Where should injections be given to a rat? - briefly
Intraperitoneal injection is the standard site for delivering most substances systemically in rats, providing rapid absorption and ease of administration. Subcutaneous or tail‑vein injections are employed when slower release or direct vascular access is required.
Where should injections be given to a rat? - in detail
Injectable agents in laboratory rats are most reliably delivered into a limited set of anatomical locations that provide consistent absorption, minimal distress, and reduced risk of injury. Selection of the site depends on the substance’s required pharmacokinetics, volume, and the duration of the experiment.
Commonly used routes and their technical specifications are:
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Intraperitoneal (IP) – puncture the lower right quadrant of the abdomen, avoiding the intestines. Insert a 25‑27 G needle at a shallow angle (10‑20°) until the tip contacts the peritoneal membrane, then advance 2–3 mm before delivering up to 2 ml/kg of isotonic solution. This route yields rapid systemic exposure for most small‑molecule drugs.
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Subcutaneous (SC) – lift a loose fold of skin on the dorsal neck or scruff region. Use a 25‑27 G needle, insert at a 45° angle, and deposit the injectate into the subdermal space. Volumes should not exceed 0.5 ml per site; larger doses can be split across multiple sites.
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Intramuscular (IM) – target the hind‑limb quadriceps or the gluteal muscle. Locate the muscle bulk by palpation, insert a 25‑27 G needle perpendicular to the skin, and deliver up to 0.5 ml per site. This route is suitable for depot formulations and vaccines.
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Intravenous (IV) via tail vein – warm the tail for 1–2 minutes to dilate vessels, then locate the lateral tail vein using a 30‑33 G needle at a 30° angle. Inject a maximum of 0.1 ml per 100 g body weight slowly to avoid venous rupture. Proper restraint and a sterile technique are essential.
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Retro‑orbital (RO) – appropriate only for short‑term procedures under deep anesthesia. Insert a 30‑33 G capillary tube at the medial canthus, advance toward the orbital sinus, and withdraw the required volume (≤0.1 ml). This method provides rapid systemic delivery but carries a higher risk of ocular injury.
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Intracerebroventricular (ICV) – performed under stereotaxic guidance for central nervous system studies. Drill a small burr hole at the appropriate coordinates (e.g., 0.8 mm posterior to bregma, 1.5 mm lateral, 3.5 mm depth). Use a 30‑33 G Hamilton syringe to inject ≤5 µl of solution. Precision is critical to avoid tissue damage.
General considerations:
- Use sterile needles and syringes for each animal.
- Verify needle gauge suitability for the volume and viscosity of the injectate.
- Apply light restraint or anesthesia consistent with the chosen route to prevent movement.
- Observe the injection site for bleeding, swelling, or signs of infection after administration.
- Record the exact site, volume, and compound concentration for reproducibility.