Neural Lamella Research Articles

The connective tissue sheath of the locust nervous system: its development in the embryo

ABSTRACT The embryological development of the connective tissue sheath around the nervous system has been investigated in Schistocerca gregaria. The sheath cells appear to be derived from outlying ganglion cells. The neural lamella is first visible when the embryo is 9 days old and it increases in thickness until hatching occurs on the twelfth day. It is produced entirely by the sheath cells. The sheath cells have numerous lipid droplets in their cytoplasm. Some neutral mucopolysaccharide and proteins are also present. The histochemical reactions of the neural lamella after its formation suggest that it is composed of collagenous proteins embedded in neutral mucopolysaccharides. The sheath cells are typical fibroblasts during the formation of the neural lamella. The cisternae of the endoplasmic reticulum are dilated into vesicles which contain a somewhat electron-dense material. No intracellular fibrils were observed. Collagen fibrils with banding of periodicity between 55 and 60 mμ are seen in the neural lamella from 11 days onwards.

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

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.

Observations on the Cyclorrhaphan Larval Peripheral Nervous System: Muscle and Tracheal Receptor Organs and Independent Peripheral Type 11 Neurons Associated with the Lateral Segmental Nerves

Muscle and tracheal receptor organs, connected to the lateral segmental nerves, are described; they are similar to the stretch receptor organs recorded in Orthoptera, Odonata, Hymenoptera, and Lepidoptera by previous workers. They contain at least one multipolar neuron and are invested in a connective tissue sheath continuous with the neural lamella of the adjoining lateral segmental nerve. Nerve connections pass to the segmental nerve, neighboring muscles, and in specific cases to a trachea when they may be involved in control of spiracular activity. Connections also sometimes occur between receptor organs of consecutive segments. The organs are located in thoracic and abdominal segments, three or more serially homologous pairs occurring in abodminal segments 1 to 7. Independent of the receptor organs, and contained within the terminal branches of the lateral nerves, are multipolar nerve cells, probably so-called Type 11, sensory neurons.

Insecticide absorbed by the Central Nervous System of Susceptible and Resistant Cockroaches exposed to Dieldrin

PENETRATION and metabolism studies carried out in this Department on susceptible and resistant houseflies, using the sulphur analogue of dieldrin or a non-insecticidal bromine derivative of aldrin1; aldrin, dieldrin, isodrin or endrin2; failed to reveal any differences between the strains which would explain the mechanism of resistance. There is some evidence that dieldrin acts on the central nervous system of susceptible insects3 and it seemed possible that dieldrin failed to reach the sensitive cells of this system in the resistant insect due to some internal local barrier, for example, a dieldrin impermeable neural lamella.

A Histochemical Study of the Connective-Tissue Sheath of the Nervous System of Periplaneta americana

ABSTRACT The connective-tissue sheath surrounding the nervous system of Periplaneta americana consists of two layers, the neural lamella and the sheath cells beneath it. The neural lamella is composed of a collagen-type protein and neutral muco-polysaccharide. The sheath cells possess numerous lipochondria and mitochondria; the former consist of phospholipid and some cerebroside. The cytoplasm of the sheath cells contains some RNA, glycogen, and lipid.

The Connective-Tissue Sheath of the Nervous System of Locusta migratoria: an Electron Microscope Study

ABSTRACT The sheath is composed of an outer non-cellular layer, the neural lamella, and an inner layer of sheath cells. The neural lamella possesses a large number of collagen fibrils arranged in layers with differing orientations. The sheath cells are flattened on the inner surface of the lamella and the cytoplasm contains lipochondria, mitochondria, and small amounts of endoplasmic reticulum.

The Nutrition of the Central Nervous System in the Cockroach Periplaneta Americana L

ABSTRACT The organs and tissues of insects are mostly composed of single layers of cells separated from the circulating blood by thin connective tissue membranes (Wigglesworth, 1956a; Pipa & Cook, 1958). The supply of nutrients to such organs presents no problem. But the central nervous system is an exception. The ganglia are the only solid organs in the insect body. They consist of densely packed peripheral cells surrounding a central neuropile, the whole ganglion being covered by a tough fibrous sheath or neural lamella continuous with the connective tissue membranes elsewhere. The total thickness of the ganglion may be 1 mm. or more.

The Connective Tissue Sheath of the Locust Nervous System: A Histochemical Study

ABSTRACT The connective tissue sheath surrounding the nervous system of Locusta migratoria has been studied histochemically. It consists of an outer non-cellular layer, the neural lamella, and an inner layer of cells, the sheath-cells. The neural lamella has been identified as being composed of a collagen-type protein and neutral mucopolysaccharide on the evidence of its histochemical reactions and the identification of hydroxyproline by paper chromatography in a hydrolysate of the neural lamella. The sheath-cells possess large numbers of lipochondria composed of phospholipids and cerebrosides, and small spherical mitochondria. The cytoplasm also contains lipids (some of which may be cerebrosides), glycogen, and RNA.

Über den komplexen Bau der Membranen des Bindegewebes von Insekten

The connective tissue sheeth around the nervous system of the cockroach and the silkworm moth is a heterogeneous and complicated structure. Microscopically one can detect small fibers, both longitudinal and circumferential, which are embedded in a seemingly non-fibrous matrix. Analysis of the optical properties with polarized light gave imbibition curves of unusual shape implying a relatively dense packing of micelles or crystallites. Tests showed recovery of length after stretching more than 100 per cent. This elasticity is accompanied by a strain birefringence that is both too great and too complicated to be explained as being due simply to improved alignment of the microscopically visible fibrils. X.ray diffraction diagrams prepared by Dr. K. M. RUDALL show the presence of the 2,86 A line considered to be characteristic of collagens, but the intensity of this line implies a collagen concentration of only 10 — 20 per cent. Optical properties imply the presence of a lipid component. Staining and solubility properties are mostly similar to the collagenous proteins but do not agree completely with either collagen (stricto sensu), elastin or reticulin of vertebrates. The imbibition curves, the elasticity, and the strain birefringence are not consistent with the known properties of the collagegenous proteins—presumably these are due to the not yet identified protein or mucoprotein that makes up the bulk of the neural lamella and confers distinctive properties upon insectan connective tissue.