Elektronenmikroskopische Untersuchungen an der Perikaryenschicht der Corpora pedunculata der Waldameise (Formica lugubris Zett.) Mit besonderer Ber�cksichtigung der Neuron-Glia-Beziehung

Abstract

1. The supraoesophageal ganglion of a common wood ant species (Formica lugubrisZett.) is separated from the fat and glycogen containing extracerebral tissue by a sheath consisting of a cell-free neural lamella and a layer of perilemma cells. 2. The neurons of the corpora pedunculata form a superficial cortical layer consisting of small perikarya (5–15 μ in diameter), which are assembled in epithelial fashion. They give rise to only one single process (axon) and receive neither dendritic nor axonic synapses. The perikarya contain a relatively poorly differentiated endoplasmic reticulum, yet an abundance of ribosomes preponderantly not organized within a typical ergastoplasmic assembly. Two types of inclusion bodies have been found which seem to be common stock of insect neuronal cytoplasm. 3. The glial cells form a complex mesh of processes surrounding the neurons of the cortical layer. Relatively few cell bodies, outnumbered 10–50 times by the neurons, develop a stupendous surface matching the one of neuronal perikarya. The inner structure is characterized by an electron dense cytoplasm (denser than that of neurons), high content in ribosomes and glycogen granules, occasional gliosomes and a dense, lobated nucleus. The Golgi apparatus of glial cells is less well developed than that of neurons. 4. The neuroglial processes reach within the glycogen packed perilemma cell layer and extend from the dorsal to the ventral surface of the cortex. Its marked glycogen content suggests that the neuroglia forms a link in glycogen transport from the extracerebral storage tissue via perilemma cells to neurons. 5. The neuroglial processes separate the neurons from the tracheal system throughout. Furthermore, conglomerations of glial endings immediately contact the distal portions of the tracheolar system forming the “tracheolar end organs”. These observations suggest specific glial functions relative to gas exchange and energy metabolism of the neuron. 6. The plasma membranes of glial cells and neurons consist of “unit membranes” of 90 A diameter. The interstitial space is conspicuously narrow (30 A) and can be experimentally expanded by means of hypertonic solutions. No decrease in extracellular space was seen with use of hypotonie fixatives. The role of interstitial space and the interposed meshwork of glial cytoplasm for the mechanism of polarisation and depolarisation of the neuron plasmalemma is discussed in the light of current theory.