Colonoscopic Guided Pinch Biopsy in a Mouse Model: A Technique to Visualize and Extract Tissue Samples from Mouse Colon

Under pathological conditions, colonoscopy enables visualization of the colon and tissue extraction by pinch biopsy for detailed analysis of inflammatory wounds.

To perform colonoscopic-guided pinch biopsy in a mouse, begin with a biopsy assembly. The assembly contains a connector unit, an endoscope sheath with a pre-inserted colonoscope of optimal diameter. The colonoscope is connected to a light source, a video source, a gas port, and an instrument port for biopsy forceps.

Next, prepare an anesthetized mouse in the prone position on the colonoscopy platform. Pull the tail upward and use a gavage needle to infuse the anus with a suitable buffer to flush any fecal matter. Then, insert the colonoscope into the anus and advance it into the rectum. Continue moving the colonoscope further toward the colon while pumping gas to keep the colon inflated.

Next, steer the forceps out of the instrument port and open the jaws. Rotate the forceps at a right angle to induce a wound of optimal depth. Wounds that are too shallow or too deep result in a superficial wound or colon perforation, respectively. Thereafter, using biopsy forceps, pinch off the colon tissue. The extracted tissue and the induced wound can be further analyzed to understand the pathophysiology.

Before beginning the procedure, insert a 1.9 millimeter rigid bore endoscope into an endoscope sheath, and attach the assembled endoscope to the light source and video imaging device per the manufacturer's instructions. Use the provided tubing to attach the air pump to the gas valve on the left side of the sheath, next to the working channel.

Ensure that the working channel is in the open position, and insert 3 Fr biopsy forceps through the working channel. Advance the forceps to the end of the sheath without protruding out of the sheath.

Next, place the anesthetized mouse onto an endoscopic staging platform on its ventral side, and confirm the appropriate level of sedation by lack of response to pedal reflex. After applying eye ointment, fill a 3-milliliter syringe with an attached rat gavage needle with room temperature PBS, and insert the needle approximately 1 centimeter into the mouse's anus. Gently infuse with PBS until the fecal material has been cleared. Several fecal pellets should exit the mouse along with the PBS that was infused.

Insert the assembled endoscope 0.5 centimeters into the anus, and advance the biopsy forceps into the cleared lumen of the rectum until the full 'jaws' of the forceps are beyond the end of the sheath. Turn the forceps 90 degrees so that the jaws open in an east-west orientation, and open the tips and advance the forceps approximately 1 centimeter, closing and retracting the forceps in one smooth quick motion to harvest the biopsy. To avoid fully insufflating the colon while performing the biopsy, leave the right side of the gas valve open.