The contribution of cholinergic enzymes and acetylcholine from the lumbar sympathetic chain to the rat sciatic nerve

Abstract

This study was performed to investigate how much of the acetylcholine (ACh), cholineacetyltransferase (ChAT) and ACh-esterase (AChE) in the rat sciatic nerve originate from the somatic motor input and from the automatic sympathetic input, respectively. The somatic motor axons to the sciatic nerve were eliminated by surgical transsection of the spinal roots, (rhizotomy) and the autonomie component was removed by surgical resection of the lumber sympathetic chain bilateraly (sympathectomy). Also combined operations were performed. In intact (non-crushed) sciatic nerve rhizotomy caused a reduction in ACh content by 70%, in ChAT-activity by 55%, and in AChE-activity by 41%. Sympathectomy alone had very little influence on ACh and ChAT, but reduced AChE by 20%. After crushing the nerve 13 hours before sacrifice, all three substances accumulated proximal to the crush region as described previously. When compared to the control group, sympathectomy alone caused a reduction in accumulated amounts of AChE only, while ACh and ChAT accumulations were essentially unchanged. Rhizotomy alone caused a substantial reduction in accumulated amounts of all three substances, but most prominently in ACh and ChAT-amounts. After symphathectomy in combination with rhizotomy ACh-accumulations were very low, and enzyme activities were reduced more than in the group with rhizotomy alone. A certain amount of residual ChAT and AChE was present in the nerve, and the location of this is discussed. The fact that combined sympathectomy and rhizotomy lowered ACh accumulations significantly more than would be expected from the results after either operation alone is commented upon. The results thus indicate that the major part of ACh enzymes in rat sciatic nerve is located in somatic motor axons. Very little ACh and ChAT, but about 20% of the ACh E is confined to the sympathetic axons. Some extraneuronal enzyme appears to be present.