Developmental distributive pattern of acetylcholinesterase in chick embryo ciliary ganglion

AChE cytochemistry was performed in the chick ciliary ganglion (CG) during various embryonic stages. AChE first appeared in the RER of the neurons at 5 days of incubation (d.i.). Synaptic AChE appeared only later, parallely to the appearance of the calyciform synapses, i.e. at 9 d.i. At first AChE was mainly localized at the calyx side facing the satellite cell, thereafter extending to the neuronal side and especially labeling synaptic contacts occurring at points along the presynaptic membrane. Finally, at 15 d.i., i.e. when the calyx is morphologically mature, AChE reaction labels the whole contour of the calyciform nerve terminal. At 10 d.i., limited AChE-positive extrasynaptic areas of the ciliary neurons surface first appeared, thereafter extending up to affect at 15 d.i. large neuronal surfaces. Some hypotheses can be drawn from our results: (i) the earliest appearance of cytoplasmic AChE seems somehow independent of the establishing of functional synaptic contacts; (ii) the pattern of development of neuronal AChE suggests the existence of a sort of transynaptic control by presynaptic nerve terminals. However, it is possible that concomitant retrograde iris-dependent influences on ganglionic AChE concur in modulating neuronal AChE; (iii) the functional role possibly played by AChE localized at extra-synaptic level still remains to be clarified.