Where should a rat be injected? - briefly
Inject subcutaneously into the loose skin over the dorsal neck (the scruff). For systemic delivery, use the intraperitoneal cavity in the lower right abdomen.
Where should a rat be injected? - in detail
Injection sites for laboratory rats are selected according to the purpose of the study, the properties of the administered substance, and the required absorption rate. Commonly used locations include:
- Intraperitoneal (IP) cavity – entry through the lower right abdominal quadrant. Needle inserted at a shallow angle to avoid puncturing the intestines. Suitable for large volumes (up to 10 ml kg⁻¹) and rapid systemic distribution.
- Subcutaneous (SC) tissue – injection into the loose connective tissue over the dorsal neck or the scruff of the shoulders. Needle placed parallel to the skin surface, depth limited to 2–3 mm. Appropriate for small volumes (≤0.5 ml kg⁻¹) and slow release formulations.
- Tail vein (IV) – catheterization of the lateral tail vein after warming the tail to dilate vessels. Needle gauge 27–30 G, injection volume not exceeding 0.5 ml kg⁻¹. Provides immediate systemic exposure; requires skill to prevent extravasation.
- Hind‑limb muscle (IM) – injection into the quadriceps or gastrocnemius muscle. Needle inserted at a 45° angle to reach muscle fibers, depth adjusted to animal size. Used for depot preparations and vaccines.
- Intracerebral (IC) or intracerebroventricular (ICV) – stereotaxic placement of a microsyringe into specific brain regions or ventricles. Requires a stereotaxic frame, precise coordinates, and a fine needle (≤33 G). Reserved for neuropharmacological studies.
Key procedural elements:
- Restraint – use of a gentle manual grip, a restraining tube, or an anesthetic plane to minimize stress and movement.
- Aseptic technique – sterilize the injection site with 70 % ethanol, use sterile needles and syringes, and dispose of sharps in designated containers.
- Volume and concentration – adhere to species‑specific limits to avoid tissue damage; adjust concentration to meet dosage requirements within allowed volume.
- Post‑injection monitoring – observe the animal for signs of pain, bleeding, or abnormal behavior for at least 15 minutes after the procedure.
Selection of the appropriate site balances experimental goals, pharmacokinetic considerations, and animal welfare. Proper technique and adherence to dosage guidelines ensure reproducible results and minimize adverse effects.