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Animal treatment with various injection and gavage methods

Animal treatment with various injection and gavage methods

Injection

Researchers in various studies involving laboratory animals, cellular and molecular research, genetics, embryology, and microbiology require different injection methods to deliver drugs, fluids, or substances under investigation. Depending on the type and dosage of the administered drug, injections are performed at various sites on laboratory animals, such as the heart, peritoneum, skin, muscle, and vein.

Types of Injections in Mice and Rats and Laboratory Animals

In animal laboratories, drug delivery to various rodents, rabbits, and other laboratory animals is conducted using several methods, including:

  • Intraperitoneal Injection

  • Subcutaneous Injection

  • Intramuscular Injection

  • Intravenous Injection

  • Intracardiac Injection

Types of Injection Needles in Mice, Rats, and Laboratory Animals

The type of laboratory animal, the injection method, and skin thickness determine the size of the needle used for injections. The needle thickness is measured in gauge (G), with each gauge being equivalent to 0.7 mm. A higher gauge number indicates a thinner needle. Different colors are used to distinguish between needles; for example, a 22-gauge needle is blue, while a 20-gauge needle is yellow.

In animal laboratories, small needles with gauges ranging from 23 to 25 are used for mice, 18 to 20 for rats, 19 to 21 for rabbits, and 20 to 21 for guinea pigs.

1- Intraperitoneal Injection in Mice, Rats, and Other Laboratory Animals

The intraperitoneal (IP) injection method is commonly used by researchers. In the IP method, the substance is quickly and safely introduced uniformly into the peritoneal cavity of the mouse or rat and is rapidly absorbed. Intraperitoneal injection is typically employed when assessing the pharmacological effects of an active compound or interfering RNA in vivo.

For IP injection, after restraining the mouse or rat and stabilizing the animal's tail, the injection is performed at a 45-degree angle from either the left or right inguinal area. Vertical or horizontal injections at incorrect angles can injure the animal's organs. The volume of the injected drug should not exceed 100 microliters. Due to the method of administration, the animal may experience more stress compared to other methods.

2- Subcutaneous Injection in Mice, Rats, and Other Laboratory Animals

In animal laboratories, subcutaneous injection (SC) is used to administer cancer cells or certain drugs with slow release. This method allows for a higher volume of injection due to the flexibility of the skin of the rat or mouse, and injections can be performed simultaneously in multiple sites due to the variety of injection points. The volume of the injected substance is critical, as excessive volume can cause painful swelling in the area.

3- Subcutaneous Injection in Laboratory Rats

For subcutaneous drug injection in mice or rats, the needle angle should be between 10 to 30 degrees, and swelling at the injection site may confirm correct administration. Subcutaneous injections are typically performed in the area behind the neck. To inject into this area, the animal is held securely, the skin is pinched with two fingers, and the needle is inserted parallel to the animal's head. The appropriate needle for injection in mice is a 25-gauge needle, with a maximum injection volume of 0.25 milliliters for mice and 1 milliliter for rats at each site.

4- Intramuscular Injection in Mice, Rats, and Other Laboratory Animals

Due to the small muscle mass in mice, intramuscular injection (IM) should be avoided whenever possible. However, if necessary, injections can be made into the quadriceps muscle (gluteal muscles) at a 45-degree angle with minimal pressure.

During the injection, to prevent kicking, the animal's knee should be restrained, and the needle should be inserted deep enough into the muscle to avoid nerve damage. The appropriate needle for intramuscular injection is a 26-gauge needle, with a maximum injection volume of 0.5 milliliters.

In this method, the injection speed should be slow to prevent muscle damage, and the drug must be non-irritating. Water-soluble drugs disperse more quickly within tissues than fat-soluble drugs.

5- Intravenous Injection in Mice, Rats, and Laboratory Animals

Intravenous (IV) injection offers distinct advantages over other methods. Drugs with high concentrations, either with low or high pH, or those causing irritation or itching can be administered via intravenous injection in mice or rats. It is also the best method for delivering drugs that have low absorption in the gastrointestinal tract. Among injection methods in mice and rats, intravenous injection has the fastest absorption rate.

IV injections can be performed at various sites on the animal's tail, including:

  • Dorsal tail vein

  • Lateral tail veins

  • Ventral or abdominal tail artery

In the animal laboratory, for dorsal or lateral tail vein IV injection, the tail is initially clamped to allow blood to pool in the vessel, making the injection site more visible. Accessing the tail veins is easier in the lower two-thirds of the tail. The needle is held at an upward angle, and the injection is performed tangentially to the tail's skin. Confirmation of intravenous injection occurs when the drug passes through the vein and the color of the solution is observed. Additionally, the presence of blood at the injection site confirms intravenous administration. The injection volume for mice is 10 ml/kg and for rats or wild mice is 5 ml/kg. The appropriate needle for injection in mice is a 30-gauge needle.

For intravenous injection, any of the lateral tail veins can be utilized. The blood supply is clamped, and once blood accumulates in the tail, the injection site is determined, then the needle is inserted at a nearly tangential angle to the tail.

Gavage

When a specific volume of a substance or drug needs to be administered orally via the gastrointestinal tract, the gavage method is employed. The maximum volume for gavage is 10 milliliters per kilogram of the animal's weight, and for pregnant animals, a smaller volume should be used. Therefore, it is essential to weigh the animal to determine the appropriate dosage for gavage. Furthermore, gavage should not exceed three times within a 24-hour period, as repeated procedures may lead to esophageal inflammation and harm to the animal.

To perform gavage, the following protocol should be followed:

Disinfect the gavage needle before use.

Weigh the animal and prepare the appropriate drug dosage and volume.

Choose the appropriate gavage needle; the length should be measured from the nose to the sternum of the animal.

While restraining the animal, gently tilt the head back and carefully insert the gavage needle into the esophagus. The gavage tube should be inserted smoothly and without pressure; if any resistance is encountered, withdraw the tube and attempt again.