Further evidence for the involvement of microtubules in the proximo-distal intra-axonal transport of acetylcholine and related enzymes in rat sciatic nerve.

The two mitotic inhibitors colchicine (COL) and podofyllotoxin (POD) and their respective isomers, lumiCOL and picropodofyllin (picPOD) were tested for their effect on the intraaxonal transport (AXT) of acetylcholine (ACh) and the cholinergic enzymes in rat sciatic nerve. The mitotic inhibitors and their isomers were dissolved in saline+10% ethanol (COL and lumiCOL) or dimethylformamid (DMFA) (POD and picPOD) and injected (3-5microliter) subepineurally into the sciatic nerve. As controls the vehicle (saline +10% ethanol or DMFA) alone were injected into some rats. 2 h later a crush operation was performed 15 mm distal to the site of injection. The accumulation of ACh or the two enzymes, ACh-esterase (AChE) and cholineacetyltransferase (CAT), in the nerve segment proximal to the crush (12 h before death) was used as a measure of the AXT. COL and POD were very effective in inhibiting AXT of all 3 substances, while their isomers, lumiCOL and picPOD, were essentially without effect on AXT in equimolar concentrations (0.1 M). The effects on AXT of the 4 test substances thus appear related to their affinity to bind to tubulin, which is several orders of magnitude higher for COL and POD than for their isomers. The results further support the view that intact microtubules are essential for AXT of both membrane-bound (ACh E) and soluble (CAT) enzymes, as well as of ACh in rat motor nerves.