Withdrawal-induced Fos-LI in the spinal cord dorsal horn. A, Cervical dorsal horn of a saline-injected withdrawing rat; B, cervical dorsal horn of a toxin-injected withdrawing rat; C, lumbar dorsal horn of a saline-injected withdrawing rat; and D, lumbar dorsal horn of a toxin-injected withdrawing rat. Note the increase in Fos-LI in laminae I and II of the toxin-treated withdrawing rats (B, D; arrowheads) and the increase in Fos-LI in laminae III and IV in the cervical spinal cord of the toxin-treated withdrawing rat (B). Scale bar, 200 μm.