Die strukturelle Organisation des Prothorakalganglions bei der Waldameise (Formica lugubris Zett.)

Summary

• 1. Serial sections of the prothoracic ganglion of a common wood ant (Formica lugubris Zett.) were examined with phase- and electronmicroscope. The material was fixed with glutaraldehyde and potassium permanganate.

• 2. The ganglion is separated from the fat and glycogen containing extraganglionic tissue by an outer capsule which consists of a cell-free neural lamella and a layer of perilemma cells.

• 3. The neurons of the ganglion form a superficial cortical layer which contains 1 to 6 rows of neuron pericarya. Two sizes of neuron cell bodies with a different ratio between nucleus and cytoplasma were encountered. The small neurons bear a striking similarity to the globuli cells of the corpora pedunculata, and may be considered internucials, while processes of many of the large neurons could be traced to the peripheral nerve supplying the foreleg and are identified with motoneurons. The pericarya give rise to only one process (stem process) which fails to form branches within the pericaryon layer; nor are there any afferent fibers synapsing with the neuron pericarya. The endoplasmic reticulum of the majority of nerve cells is poorly differentiated, but some of the large neurons have a dense cisternal system arranged concentrically around the nucleus.

• 4. Aside from the perilemma cells, three types of neuroglia could be distinguished: The pericaryon glia, the neuropil glia, and the Schwann cells. While these cells are different with respect to localization, process formation and fine structure, they seem to form a continuous network across the ganglion. The fine processes of these cells, by forming delicate sheets for the nerve elements, not only tend to separate neural pericarya and processes from each other, but also seem to form a tissue barrier between the neurons and the trachéal system and the hemolymph system as well.

  On the basis of differences in structure and size tracheae and tracheoles are identified in the ganglion.

• 5. Interneuronal contacts are observed in the pericaryon layer and between fibers of the neuropil. Soma-somatic junctions are found to be similar to those described by Landolt and Ris (1965) occurring between small neurons of the corpora pedunculata of the same species; however, with respect to the ganglion large nerve cells also take part in soma-somatic junctions. In the neuropil, enlarged fiber processes containing mitochondria and typical vesicles of 300–500 Å or plurivesicular material (de Robertis) seem to correspond to presynaptic endings. No specific characteristics of junctional membranes and subsynaptic regions could be identified.

• 6. The interstitial space is narrowest in the pericaryon layer (90–110 Å). Enlargements are found in connection with neuropil glia. A typical lacunar system of interstitial spaces, filled with an amorphous material, is localized within the border between pericaryon layer and neuropil. Its relationship with extracellular spaces and basement membranes of peripheral nerve glia system is demonstrated.