Acetylcholinesterase Molecular Forms in Chick Ciliary Ganglion: Pre- and Postsynaptic Distribution Derived from Denervation, Axotomy, and Double Section

Abstract: Four main molecular forms of acetylcholinesterase (AChE) characterized by their sedimentation coefficients (5S, 7.5S, 11.5S, and 20S), are found in chick ciliary ganglion. After transection of the preganglionic nerve (denervation), total AChE activity in the ganglion dropped by 35% in 2 days. By then, 11.5s and 20s forms had diminished by 60 and 75% respectively, where as 7.5s remained practically unchanged. Since presynaptic structures disappeared 2 days after denervation, we inferred that at most 35% of total ganglion AChE was presynaptic: 11.5s and 20s might be mainly presynaptic and 7.5S, postsynaptic. At later time intervals. total AChE continued to decline up to day 5, possibly as a result of orthograde transynaptic regulation of the enzyme activity. After transection of postganglionic nerves (axotomy), total ganglion activity showed little change; 11.5s and 20s decreased by 40 and 6076, respectively, in 5 days, but these drops were compensated for by an early increase in 7 5S, which started the day after axotomy. After simultaneous transection of both pre- and postganglionic nerves (double section), total ganglion AChE dropped rapidly by 35% in 1 day and remained at that level up to 21 days. The 11.5S diminished rapidly by 60% in 1 day. The early increase of the 7.5s form induced by axotomy alone did not occur. Since the effect resulting from double section was not the equivalent of the cumulative effects observed after denervation and axotomy, respectively, the level of AChE forms in the ganglion may be regulated by reciprocal interaction of pre- and postsynaptic elements. After denervation and double section but not after axotomy alone, the contralateral non-operated ganglion exhibited a fall in the 20s form. This suggests that a transynaptic effect is exerted on AChE by the contralateral preganglionic neuron. Taken together, these results indicate that the various AChE molecular forms in chick ciliary ganglion are preferentially but not exclusively distributed as follows: the pre- and postganglionic axons contain mainly the 11.5S form, whereas nerve endings and synaptic structures are enriched in 20S, and ganglion cell bodies, in 7.5s.