Resume
Summary Toxins in Amphibians and Reptiles - VUB
- Cours
- Établissement
Summary of all lectures of the course Toxins in Amphibians and Reptiles given by prof. Kim Roelants at the VUB.
[Montrer plus]
Vendeur
S'abonner
lunawillems1
Avis reçus
Aperçu du contenu
TOXINS IN AMPHIBIANS AND REPTILESCHAPTER 1: GENERAL INTRODUCTION AND OVERVIEW OF POSIONOUS / VENOMOUS TAXA
• The study of animal toxins is beneficial for a number of biological and applied science fields…
→ Animal physiology, biochemistry, cellular biology, ecology, ethology, evolutionary biology, immunology,
molecular genetics, pharmacology, medicine, taxonomy, organic chemistry…
→ … and knowledge of these fields = possible to study animal toxins
• Example: 3D structure of Erabutoxin b
→ A neurotoxin produced by the sea snake Laticauda semifasciata (the black-banded
sea krait)
• Most toxins are proteins → genetic material codes for a toxin
1.1. SOME TERMINOLOGY TO START WITH
1.1.1. WHAT IS A TOXIN?
• Theophrastus of Hohenheim (Paracelsus) (1493-1541)
→ “All things are poison and nothing is without poison. Only the dose makes a thing not to be a poison.”
▪ Eg. water can be toxic
▪ Biological context: low dose and still a hard effect (eg. lethal, but a slight pain or an itch as well!)
• Wikipedia:
→ “A natural occurring organic poison produced by metabolic activities of living cells or organisms.”
→ So, Wikipedia shifts the problem → what is a poison? → Wikipedia:
▪ “Any chemical substance that is harmful or lethal to living organisms.”
→ The Wikipedia definitions emphasize the potential negative effect of a substance
→ These definitions differ from what is currently used in scientific literature
→ Eg. because what is the difference between a venom and a poison?
• Ecological definition:
→ “A molecule used by one organism to cause a biochemical effect in another in function of predation,
defense or competition.”
▪ Eg. competition: the cane toad in Australia: their tadpoles release toxins that inhibit growth of
additional toads of the same species! = intraspecific competition to ensure they are not too
abundant
▪ Eg. competition: platypus: venom for intraspecific competition
→ The prof has helped invent this definition!
→ This definition emphasizes the functional value of a molecule (so, why the molecule is used)
→ It doesn’t say anything about how harmful it is or what the negative effects are
• Revised definition:
→ A classification based on type of toxin
→ Biological toxin (biotoxin): a substance produced by a living organism that is capable of causing dose-
dependent pathophysiological injury to itself (suicide toxin) or another living organism
→ Environmental toxin: a naturally occurring substance in the environment that is not produced by an
organism but it capable of causing dose-dependent pathophysiological injury to a living organism
▪ Eg. mercury, arsenic, lead
→ Anthropogenic toxin (a toxicant): a substance produced by humans that does not otherwise occur in
the environment, which is capable of causing dose-dependent pathophysiological injury to a living
organism
▪ Eg. DDT, dioxin, PCBs
• On exam: you don’t have to give a the definition because you could write ‘a whole page about it’
• Just know that it is not that simple !
1
,1.1.2. WHAT IS A BIOACTIVE MOLECULE?
• A term commonly used in the field of pharmacology
• “A molecule with a biological effect on living matter (cells, tissues or organisms)”
→ Eg. lytic effect, increase of blood pressure…
→ The effect is not necessary toxic related
• Note: this definition does not specify whether this effect is beneficial or adverse
→ Toxins (-) are bioactive molecules, but drugs are too (+)
• Bioactivity mostly used in terms of a desired effect of a potential drug candidate → mostly used by scientists
• Scientist are interested in toxins:
→ Eg. a toxin that lowers the blood pressure = bad for certain animal, but some people need it
1.1.3. TOXICOLOGY vs. TOXINOLOGY
Toxicology:
• The scientific discipline dealing with the adverse effects of chemicals on living organisms, communities,
ecosystems. It is the study of symptoms, mechanisms, treatments and detection of poisoning
• Eg. release of mercury in a lake
Toxinology:
• “The scientific discipline dealing with microbial, plant and animal venoms, poisons and toxins”
• “The science of toxic substances produced by or accumulated in living organisms, their properties, and their
biological significance for the organisms involved”
• So: the study of biological toxins and all of their aspects (pathophysiol., treatment, ecology, evolution)
• Eg. snake envenomation (vergiftiging)
Snake bites
• Are considered a tropical disease (World Health Organization)
• Toxino: examine the snake toxin itself
• Toxico: it has an effect on the whole human population
1.1.4. VENOM vs. POISON
Venom
• A toxin or mixture thereof used by an animal and injected into the circulatory system (eg. blood stream or
lymphatic system) of another animal, often by means of a specialized venom delivery structure (eg. fangs,
beaks, spines, stinger…) + often causing a wound
• They may have a predatory and/or defense function
• Derived words: venomous, envenomation, venom glands
• Venom and venomous only apply to animals
• Eg. some protist single cells use a harpoon to paralyze other cells (even though they have no CNS!)
Poison
• A toxin or mixture thereof that is passively administered through epithelia (eg. skin, gills, lungs, intestines) by
absorption, ingestion or inhaling
• Poisons in biology mostly have a defensive function
• Derived words: poisonous, poisoning, poison glands
• Almost all amphibians are poisonous (producing toxins in their skin) → must be ingested
• Plants are called poisonous, not venomous, even if they use spines to inject the toxins!
→ Eg. you have to touch them, so it is passive ↔ but what with carnivore plants?
2
, • So phylogenetically, poison is wider than venom because plants are incorporated
But: sea urchin = venomous, although you have to step on it = passive → so: venom/poison is hard to determine
→ there is no clear definition, it is more subjective
Venom is often more effective than poison: it has a faster response
Toxunogen
• A toxic substance (comprised of one or more toxins) causing dose-dependent physiological injury tat is
actively transferred via a delivery mechanism from one organism to the external surface of another organism
without mechanical injury
• Eg. secretions that are projected or sprayed to fend off an attacking predator
• They “launch” their toxin
EXAMPLES: VENOMOUS OR POISONOUS
1. Irukandji jellyfish: venomous → they sting other animals and
make a small injury
→ Nematocyst ; via mechanical triggering
2. Sea apple (echinoderm): poisonous → they are advertising
their toxicity by bright colors: “don’t eat me”
3. Flower urchin: venomous → special sea urchin, it has claws: it
will grab you and inject its toxin
4. Blue-ringed octopus:
→ venomous → lethal bite via a beak (< chitine, so a hard
bite) = neurotoxin
→ poisonous → it tissue is toxic via symbiotic bacteria that live
in there
5. Bulldog ant: venomous → stinger like a wasp (so not a beak) ; sit
on flowers and grab bees
→ Primitive! Most ants lost their toxicity
6. Pyrenean brook salamander: poisonous
7. Spanish rib salamander: poisonous (same glands as previous one
in skin) + venomous (!) → uses its ribs to attack the predator via a mechanical injury
→ When under attack, they’ll perforate their own skin (will regrow) → toxin secreted
through the spines
8. Fire salamander: toxunogen ? → spray toxins in face of predator ; poisonous (bright
colors)
1.2. POISON/VENOM IN THE ANIMAL KINGDOM
• Poison and venom systems are widespread in Animalia/Metazoans
and occur in modern representatives of the major animal lineages
• 3 major names: Metazoa, Bilateria, Deuterostomia
• Metazoa = all animals having the body composed of cells
differentiated into tissues and organs and usually a digestive cavity
lined with specialized cells
• Red = venom ; purple = poison
3
, 1.2.1. PORIFERA
• The sponges = primitive lineage → although already toxins present → not per se lethal
→ Animals limited in their tissue differentiation and
development
• Secreting molecules that can be irritating + can cause an injury
→ Needle-like strands of spicules containing irritating toxins
• So poisonous because passive
• But venomous as well because sometimes injury
1.2.2. CNIDARIANS
• Anthozoa: corals and sea anemones
• Medusozoa: jellyfish
• All of them venomous
• They all use the same toxin delivery system at
subcellular level (although a very diverse body plan)
• Fish can be paralyzed within seconds (sometimes
humans as well)
• Corals = less dangerous because sessile
• Nematocyste (cnidocyte)
→ Specialized cells that ‘fire’ venom
→ Organelle (nematocyst) into prey when triggered
→ Sticky
1.2.3. PLATYHELMINTES
• Flatworms
• Planicera multitentaculata (picture): the neurotoxin Tetradotoxin (TTX) has been
detected in various tissues, including eggs: defense function?
• ‘Planocerid sp.1’ uses TTX to immobilize gastropod prey by enveloping the victim and
secreting TTX (hunting)
→ A poison for predation! So NOT always as defense!!! Unique!
1.2.4. NEMERTEA
• Ribbon worms (snoerwormen)
• Carnivorous nemerteans use a proboscis to entangle or stab prey
→ In some species, like Paranemertes peregrina, this structure secretes paralytic toxins, incl. TTX
→ Small claws sometimes on proboscis
→ Paralyze prey
INTERMEZZO: toxins evolved multiple times in evolution
➔ Almost all marine organisms use same toxin: TTX → via a symbiosis with bacteria that produce the TTX
➔ Sometimes TTX in amphibians as well
1.2.5. MOLLUSCA
Gastropoda
• Different delivery modi known
• Most cone snails (genus Conus) use a venomous harpoon to capture and paralyze prey
→ Often used as painkilling drugs in pharmacology (paralyzing nervous system)
• Some Conus species however, engulf their fish prey and release a ‘nirvana cabal’ (a mixture of toxins)
→ Several are highly potent insulin analogs → rapidly depleting sugar levels in the prey’s blood
4
Les avantages d'acheter des résumés chez Stuvia:
Qualité garantie par les avis des clients
Les clients de Stuvia ont évalués plus de 700 000 résumés. C'est comme ça que vous savez que vous achetez les meilleurs documents.
L’achat facile et rapide
Vous pouvez payer rapidement avec iDeal, carte de crédit ou Stuvia-crédit pour les résumés. Il n'y a pas d'adhésion nécessaire.
Focus sur l’essentiel
Vos camarades écrivent eux-mêmes les notes d’étude, c’est pourquoi les documents sont toujours fiables et à jour. Cela garantit que vous arrivez rapidement au coeur du matériel.
Foire aux questions
Qu'est-ce que j'obtiens en achetant ce document ?
Vous obtenez un PDF, disponible immédiatement après votre achat. Le document acheté est accessible à tout moment, n'importe où et indéfiniment via votre profil.
Garantie de remboursement : comment ça marche ?
Notre garantie de satisfaction garantit que vous trouverez toujours un document d'étude qui vous convient. Vous remplissez un formulaire et notre équipe du service client s'occupe du reste.
Auprès de qui est-ce que j'achète ce résumé ?
Stuvia est une place de marché. Alors, vous n'achetez donc pas ce document chez nous, mais auprès du vendeur lunawillems1. Stuvia facilite les paiements au vendeur.
Est-ce que j'aurai un abonnement?
Non, vous n'achetez ce résumé que pour 9,79 €. Vous n'êtes lié à rien après votre achat.
Peut-on faire confiance à Stuvia ?
4.6 étoiles sur Google & Trustpilot (+1000 avis)
60904 résumés ont été vendus ces 30 derniers jours
Fondée en 2010, la référence pour acheter des résumés depuis déjà 14 ans