What to drop into a rat's nose? - briefly
Only sterile saline or a precisely measured anesthetic solution should be instilled intranasally in a rat under controlled experimental protocols; all other substances risk toxicity and violate ethical standards.
What to drop into a rat's nose? - in detail
When administering substances intranasally to laboratory rats, the choice of material depends on the experimental objective, safety profile, and the physiological properties of the rat’s nasal cavity.
Aqueous solutions are the most common vehicles. Sterile isotonic saline (0.9 % NaCl) provides a neutral medium for delivering dissolved compounds, peptides, or small‑molecule drugs. Buffering agents such as phosphate‑buffered saline (PBS) maintain pH within the 7.2–7.4 range, preventing irritation. Viscosity enhancers—methylcellulose (0.5–1 % w/v) or hydroxypropyl‑methylcellulose—slow clearance, improving contact time for mucosal absorption.
Organic solvents must be used sparingly. Dimethyl sulfoxide (DMSO) at concentrations ≤10 % v/v can solubilize lipophilic agents, but higher levels cause epithelial damage. Ethanol, propylene glycol, or polyethylene glycol are acceptable only as minor co‑solvents, with concentrations limited to ≤5 % v/v.
Particulate formulations include microspheres, nanocarriers, and dry powders. Polylactic‑co‑glycolic acid (PLGA) microspheres release drug over hours to days; particle size should remain below 10 µm to avoid aspiration. Lyophilized powders reconstituted in saline can be delivered as a fine mist using a calibrated pipette or micro‑sprayer.
Pharmacological agents commonly introduced intranasally include:
- Anesthetics: ketamine (10 mg/kg) or xylazine (5 mg/kg) diluted in saline for short‑duration sedation.
- Analgesics: lidocaine 2 % solution (10 µL) for localized nasal analgesia.
- Irritants for sensory testing: capsaicin (0.1 % in ethanol‑saline) or zinc sulfate (0.1 M) to provoke trigeminal responses.
- Antigens for immunization: ovalbumin (100 µg) in alum adjuvant, delivered in 20 µL volume.
Dosage volume must not exceed 20–30 µL per nostril to prevent overflow and aspiration. Administration technique involves gently restraining the animal, tilting the head back 10–15°, and delivering the fluid dropwise at the entrance of each nostril using a calibrated micropipette. After delivery, maintain the animal in a supine position for 30–60 seconds to allow absorption.
Safety considerations require confirming the absence of nasal lesions before each procedure, monitoring respiratory rate during and after administration, and adhering to institutional animal‑care guidelines. Toxic substances, such as high‑concentration acids or strong irritants, are restricted to studies with explicit ethical approval and appropriate anesthesia.