Arachnoiditis following myelography with water-soluble agents. The role of contrast medium osmolality

The role of contrast medium osmolality in postmyelographic arachnoiditis was studied. Monkeys were injected intrathecally with isotonic saline (290 mOs/kg), hypertonic saline (1,449 mOs/kg), metrizamide (456 or 300 mOs/kg), or methylglucamine iocarnate (1,049 mOs/kg). After 12 weeks the animals were examined for evidence of arachnoiditis, with myelography just prior to sacrifice and microscopic examination of the excised dural sac and its contents. Intrathecal injections of methyglucamine iocarmate or metrizamide caused arachnoiditis while saline did not. Only one animal given 170 mg l/ml (300 mOs/kg) exhibited a more severe reaction than the controls. An increase in the cerebrospinal fluid osmolality alone does not cause arachnoiditis.

Experimental production of arachnoiditis with water-soluble myelographic media

After myelography with either metrizamide (300mg l/ml) or meglumine iocarmate (280 mg l/ml), mild to severe arachnoid fibrosis was demonstrated radiographically and histologically in primates. Intrathecal injections of metrizamide (170 mg l/ml) or autologous cerebrospinal fluid produced less arachnoiditis. The risk of arachnoiditis is probably minimized by the use of reduced volumes and concentrations of water-soluble media. Controlled studies of arachnoiditis following myelography are probably more reliable in the primate model than in other experimental animals.

The relation of axonal transport of mitochondria with microtubules and other axoplasmic organelles

Axonal transport of mitochondria was studied in frog sciatic nerves incubated in agents selected for their known or alleged effect on microtubules or axonal flow. Quantitative data on mitochondria, microtubules, neurofilaments, endoplasmic reticulum, and cross-sectional area of the axon indicate that axonal transport of mitochondria is dependent on microtubules. When more than half of the microtubules are destroyed, the axonal transport of mitochondria is diminished in proportion to the destruction of microtubules. Axonal transport of mitochondria is not related to neurofilaments and endoplasmic reticulum. Changes in the cross-sectional area of axons, even upon reduction to half the normal size, do not noticeably affect mitochondrial transport. Cyanide which blocks oxidative metabolism also blocks axonal transport of mitochondria, but analysis of fine structure indicates that cyanide is destructive to microtubules as well.

The SN mechanism in aromatic compounds. XXXII. Reactivity of some perhalogenobenzenes

Substituent effects in a series of pentafluorophenyl compounds (C6F5X) ranging from powerful activating to powerful deactivating substituents are considered, both as regards orientation and rates, and shown to be simply and reliably predicted by considering the change as made up of two components, viz. from C6F6 to C6F5H and from C6F5H to C6F5X. The same principle applies generally to C6Hal5X compounds, and the necessary orientation and rate data are obtainable from the existing large body of substituent effects in aromatic SN reactions. Comparisons are thus also easily possible with substituent effects in aromatic SE reactions, and more generally. The reasons for predominant para direction for almost all groups, except the more powerful deactivating substituents which are meta directing, and the expectation of a few borderline cases, emerge clearly from discussion. While orientation is largely known already, there have been very few precise rate determinations apart from the present work. Some brief consideration of the admixture of dioxan with protic solvent is given. The reactivities of hexafluorobenzene and hexachlorobenzene are compared. The substantially greater reactivity reported with the former is regarded as due solely to the greater mobility of fluorine than chlorine, with first row nucleophdes in protic solvents; whereas in contrast it is predicted that the C6Cl5 group is slightly more activating for aromatic S, reactions than the C,F, group. The relative reactivities of C6F6 and C6H5F, and C6Cl6 and C6H5Cl are also compared. Rate ratios are c.108; ΔΔE? c.15 kcal mole-1; and Δlog10B c.+1.