This study outlines a surgical procedure to create a denervated area in the dorsal skin of a mouse, allowing for the assessment of sensory nerve function. The methodology includes careful nerve removal and subsequent testing of the animal's response to mechanical stimulation.
Begin with an anesthetized mouse with exposed dorsal skin. Disinfect the area and cover it.
Make a midline incision from the neck to just above the tail.
Pull the left-side skin to create a skin flap and expose the underlying tissue.
Place the mouse under a microscope and locate the sensory nerves.
Carefully pull and remove these nerves without disrupting the blood vessels.
Moisten the tissue and remove the remaining nerves from the skin flap, creating a denervated area.
On the right side, leave the nerves intact as a control. Suture the skin incision.
Allow the mouse to recover.
To assess stable denervation several weeks after surgery, use the same denervated mouse with shaved dorsal skin.
Using a needle, prick at the control area, generating a mechanical stimulation.
This excites the underlying nerves, sending a signal to the brain and causing the mouse to respond.
However, pricking the denervated area fails to generate a response, confirming the role of sensory nerves.
Anesthetize the animal. Shave the entire dorsal skin and clean the area similar to the biopsy procedure. Now, make an incision using a sterile scalpel along the dorsal midline from the base of the neck, to roughly half a centimeter above the tail. Using sterile blunt forceps, gently reflect the skin on the left side away from the flank, to visualize the underlying tissue from the scapular fat pads near the neck to just above the hind limb.
Now, identify the dorsal cutaneous nerves under a dissecting light microscope. These appear as white strands that travel caudally through the translucent fascia of the trunk wall before making sharp bends and entering the loose connective tissue underneath the skin. Next, using ultra-fine forceps, remove the nerves exclusively from the left side of the animal located at anatomical sites T3 to T12 by plucking them from where their segments bend at the trunk wall to their entry sites into the skin.
Orient the forceps vertically and grasp the nerves about half a centimeter below their bend sites. Once grasped, pull upwards to cause the nerve to stretch and separate from the surrounding tissue to remove them. Avoid damaging the adjacent blood vessels. Be sure to keep the tissue moist throughout the procedure by periodically applying drops of 0.9% sterile saline solution.
Continue removing all nerves extending from the trunk wall to the skin, but do not disrupt the nerves within the dense fascia of the trunk wall. Next, remove any nerves from the exposed skin flap. These fibers comprise the distal branches of the dorsal cutaneous nerves, and appear as white branching strands located sporadically within the connective tissue on the dermal side of the skin flap.
To remove these fine branches, position the forceps roughly parallel to the dermal surface, grasp the nerves, and pluck upwards. Remove all the visible nerves in this fashion. Do not puncture the blood vessels and skin.
During this step, it's important to avoid rupturing neighboring blood vessels. If you find a nerve with an adjacent blood vessel, follow it ventrally to an area where there is no adjacent vessel, and remove it by plucking.
Now, bluntly reflect the skin on the right side of the dorsal midline incision, but do not remove any nerves. This will serve as the contralateral sham-operated control. Finally, suture up the animal and monitor postoperatively as before. Later, to confirm the stable loss of nerves weeks after surgery, gently prick the denervated area using a sterile hypodermic needle. Note whether the animal responds typically by shuddering or turning its head. If the skin area has been stably denervated, the animal will exhibit little or no response.
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