Where should dexamethasone be injected in a rat? - briefly
Intraperitoneal injection is the preferred site for systemic delivery of dexamethasone in rats, offering rapid absorption and consistent plasma levels. Alternative routes such as subcutaneous or intravenous administration are possible but less frequently employed.
Where should dexamethasone be injected in a rat? - in detail
Dexamethasone administration in rats requires selection of an anatomical site that ensures reliable absorption, minimal stress, and compatibility with experimental objectives. The most commonly employed routes, along with technical specifications, are listed below.
-
Intraperitoneal (IP) injection
• Position the animal in dorsal recumbency; locate the lower right quadrant of the abdomen, avoiding the cecum and urinary bladder.
• Use a 25‑27 G needle; inject a volume not exceeding 2 mL kg⁻¹.
• Aspirate before delivery to confirm entry into the peritoneal cavity. -
Subcutaneous (SC) injection
• Identify the loose skin over the dorsal neck or the flank region.
• Employ a 27‑30 G needle; limit volume to 0.5 mL kg⁻¹ to prevent tissue distension.
• Inject at a shallow angle (10‑15°) to remain within the subcutaneous layer. -
Intramuscular (IM) injection
• Target the quadriceps femoris or the gluteus maximus; palpate the muscle belly to locate a safe injection point.
• Use a 25‑27 G needle; keep volume ≤0.1 mL g⁻¹ to avoid excessive pressure.
• Insert the needle perpendicular to the skin, advancing until resistance is felt, then withdraw slightly before delivery. -
Intravenous (IV) injection (tail vein)
• Warm the tail to dilate vessels; visualize the lateral tail vein using a magnifying lens.
• A 30‑32 G catheter or needle is appropriate; inject a maximum of 0.1 mL kg⁻¹ rapidly.
• Verify successful venous entry by observing blood backflow prior to injection. -
Intracerebroventricular (ICV) injection (for central nervous system studies)
• Secure the rat in a stereotaxic frame; locate bregma and calculate coordinates relative to the lateral ventricle (approximately 0.8 mm posterior, 1.5 mm lateral, 3.5 mm depth).
• Use a 33‑34 G Hamilton syringe; inject ≤10 µL over 1‑2 minutes.
• Allow a dwell time of 1‑2 minutes before needle withdrawal to prevent reflux.
General procedural guidelines
- Maintain aseptic technique: disinfect the injection site with 70 % ethanol, wear sterile gloves, and use sterile syringes.
- Restrain the animal gently to minimize stress; consider brief isoflurane anesthesia for invasive routes (IV, ICV).
- Record the exact dose (µg kg⁻¹), injection volume, and site in the experimental log.
- Observe the rat for at least 15 minutes post‑injection for signs of distress, hemorrhage, or abnormal behavior.
Selection of the appropriate site depends on pharmacokinetic goals, required speed of onset, and the experimental design. Intraperitoneal delivery provides rapid systemic exposure with moderate technical demand, while subcutaneous administration offers prolonged release with minimal discomfort. Intramuscular injection delivers a depot effect, intravenous injection yields immediate plasma concentrations, and intracerebroventricular administration targets central pathways directly. Use the described techniques to achieve consistent, reproducible dexamethasone dosing in rat models.