TIME-COURSE OF NOCICEPTIVE DISORDERS INDUCED BY CHRONIC LOOSE LIGATURES OF THE RAT SCIATIC-NERVE AND CHANGES OF THE ACETYLCHOLINESTERASE TRANSPORT ALONG THE LIGATED NERVE

Changes in the axonal transport of acetylcholinesterase (AChE) were st udied in the painful mononeuropathy induced by setting 4 loose ligatur es around the right sciatic nerve of the rat. Since changes in the axo nal transport of AChE can be used to assess axonal degeneration/regene ration, we used this marker to investigate whether the time course of pain-related behavioral disorders observed following chronic constrict ion injury (CCI) to the sciatic nerve are related to the time course o f the regeneration of the injured axons. In addition, a comparison was made between changes in AChE observed in this moder of nerve injury a nd those observed after sciatic nerve crush. The rats were examined fo r pain-related disorders daily during the first postoperative week the n at 7, 14 and 21 days after nerve ligation. The pain-related disorder s, only detected from 7 days after ligation, were maximal at 14 days p ostinjury, and began to lessen at the end of the 3rd postoperative wee k. Within the first 3 days after loose ligation, the AChE transport dr opped to 40% of its normal value, but recovered rapidly during the 3rd week post-surgery, indicating that most of the injured neurons were r econnecting 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 disord ers lasted after most of the re-elongating axons had reconnected their target. Changes in the AChE transport following CCI differed from tho se observed after crush injury in that: (1) after CCI, the initial dec rease in AChE transport was rapid but delayed by 24 h compared to crus h, indicating that the loose ligatures did not immediately injure the nerve axons but rather induced a secondary process which, once started , produced rapid axotomy of most sciatic axons; and (2) after CCI, ACh E transport decreased by 60%, while it decreased by 82% after crush, i ndicating that some axons were spared in the loosely ligated nerves.