Neurotoxic Weapons and Syndromes.

The modern era of chemical and biological warfare began in World War I with the large-scale production and use of blistering and choking agents (chlorine, phosgene and mustard gases) in the battlefield. International treaties (the 1925 Geneva Protocol, the 1975 Biological and Toxin Weapons Convention and the 1993 Chemical Weapons Convention) banned biological and chemical weapons. However, several countries are probably still engaged in their development. Hence, there is risk of these weapons being used in the future. This chapter will focus on neurotoxic weapons (e.g. nerve agents, chemical and biological neurotoxins, psychostimulants), which act specifically or preeminently on the central nervous system and/or the neuromuscular junction. Deeply affecting the function of the nervous system, these agents either have incapacitating effects or cause clusters of casualties who manifest primary symptoms of encephalopathy, seizures, muscle paralysis and respiratory failure. The neurologist should be prepared both to notice patterns of symptoms and signs that are sufficiently consistent to raise the alarm of neurotoxic attacks and to define specific therapeutic interventions. Additionally, extensive knowledge on neurotoxic syndromes should stimulate scientific research to produce more effective antidotes and antibodies (which are still lacking for most neurotoxic weapons) for rapid administration in aerosolized forms in the case of terrorist or warfare scenarios.

Wormwood (Artemisia absinthium L.)--a curious plant with both neurotoxic and neuroprotective properties?

The medical use of the wormwood plant Artemisia absinthium L. dates back to at least Roman times, while during the last century this tradition was seemingly on the decline due to fears of absinthism, a syndrome allegedly caused by the wormwood-flavoured spirit absinthe and more specifically as a result of thujone, a monoterpene ketone often present in the essential oil of wormwood. If threshold concentrations are exceeded, thujone does in fact exhibit neurotoxic properties leading to dose-dependent tonic-clonic seizures in animals, likely caused by GABA type A receptor modulation. Research has shown that the concentrations of thujone present in absinthe were not sufficient to exceed these thresholds, and the marketing of wormwood-flavoured alcoholic beverages has ultimately been reinstated. The declining fears of absinthism may have led to a revival of the medical uses of wormwood, evidenced by several experimental reports, e.g. on the treatment of Crohn's disease. Most recently in this journal, neuroprotective properties of wormwood were detected in rats, and the plant was suggested to be possibly beneficial in the treatment of strokes. While these results sound promising and worthwhile for further investigation, the well-defined profile of adverse properties of wormwood demands a more cautious interpretation of these results. It remained unclear in the studies, for example, if the threshold dose for thujone (e.g. as set by the European Medicines Agency) would be exceeded during therapeutic usage. Due to the colourful history of wormwood, its application in humans should be preceded by a thorough and careful risk-benefit analysis.

Exploring neurocircuitries of the basal ganglia by intracerebral administration of selective neurotoxins.

The detailed anatomy of the monoamine pathways of the rat, first described by the students of Nils Ake Hillarp in Sweden, provided the basis for a neurocircuitry targeted pharmacology, leading to important therapeutic breakthroughs. Progress was achieved by the introduction of accurate lesion techniques based on selective neurotoxins. Systematic intracerebral injections of 6-hydroxydopamine let Urban Ungerstedt at the Karolinska Institutet, Stockholm, Sweden, to propose the first stereotaxic mapping of the monoamine pathways in the rat brain; and the 'Rotational Behaviour', as a classical model for screening drugs useful for alleviating Parkinson's disease and other neuropathologies. The direction of the rotational behaviour induced by drugs administrated to unilaterally 6-hydroxydopamine-lesioned rats reveals their mechanism of action at dopamine synapses, as demonstrated when rotational behaviour was combined with microdialysis. The model was useful for proposing a role for dopamine receptors in the gating of the flow of information integrated and/or modulated by the basal ganglia, through different efferent pathways; notably the striatopallidal system, via D(2) receptors, and the striatonigral system, via D(1) receptors. The role of other dopamine receptor subtypes on rotational behaviour has not yet been clarified.

Contribution of a snake venom toxin to myasthenia gravis: the discovery of alpha-bungarotoxin in Taiwan.

Myasthenia gravis (MG) is now recognized as an autoimmune disorder in which antibodies to acetylcholine (ACh) receptor lead to impairment of neuromuscular transmission. The discovery of alpha-bungarotoxin by Chang and Lee in 1963 has played a crucial role in establishing the new concept of MG. However, isolation of bungarotoxins from the venom of Taiwan banded krait, Bungarus multicinctus, was accomplished in the poorly funded and under equipped laboratory of the Department of Pharmacology, National Taiwan University, during the post-WWII period of economic depression and research isolation. Because alpha-bungarotoxin binds specifically and irreversibly with the muscle type nicotinic ACh receptor, it was used to localize ACh receptor and to isolate the ACh receptor protein, opening up a new era of receptor studies. It was also used to produce an antibody to ACh receptor and eventually an experimental autoimmune model of MG and clinical confirmation. The discovery of alpha-bungarotoxin has been considered the most important contribution to neurosciences from Taiwan.

Beyond BOTOX: advantages and limitations of individual botulinum neurotoxins.

Botulinum neurotoxins are the most potent toxins designed by nature. They are produced by Clostridium bacteria to cause long-lasting paralysis and death. However, in the past century one member of the botulinum family--botulinum neurotoxin type A--has been put to good use, and is now widely employed in clinical neurology and, even more often, in beauty clinics. This article will critically assess the value of individual members of the botulinum family for experimental neuroscience and medicine. The seven botulinum neurotoxins all act by targeting the same vesicle fusion machinery, and yet they cause paralysis of different durations. The distinct behaviors of botulinum neurotoxins will be discussed, with the aim of highlighting advantages and limitations for their future exploitation.

Historical neurotoxins: what we have learned from toxins of the past about diseases of the present.

Throughout history, humans have fallen victim to a variety of neurotoxins, with exposures coming in the form of tainted products, industrial pollution, drugs of abuse, and even the bread and water that sustain them. Despite this long and tumultuous history, neurotoxic outbreaks still occur with regular frequency. Although many difficulties currently exist in linking many of today's unexplained neurologic disorders to toxins, the past suggests a prominent role for neurotoxins in diseases (such as amyotrophic lateral sclerosis and PD), unexplained peripheral neuropathies, neurodevelopmental disorders, and many psychiatric disturbances.

How environmental hazards in childhood have been discovered: carcinogens, teratogens, neurotoxicants, and others.

Review of the literature reveals that environmental hazards cause adverse health effects that include sterility, infertility, embryotoxicity, low birth weight, skin lesions, neurodevelopmental defects, immunologic disorders, cancer, and fear of late effects. They have been identified mostly by astute practitioners but also by a bacteriologist, an animal experimentalist, 5 factory workers in childless marriages, and a tipsy bystander in an economically impoverished area of Baltimore. Dust on a parent's work clothes has transported a hazard at work to a hazard at home (lead, asbestos, and chlordecone). Causality is established by showing a dose-response effect and reproducing the effect in studies of other exposed groups or by using another epidemiologic method, eg, prospective instead of retrospective study. Also, the findings should be biologically plausible and not attributable to a concomitant variable such as cigarette smoking. Contrary to front-page newspaper headlines, incidence rates for childhood leukemia are not rising. Preserving specimens for future studies has been valuable: blood from people who were exposed to dioxin in Seveso, Italy; mummified umbilical cords containing methyl mercury at Minamata Bay, Japan; and Guthrie dried blood spots to screen retrospectively for 43 genetic disorders and a specific prenatal cytogenetic abnormality in some children with 1 form of leukemia. Recommendations are given for enhancing interest in environmental hazards and their discovery by clinicians.

Historical notes on botulism, Clostridium botulinum, botulinum toxin, and the idea of the therapeutic use of the toxin.

Food-borne botulism probably has accompanied mankind since its beginning. However, we have only few historical sources and documents on food poisoning before the 19th century. Some ancient dietary laws and taboos may reflect some knowledge about the life-threatening consumption of poisoned food. One example of such a dietary taboo is the 10th century edict of Emperor Leo VI of Byzantium in which manufacturing of blood sausages was forbidden. Some ancient case reports on intoxications with Atropa belladonna probably described patients with food-borne botulism, because the combination of dilated pupils and fatal muscle paralysis cannot be attributed to an atropine intoxication. At the end of the 18th century, some well-documented outbreaks of "sausage poisoning" in Southern Germany, especially in Württemberg, prompted early systematic botulinum toxin research. The German poet and district medical officer Justinus Kerner (1786-1862) published the first accurate and complete descriptions of the symptoms of food-borne botulism between 1817 and 1822. Kerner did not succeed in defining the suspected "biological poison" which he called "sausage poison" or "fatty poison." However, he developed the idea of a possible therapeutic use of the toxin. Eighty years after Kerner's work, in 1895, a botulism outbreak after a funeral dinner with smoked ham in the small Belgian village of Ellezelles led to the discovery of the pathogen Clostridium botulinum by Emile Pierre van Ermengem, Professor of bacteriology at the University of Ghent. The bacterium was so called because of its pathological association with the sausages (Latin word for sausage = "botulus") and not-as it was suggested-because of its shape. Modern botulinum toxin treatment was pioneered by Alan B. Scott and Edward J. Schantz.

Professor Chen-Yuan Lee, MD (1915-2001), pharmacologist: snake venom research at the Institute of Pharmacology, National Taiwan University.

Professor Chen-Yuan Lee was born in Tainan, Taiwan. In 1940, he joined the staff of the Institute of Pharmacology of the university, now named National Taiwan University. Dr Lee began a study of Daboia russelli formosensis venom under the direction of Professor Tsungming Tu who, in the 1930s, initiated the pharmacological studies of Formosan snake venoms carried out at the Institute. Under Professor Lee's direction, the Institute became known internationally for its work on the isolation, composition and characterization of the pharmacological properties of neurotoxins isolated from Formosan elapid venoms. Sophisticated use of the latest techniques revealed the mode of action of postsynaptic -bungarotoxin and presynaptic -bungarotoxin from Bungarus multicinctus venom, postsynaptic cobrotoxin, cytotoxic cardiotoxin and phospholipase A2 from Naja naja atra venom. Through work undertaken with colleagues at the Institute and in foreign countries, Professor Lee made an important contribution to our understanding of the mode of action of snake neurotoxins, and to their use in the elucidation of neuromuscular transmission. In the past decade, C.-Y. Lee was a prominent campaigner for social and political justice in Taiwan.

Twenty years of dendrotoxins.

Dendrotoxins are small proteins that were isolated 20 years ago from mamba (Dendroaspis) snake venoms (Harvey, A.L., Karlsson, E., 1980. Dendrotoxin from the venom of the green mamba, Dendroaspis angusticeps: a neurotoxin that enhances acetylcholine release at neuromuscular junctions. Naunyn-Schmiedebergs Arch. Pharmacol. 312, 1-6.). Subsequently, a family of related proteins was found in mamba venoms and shown to be homologous to Kunitz-type serine protease inhibitors, such as aprotinin. The dendrotoxins contain 57-60 amino acid residues cross-linked by three disulphide bridges. The dendrotoxins have little or no anti-protease activity, but they were demonstrated to block particular subtypes of voltage-dependent potassium channels in neurons. Studies with cloned K(+) channels indicate that alpha-dendrotoxin from green mamba Dendroaspis angusticeps blocks Kv1.1, Kv1.2 and Kv1.6 channels in the nanomolar range, whereas toxin K from the black mamba Dendroaspis polylepis preferentially blocks Kv1.1 channels. Structural analogues of dendrotoxins have helped to define the molecular recognition properties of different types of K(+) channels, and radiolabelled dendrotoxins have also been useful in helping to discover toxins from other sources that bind to K(+) channels. Because dendrotoxins are useful markers of subtypes of K(+) channels in vivo, dendrotoxins have become widely used as probes for studying the function of K(+) channels in physiology and pathophysiology.