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Q1: What factors should be considered when planning to administer an experimental agent to a mouse?
Key factors include the appropriate dose, calculated relative to the animal's weight, and the route of administration. The agent's properties—such as palatability, viscosity, and the amount to be administered—along with the target tissue and desired rate of dissemination, determine which administration route is most suitable for your experiment.
Q2: How do you prepare a syringe to remove air bubbles before injection?
After drawing the agent into the barrel by pulling back the plunger, invert the syringe and gently flick the barrel so bubbles move toward the tip and escape. If possible, expel some excess agent to ensure all bubbles are completely removed, since air bubbles injected with the agent can disrupt tissues and harm the animal.
Q3: What is the proper restraint technique for performing a subcutaneous injection in mice?
Hold the mouse by the tail and allow it to grip the cage lid. Then firmly grasp the scruff, raising a tent of skin across the animal's shoulders. Insert the needle at the base of the tented skin and apply firm, consistent pressure to the plunger to dispense the agent, which will be slowly absorbed into the bloodstream.
Q4: Why is warming mice under a heat lamp important before performing intravenous injections?
Warming mice under a heat lamp for a few minutes causes the veins to swell, making needle insertion easier and more successful. This preparation step is essential for identifying and accessing the correct tail veins, which are the most common sites for intravenous injections in mice.
Q5: How can you confirm that an intravenous injection has been placed correctly in the tail vein?
If the needle is correctly placed in the vein, injection will cause the vein to change from dark blue to pale white in color as the agent moves through the vessel. This color change indicates successful delivery and proper needle positioning in the caudal vein, not the artery on the underside of the tail.
Q6: What are some practical applications of subcutaneous and intraperitoneal injections in mouse research?
Subcutaneous injections of antibiotic-resistant bacteria can cause lesions whose size indicates pathogen virulence, while footpad injections enable live imaging of immune cell recruitment. Intraperitoneal injections are absorbed at a rate similar to ingestion and can deliver several hundred microliters of agent for studying disease progression and host-pathogen interactions.
Q7: What alternative routes of agent administration exist besides injection in mice?
Intranasal inoculation delivers agents directly to the lungs to mimic and study respiratory disease progression. Gavage allows direct administration of agent to the stomach, ensuring precise and accurate dosing not achievable through food- or water-based treatment, making it useful when exact dosing is critical.