THE RELATIONSHIP BETWEEN ENZYME ACTIVITY AND NEUROGLIA IN THE PRODROMAL AND DEMYELINATING STAGES OF CYANIDE ENCEPHALOPATHY IN THE RAT

A new 90-day drinking water study of sodium cyanide in rats to further evaluate National Toxicology Program findings and inform risk assessment

BACKGROUND

The National Toxicology Program (NTP, 1993) reported male reproductive effects in a sodium cyanide (NaCN) drinking water study. The critical effect, decreased cauda epididymis weights, was used by U.S. Environmental Protection Agency for their hazard characterization and risk assessment of hydrogen cyanide and cyanide salts. To further investigate potential male reproductive effects, we conducted a new 90-day drinking water study.

METHODS

Our study expanded evaluations of testes and thyroid. Male F344 rats received NaCN in drinking water at 0, 0 (water restricted; paired to top dose), 3, 10, 30, 100, and 300 ppm for 13 weeks, followed by 10-weeks recovery.

RESULTS

Plasma thiocyanate increased dose-dependently but returned to baseline during recovery. NaCN caused neither effects on survival, body weight, food consumption, hematology, serum chemistry, urinalysis, thyroid hormones, testes or epididymides weights, sperm motility/viability, sperm morphology, or sperm production; nor clinical, ophthalmic, or histopathologic findings. Increased organ weights in thyroid/parathyroid and liver occurred at 300-ppm but were recoverable. No changes occurred in male reproductive organs.

CONCLUSIONS

Absent adverse effects, the NOAEL was 300 ppm (21.66 mg/kg/day; highest dose tested). Based on organ weight increases at 300 ppm, the NOEL was 100 ppm (7.46 mg/kg/day).

Understanding a role for hypoxia in lesion formation and location in the deep and periventricular white matter in small vessel disease and multiple sclerosis

The deep and periventricular white matter is preferentially affected in several neurological disorders, including cerebral small vessel disease (SVD) and multiple sclerosis (MS), suggesting that common pathogenic mechanisms may be involved in this injury. Here we consider the potential pathogenic role of tissue hypoxia in lesion development, arising partly from the vascular anatomy of the affected white matter. Specifically, these regions are supplied by a sparse vasculature fed by long, narrow end arteries/arterioles that are vulnerable to oxygen desaturation if perfusion is reduced (as in SVD, MS and diabetes) or if the surrounding tissue is hypoxic (as in MS, at least). The oxygen crisis is exacerbated by a local preponderance of veins, as these can become highly desaturated 'sinks' for oxygen that deplete it from surrounding tissues. Additional haemodynamic deficiencies, including sluggish flow and impaired vasomotor reactivity and vessel compliance, further exacerbate oxygen insufficiency. The cells most vulnerable to hypoxic damage, including oligodendrocytes, die first, resulting in demyelination. Indeed, in preclinical models, demyelination is prevented if adequate oxygenation is maintained by raising inspired oxygen concentrations. In agreement with this interpretation, there is a predilection of lesions for the anterior and occipital horns of the lateral ventricles, namely regions located at arterial watersheds, or border zones, known to be especially susceptible to hypoperfusion and hypoxia. Finally, mitochondrial dysfunction due to genetic causes, as occurs in leucodystrophies or due to free radical damage, as occurs in MS, will compound any energy insufficiency resulting from hypoxia. Viewing lesion formation from the standpoint of tissue oxygenation not only reveals that lesion distribution is partly predictable, but may also inform new therapeutic strategies.

Combined administration of hyperbaric oxygen and hydroxocobalamin improves cerebral metabolism after acute cyanide poisoning in rats

Hyperbaric oxygen therapy (HBOT) or intravenous hydroxocobalamin (OHCob) both abolish cyanide (CN)-induced surges in interstitial brain lactate and glucose concentrations. HBOT has been shown to induce a delayed increase in whole blood CN concentrations, whereas OHCob may act as an intravascular CN scavenger. Additionally, HBOT may prevent respiratory distress and restore blood pressure during CN intoxication, an effect not seen with OHCob administration. In this report, we evaluated the combined effects of HBOT and OHCob on interstitial lactate, glucose, and glycerol concentrations as well as lactate-to-pyruvate ratio in rat brain by means of microdialysis during acute CN poisoning. Anesthetized rats were allocated to three groups: 1) vehicle (1.2 ml isotonic NaCl intra-arterially); 2) potassium CN (5.4 mg/kg intra-arterially); 3) potassium CN, OHCob (100 mg/kg intra-arterially) and subsequent HBOT (284 kPa in 90 min). OHCob and HBOT significantly attenuated the acute surges in interstitial cerebral lactate, glucose, and glycerol concentrations compared with the intoxicated rats given no treatment. Furthermore, the combined treatment resulted in consistent low lactate, glucose, and glycerol concentrations, as well as in low lactate-to-pyruvate ratios compared with CN intoxicated controls. In rats receiving OHCob and HBOT, respiration improved and cyanosis disappeared, with subsequent stabilization of mean arterial blood pressure. The present findings indicate that a combined administration of OHCob and HBOT has a beneficial and persistent effect on the cerebral metabolism during CN intoxication.

The effect of smoking on the symptoms and progression of multiple sclerosis: a review

Multiple sclerosis (MS) is a chronic inflammatory neurodegenerative disorder of the central nervous system with characteristic demyelinating lesions and axonal loss. MS accounts for the most common cause of neurological disability in young adults in the Western world. The clinical manifestations and the course of MS are highly variable. The early stage of the disease is usually characterized by attacks of neurological dysfunction with complete or incomplete recovery, however, with time disability accumulates in many patients. MS is believed to result from an interplay between susceptibility genes and environmental factors, one of which is smoking. Smoking, a worldwide epidemic, can be regarded as an important risk factor for MS particularly because of its modifiable nature in the quest to prevent or temper the disease course in MS as well as providing possible insights into MS pathogenesis. There are also reports that smoking may influence the symptoms and disease progression in patients with MS. The purpose of this article is to review the effects of smoking on MS symptoms and progression. We conclude that (1) although there are some early reports on worsening of MS symptoms by smoking, the existing evidence is insufficient to thoroughly assess the effects of smoking on the myriad of MS symptoms and (2) smoking seems to adversely influence disease progression in MS patients. We also discuss the potential biological mechanisms linking smoking and MS.

Karyometric and cytophotometric studies of the oligodendroglia in the corpus callosum of the rat after hypoxia

Karyometric and cytophotometric investigations were conducted using an automatic analyser "Morphoquant" on oligodendroglial nuclei of corpus callosum following acute or moderate hypoxia in Wistar rats. Results of our studies demonstrated karyometric changes in nuclei of oligodendroglia cells after hypoxia, with deviations distinct in the early and late period after exposure to hypoxia. Cytophotometric analysis of a relative DNA content in cell nuclei of oligodendroglia demonstrated an increased extinction of DNA in the early period and a decreased extinction in the late period after acute or moderate hypoxia. The changes in oligodendroglia may be primarily responsible for the molecular structure lesion in myelin, observed as a result of hypoxia.

Histoenzymic studies in the myelinopathy provoked by the cerebrospinal fluid exchange

A histochemical study was performed on the activity of several phosphatases, esterases and oxidoreductases in the spinal cord of cat in the course of the myelinopathy provoked by the cerebrospinal fluid (CSF) exchange. The following results were obtained: 1. Neuroglial cells of the spinal cord react with a slight, focal increase of TPP-ase activity already during the early stage of myelinopathy evoked by repeated withdrawal and reinjecting of CSF into the Cisterna magna of experimental cats. 2. During the late stage of this experimental disease-- the oligo-and astroglia of the spinal cord dtsplay considerably increased activities of ATP-ase, acP, and of various oxidoreductases. 3. The observed morphological and functional (increased enzymic activity) changes of the oligodendroglia as well as the demonstrable damage of myelin sheath, seem to be the results of vasogenous edema. 4. The results of investigations performed did not yield any arguments, which would speak in favour of the assumption, that the changes of the oligodendroglia cells function as the primary cause in the myelinopathy provoked by the CSF exchange, affecting secondary the myelin sheaths. 5. The decissively increased lysosomal acP activity in oligodendroglial cells of the spinal cord investigated during the early stage of this myelinopathy, accompanied by an evidently damaged Golgi apparatus, may be explained when the Golgi zone is not necessarily the only cellular site where acid phosphatase may be performed.

Glycogen and phosphorylase activity in rat brain during recovery from several forms of hypoxia

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Effect of cyanide intoxication on the metachromatic material found in the central nervous system

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Cyanide, vitamin B-12, experimental demyelination and tobacco amblyopia

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HISTOCHEMISTRY OF THE NEUROGLIA AND MYELIN IN EXPERIMENTAL CEREBRAL OEDEMA

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