Changes in choline acetyltransferase activity and distribution following incomplete cervical spinal cord injury in the rat.

Incomplete cervical spinal cord injuries were produced in rats by placing 10 g or 20 g weight on exposed dura at the C6 level for 5 min (Mild or Moderate injury). These two degrees of the injury resulted in initial motor functional deficits, followed by recoveries. In this study, changes in choline acetyltransferase activity and distribution following the incomplete cervical cord injuries were investigated using radioenzyme assay, and fluorescence microphotometry. We demonstrated that mild injury led to a transient decrease of choline acetyltransferase activity in the compressed spinal cord segment, but showed almost no histologic change at two days after injury. Although a low level of choline acetyltransferase immunofluorescence was found in the ventrolateral anterior horn at two days after injury, it recovered completely by one week after injury. These findings suggest that there was a strong correlation between the transient motor functional deficit and the decrease in choline acetyltransferase activity following mild injury. Moderate injury resulted in persistent low level of choline acetyltransferase activity in the compressed spinal cord segment accompanied by a striking loss of gray matter. On the other hand, at seven, 14 and 28 days after injury, over-expression of choline acetyltransferase activity was found in the neighboring spinal cord segments located both rostral and caudal to the injury, which showed no histologic change. In addition, excessively high levels of choline acetyltransferase immunofluorescence were found in the ventrolateral anterior horn of these segments. A strong correlation was found between the motor functional recovery and the late, excessive high levels of choline acetyltransferase activity in the neighboring regions. These results suggest that cholinergic neurons, especially spinal motor neurons may play an important role in the motor functional recovery following incomplete cervical spinal cord injury.