Evidence for a noncholinergic function of acetylcholinesterase during development of chicken retina as shown by fasciculin

Fasciculin 2 (FAS), an acetylcholinesterase (AChE) peripheral site ligand t hat inhibits mammalian AChE in the picomolar range and chicken AChE only at micromolar concentrations, was used in chick retinal cell cultures to eval uate the influence of AChE on neuronal development. The effects of other AC hE inhibitors that bind the active and/or the peripheral site of the enzyme [paraoxon, eserine, or 1,5-bis(4-allyldimethylammoniumphenyl) pentan-3-one dibromide (BW284c51)] were also studied. Morphological changes of cultured neurons were observed with the drugs used and in the different cell cultur e systems studied. Cell aggregates size decreased by more than 35% in diame ter after 9 days of FAS treatment, mainly due to reduction in the presumpti ve plexiform area of the aggregates. Eserine showed no effect on the morpho logy of the aggregates, although it fully inhibited the activity of AChE. I n dense stationary cell culture, cluster formation increased after 3 days a nd 6 days of I;AS treatment. However, FAS, at concentrations in which chang es of morphological parameters were observed, did not inhibit the AChE acti vity as measured histochemically. In contrast, paraoxon treatment produced a slight morphological alteration of the cultures, while a strong inhibitio n of enzyme activity caused by this agent was observed. BW284c51 showed a h armful, probably toxic effect, also causing a slight AChE inhibition. It is suggested that the effect of an anticholinesterase agent on the morphologi cal modifications of cultured neurons is not necessarily associated with th e intensity of the AChE inhibition, especially in the case of FAS. Moreover , most of the effects of AChE on culture morphology appear to be independen t of the cholinolytic activity of the enzyme. The results obtained demonstr ate that FAS is not toxic for the cells and suggest that regions of the ACh E molecule related to the enzyme peripheral site are likely to be involved with the nonclassical role of AChE.