Richard Caton (1842-1926): pioneer electrophysiologist and cardiologist.

Richard Caton is recognized as the discoverer of the waves of electrical potential which today form the basis of electroencephalography. He reported his finding in three communications, two in the British Medical Journal and one to the Ninth International Congress of Medicine at Washington, DC. After defending his priority in having made this discovery, he did no further work on the brain: his family and colleagues were unaware of his discovery for many years after his death.

Hypothesis: the significance of Winterbottom's sign.

Swollen glands in the neck in African sleeping sickness is usually considered to be a sign of peripheral trypanosomiasis without cerebral involvement. Experimental evidence of connection between these glands and the ventricles of the brain is reviewed. The evidence suggests that Winterbottom's sign may indicate also a cerebral infection.

Degeneration of serotonin-specific neurons in the brain in experimental Trypanosoma brucei infection.

ORMEROD and HUSSEIN (1986) have shown that an intracellular stage of Trypanosoma brucei rhodesiense causes the destruction of ependymal cells lining the ventricles of the brain. The ventricular ependymal cells are intimately associated with a plexus of nerves that react specifically with monoclonal antibody raised against serotonin. We have shown that in areas where the ependyma is damaged, the supraependymal plexus also undergoes destruction and that retrograde degeneration of the neuron as far as the dorsal raphe nucleus also occurs.

Screening compounds for sleeping sickness therapy without relapse.

The finding of an intracellular stage of Trypanosoma brucei in ependymal cells of the choroid plexus (Abolarin et al., 1986) and of the lining of the ventricles (Ormerod and Hussein, 1986) has suggested a new technique for screening trypanocidal compounds against the failure of drugs to eliminate "occult" stages of the infection (Raseroka and Ormerod, 1986). A (donor) mouse, infected for 28 days, is dosed with a drug, or combination of drugs, and samples of blood, cerebral cortex, choroid plexus and lining of ventricle are injected into clean (recipient) mice.

The trypanocidal effect of drugs in different parts of the brain.

Three parts of the brain, cerebral cortex, lining of ventricle and choroid plexus, are cleared of trypanosomes to different extents by different drugs. There appear to be several barriers preventing drugs from acting in different parts of the brain, the concept of a single "blood-brain barrier" does not account for the phenomena observed. The protection of trypanosomes from certain drugs by the choroid plexus and ventricular wall supports the concept of an intracellular stage of Trypanosoma brucei in the ependymal cell; this concept is also supported by differences in parasitaemia resulting from the inoculation of ependymal and of other tissues.

The ventricular ependyma of mice infected with Trypanosoma brucei.

The fine structure of ependymal cells lining the cerebral ventricles of normal mice and of mice infected with Trypanosoma brucei was examined by transmission electron microscopy. Most of the ependymal cells had been stripped from the ventricular surface of the brain in infected animals but some of the remaining ependymal cells contained intracellular trypomastigotes. The same process of stripping had occurred in a single human brain that was included in the series, but intracellular forms were not found.

Interaction between Trypanosoma brucei and the ependymal cell of the choroid plexus.

The fine structure of the normal choroid plexus of rats and mice and of those infected with Trypanosoma brucei was examined by transmission and scanning electron microscopy: extracellular trypomastigotes in the perivascular stroma predominate but the evidence presented suggests that they are derived both from stages in the blood and from others undergoing division within ependymal cells, a process which results in destruction of a large proportion of ependymal cells in the parts of choroid plexus affected. The choroid plexus maintains its integrity by regeneration of an outer layer of ependymal cells.

Phagocytosis of Trypanosoma brucei rhodesiense by peritoneal macrophages: a study by scanning electronmicroscopy.

Phagocytosis of Trypanosoma brucei rhodesiense by peritoneal macrophages takes place by seizure of the trypomastigote by either end but usually by the anterior. A lamellar sheath similar to that seen in phagocytosis of the promastigote of Leishmania is observed, but it is smaller and does not proceed to envelop the living parasite. The attached trypomastigote becomes pitted and appears to have been killed and partially destroyed before it is completely engulfed.

Cryptic stage of sleeping-sickness trypanosome developing in choroid plexus epithelial cells.

Electronmicrographs of the choroid plexus from rats infected with Trypanosoma brucei rhodesiense showed that trypomastigotes from the perivascular spaces may penetrate and undergo multiple division in the ependymal cells which locally constitute the blood-brain barrier. Progressive degeneration of the ependymal cell liberates trypomastigotes back into the perivascular space, from which re-entry into the blood may occur. Re-entry to the blood does not take place from any tissues other than the brain and its membranes.

Factors affecting vesicle formation and acetylene reduction (nitrogenase activity) in Frankia sp. CpI1.

Vesicle formation and acetylene reduction (nitrogenase activity) were observed when washed hyphae from cultures of Frankia sp. CpI1 were transferred to a nitrogen-free medium containing ethylenediaminetetraacetic acid and succinate. Succinate could be replaced by malate or fumarate, but not other carbon sources.