Influence of descending bulbospinal monoamine neurons on axonal transport of acetylcholine and cholinergic enzymes

Summary The influence of descending bulbospinal monoamine (MA) neurons on the intra-axonal transport of acetylcholine (ACh) and related enzymes (cholineacetyltransferase, CAT, and ACh-esterase, AChE) in rat sciatic nerve was studied in crush experiments following intracisternal injections of specific neurotoxins. The injection of 6-hydroxydopamine (6-OH-DA) and 5, 6-dihydroxytryptamine (5, 6-diOH-TA) (50g×2) caused a degeneration of catecholamine (CA) and 5-hydroxytryptamine (5-HT) nerve terminals, respectively, and a combination of the two neurotoxins caused a loss of virtually all MA terminals in the lumbar spinal cord. The results of the neurotoxin injections were controlled by the Falck-Hillarp fluorescence method. The effect of neurotoxin treatment on the enzyme activities in the sciatic nerve was very small. The ACh levels of uncrushed nerves and in nerves proximal to a crush performed 12 hours before dissection decreased following either 6-OH-DA or 5, 6-diOH-TA. However, the combined treatment with both 6-OH-DA and 5, 6-diOH-TA had no influence on ACh accumulation and transport, as compared to the control group.In a previous study we have shown that mid-thoracic spinal cord transection increased AChE-transport while ACh-transport was decreased. The results of this study indicate that the bulbospinal MA neurons may be involved (perhaps indirectly) in the regulation of ACh levels and transport in motor neurons, but less important for the modulation of the cholinergic enzymes.