Welcome to tadpoles.org.uk

Tadpoles and using them to understand brains


Meet the scientists and explore the lab


Bristol University Xenopus Neurobiology

We use very young tadpoles of the South African Clawed toad or frog (Xenopus) to study how  brains work. Our research is supported by grants from the  Biotechnology  and Biological Sciences Research Council  (BBSRC). Previously  the Wellcome Trust supported us. Here are some of the scientists who have worked in our lab recently.Bottled-scientists-all-P1010033f

The Laboratory


Bristol University Life Sciences Building

Our laboratory is in the Life Sciences Building up St Michael’s Hill from the centre of Bristol. It was opened by Sir David Attenborough on 6th October 2014.

The Xenopus Tadpole lab is on the ground floor of the shiny, aluminium-clad lab wing (the arrow shows one of our windows).Life-Sciences-Building-P1000994arrow-f

The central atrium has offices on the right and labs on the left behind all the glass meeting spaces.Atrium-P1000993f

Our main lab has places: to raise tadpoles at different temperatures; to make instruments for dissection; to take videos of tadpole behaviour;  to prepare and mount brains on microscope slides; to wash glassware. There are also three stations to record electrical activity in tadpole nervous systems. On the right are doors to smaller rooms used for recording and microscopy.Laboratory-P1010031f

The Scientists

Four people work routinely in the lab and undergraduate students do projects here during term-time:Bottled-scientists-P1000998f

The head of the lab is Dr Steve Soffe who is a senior lecturer in Zoology. Here he is using a surgeon’s miscroscope (200x magnification) to place electrodes on the motor nerves in an immobilised tadpole. These record nerve impulses which show when the tadpole is swimming .Steve-Soffe-P1010001f

Dr Alan Roberts has been working on tadpoles with Dr Soffe since 1979. He is an Emeritus professor which means he works but is not paid! He uses this compound microscope with up to 1000x magnification to see the brain nerve cells filled with dye during electrical recording.Alan-Roberts-P1010003f

Dr Stella Koutsikou came originally from Greece. Before she came to our lab 2 years ago she worked on how rats respond to sensory stimulation. She is supported by our BBSRC research grant. She makes electrical recordings from nerve cells in the tadpole brain using the microscope (500x) and equipment shown here.Stella-Koutsikou-P1010027f

After making recordings she mounts the fixed tadpole brains on a slide. Then we can see the nerve cells which she filled  with dye during recordings.Stella-Koutsikou-histology-P1010029f

Mark Olenik  came originally from Kyrgyzstan but his home is now  in Hamburg. He is a post-graduate student supported by the Wellcome Trust . He uses computer models to study how networks of nerve cells allow tadpoles to make rhythmic movements.Mark-Olenik-P1000997f

During University term time in the winter final year undergraduate students do short research projects in the lab .

The Frogs and tadpoles

The tadpoles we study are produced by  a small colony of adult Xenopus laevis  looked after by the University Animal Services Unit. These are the tanks where the adult toads live in a carefully controlled environment:Holding-tanks-IMG_5137f

Each week mating is induced by injecting a pair of adults with a hormone in late afternoon. If all goes well, the pair are clasped and eggs (about 1 mm across) have been laid by next morning.


Mating Clawed Toads or Frogs with eggs

The female is large and the male clasps her around the waist. He can then fertilise the eggs as they are laid . The eggs  stick to the sides or bottom of the tank.

We collect the eggs and take them to the lab to grow into tadpoles. Find out more by going to the “A Tadpole Laboratory” page.


Tadpole swims when touched at *

The details of swimming movements which hatchling Xenopus tadpoles make in response to touch with a fine hair  have been studied by making high speed videos at 200 fps. In these examples touch on the left (*) leads to a bend to the right followed by swimming. Waves of bending travel from the head to tail (at ~ 14 cm per second) and increase in amplitude as they travel along the body. They move the tadpole in the direction shown by the arrows. Swimming speeds at ~ 20 oC range from 4 to 6 cm per second.hatchling tadpole swims when touched at *

Kahn J.A., Roberts A. & Kashin S. (1982) The neuromuscular basis of swimming movements in embryos of the amphibian Xenopus laevis. J. exp. Biol.  99, 175‑184. http://jeb.biologists.org/cgi/reprint/99/1/175

Adult South Africal Clawed toad Xenopus laevis


         Xenopus laevis

What Tadpoles Look Like

Tadpoles can start swimming spontaneously or when they are stimulated but it is just as important that they can stop. This normally happens when their head and cement gland bumps into the surface of the water or some other solid tadpoles swimmingobject like a plant or the side of a dish. This kind of stimulus and the tension in the mucus strand when the tadpole is hanging attached have an inhibitory effect on the tadpole. While hanging, it never moves spontaneously and is much less responsive to stimulation. This ability to keep still may make it more difficult for predators to detect and eat tadpoles. 

Types of Neurons

There are different types of neurons in a nervous system and they are named depending on their function.


Interneuron from Xenopus laevis tadpole

Broadly there are 3 main types:

  1. Sensory neurons
  2. Motor neurons
  3. Interneurons 





Flexion behaviour of hatchling tadpole in response to skin stimulation (represented by arrow).

When the skin of Xenopus laevis hatchling is touched, sensory neurons are activated, passing on exitation to sensory pathway neurons (interneurons) in the spinal cord, which in turn excite motor neurons, causing flexion behaviour

For more info on research into flexion behaviour click here. 

Synaptic transmission (blank diagram)

pencil22small_foka.tkPrint and fill in the blank diagram with the key steps in the process of synaptic transmission:



Resting potential and action potential confusion!



The terms resting potential and action potential can be confusing, as they seem to suggest that one is an active process and the other not.


Action potentials are actually produced by a passive process- sodium ions diffusing into the axon, causing depolarisation. 

Resting potentials are generated by an active process, which needs ATP. The sodium-potassium pump carries out active transport of ions in and out of the axon to generate a potential difference across the cell and a voltage of -60/70 mV inside the axon.

So even though the axon is said to be at “rest”, an active process involving energy in the form of ATP is actually going on. And even though the action potential sounds like it needs energy, it is actually a passive process.

Make sure you are clear on this!

Axon, membrane or axon membrane?!



Some exam boards prefer you to mention simply the “axon”, others just the “membrane”, or the “membrane of the axon”. 


When we are talking about a difference in charge over an area, we always refer to what area that is- for example a potential difference over the axon membrane. 

Some exam boards will prefer you say that the “membrane” or “axon membrane is depolarised”…but others will be happy with just the “axon is depolarised”

Check what is preferred by your exam board and incorporate into your notes links below:





Exam Board Links

pencil22small_foka.tkClick on the links below to access the specifications for listed exam boards:







Toad spawn

Toad eggs are the same size as Frog eggs but are laid in a string, often among weeds in the pond. The string can be more than 1 meter long and contain a double row of eggs. Here is a photo of a small piece from a pond in Hampshire.

A small piece of toad spawn from a pond in Hampshire.

American Bullfrog

Below is an American Bullfrog. The Latin name of this frog is Lithobates catesbeianus. It is sometimes also called Rana catesbeianus. 

American_Bullfrog_(Rana_catesbeiana)_-_Algonquin_Provincial_Park_Ontario_By Ryan Hodnett Own work

Click here for more information on the American Bullfrog from the ARKive website.

Media credits: American Bullfrog-Ryan Hodnett