Influence of acetylcholinesterase on embryonic spinal rat motoneurones growth in culture: a quantitative morphometric study.

Rat spinal motoneurones sampled at day embryonic 15 were purified using a Nycodenz gradient and cultured in defined medium, during 7 days, on glass coverslips coated with poly-L-lysine and laminine. Purified acetylcholinesterase (AChE), ecothiopate, BW 284C51 and fasciculin II, inhibitors of either the catalytic or peripheral site of AChE, were added to the defined medium. Morphological changes of spinal motoneurones were measured using a statistical quantitative morphometric method, allowing the determination of various parameters such as the number of neurites and bifurcations, the length of neurites, the surface and spreading index. Presence of AChE in the medium (4 units/mL) increases the surface and the total length of neurites and axons without any change in the spreading index. When spinal motoneurones were cultured on AChE coated substrate, neurones rapidly migrate and form clusters. Addition of ecothiopate (10(-6) M) in the medium, which selectively blocks the catalytic site of AChE, leads to a slight increase in the number of primary neurite and a decrease of the spreading index during the three first days in culture. BW 284C51 (10(-5) M) which blocks the catalytic site but also affect the peripheral one, significantly reduces the number of primary neurites and increases the number of bifurcations. Fasciculin II, a potent blocker (10(-9)M) of the AChE peripheral site induces a decrease of both primary neurites and bifurcations with a significant increase of the length and growth velocity of the axon, giving a drastic enhancement of the spreading index. These phenomena are discussed in terms of catalytic and non-catalytic function of AChE, including the involvement of the enzyme in adhesive processes, occurring during growth and differentiation of spinal motoneurones.