Arachnid Science: Article Reviews

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Escoubas. P, & L. Rash. 2004. Tarantulas: Eight-legged pharmacists and combinatorial chemists. Toxicon. 43: 555-574.

This paper reviews the known links between the symptoms that typically occur after tarantula venom exposures, such as pain and swelling, and the changes in cellular activity that produce these symptoms. Sometimes review articles can read like nothing more than a long a list of facts. In contrast, this paper begins more like you are reading a story. Advances in understanding how tarantula venoms work is the story of many interacting factors: progress in basic research about the nervous system, scientists' use of improved techniques to isolate and study individual proteins, the need to apply this venom knowledge towards making medical treatment of envenomation more effective, what we know and still need to know (especially related to gene mapping) about correct taxonomy, and the contribution of arachnoculture by increasing the availability of new species as the hobby grew. Tarantulas are now proving to be rich sources of newly discovered compounds that have important uses in pharmacology research and in novel medical treatments. The authors suggest that the use of tarantula venoms is leading to a "new era of toxin research&qout;.

Tarantula venom is comprised of a collection of peptides that are of relatively of short length, usually with an average length of 30-40 amino acids. These toxic peptides can cause specific neurons to dramatically increase or decrease their activity, both effects that have been recognized for years in many studies. A more recently discovered means by which venoms may also act is by becoming a physical blockade in the cell membrane. As a broken key within a lock will prevent another key from opening that lock, some venom peptides seem to work by making the native neurotransmitters unable to enter the blocked channel of their targeted cells. For example, some toxins may indirectly produce paralysis in the prey by simply sabotaging the neurotransmitters that enable muscle contraction, causing the preyÕs muscles to effectively freeze in place. By disrupting the normal function of the prey nervous system in controlled lab studies, tarantula venom is yielding answers to some basic questions of how peptide patterns are selective for specific types of receptive tissue in the prey by mimicking neurotransmitters, and how these peptides cause widespread physiological changes that cause the symptoms following envenomation. Discovering the typical physiological effects that a venom produces is, in turn, improving our ability to identify and document new tarantula species.

New experimental data are presented on the venom potency of 55 tarantula species. Mice (20g each) were injected with a fixed amount of venom and their time to death was recorded. Comparisons across species revealed support for one long-held belief of many tarantula keepers: Old World species tend to have more potent venom than do New World species. (While the accuracy of this claim is not questioned at all, it should be pointed out that the delivery method of the venom — an ICV injection — makes it difficult to generalize to how long it would take mice or other prey to die following a scorpion sting. This type of injection delivers the full dose of toxin to the ventricles of the brain, allowing for more rapid distribution of the toxin throughout the brain and therefore more rapid onset of symptoms and death.)

Great advances have been made in our appreciation of the venom of many tarantula species, but much more work is still needed. Unfortunately, studies on the relative effects of venom across tarantula species are rare and, because differences in the methods used to deliver the venom can affect the potency and timing of the symptoms following envenomation, it is hard to draw broad conclusions across results of the studies that have been published.

This article is highly recommended reading. Although some sections are technical, such as the information on toxin molecular structure, the paper is extremely well written and the authors do a fine job of making those challenging sections more comprehensible to the nonspecialist. This review of research on tarantula venom should demonstrate, even to the most spider-phobic critic, the benefits that have emerged from the interaction of man and these amazing creatures.

For more information: www.elsevier.com/locate/toxicon

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