Aug 13, 2025
Bead expulsion
- Anastasiya Moiseyenko1
- 1California Institute of Technology
Protocol Citation: Anastasiya Moiseyenko 2025. Bead expulsion. protocols.io https://dx.doi.org/10.17504/protocols.io.n92ld6zn7g5b/v1
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it's working
Created: August 01, 2025
Last Modified: August 13, 2025
Protocol Integer ID: 223859
Keywords: ASAPCRN, bead expulsion, bead assay, bead expel, rectal function, parkinson's disease, bead expulsion, measures mouse rectal function, measures mouse, bead, assay, glass bead, inserted glass bead, animal
Funders Acknowledgements:
Heritage Medical Research Institute
Aligning Science Across Parkinson’s
Grant ID: ASAP-020495
Aligning Science Across Parkinson’s
Grant ID: ASAP-000375
Abstract
This assay measures mouse rectal function using a rectally-inserted glass bead. Animals are timed for how quickly they are able to expel the bead.
Materials
Heating pad
Glass beads - 1.5-2mm size (autoclaved)
Metal straight gavage tubes
- Marked at 2cm with sharpie
Vaseline
Small weigh boats for holding beads
Clean empty standard mouse cages
Sticky notes
Optional - second researcher to watch for bead expulsion while the other performs insertions
Troubleshooting
Set up
Habituate animals to behavior testing room for 1hr prior to start of assay.
Clean and lay out heating pad - set to low. Clean isoflurane box and nose cone and set up on top of the heating pad.
Set up beads in weigh boats, vaseline, gavage tubes. Mark 2cm on gavage tube.
Set up isoflurane machine according to institution guidelines.
Label empty, bedding-free mouse cages with animal numbers.
Procedure
Place mouse into isoflurane chamber
Wait for mouse to be anesthetized, looking for about 1 breath/second and no movement (can tilt box sideways to make mouse roll)
Once fully asleep, transfer animal to nose cone facing belly-down. Check for response using a firm paw press.
Optional - Put eye ointment on mouse eyes to prevent drying (if learning/working slowly and mouse will be unconscious for more than ~2 min)
Dip gavage tube in vaseline
Lift up mouse tail and move away fur from anus while rubbing in vaseline
Clean out any feces in rectum: Gently insert gavage tube, moving very slowly, up to 2cm mark.
Angle of rectum goes down at first then levels out - try to follow curve with tube
Slowly take out tube, repeat if there are any feces
Once tube goes in easily and there are no more feces, proceed to inserting bead.
Pick up a bead with fingers and gently press it onto anal opening, holding it there until feel it has gone in.
Use gavage tube to push in the bead further, up to the 2cm mark, and gently remove.
Before taking the tube out, check that can feel the bead in there by making small movement up and down/side to side with tube to try to feel glass scratching on metal tube.
Also check that the bead is in far enough by squeezing sides of mouse rectum (on the rump) to see if you can feel the bead (should not be able to if it is placed correctly)
Take animal off nose cone and let wake up for ~1 min on heating pad
Wipe down and disinfect all equipment in between animals.
Check for responsiveness by turning onto side - if the animal is able to right itself, then transfer to individual clean cage. Record the start time.
Move cage to a well-light table top to observe for bead expulsion. Record time (to the minute) of when the animal has expelled the bead, with a maximum time of 60 minutes.
After the bead has been expelled, animal can be returned to the home cage.
Protocol references
1. Camilleri, Michael, and David R. Linden. "Measurement of gastrointestinal and colonic motor functions in humans and animals." Cellular and molecular gastroenterology and hepatology 2.4 (2016): 412-428.