ABSTRACT
In a previous paper we described a pronounced increase of apoptotic nuclei in rat corpus luteum of pregnancy whose programmed chromatin degeneration was induced by the progesterone antagonist mifepristone. Those observations encouraged us to study the apoptotic nuclear membrane during pregnancy and after parturition and pup removal, by using a freeze-fracture technique which allows us to observe 'en face' the nuclear envelop and also permits nuclear pore counting. This study was complemented with the TUNEL assay (TdT-mediated dUTP nick-end labelling). Changes in nuclear pores during pregnancy begin with an intense reduction in number but still showing an even distribution on the nuclear membrane, never forming aggregations sharply separated from pore-free areas, which are characteristic of other apoptotic models. Electron microscopy of thin-sections shows, coincidently with findings in the freeze-fracture replicas, a moderately irregular aggregation of marginal heterochromatin condensations. After nuclear fragmentation and micronuclear formation, pores behave in the usual manner in other apoptotic models, i.e., mainly showing migrations of nuclear pores toward the chromatin-free areas. The present results support the hypothesis that nuclear pore complexes are dynamic structures, which permit their migration toward nuclear membrane areas devoid of chromatin aggregations that might block the nucleocytoplasmic transport in such areas.
Subject(s)
Male , Animals , Female , Pregnancy , Rats , Corpus Luteum/cytology , Nuclear Pore/ultrastructure , Freeze Fracturing/methods , In Situ Nick-End Labeling , Parturition , Pregnancy, Animal , Rats, WistarABSTRACT
In this study we describe the early changes of the myelin sheath following surgical nerve crush. We used the freeze-fracture technique to better evaluate myelin alterations during an early stage of Wallerian degeneration. Rat sural nerves were experimentally crushed and animals were sacrificed by transcardiac perfusion 30 h after surgery. Segments of the nerves were processed for routine transmission electron microscopy and freeze-fracture techniques. Our results show that 30 h after the lesion there was asynchrony in the pattern of Wallerian degeneration, with different nerve fibers exhibiting variable degrees of axon disruption. This was observed by both techniques. Careful examination of several replicas revealed early changes in myelin membranes represented by vacuolization and splitting of consecutive lamellae, rearrangement of intramembranous particles and disappearance of paranodal transverse bands associated or not with retraction of paranodal myelin terminal loops from the axolemma. These alterations are compatible with a direct injury to the myelin sheath following nerve crush. The results are discussed in terms of a similar mechanism underlying both axon and myelin breakdown
Subject(s)
Animals , Rats , Freeze Fracturing/methods , Myelin Sheath/metabolism , Nerve Crush , Sural Nerve/surgery , Wallerian Degeneration/surgery , Microscopy, Electron , Rats, Wistar , Wallerian Degeneration/physiopathologyABSTRACT
The double replica device was used to obtain freeze-fracture replicas of gently pressed cells, allowing the visualization of a large number of longitudinally fractured epimastigote and trypomastigote forms of Trypanosoma cruzi. This technique revealed large areas of the plasma membrane, the region of attachment of the flagellum to the cell body and the branched mitochondria.
Subject(s)
Animals , Freeze Fracturing/methods , Trypanosoma cruzi , Cell Membrane , Microscopy, Electron , Freeze Fracturing/instrumentationABSTRACT
A new rotary-shadowing process to obtain freeze-drying replicas is described for the analysis of virus ultrastructure, using the inner capsid of human rotavirus as a model. The findings corroborate the icosahedral symmetry with an arrangement pattern of capsomers of T=13L