Oxygen radicals in CNS damage

The osmotic/calcium stress theory of brain damage: are free radicals involved?

This overview presents data showing that glucose use increases and that excitatory amino acids (i.e., glutamate, aspartate), taurine and ascorbate increase in the extracellular fluid during seizures. During the cellular hyperactive state taurine appears to serve as an osmoregulator and ascorbate may serve as either an antioxidant or as a pro-oxidant. Finally, a unifying hypothesis is given for seizure-induced brain damage. This unifying hypothesis states that during seizures there is a release of excitatory amino acids which act on glutamatergic receptors, increasing neuronal activity and thereby increasing glucose use. This hyperactivity of cells causes an influx of calcium (i.e., calcium stress) and water movements (i.e., osmotic stress) into the cells that culminate in brain damage mediated by reactive oxygen species.

Brain levels of polyethylene glycol-conjugated superoxide dismutase following fluid percussion brain injury in rats

Polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) is being explored as an agent to reduce oxygen radical-mediated damage following brain injury. Yet little is known concerning the site of action of IV-administered PEG-SOD or the capacity of this conjugated enzyme to enter the brain. The purpose of this study was to determine the brain content of PEG-SOD in normal and fluid percussion injured rats. The fluid percussion device was attached over the right parietal cortex and a moderate (2.0 atm) intensity injury was produced. PEG-SOD was conjugated with 125I and given (2000 U/kg, 5 microCi/kg) to rats either 30 min before or 30 min after brain injury. Another group received [125I]PEG-SOD but was not injured. Plasma and left and right brain hemispheres were counted for [125I]PEG-SOD. Plasma levels of [125I]PEG-SOD declined similarly in all three groups during the 90-min period after IV administration. Brain [125I]PEG-SOD was low in control animals (0.034 U/g wet wt). In animals given PEG-SOD after injury the brain level was elevated sixfold in both the left and right hemispheres, compared to control. In rats given the drug before injury, [125I]PEG-SOD was 10 times control level in the right hemisphere, which is the side on which the injury device is attached, and 6 times control level in the left hemisphere. We conclude that traumatic brain injury produces an increase in brain PEG-SOD. The exact cellular site of the increased brain PEG-SOD remains to be clarified.

Vascular factors in the neurotoxic damage caused by 1,3-dinitrobenzene in the rat

Using a 3 x 10 mg/kg dose schedule of 1,3-dinitrobenzene (DNB) over two days in Fischer rats, we have found the following changes in vascular function and structure during the early phase of the symmetrical brain stem lesions. 1. Marked increase in cerebral blood flow generally but especially in the inferior colliculi, from 6 h after the final dose of DNB. 2. Increasing incidence of petechial haemorrhages in inferior colliculi, cerebellar roof, vestibular and superior olivary nuclei from 12 h. 3. Focal leakage of horseradish peroxidase and many sleeve-like arteriolar haemorrhages seen in vibratome sections and by scanning electron microscopy (SEM) in these regions from 12 h. 4. Periarteriolar oedema and protein leakage present in step-serial sections in these regions from 12 h, with astrocyte swelling and occasional small infarcts. These changes suggest that the vascular bed may play an important role in the pathogenesis of these lesions, perhaps in parallel with early astroglial damage. They are discussed in relation to (i) the known presence of xanthine oxidase in the vascular bed of the brain and the likelihood of "useless redox cycling' with free radical generation from this enzyme's interaction with nitroheterocyclic compounds, and (ii) the possible role of free radical damage to endothelial cells in this intoxication and in the analogous lesions of natural and experimental Wernicke's encephalopathy.

Anoxia-resistant turtle brain maintains ascorbic acid content in vitro

The isolated turtle brain maintains intra- and extracellular concentrations of ascorbate when incubated in ascorbate-free physiological saline for as long as 24 h. After incubation for 1 h, total tissue content of ascorbate in the turtle cerebellum was the same as in unincubated controls. After 20-24 h, tissue ascorbate content remained at 65% of control levels, while extracellular ascorbate concentration, measured with carbon fiber voltammetric microelectrodes, was 56% of the initial value. For an intermediate incubation period of 6 h, reduced ascorbate content was maintained at about 80% of control levels, regardless of whether incubation was under normal conditions or in the absence of glucose or oxygen. By contrast, only 4% of the ascorbate content of guinea pig brain slices remained after a 6 h incubation. Maintenance of high levels of ascorbate by the anoxia-resistant turtle brain could be an important factor in the amelioration of oxidative injury in this tissue. Inclusion of ascorbate in media used for in vitro studies of mammalian brain tissue is recommended.

Hemodynamic consequences of common carotid artery thrombosis and thrombogenically activated blood in rats

We documented the hemodynamic consequences of nonocclusive common carotid artery thrombosis (CCAT) and tested the hypothesis that vasoactive substances capable of altering local CBF (LCBF) are released into the systemic circulation following cerebrovascular injury. Ten minutes after photochemically induced CCAT, an autoradiographic determination of LCBF was conducted with [14C]iodoantipyrine. In blood transfusion studies using donor and recipient rats, a 1-ml sample of thrombogenically activated blood (TAB) collected downstream from the forming thrombus was reinjected into a recipient rat 15 or 60 min before CBF study. A heterogeneous pattern of abnormal LCBF was documented in the ipsilateral hemisphere of CCAT rats and recipient rats receiving TAB 15 min before CBF study. Acute hemodynamic abnormalities included ischemic (less than 35% of control) and hyperemic (greater than 125% of control) foci and more global reductions (50-80% of control) in cortical and subcortical LCBF. Border zone hyperemia exceeding 2.0 ml/g/min was associated with focal sites of severe LCBF reductions. Although recipient rats that received TAB 15 min before CBF study displayed similar hemodynamic abnormalities, LCBF values in 60-min recipient rats were not significantly different from control despite ischemic foci. Humoral factors generated during CCAT appear to be responsible for the acute LCBF consequences of cerebrovascular thrombosis. Vasoactive substances released from a thrombotic site, capable of regionally affecting vascular reactivity in a time-dependent fashion, might be expected to participate in the pathogenesis of transient ischemic attacks and acute stroke.