Studies on hexachlorophene-induced myelin lesions in the trigeminal root transitional region in developing and adult mice

Myelin toxicity of chlorhexidine in zebrafish larvae

BACKGROUND

Chlorhexidine gluconate (CHG) is a topical antiseptic solution recommended for skin preparation before central venous catheter placement and maintenance in adults and children. Although CHG is not recommended for use in children aged <2 months owing to limited safety data, it is commonly used in neonatal intensive care units worldwide. We used zebrafish model to verify the effects of early-life exposure to CHG on the developing nervous system, highlighting its impact on oligodendrocyte development and myelination.

METHODS

Zebrafish embryos were exposed to different concentrations of CHG from 4 h post fertilization to examine developmental toxicity. The hatching rate, mortality, and malformation of the embryos/larvae were monitored. Oligodendrocyte lineage in transgenic zebrafish embryos was used to investigate defects in oligodendrocytes and myelin. Myelin structure, locomotor behavior, and expression levels of genes involved in myelination were investigated.

RESULTS

Exposure to CHG significantly induced oligodendrocyte defects in the central nervous system, delayed myelination, and locomotor alterations. Ultra-microstructural changes with splitting and fluid-accumulated vacuoles between the myelin sheaths were found. Embryonic exposure to CHG decreased myelination, in association with downregulated mbpa, plp1b, and scrt2 gene expression.

CONCLUSION

Our results suggest that CHG has a potential for myelin toxicity in the developing brain.

IMPACT

To date, the neurodevelopmental toxicity of chlorhexidine gluconate (CHG) exposure on the developing brains of infants remains unknown. We demonstrated that CHG exposure to zebrafish larvae resulted in significant defects in oligodendrocytes and myelin sheaths. These CHG-exposed zebrafish larvae exhibited structural changes and locomotor alterations. Given the increased CHG use in neonates, this study is the first to identify the risk of early-life CHG exposure on the developing nervous system.

The central-peripheral transition zone of cervical spinal nerve roots in Jimpy mutant and normal mice. Light- and electron-microscopic study

Comparative morphological and ultrastructural investigations on the cervical dorsal and ventral central-peripheral transition zones (CPTZs) of Jimpys and control mice have been performed at early and advanced myelination stages. After postnatal development a characteristic cone-shaped glial outgrowth extends into the proximal part of the dorsal roots, while the ventral roots exhibit short Schwann cell and peripheral nervous tissue invaginations into the spinal cord at the ventral root-spinal cord junction in both animal groups. In Jimpys, although there is marked central myelin deficiency and absence of oligodendroglial development on the CNS side, the normal general aspect of the CPTZs is maintained. Previously postulated astrocytic and neuroaxonal abnormalities in the mutants do not alter the central-peripheral borderline, and Schwann cell migration from the spinal nerve roots into the cord does not occur.

Growth of nerve-cell body and myelinogenesis in mouse trigemnal ganglion and root: a combined cytofluorometric and morphometric study

Postnatal growth of mouse trigeminal ganglion cells and myelinogenesis in the central and peripheral portions of the trigeminal root were studied in animals aged 0-120 days. The trigeminal ganglion cells were dispersed into single cell suspensions. The growth of individual nerve cells was quantitated by measuring total protein content with a new cytofluorometric method based on o-phthaldialdehyde binding to cells fixed in a mixture of ethanol and acetic acid. White matter from the C.N.S. protrudes from the brainstem into the trigeminal root, comes into direct contact with the P.N.S. in a transitional region. C.N.S. and P.N.S. and myelinogenesis were studied in the same population of trigeminal sensory nerve fibres. Myelinogenesis was quantitated at the ultrastuctural level by morphometric techniques. A prominent peak in nerve cell body growth occurred between 3 and 6 days. Myelinogenesis in terms of established contacts between axons and their myelinating cells started at the same time in C.N.S. and P.N.S. and the transformation from nonmyelinated to promyelinated and myelinated fibres occurred concurrently in the central and peripheral parts of the trigeminal root. The growth of the myelin sheath, that is, the addition of myelin lamellae, was faster and more intense in P.N.S. than in C.N.S. This could reflect the fact that a Schwann cell myelinates only one internode, whereas an oligodendrocyte provides myelin for several internodes in different axons. These results support the concept of a common 'signal' for myelinogenesis in C.N.S. and P.N.S.

Latent herpes simplex virus trigeminal ganglionic infection in mice and demyelination in the central nervous system

Mice were inoculated with herpes simplex virus (HSV) type 1 by gently scraping the skin of the nose with a fine needle. About 80% of the animals developed latent inapparent HSV infections in trigeminal ganglia. Virus was demonstrable for at least 6 months post inoculation (p.i.) by cocultivation of ganglionic tissue with GMK cells. Histologically, trigeminal ganglia revealed infiltrations of inflammatory cells even 6 months p.i. In addition, lesions occurred in the brainstem corresponding to the entry of trigeminal roots, trigeminal tracts and nuclei. Inflammatory cell infiltration, disruption of myelin sheaths and macrophages laden with myelin degradation products were observed 7 days p.i. Fourteen to 30 days p.i. electron microscopy demonstrated completely naked axons. In the transitional region of the trigeminal root denuded axons occurred in the central part of the region while the peripheral myelin, bordering the demyelinated central segments, was intact. Small areas of demyelination were still detectable 3 and 6 months p.i. but there were then also signs of remyelination. Possible mechanisms causing the demyelinations are discussed.