Changes in the axonal transport of acetylcholinesterase (AChE) were studied in the painful mononeuropathy induced by setting 4 loose ligatures around the right sciatic nerve of the rat. Since changes in the axonal transport of AChE can be used to assess axonal degeneration/regeneration, we used this marker to investigate whether the time course of pain-related behavioral disorders observed following chronic constriction injury (CCI) to the sciatic nerve are related to the time course of the regeneration of the injured axons. In addition, a comparison was made between changes in AChE observed in this model of nerve injury and those observed after sciatic nerve crush. The rats were examined for pain-related disorders daily during the first postoperative week then at 7, 14 and 21 days after nerve ligation. The pain-related disorders, only detected from 7 days after ligation, were maximal at 14 days postinjury, and began to lessen at the end of the 3rd postoperative week. Within the first 3 days after loose ligation, the AChE transport dropped to 40% of its normal value, but recovered rapidly during the 3rd week post-surgery, indicating that most of the injured neurons were reconnecting their target cells. Thus, the injury produced by the loose ligatures was registered by the neurons several days before the first nociceptive manifestations of the injury, and the pain-related disorders lasted after most of the re-elongating axons had reconnected their target.(ABSTRACT TRUNCATED AT 250 WORDS)