Buckthorn neuropathy in vitro : evidence for a primary neuronal effect

The neuropathy produced by toxins isolated from the buckthorn shrub (Karwinskia humboldtiana) has previously been proposed as a model for primary PNS demyelination in vivo. These toxins have been suggested to act through a metabolic effect on the Schwann cell. The aim of the present study was to use myelinated organotypic cultures of nervous tissue to dissect further the pathologic effects of these compounds. Combination cultures of mouse spinal cord and dorsal root ganglia were exposed to buckthorn toxins T/496 or T/544 at doses of 1-5 microgram/ml for periods of 48 hours (h) to 14 days. Ultrastructural findings from toxin-treated cultures indicated a primary effect upon the PNS axon, both myelinated and unmyelinated. The effect was expressed mainly as a widening of the periaxonal space, and also as a redistribution of most axonal organelles to a marginal position within the axon or to their close association with stacks of smooth endoplasmic reticulum, leaving more central regions occupied largely by neurofilaments. These changes were followed by focal axonal swelling, floccular disruption of the axoplasm and, ultimately, Wallerian degeneration. Myelin degeneration and chromatolytic changes in ganglion cell bodies appeared to be secondary to axonal alterations. This tissue culture model reproduces many of the features of buckthorn intoxication in vivo. However, the present results suggest that the toxic effect is primarily upon the axon rather than the Schwann cell, and would appear to be consistent with an abnormality in axoplasmic transport.