Retroductal Nanoparticle Injection to the Murine Submandibular Gland

The overall goal of this procedure is to administer nanomaterials directly to the murine submandibular gland. The main advantage of this technique is that it achieves direct delivery of compounds to the submandibular gland while bypassing the systemic circulation. The implications of this technique extend toward therapy of salivary gland disfunction following radiation treatment for head and neck malignancy.

Generally, individuals new to this method may be challenged by locating and cannulating the submandibular duct while the animal is sedated. To begin this procedure, cut three centimeters of a 32 gauge intracranial catheter tubing with wire inset to form a beveled end approximately 45 degrees to the long axis. Confirm that the wire is at least one centimeter longer than the tubing.

Creating a beveled edge to the tubing will ease ductal cannulation. If the tubing gets bent during the procedure, a fresh beveled edge should be cut. Next, load 50 microliters of PSMA nanoparticle solution or other injection material into a Hamilton syringe.

To reduce the probability of burrow trauma during injection, attach the catheter tubing to the syringe and expel dead volume. Inspect the injection solution to ensure the nanoparticle is fully solvated to prevent ductal obstruction. Then prepare atropine solution at 0.1 milligram per milliliter.

To visualize the ductal entry point, place an anesthetized mouse in the prone position on a custom stage. Then apply ointment to the eyes to prevent dryness during the procedure. Afterward, secure the maxillary incisors over a metal beam and use an elastic band to apply downward tension behind the mandibular incisors.

Align the mouse beneath the dissecting microscope to visualize the base of the jaw. To widen the mouth, use a custom curved steel retractor to apply tension to the buccal mucosa bilaterally. To visualize the submandibular papilla, grasp and gently lift the tongue from the floor of the mouth using blunt forceps.

Place a piece of cotton between the tongue and the buccal mucosa to enable further manipulation within the oral cavity. To perform ductal cannulation and line placement, grasp the catheter tubing with a wire inset. For optimum manual control during cannulation, align the tubing with the curvature of the forceps.

Using the dissecting microscope, move the forceps and wire into the field of view. Using the wire inset, gently apply pressure into the base of one submandibular papilla to produce a small superficial mucosal puncture that will facilitate later entry of the catheter tubing. If resistance is encountered, cut fresh beveled tips on both the tubing and wire inset with sharp dissecting scissors.

Following the entry, withdraw the stylet, then, using the dissecting microscope, confirm the presence of saliva at the puncture site. Subsequently, retract the stylet further within the tubing. Avoid forceful or sudden movement of the stylet that may cause bleeding or compromise ductal integrity.

To ensure that injection tubing will fit into the Wharton's duct opening, insert tubing containing the stylet as a rigid guide into the previously made puncture. To prevent back pressure from prolonged to ductal obstruction, withdraw the tubing. Under the microscope, ensure that an opening can be seen in the submandibular papilla.

If visible bleeding occurs, remove the stylet and reattempt the procedures on the opposing submandibular papilla. Next, without moving the mouse, administer one milligram per kilogram atropine solution intraperitoneally to reduce elevation during the procedure. Then, wait for five to 10 minutes.

Under the dissecting microscope, insert the syringe tubing into the orifice. If resistance is encountered, cut a fresh beveled end on the tubing and reattempt it. Once the tubing is in place within the submandibular papilla, slowly advance three to five millimeters into the duct.

Then, release the tubing from the forceps. To improve the seal between the tubing and the submandibular papilla, dry the interface by gently blotting with gauze for one minute. Inspect to confirm that the position of the tubing has not shifted during drying.

In this procedure, inject the material at a rate of 10 microliters per minute. Ensure that the mouse remains sedated and is not showing signs of distress. Following the injection, maintain syringe pressure for five minutes to improve the retention of material within the Wharton's duct and the submandibular gland.

Inspect the submandibular papilla periodically to ensure that tubing does not exit the ductal orifice. Maintaining injection pressure will enhance the effectiveness of retroductal delivery. Using fine forceps, grasp and gently and withdraw the tubing from the submandibular papilla.

Remove the retractor and cotton from the oral cavity before moving the mouse away from the stage. To verify nanoparticle delivery, in vivo imaging system shows the lateralization of red fluorescent signal to the treated side of the mouse one hour post injection. And this image shows that the nanoparticle signal has decreased significantly 24 hours after injection.

To confirm nanoparticle persistence in the submandibular glands 24 hours following injection, they were sectioned and viewed by fluorescent imaging. Shown here are the uninjected control submandibular glands stained for aquaporin 5 and keritin five marking the secretory acini and ductal cells respectively. In retroductal nanoparticle injected submandibular glands, aquaporin five and keritin five stains show normal gland morphology and nanoparticles taken up in both acini and ducts.

Once mastered this technique can be done in 20 minutes if it is performed properly. While attempting this procedure, it's important to remember to avoid any extraneous movements that could dislodge the cannula or disrupt the seal made between the tubing and the submandibular papilla. Following the procedure, other methods like immunostaining, RNA extraction, or flow cytometry can be performed in order to evaluate gene expression or nanomaterial localization in the submandibular gland.

After its development, this technique paved the way for salivary gland researchers to screen and test compounds for xerostomia prevention. After watching this video, you should have a good understanding of how to administer nanomaterials directly to the murine submandibular gland via cannulation of Wharton's duct.