Forth those of you who do not know me, I want to share with you one of my favorite research subjects, a particular type of invertebrates (more precisely, flatworms) generically called planarians. Planarians are non-parasitic and are widely distributed in nature; they can be found in the ocean or freshwater. There are terrestrial species as well. In my laboratory, we use three species of the freshwater type (Figure below; the worms shown are close to 1 cm long).
These flatworms possess a very peculiar characteristic, an impressive capacity for regeneration. All organisms possess some degree of regenerative capacities. For example, if you get a small cut (while shaving, for example), if you are healthy, with time, your skin will heal, leaving a scar, or even recover completely if the cut is small enough. On the other hand, when a person has brain damage due to an accident or illness, the healing process is much more difficult or even impossible, as the nervous system cells in vertebrates display minimal regeneration capacities. In contrast, if you cut a planarian into two pieces, first, you will not kill it. Second, each part will develop into a complete worm half the original size in about a week (give or take, depending on the species).
Remarkably, the tail segment will regenerate a complete nervous system, including a fully functional brain!
It gets better; if you cut one of them into 100 or even more than 200 pieces (the “record” seems to be 279 pieces, but take that with a grain of salt…), each tiny piece will eventually form a tiny complete worm, which will grow to its normal size (up to ¾ inches, again, depending on the species) if food is readily available. Based on these facts, it is no surprise that, traditionally, flatworms have been used as an animal model in developmental biology and regeneration research. Can you imagine all the benefits that we could get if we learn the secrets of regeneration, particularly of the nervous system? Think about the people with spinal cord injury or brain damage. Research on this subject has the potential to result in treatment strategies for these and maybe other related conditions.
Part of my research focuses on studying behavioral pharmacology and neuropharmacology, using freshwater planarians as a model organism. Doing research with planarians has many distinct advantages. Working with them is technically easy and relatively inexpensive; we do not need complex incubators or big tanks to keep them. A big plus is that they do not bite or can harm you in any way! Also, these organisms provide an excellent animal model for when experiments using vertebrate animals are ethically, experimentally, or financially impractical.
Planarians also use virtually every major neurotransmitter found in vertebrates (and some that vertebrates do not have), including humans (neurotransmitters are chemicals that control many of the functions of your nervous system and mine). Planarians are, therefore, becoming increasingly popular in neuropharmacology research, as they exhibit a variety of responses when exposed to psychoactive substances.
Interestingly, these worms display many behavioral responses when exposed to the same type of drugs that are abused by humans. For example, if you treat them with nicotine, one of the most addictive and abused drugs, they will slow down (think of a human relaxing when smoking). They can even display seizure-like behaviors when exposed to high nicotine amounts (nicotine can be toxic to humans, too). Even more interestingly, if you give them nicotine for a certain period of time and then take it away, they behave as if they were addicted to nicotine! They squirm, twitch, and move faster, behaviors that, in humans, would be interpreted as “nervousness”.
In summary, neuropharmacology research using planarians is exciting and shows a lot of promise, as it can contribute to fundamental research in unexpected ways.
IF YOU WANT TO KNOW MORE
Pagán OR (2017) Planaria: an animal model that integrates development, regeneration and pharmacology. Int J Dev Biol. 61(8-9):519-529.
The paper above can be downloaded for free from HERE. If you cannot, please send me a message, and I’ll happily send you the pdf.
Pagán OR (2014) The First Brain: The Neuroscience of Planarians. Oxford University Press.
DO NOT TRY TO BUY THIS BOOK; I’M WORKING ON A SECOND EDITION AS WE “SPEAK” (:-).
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