NR2B transgenic mice. Similar increases in behavioral nociceptive responses were found in the second line of NR2B transgenic mice. Modified from Wei et al. (2001).