RESUMEN
Observations have been made on the structure of the paranodal region at nodes of Ranvier in the sural nerve of patients with diabetic sensory polyneuropathy. The structure of the paranodes was examined with particular attention to the definition and assessment of axoglial dysjunction, which has been claimed to be a characteristic feature of both human and experimental diabetic neuropathy and which has been related to paranodal swelling. In the present series of cases it was not possible to confirm that axoglial dysjunction is a distinctive feature of diabetic polyneuropathy in fibres not undergoing active demyelination or wallerian-type degeneration, neither was excessive paranodal enlargement found.
Asunto(s)
Neuropatías Diabéticas/patología , Nódulos de Ranvier/patología , Trastornos de la Sensación/patología , Nervio Sural/patología , Adulto , Femenino , Humanos , Masculino , Microscopía Electrónica , Persona de Mediana Edad , Enfermedades del Sistema Nervioso Periférico/patología , Nódulos de Ranvier/ultraestructuraRESUMEN
Peripheral nerves in rats fed a diet containing 40% galactose develop endoneurial oedema related to the accumulation of interstitial galactitol and sodium. Biochemical studies of the perineurium in galactose neuropathy indicate an increase in membrane bound Na+/K(+)-ATPase activity. The present study has analysed the intramembraneous particles (IMPs) on the P membrane fracture faces of the perineurium in galactose-fed rats and has demonstrated a significant increase in the density of IMPs. This finding may reflect changes in the perineurial cell membranes in galactose neuropathy, such as increased membrane bound Na+/K(+)-ATPase activity.
Asunto(s)
Enfermedades del Sistema Nervioso Periférico/patología , Animales , Membrana Celular/ultraestructura , Técnica de Fractura por Congelación , Galactosa , Proteínas de la Membrana/ultraestructura , Enfermedades del Sistema Nervioso Periférico/inducido químicamente , Ratas , Ratas Sprague-DawleyRESUMEN
Feeding rats with galactose as 40% of their diet results in peripheral nerve oedema related to the intrafascicular accumulation of galactitol and sodium. In this study, associated changes in the perineurium were examined by the freeze-fracture replication technique. Perineurial cells are linked by tight junctions (zonulae occludentes). In normal animals these are made up of anastomosing strands organized in a belt-like arrangement along the margins of continuous cells. The majority of the tight junctions in the galactose-fed animals displayed structural abnormalities. These ranged from slight separation of the strands to fragmentation and dispersal, with looping of isolated strands. Some of the tight junctions contained large dilated compartments within the junctional network. Short lengths of intramembranous particles, probably representing assembly or disassembly of tight junctional strands, were also observed. The membranes of perineurial cells normally possess numerous openings of caveolae. A quantitative assessment showed that the mean density of these caveolae openings was increased in the galactose-fed rats as compared with controls. The alterations in the tight junctions resemble those that have been produced experimentally in epithelia by subjecting them to abnormal osmotic gradients. They also resemble those seen in human diabetic neuropathy in which osmotic disturbances involving the perineurium have been considered to occur. If the alterations involve the inner layers of the perineurium, they are likely to impair its barrier function. The increased number of caveolae openings in galactose neuropathy may represent a reaction to the endoneurial oedema and indicate that the pinocytotic-like vesicles have a transport function.
Asunto(s)
Edema/patología , Técnica de Fractura por Congelación , Galactosa , Uniones Intercelulares/patología , Enfermedades del Sistema Nervioso Periférico/patología , Animales , Membrana Celular/patología , Edema/inducido químicamente , Enfermedades del Sistema Nervioso Periférico/inducido químicamente , Ratas , Ratas EndogámicasRESUMEN
Observations have been made using the freeze-fracture replication technique on the perineurium of normal and protein-deprived rats in which its permeability barrier function is known to be deficient. The perineurial cells of young normal rats possessed belt-like tight junctions (zonulae occludentes) at the borders and maculae occludentes at sites remote from their borders. In older rats, the zonulae occludentes were more prominent and the maculae occludentes relatively less frequent. No abnormalities were detected in the tight junctions of young rats with early induction of protein deficiency but this may have been related to sampling problems. In older severely protein-deficient animals, although many of the tight junctions were normal, some were abnormal and contained focal regions of dispersed strands. The density of caveolae in the surface membrane of the perineurial cells of older rats with severe protein deficiency was significantly greater than in the control animals. This provides support for the view that the pinocytotic-like vesicles of perineurial cells are involved in transport of substances across the cells. The increased numbers of caveolae in the protein deficient rats may reflect increased transcellular traffic. There were considerable differences in the density of P-face IMPs between the different perineurial lamellae, but the results did not allow a decision to be made as to whether there was a polarization of the cells between their endoneurial and epineurial aspects. No differences were detected in the density of P-face IMPs between the young control and protein-deprived rats. In the perineurium of the older rats with protein deficiency, IMP density was significantly greater in the E face than in the controls but not different in the P face. The delay in the development of enzymatic activity in the perineurium of protein-deficient rats that has been demonstrated histochemically is therefore not paralleled by a reduction in IMPs.
Asunto(s)
Células del Tejido Conectivo , Nervios Periféricos , Deficiencia de Proteína/patología , Animales , Membrana Celular/ultraestructura , Tejido Conectivo/patología , Tejido Conectivo/ultraestructura , Femenino , Técnica de Fractura por Congelación , Uniones Intercelulares/ultraestructura , Ratas , Ratas Endogámicas , Nervio Tibial/citologíaRESUMEN
Perineurial cells in the human sural nerve possess tight junctions which in freeze-fracture replicas are seen to be composed of networks of branching and anastomosing P face strands and E face grooves. Isolated circular tight junctions (maculae occludentes) may represent attachment devices between adjacent perineurial lamellae. At the overlapping margins of the cells, a belt-like tight junction (zonula occludens) encircles the cells and is believed to comprise a paracellular diffusion barrier. As the permeability of the perineurium has been found to be altered in diabetic polyneuropathy, the zonulae occludentes have been studied. In freeze-fracture replicas from cases of diabetic polyneuropathy a mixed population of structurally normal and abnormal junctions was observed. In some, the strands were abnormally curved with reduced numbers of intersections, the intervening plasma membrane displaying prominent P face concavities and E face convexities. At other sites, the junctions were severely disorganized and represented by fragmented and isolated strands with few intersections and numerous free ends. These abnormalities resemble changes that have been produced experimentally in epithelial tight junctions by osmotic damage. The possibility is considered that similar mechanisms could result in the alterations of the perineurial tight junctions in diabetic polyneuropathy and account for its impaired permeability barrier properties.