Some Biology

Toxicology testing is seldom done in humans. We'll talk about the consequences of that in later modules. While this course treats the human health effects, almost all the toxicology testing we will study was done in the non-human part of the biological world. That world contains millions of different types of critters. It's easy to get lost or intimidated by the names of these critters in toxicology literature. This sub-module will discuss "where the names come from." But first, here's some basic information about biology (the links from this page are optional, but if they are totally unfamiliar to you, its probably worth the time to glance at them)[Use the BACK button of your browser when you are done.] What is life?

Being bewildered by the plethora of names of life-forms is not new to science. In the 18th century Linnaeus authored a system of classification to sort animals and plants into groups with similar characteristics. An easy way to remember the hierarchical classification system:

King Philip Came Over From Germany Soused.

Where the first letters of that sentence stand for the classification system: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Look at the top of this page to see how the panther is classified. Panther.

Today we recognize five kingdoms. Linnaeus was happy with two kingdoms, plants (plantae) and animals (animalia), but then he didn't have a good microscope. The other three kingdoms are Fungi, Monera (bacteria*), and Protista (mostly one-celled animals and a variety of miscellaneous very small critters and few big ones. If you want some more info on Protists .) Phylum (plural phyla) are the major divisions within the animal kingdom: Chordata (which includes vertebrates), arthropods (insects and such), echinoderms (starfish), and and so on. Here's a site with all the phyla, great and small. From the drop-down menu you can move to one of the 23 phyla listed. You might find the page fun, but most of our toxicology involves the phylum Chordata, especially the sub-phylum Vertebrata. (The authors of the site helps our humility, or awe of nature, by listing mammals at the bottom of the 23 phyla, and last of the five classes of vertebrate.)

*Today "bacteria" remains the common term for prokaryotes(microorganisms without a nucleus), but specialists often divide that into two classifications: bacteria and "archaea."

You may have noted in the pages above the authors mention sub-categories such as "suborders." Yup. And there's sub phyla and super-classes and lots of other bus stops in classification schemes for the taxonomic aficionados, but the seven main one are adequate for everyone else. At the fine end of the system are genus and species, such as Panthera pardus in the panther example. In a sense, "species" is the only biologically real part of the classification system, all the rest is paper. For higher animals, different species don't interbreed and that is the key to their definition. [Hybrids challenge the definition, or even existence, of species, but let's not get sidetracked] Genus (plural, genera) is a group of closely related species. The formal (AKA [short for "also known as"] Linnaen or binomial) name for an animal consists of the genera name starting with a capital letter and the species starting with a lower case. For example, Canis lupus is the wolf, and Canis familiaris is Fido. The formal name is in italics. Usually, after the first time the formal name is used, the genera is abbreviated by it first letter, so we have C. lupus and C. familiaris. The genera name is important, for example much biological research is done with Drosophila melanogaster, but little with Thamnophis melanogaster. D. melanogaster is a fruit fly which was the workhorse of genetic research for many years.

How would you find out what kind of critter T. melanogaster is? Probably the fastest way is to do a web search. I use Raging Search, but there are lots of others. We'll talk more about that, but for now, go to your favorite search engine and in the box type "Thamnophis melanogaster" with the quotation marks, if your search engine will allow that. Hit search and you'll get hits. Poke through them and you find out what T. melanogaster is. (Some of the hits are long web pages. A trick there is copy "Thamnophis" from this page before you search, then when you open one of the results of your search and find it very long, use your edit button on your browser, then find from the edit menu, paste in the "thamnophis," then let the browser find that entry on the page.) So what is T. melanogaster Which is a long way from the fruit fly. A fact that I am supposed to be ashamed of, but am not, is the use of Wikipedia. http://en.wikipedia.org/wiki/Main_Page. It is very handy.

So why all the strange species and names in toxicology and experimental biology? Experimenters often confine themselves to a few species, so they often just use the species name and forget the genera. They are careless about italics. For example, you may read that the experiment was done with "xenopus oocytes." Xenopus, which you can buy from here (and lots of other places), is a frog that has a particularly large egg (that what "oocyte" means). So long ago, toxicologists and reproductive biologists were looking for a sturdy species that gave large eggs. Someone started with Xenopus, published the results, and through the years thousands and thousands of experiments were done with Xenopus. (You may have noted that Xenopus is a genera name, so there are many Xenopus species.) It became a standard for certain types of experiment. Likewise the cat (sorry, Shasha and Rho-C) became a standard for certain types neurological experiments, the beagle dog (sorry, Snoopy) for certain drugs, and lots of species unknown to most of us, for other types of experiments. (I worked with a toxicologist who was using earthworm eggs, exclusively - built his career around them.) Although why the certain species is used might be obscured in experimental biology history, once a species becomes a standard, experimenters need a good reason to start on a new species.

Fortunately for cat and dog lovers, most toxicology work is done with rats and mice. Go to this supplier Charles River, then click on the + by Animal Type,then and check on first rats and then mice, you might glance at the other popular species. Within the rat and mouse categories, just scroll through the list to get a feel for the many strains of rodents. While in the rat section, note the Fisher 344 and Sprage-Dawley, these are the workhorses (workrodents?) of tox testing. A strain is the result of purposeful breeding; the "breeds" of domestic animal are strains. The beagle and the rotweiler are different strains of C. familiaris. Although strains are the same species, the effect of a chemical might be different. For example you would expect a wider range of effects in an out-bred strain than an inbred strain. So, most toxicology laboratory testing will specify the strain of animal, but having done that, the species might not be mentioned. Lastly, there are some highly specialized strains of lab animals that have certain genetic characteristics, such as a propensity toward obesity, high blood pressure, anxiety, or whatever. While looking at the mice section, read about "nude mice" and see learn what they lack (make a note of what organ they are missing) and what kinds of research they are useful for. (There are many types of nude mouse, but you'll see the most common organ and issue.)

In summary, toxicology research uses a variety of animal models. It is generally necessary to state the species and stain of test animal and some caution is needed when comparing test results for different strains of animal. Later we'll explore the notion that species that are closely related photogenically are more likely to have the same reactions to chemicals. Internet searching is often the quickest way to decipher what type of animal has been described.

Module01 Index