Effect of hypoxia on protein metabolism in neuron- and neuroglia cell-enriched fractions from rabbit brain

CNS hypoxia is more pronounced in murine cerebral than noncerebral malaria and is reversed by erythropoietin

Cerebral malaria (CM) is associated with high mortality and risk of sequelae, and development of adjunct therapies is hampered by limited knowledge of its pathogenesis. To assess the role of cerebral hypoxia, we used two experimental models of CM, Plasmodium berghei ANKA in CBA and C57BL/6 mice, and two models of malaria without neurologic signs, P. berghei K173 in CBA mice and P. berghei ANKA in BALB/c mice. Hypoxia was demonstrated in brain sections using intravenous pimonidazole and staining with hypoxia-inducible factor-1α-specific antibody. Cytopathic hypoxia was studied using poly (ADP-ribose) polymerase-1 (PARP-1) gene knockout mice. The effect of erythropoietin, an oxygen-sensitive cytokine that mediates protection against CM, on cerebral hypoxia was studied in C57BL/6 mice. Numerous hypoxic foci of neurons and glial cells were observed in mice with CM. Substantially fewer and smaller foci were observed in mice without CM, and hypoxia seemed to be confined to neuronal cell somas. PARP-1-deficient mice were not protected against CM, which argues against a role for cytopathic hypoxia. Erythropoietin therapy reversed the development of CM and substantially reduced the degree of neural hypoxia. These findings demonstrate cerebral hypoxia in malaria, strongly associated with cerebral dysfunction and a possible target for adjunctive therapy.

Neuroglobin is up-regulated in the cerebellum of pups exposed to maternal epileptic seizures

To evaluate a potential insult in the cerebellum of pups exposed to maternal epileptic seizures during intrauterine life, female rats were subjected to pilocarpine-induced epilepsy. Pups from different litters were sacrificed at 1, 3, 7 and 14 post-natal days (PN) and neuroglobin (Ngb) and gliosis were analyzed in the cerebellum by Western blotting (WB) and RT-PCR. (14)C-l-leucine-[(14)C-Leu] incorporation was used to analyze protein synthesis at PN1. Nitric Oxide (NO) and thiobarbituric acid-reactive substances (TBARS) levels were also measured. Pups from naive mothers were used as controls. The mRNA level of Ngb was increased in experimental animals at PN1 ((**)p ≤ 0.001) and PN3 ((**)p ≤ 0.001), at PN7 ((***)p ≤ 0.0001) and at PN14 ((**)p ≤ 0.001) compared to the respective controls. The protein level of Ngb increased significantly in the experimental pups at PN1 ((*)p ≤ 0.05) and at PN3 ((**)p ≤ 0.001), when compared to the control pups at PN1 and PN3. At PN7 and PN14 no difference was found. The mRNA level of GFAP increased significantly about two times at PN3 ((*)p ≤ 0.05) and PN7 ((*)p ≤ 0.05) in the experimental pups when compared to the respective controls, but was unchanged in the other studied ages. Data showed that experimental pups at PN1 exhibited reduced (about 2 times, (*)p ≤ 0.05) total protein synthesis in the cerebellum when compared to control. No differences were found in the NO and TBARS levels. Our data support the hypothesis that an up-regulation of Ngb could be a compensatory mechanism in response to the hypoxic-ischemic insults caused by seizures in pups during intrauterine life.

Astrocytes and stroke: networking for survival?

Astrocytes are now known to be involved in the most integrated functions of the central nervous system. These functions are not only necessary for the normally working brain but are also critically involved in many pathological conditions, including stroke. Astrocytes may contribute to damage by propagating spreading depression or by sending proapoptotic signals to otherwise healthy tissue via gap junction channels. Astrocytes may also inhibit regeneration by participating in formation of the glial scar. On the other hand, astrocytes are important in neuronal antioxidant defense and secrete growth factors, which probably provide neuroprotection in the acute phase, as well as promoting neurogenesis and regeneration in the chronic phase after injury. A detailed understanding of the astrocytic response, as well as the timing and location of the changes, is necessary to develop effective treatment strategies for stroke patients.

Blood vessel endothelia of the cerebral white matter of rats exposed to hypoxia. Karyometric and cytophotometric evaluation

Hypoxic hypoxia is used as one of the models for examining the unfavourable effect of oxygen deficit on the nervous system. Since some morphological studies concerning the effect of hypoxia on the central nervous system have given consideration to perivascular lesion zones and glia alterations in the white matter, the present evaluation of the effect of hypoxia has been directed to vascular endothelia of the white matter. Examinations were conducted on adult rats of the Wistar strain which were exposed to acute hypoxia by being placed in a gas mixture containing 2% O2 or to moderate hypoxia - in a gas mixture containing 7% O2. Experimental animals were sacrificed 4 and 24 h after hypoxia and 14 and 60 d after hypoxia. The behaviour of vascular endothelia after hypoxia was evaluated by karyometric and cytophotometric methods. The measurements show an edema of endothelial nuclei in capillaries of the cerebral white matter of the rat in the first 24 h after hypoxia accompanied by nuclear chromatin index alterations proportional to the intensity of hypoxia. The measurements of endothelial nuclei 14 and 60 d after hypoxia show a development of a degenerative process in these nuclei, manifested by their decreasing size and by nuclear chromatin concentration in their central parts. The morphometric and cytophotometric examinations point to long-term alterations induced by hypoxic hypoxia.

Effect of hypoxia on nucleic acid and protein synthesis in different brain regions

The incorporation of [methyl-3H]thymidine into DNA, of [5-3H]uridine into RNA, and of [1-14C]leucine into proteins of cerebral hemispheres, cerebellum, and brainstem of guinea pigs after 80 hr of hypoxic treatment was measured. Both in vivo (intraventricular administration of labeled precursors) and in vitro (tissue slices incubation) experiments were performed. The labeling of macromolecules extracted from the various subcellular fractions of the above-mentioned brain regions was also determined. After hypoxic treatment the incorporation of the labeled precursors into DNA, RNA, and proteins was impaired to a different extent in the three brain regions and in the various subcellular fractions examined; DNA and RNA labeling in cerebellar mitochondria and protein labeling in microsomes of the three brain regions examined were particularly affected.

Effect of hypoxia, ischemia and carbon monoxide intoxication on in vivo protein synthesis in neuron and glia cell enriched fractions from rat brain

The dynamics of changes in the in vivo amino acid incorporation into proteins of the neuron and glia cell enriched fractions of rat brain following application of a number of hypoxic conditions were investigated. The experimental models include: a) simple hypoxia, b) ischemic-hypoxic hypoxia and c) carbon monoxide intoxication. Irrespective of the experimental model used, neuronal protein synthesis was more markedly inhibited than glial, maximal inhibition being observed 2 hrs after cessation of the experimental procedure. The changes were of transient character, whereby 24 hrs after the experiment the glial synthesis appeared activated above the control value. The higher sensitivity of the neuronal protein synthesis to the applied experimental procedures produced more significant changes of the protein/total radioactivity ratio in neurons than in glia, the ratio expressing the extent of radioactive amino acid utilisation in the synthesis.

Effect of anoxia on protein metabolism in subcellular fractions of rabbit brain

The effect of cerebral anoxia on leucine incorporation into proteins of various subcellular fractions from rabbit brain was studied by using a previously reported in vitro model. Although the decrease in leucine incorporation was observed earlier in nuclei and microsomes, other fractions also demonstrated a rapid decrease. These results were quite different from the pattern of leucine incorporation observed in a type of reversible suppression produced with diphenylhydantoin.

Cerebral anoxia: protein metabolism during recovery in in vitro model

Amino acid incorporation into proteins of rabbit brain slices was studied during the recovery stage after various anoxic periods in an in vitro experimental model. There was a distinct difference between anoxic periods up to five minutes and those beyond ten minutes. In the former, inhibition of amino acid incorporation was of lesser degree and was reversible. On the other hand, more than 50% inhibition was observed following anoxic periods of 30 minutes and this inhibition was irreversible. Amino acid incorporation into proteins was more sensitive to anoxia than was amino acid transport into brain slices.