Cytochemical localization of cholinesterase activity at the giant synapse of the squid

Evolutional study on acetylcholine expression

Acetylcholine (ACh) is a well-known neurotransmitter in the cholinergic nervous systems of vertebrates and insects; however, there is only indirect evidence for its presence in lower invertebrates, such as plants and fungi. We therefore investigated the expression of ACh in invertebrates (sea squirt, sea urchin, trepang, squid, abalone, nereis, sea anemone, coral and sponge), plants (arabidopsis, eggplant, bamboo shoot, cedar, hinoki, pine, podcarp, fern, horsetail and moss), fungi (yeast and mushroom) and bacteria by assaying ACh content and synthesis, focusing on the presence of two synthetic enzymes, choline acetyltransferase (ChAT) and carnitine acetyltransferase (CarAT). Using a specific radioimmunoassay, ACh was detected in all samples tested. The levels varied considerably, however, with the upper portion of bamboo shoots having the highest content (2.9 micromol/g). ACh synthesis was also detected in all samples tested; moreover, the activity in most samples from the animal kingdom, as well as bamboo shoots and the stem of the shiitake mushroom, were sensitive to both ChAT and CarAT inhibitors. Levels of ACh synthesis were lower in samples from other plants, fungi and bacteria and were insensitive to ChAT and CarAT inhibitors. These findings demonstrate the presence of ACh and ACh-synthesizing activity in evolutionally primitive life as well as in more complex multicellular organisms. In the context of the recent discovery of non-neuronal ACh in various mammalian species, these findings suggest that ACh been expressed in organisms from the beginning of life, functioning as a local mediator as well as a neurotransmitter.

A comparison between the one-step and the two-step copper thiocholine procedure for the cytochemical localization of cholinesterases

A comparison between the one-step and the two step copper thiocholine procedure for the subcellular localization of cholinesterases was undertaken. The results indicate that only under experimental conditions with short incubation times and precise control of the conversion into sulphide is the localization of the primary precipitate and that of the secondary precipitate identical. It was concluded that the conversion of the primary precipitate into Cu-sulphide is not necessary and can lead to artefacts.

Acetylcholinesterase activity of synaptic structures in the spinal trigeminal nucleus

The electron microscope has been used to study the localization of acetylcholinesterase (AChE) activity in the spinal trigeminal nucleus of normal cats with special emphasis on the distribution near synaptic structures. Reaction product is found around both round and flattened synaptic vesicle-containing axon terminals, particularly in synaptic clefts and often specifically associated with the presynaptic, or less frequently the postsynaptic membrane. The presence of reaction product at these specific sites suggests that these are areas of high AChE activity and that acetylcholine may be important in neurotransmission in these regions.

Iodide, thiocyanate and cyanide ions as capturing reagents in one-step copper-thiocholine method for cytochemical localization of cholinesterase activity

The necessity of the presence of iodide in Cu-ThCh reaction was investigated by following the precipitate formation "in vitro" and by evaluating the ultrastructural localization of the precipitate in sympathetic ganglion cells of the frog and in the end-plate regions of the rat diaphragm. It was found that thiocyanate or cyanide is the only anion that can be substituted for iodide as the capturing agent in precipitation. The optimal concentration in the preincubation and incubation media of any one of the three anions is from 2 to 5 mM. At a concentration below 1 mM precipitation "in vitro" is considerably delayed as a result of which in electron microscopy diffusion artefacts appear in tissue sections. The unconverted primary precipitate obtained in the presence of iodide had been used for ultrastructural localization of ChE activity and now this use has been extended to precipitates obtained in the presence of CN- or CNS-. Better-quality localization in the presence of either one of the latter anions suggests that they, and particularly CN-, should be substituted for I- in the one-step Cu-ThCh method for the cytochemistry of cholinesterases.