What are the recommended methods for handling rats and mice in a laboratory setting, including routes of drug administration?

Handling and Drug Administration in Laboratory Rats and Mice

Handling Methods

Proper handling and restraint techniques are essential for both animal welfare and handler safety, requiring confident, direct movements to minimize stress and prevent injury to both parties. 1, 2

Basic Handling Principles

• Acclimation to handling is critical and should occur before experimental procedures begin, as this reduces stress responses and produces more reliable data by ensuring animals react to experimental stimuli rather than to the handler 3
• Use one-handed, two-handed, or specialized restraint devices depending on the procedure and animal size 1
• Employ sure, direct movements with a determined attitude to prevent animal anxiety and reduce risk of bites or scratches 2
• Avoid housing mice and rats together, as mice exhibit significant distress when co-housed with rats 4

Stress Minimization During Handling

• Allow adequate habituation time before testing: rats require 10-15 minutes, while mice need 2-4 hours depending on strain 4
• Transport stress (by cart or hand) temporarily elevates corticosterone levels, necessitating proper acclimation periods 4
• Male experimenters induce stress responses in mice through olfactory cues, reducing pain sensitivity for the first 60 minutes of exposure 4
• Perform procedures at consistent times daily to account for circadian fluctuations in biological parameters 4
• Interexperimenter variability impacts behavioral outcomes more than genetic or environmental factors, so maintain consistent personnel 4

Housing Conditions

Mouse Housing Standards

• Maximum 5 mice per cage (including litters) with minimum 60 cm²/mouse 4
• Temperature: 21-24°C with 40-80% humidity 4
• 12/12-hour light/dark cycle 4
• Standard rodent chow and fresh water ad libitum 4
• Never house mice with rats due to distress responses 4

Rat Housing Standards

• Maximum 3 rats per cage with minimum 250 cm²/rat 4
• Temperature: 21-24°C with 55 ± 10% humidity 4
• 12/12-hour light/dark cycle with lights on from 7:00 a.m. 4
• Standard rat chow and water ad libitum 4

Environmental Enrichment

• House animals with at least one phenotypically similar conspecific (injured with injured, naive with naive) to reduce stress 4
• Add inanimate environmental enrichment to cages 4
• Maintain consistent food, water, and bedding suppliers throughout experiments 4
• Randomize cage assignments to mitigate cage/cohort effects 4

Routes of Drug Administration

Injectable Routes - Mice

Injection volumes must be minimized for accuracy and animal welfare, with frequency and duration of dosing as important as volume and composition. 4

• Intravenous (IV) bolus: 10 ml/kg (200 μl for 20g mouse) 4
• Intraperitoneal (IP) bolus: 20 ml/kg 4
• Subcutaneous (SC) bolus: 20 ml/kg, maximum 2 sites 4
• Intramuscular (IM): 0.05 ml per site using contralateral limbs, or 0.1 ml single occasion 4
• Intradermal: 0.05 ml per site, maximum 2 sites 4
• Intratumor: 0.1 ml 4
• Slow IV injection: 0.8 ml over 2 minutes 4
• Constant IV infusion: 0.04 ml/min 4
• Constant IP infusion: 0.04 ml/min 4

Injectable Routes - Rats

• Intravenous (IV) bolus: 5 ml/kg 4
• Intra-arterial bolus: 0.1 ml 4
• Intraperitoneal (IP) bolus: 10 ml/kg 4
• Subcutaneous (SC) bolus: 10 ml/kg 4
• Intramuscular (IM): 0.1 ml per site using contralateral limbs, or 0.2 ml single occasion 4
• Intradermal: 0.1 ml per site 4
• Intratumor: 0.1 ml 4
• Slow IV/arterial injection: 5 ml over 2 minutes 4
• Constant IV infusion: 0.2 ml/min (maximum 2.5 ml/min for <1 min total) 4
• Constant intra-arterial infusion: 0.1 ml/min 4
• Constant IP infusion: 0.2 ml/min 4

Oral Administration

• Mice: 20 ml/kg by gavage, or 50 ml/kg on single occasion only 4
• Rats: 20 ml/kg by gavage, or 30 ml/kg on single occasion only 4
• Multiple administrations should be separated by 6-8 hours 4

Vehicle and Formulation Requirements

Solutions should be as physiologically compatible as possible, with organic solvents and detergents strictly limited. 4

• Organic solvents (DMSO, DMA, ethanol) must not exceed 10% of formulation 4
• Detergents/emulsifiers must not exceed 20% of formulation 4
• For mice: organic solvents should not exceed 5 ml/kg or 10% of injected volume 4
• Cyclodextrins should not exceed 2 ml/kg or 45% of injected volume 4
• When cyclodextrins exceed 20% of volume, rehydrate animals within 2-4 hours 4
• Use aqueous solutions (sterile water, 0.9% saline, or 5% dextrose/saline) as close to physiological pH as possible 4
• Oil suspensions should be discouraged 4
• Poorly water-soluble compounds may exceptionally use up to 50 ml/kg in mice to avoid organic solvents 4

Pharmacokinetic Sampling Considerations

• In mice, repeat sampling from superficial veins over multiple time points reduces animal numbers 4
• Typical mouse PK studies use 2-3 mice per dose with 5-8 time points over 24-48 hours for small molecules 4
• In rats, 5-8 time-point PK profiles can be generated using 2-6 animals total through repeated blood sampling 4
• Consider cassette dosing (low-dose compound mixtures) to reduce animal usage 4

Critical Welfare Considerations

Analgesia and Antibiotics

Preoperative analgesia and antibiotics are mandatory for surgical procedures to minimize suffering and prevent infections. 4

• Buprenorphine: 0.1 mg/kg SC twice daily (note: opioids have cardioprotective effects that may confound certain studies) 4
• Carprofen: 2-5 mg/kg SC pre- and post-operatively 4
• Cefuroxime: 100 mg/kg IP for rats, 25 mg/kg IM for rabbits 4
• Ampicillin: 100 mg/kg IM for rats immediately prior to surgery 4
• Avoid tramadol in cardioprotection studies as it reduces infarct size at 12.5 mg/kg IV 4

Monitoring and Humane Endpoints

• Inspect tumor-bearing animals daily at minimum, with increased frequency during critical periods 5
• Death should no longer be used as an endpoint 5
• Tumor burden should not exceed 10% of normal body weight in therapeutic experiments (5% for routine passage) 5
• Establish clear chains of responsibility for prompt action when welfare problems arise 5
• Design experiments so critical periods do not occur during staff absence 5