PREDICTED ACETYLCHOLINE LAYER AROUND EMBRYONIC MOTONEURONS

THE secretion of acetylcholine (ACh) from cultures of dissociated rat purified embryonic motoneurones into the medium was measured at differ ent times using a chemiluminescent assay. From these results it is pro posed that a motoneurone is able to generate an extracellular ACh laye r surrounding its membrane. This layer is expected to modulate the ACh concentration at the membrane in a range where ACh receptors can be s ensitive, and thus to affect the response of the motoneurone. The infl uences of both membrane-bound and soluble-secreted acetylcholinesteras e (AChE) were simulated and a local ACh membrane efflux was deduced. S ince ACh usually exerts an inhibitory effect on neurite outgrowth, a p ossible autocrine influence of the ACh layer in motoneurone morphogene sis is discussed.