An ultrastructural study of tumefactive lesions induced by nerve severance in the midgut of the cockroaches Leucophaea maderae and Periplaneta americana

Abstract

Tumefactive lesions developing as a result of nerve severance in the insects Leucophaea and Periplaneta were studied under the electron microscope. The fine structure of the lesioned cells found in the gastric ceca and midgut differs very markedly from that of the columnar epithelial cells lining these organs in the normal animal. The morphological changes vary in degree and seem to reflect a sequence of events during which a phase of cellular proliferation gradually gives way to the appearance of abnormal structures and regression of parts of the tissue. The nuclei show progressive signs of degradation (clumping of chromatin, disruption and loss of nuclear membranes). Cytoplasmic alterations include vastly dilated Golgi elements, abnormally structured mitochondria, and strikingly altered configurations of the rough endoplasmic reticulum. There is a gradual increase in the amount of smooth endoplasmic reticulum and, concomitantly, of free ribosomes. Cytoplasmic vacuoles containing a flocculent material are more numerous in the vicinity of Golgi complexes and near the cell's periphery than in control tissues. Lysosomes gradually become far more numerous and pleomorphic than in control cells. Autophagic vacuoles and multivesicular bodies take precedence over other organelles as degradation proceeds. Myelin figures are frequent and, in older lesions, may reach enormous proportions. In rare instances bundles of cytoplasmic filaments are observed. The structural features listed are interpreted as expressions of stepwise functional alterations leading from heightened proliferative activities to the ultimate regression of the tissue components in response to disturbance in their nerve supply.