Ultrastructure of the central nervous system after prolonged hypoxia. II. Neuroglia and blood vessels

Ion homeostasis in brain cells: differences in intracellular ion responses to energy limitation between cultured neurons and glial cells

Intracellular concentrations of sodium, potassium and calcium together with membrane potentials were measured in cultured murine cortical neurons and glial cells under conditions which mimicked in vivo hypoxia, ischemia and hypoglycemia. These included; glucose omission with and without added pyruvate, addition of rotenone in the presence and absence of glucose and substitution of 2-deoxyglucose for glucose with and without rotenone. Cellular energy levels ([ATP], [ADP], [phosphocreatine], [creatine]) were measured in suspensions of C6 cells incubated in parallel under identical conditions. [Na+]i and [Ca2+]i rose while [K+]i fell and plasma membrane depolarized when energy production was limited. Intracellular acidification was observed when glycolysis was the sole source for ATP synthesis. There was a positive correlation between the extent of energy depletion in glial cells and the magnitude and velocity of alterations in ion levels. Neither glycolysis alone nor oxidative phosphorylation alone were able to ensure unaltered ion gradients. Since oxidative phosphorylation is much more efficient in generating ATP than glycolysis, this finding suggests a specific requirement of the Na pump for ATP generated by glycolysis. Changes in [Na+]i and [K+]i observed during energy depletion were gradual and progressive whereas those in [Ca2+]i were initially slow and moderate with large elevations occurring only as a late event. Increases in [Na+]i were usually smaller than reductions in [K+]i, particularly in the glia, suggestive of cellular swelling. Glia were less sensitive to identical insults than were neurons under all conditions. Results presented in this study lead to the conclusion that the response to energy deprivation of the two main types of brain cells, neurons and astrocytes, is a complex function of their capacity to produce ATP and the activities of various pathways which are involved in ion homeostasis.

Cellular and molecular effects of trimethyltin and triethyltin: relevance to organotin neurotoxicity

Many of the neurotoxic aspects of organotin exposure have been described. Organotin exposure culminates in its accumulation in the CNS and PNS. The clinical picture is dominated by neurological disturbances; yet, the primary basis for their neurotoxicity is unknown. Trimethyltin (TMT) is primarily a CNS neurotoxin affecting neurons within the hippocampal pyramidal band and the fascia dentata. Triethyltin (TET) is a neurotoxin that produces a pathological picture dominated by brain and spinal cord edema. The first part of this review summarizes the current understanding of the interaction of TMT and TET with biologically active sites in the induction of neurotoxicity. In the second part, several hypotheses for the differential neurotoxic effects of these organotins and their shortcomings are discussed.

Brain changes in experimental chronic hypoxia

A model of normobaric hypoxia was developed in which adult female cats were exposed to decreasing amounts of oxygen (21, 15, 10, 8, 7, and 5 vol.%) over a period of 320 days. Blood flow as well as the blood flow responses to changes of pCO2 were depressed in both cerebrum and cerebellum. These decreases were more severe in the cerebellum. The metabolic rate for oxygen was also depressed. A decrease in the Purkinje cell number was evident. A different degree of damage was observed in the top, the intermediate and the bottom region of the cerebellar gyri. Microvascular proliferation occurred in the whole brain.

Altered glial fibrillary acidic protein immunoreactivity in rat brain following chronic hypoxia

Glial fibrillary acidic immunoreactivity in brain was examined in normal animals and in rats subjected to chronic hypoxia. Animals were exposed to a chronic normobaric adaptive hypoxia with decreasing amounts of oxygen (finally 6%) for a period of 59 and 114 days, respectively. In paraffin-embedded sections the glial fibrillary acidic protein immunoreactivity in normal and hypoxic animals was examined at three coronal levels. A mild glial fibrillary acidic protein immunoreactivity in the perivascular glial layer, external glial limitans membrane and periventricular astrocytes, as well as in some areas of hippocampus and cerebellum, was noted in normal animals. Chronic hypoxia for 114 days resulted in a marked increase of glial fibrillary acidic protein immunoreactivity in dentate gyrus of hippocampus, Bergmann glia of the cerebellum, internal capsule and pyramidal tract. On the other hand, the glial fibrillary acidic protein activity following 59 days hypoxic exposure was almost the same as controls. These results show that systemic deep chronic hypoxia (depending on the intensity and the duration) activates the endogenous expression of glial fibrillary acidic protein in astrocytes of specific brain regions. The probable significance of this finding is discussed.

Blood vessel ultrastructure in the chick optic tectum developing under chronic hypoxia conditions

The maturation process of blood vessels has been ultrastructurally investigated in the optic tectum of chick embryos kept in a condition of aerogenic hypoxia and of chickens born from fertilized eggs incubated under hypoxia but kept in the open air after hatching. By comparing the fine structure of the intratectal vessels of chick embryos exposed to hypoxia to that of embryos developed under normal conditions, the conclusion has been drawn that O2 deprivation does not prevent the temporal sequence of appearance and/or differentiation of the various vascular wall components (endothelium, endothelial basement lamina, pericytes, perivascular glia), but it produces, at least in a part of the latter, modifications, the type and degree of which apparently depend upon hypoxia duration.