Intestinal Swiss Rolls

• Materials and supplies
• Preparations
• Procedure

Materials and supplies

• CO euthanizing chamber
• PBS
• 10% neutral buffered formalin (Expredia Cat. #5725)
• 50-100 ml specimen containers (small cups)
• Petri dish with lid or 2x reservoirs
• 3 ml syringes
• Gavage needle (preferably with ball end)
• Surgical scissors
• Fine curved forceps
• Wooden toothpicks
• Tissue cassette
• Ice bucket
• Paper towels
• Ruler

Preparations

• Chill PBS and 10% neutral buffered formalin
• Fill specimen containers with formalin and keep on ice
• Rule of thumb is 20x fixative volume to sample volume
• 50 ml formalin per 5-10 cm intestinal sample
• Mark out 5 cm (or desired length of tissue) on a piece of paper

• Place chilled PBS in petri dish or reservoir for flushing, and have one empty to flush into
• Attach gavage needle to syringe and fill with c. 3 ml of PBS
• Have paper towels ready to dissect mice and roll tissue on

Procedure

1. Euthanize mouse and dissect out the most distal 5 cm of ileum
• Cut one end of the ileum (I do most distal end first, right next to cecum) and gently peel the mesentery membrane away from the intestine as best as possible (I find it easier to do this with my fingers than with forceps)
• Then cut the other (proximal) end of ileum and remove from the abdomen
• Trim off proximal end to 5 cm by aligning to paper marker
• Keep track of which end is which
• Can cut longer sections here if needed but 5 cm allows for 3 samples to fit in one cassette
2. Holding one end of the ileum (I always hold the proximal end), place the gavage in the end of the intestine and flush through 1-3 ml pre-chilled PBS
• Enough PBS so that luminal debris is removed – may need to flush through more or gently manipulate the tissue if the debris gets stuck
• Flush in to waste reservoir
3. After removing as much luminal debris as possible, flush through 1 ml of pre-chilled formalin
4. Lay the intestine down on a paper towel
• Again, keep track of which end is which (I lay proximal end closest to me)
• Make sure intestine is straight and not twisted and the side that attached to the mesentery is facing upwards
• To get the intestine flat and push out any remining debris dip a finger in PBS and brush it down the length of the intestine
5. Holding on to end closest to you with forceps cut along the mesenteric line
6. Gently open the intestine using forceps so it lays flat on the paper towel with the luminal side facing up. Pick out any remaining debris if necessary
7. Place a toothpick at the end of the intestine that’s closest to you (proximal end) and roll the toothpick away from you so the intestine rolls up around the toothpick
• You can dampen the toothpick so the intestine doesn’t stick to it too much, but don’t make it too wet or the tissue will slide around while rolling
• You can also dampen the paper towel slightly if it is sticking too much
8. Once completely rolled up, place one end of the toothpick onto the tissue cassette and slowly push the Swiss rolled tissue down the toothpick into the cassette.
• Be careful here as the middle of the Swiss roll can stick to the toothpick causing it to unravel as you push it. Gently squeezing the tissue back into a tight roll on the toothpick with your fingers can help prevent this
9. Close the cassette and place in the chilled formalin in the specimen container
• Up to 3 samples can fit in one cassette
• For 3x 5 cm samples fix in a minimum of 100 ml formalin
10. Incubate at 4 °C for 18-24 hours – no longer than 24 hours