Morphological changes of the smooth endoplasmic reticulum (SER) in rat cerebellar Purkinje cell dendrites were examined under apneic conditions for 1-5 minutes, induced by an incision of the diaphragm and the collapse of the lungs. The dendrites obtained from control rats contained a tubular network of the SER and hypolemmal cisterns adjacent to the plasma membrane. After a 3-5-minute apnea, the cytoplasm was occupied by many flattened cisterns stacked into lamellae, referred to as "lamellar bodies." A quantitative analysis revealed that the number of lamellar bodies became maximum after 3 minutes of apnea. After the treatment time, they increased in size by adding new cisterns to the previous core lamellae. This analysis also showed that the total amount of the SER membranes contained in a dendrite did not change during anoxia. Conformational changes from the tubular or hypolemmal SER to lamellar bodies during brief anoxia might occur through a transient and intermediate form of "fenestrated cisterns," flat across the transverse plane and penetrated by many longitudinally arranged microtubules. We suggest that these morphological changes of the SER during brief anoxia are not fixation artifacts but represent a biological reaction for protecting against intracellular abnormalities during anoxia.
Abstract The cranial meninges of the goldfish were studied by means of transmission electron microscopy combined with the freeze‐fracturing technique. The goldfish has three cranial meninges. The outer layer consists of flattened cells, which are stratified in 3 to 7 layers and are packed densely with many interdigitations of cell processes. The constituent cells in the outer layer have copious smooth endoplasmic reticulum and are joined by gap junctions but have no desmosomes. The intermediate layer is thin, continuous, and single cell. In the replicas, both the upper and the lower surfaces of the intermediate layer cells have numerous openings of pinocytotic vesicles, but the upper surface is characterized by round gap junctions, whereas the lower surface is identified by a linear continuation of a combination of tight junctions and gap junctions and by desmosomes. The lateral surface has a hexagonal network of tight junctions and gap junctions with internally located desmosomes, which functions as a barrier to intercellular movement of lanthanum. The inner layer consists of a meshwork of reticular cells and large intercellular spaces, in which fine granular material, capillaries, and different types of blood‐derived free cells can be found. Cells in the inner layer contain rough endoplasmic reticulum stacked in lamellae and have irregular processes joined by desmosomes. The goldfish meninges are compared with the meninges of mammals.
