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Cholinergische Synapsen im Oberschlundganglion der Waldameise (Formica lugubris Zett.)

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The corpora pedunculata of the wood ant (Formica lugubris Zett.) consist of two sharply defined layers: The perikaryon layer and the subjacent neuropil. Synaptic endings are found exclusively in the neuropil. The synapses consist of a central, presynaptic end knob of 1.2–2.5 μ diameter and a relatively large number of surrounding postsynaptic processes of 0.3–1.1μ diameter. These junctions are analogous to axodendritic synapses of the vertebrates. The presynaptic process contains mitochondria and a multitude of light vesicles (300–600 Å diameter). Larger vesicles 700–1000 Å with a dark center are seen more rarely. The synaptic cleft has a diameter of approximately 130 Å and varies somewhat with different fixation methods. With glutaraldehyde-osmium fixation, this relatively wide gap is maintained only in circumscribed areas of the junction, while in adjacent areas it tends to contract and an “external compound membrane” is formed. The postsynaptic region is characterized by the presence of a subsynaptic network which is revealed only by suitable fixation methods. This and the persistent synaptic cleft are the main structural differentiations found in junctional areas thus far.

Cholinesterase is located with the aid of thiolacetic acid (Barnett) and Eserin control studies. The enzyme is found in the cytoplasm immediately adjacent to the pre- and postsynaptic membranes. In two thirds of our observations the reaction is far more concentrated postsynaptically than presynaptically. In one third, the distribution is reversed. Only an insignificant amount of cholinesterase is present within the synaptic cleft. There is no evidence that cholinesterase is evenly distributed along the entire junctional region. In contrast, only small circumscribed areas show a positive reaction and these coincide with the extent of the synaptic cleft and the subsynaptic network. Such areas seem to correspond to the “active junctional areas”.

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Herrn Prof. Dr. W. Bargmann zum 60. Geburtstag gewidmet.

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Landolt, A.M., Sandri, C. Cholinergische Synapsen im Oberschlundganglion der Waldameise (Formica lugubris Zett.). Z.Zellforsch 69, 246–259 (1966). https://doi.org/10.1007/BF00406277

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