Herpitological Neurotoxins Essay, Research Paper

Herpetological Neurotoxins A herpetological neurotoxin, more commonly known as snake venom, is essentially modified saliva. It s primary functions are to slow down (or kill depending on the potency of the venom) the prey of the snake, and to help in the early stages ofdigestion. Three types of venomous snake: Opisthoglyphs, Proteroglyphs, andSolenoglyphs; and many types of snake venom: hemotoxic and neurotoxic venoms are some of those that will be discussed in this paper. The first type of venomous snake, the Opisthoglyph, contains rear fanged snakes. These rear fanged snakes have enlarged back teeth, each with a small groove that allowsvenom to flow down the tooth and into the prey. Most Opisthoglyphs are harmless,although two, the Boomslang (Dispholidus typus) and the Twig snake ( Thelotorniskirtlandi) have killed humans before. Other examples of rear fanged snakes are theMangrove ( B. dendrophilia) and the Hognose snakes (Heterodon ssp.). The second type of venomous snakes are the fixed front fanged snakes, orProteroglyphs. These snakes have small non-movable front fangs. When they bite theyhang on and ‘chew’ to envenomate the prey. Obvious examples of this type of snake arethe cobras (Naja), kraits (Bungarus), mambas (Dendroaspis), and coral (Micrurus)snakes. These are some of the deadliest snakes in the world. The third type of venomous snake is the Solenoglyph. These snakes have movablefront fangs. The fangs fold back into the mouth until they are needed. This is what makesthese snakes more dangerous to work with then any of the previously mentioned ones.They can grab on to your hand like a cobra would but they can also open their mouthalmost 180 degrees with the fangs extended straight out. This enables them to strike atany portion of your body because it is more of a ’stab’ than a bite. Examples includerattlesnakes (Crotalus), eyelash vipers (Bothriechis), gaboon vipers (Bitis), cottonmouthsand copperheads (Agkistrodon). Snake venom is made up of about 20 different enzymes. Each species usually has6-12 of these enzymes. These enzymes determine the toxicity of the snake s venom, andwhether it is hemotoxic or neurotoxic. Venoms that are referred to as hemotoxic arecalled so because they primarily affect the blood. Almost all American pitvipers fall intothis category. A hematoxic venom destroys tissue and is very painful, having beencompared to placing lit cigarettes on your skin. Neurotoxic venoms attack the nervoussystem and brain. These may cause almost no pain, but shut down the respiratory systemsand interfere with heart functions. Good examples of these types of snakes are the cobraand the beautiful coral snakes. All of the snakes mentioned so far have come from various places such as theUnited States, and Africa. While research on non-Australian snake venoms has beenintensive with several major toxin classes being characterized at the molecular level,Australian snake toxin research is in its infancy. So far only three toxin classes have beenidentified: Procoagulants ,Phospholipase A2s , and Neurotoxins. Also, few researchers inAustralia have taken up the challenge with the result that of the 35 Australian snaketoxins with complete amino acid sequences identified to date 28 of them have been by

overseas researchers(Australian Venom and Toxin Database). Most procoagulants areprothrombin activating enzymes. None have been fully characterized at the molecularlevel. Procoagulants lead to disseminated intravascular coagulation with defibrinationwith the net effect being hypo-coagulable blood. The use of these activators are well documented and they are to diagnosedysprothrombin aemias, to determine prothrombin concentration, and are excellent toolsto activate prothrombin to thrombin. They are also useful in activatingdescarboxyprothrombin. A recent use is to make FDA approved fibrin film for surgicalprocedures, Taipan activator is used to activate recombinant prethrombin to alphathrombin. An extremely interesting, and useful, aspect of venom components fromAustralian elapids is in the characterization of lupus using the procoagulant textarin fromthe eastern brown snake (Pseudonaja textilis). Lupus anticoagulants (LA) are secretoryIgA, or serum IgG and IgM, immunoglobins which characteristically interfere withphospholipid dependent in vitro coagulation tests. A sensitive and rather specificconfirmatory test has been developed using textarin in conjunction with ecarin from thesaw-scaled viper (Echis carinatus). In the presence of LA the activation time ofprothrombin by textarin is prolonged but that of ecarin is unaffected, thus the test consistsof a useful comparative ratio between textarin/ecarin (Pubmed online). Snake venoms, no matter the type, are potentially dangerous to humans. Medicalemergencies are created when humans are envenomed. Most venoms are different butmany have common toxins. Most venoms contain either neurotoxins, hemorrhagic toxinsor both. In the past toxicity was measured by injecting test animals (mainly mice) withvenom; however, many different types of animals have been used. Mice were theuniversally accepted test animal and comparative toxicity was expressed as an LD50(lethal dose that kills 50% of test animals). The LD50 is usually determined by injectingthe crude venom (by various routes) into mice at varying concentrations. Today, thesetypes of experiments are not generally performed because of animal welfare concerns,however they have been valuable in understanding the toxicity of snake venom. Thereare other specific tests that look at the effect of single toxins. These can be clotting assaysto measure the effect of coagulants, nerve-muscle preparations to measure neurotoxicactivity, phospholipase and phosphodiesterase assays which measure these respectiveagents in the venoms. Even muscle or myoblast preparations to measure the myotoxicactivity of venoms have been used. These tests are very useful to investigate the relativetoxicity of the venoms. No matter the type of snake, or the type of venom, when bitten a person shouldseek immediate medical help. If bitten by a very venomous snake, antivenin will usuallybe given to the patient. Most types of snake-venom poisoning can be treated with the useof antivenins, serums that neutralize specific venoms. Because some persons may have apotentially fatal allergic reaction to these serums, however, it is generally advised thatantivenins be administered only by medically trained personnel. Antivenins aredeveloped by injecting small amounts of snake venom into animals (usually horses) untilthe animals become immune. The antivenin is then prepared from the animals’ blood(World Book Encyclopedia).