Introduction to Laboratory Animals & Ethical Guidelines
Before touching any pharmacological experiment, a researcher must thoroughly understand the ethical framework governing animal use and the practical techniques of handling laboratory animals. This foundational unit covers the strict CPCSEA and OECD guidelines that regulate every aspect of animal experimentation in India and internationally, introduces the common species and strains of laboratory animals, details the precise routes of drug administration, and teaches the humane techniques of blood collection and euthanasia.
Syllabus & Topics
- 1CPCSEA Guidelines: CPCSEA (Committee for the Purpose of Control and Supervision of Experiments on Animals): A statutory body established under the Prevention of Cruelty to Animals Act, 1960 (India). Mandates: Every institution MUST register with CPCSEA. Must establish an Institutional Animal Ethics Committee (IAEC) with at least one CPCSEA nominee. All animal experiment protocols require PRIOR IAEC approval. Mandatory inspection of animal facilities. The 3R Principle: Replace (use non-animal alternatives like cell culture, computer simulations wherever feasible), Reduce (use the minimum number of animals needed for statistically valid results through proper experimental design), Refine (modify procedures to minimize pain, distress, and suffering—use anesthesia, analgesics, humane endpoints).
- 2OECD Guidelines: The Organisation for Economic Co-operation and Development publishes internationally harmonized Test Guidelines for preclinical safety assessment. Key OECD Guidelines: TG 420 (Fixed Dose Procedure for Acute Toxicity), TG 423 (Acute Toxic Class Method), TG 425 (Up-and-Down Procedure). These guidelines standardize testing globally, ensure data acceptability across regulatory agencies (FDA, EMA, CDSCO), and heavily emphasize animal welfare and statistical rigor. GLP (Good Laboratory Practice): All preclinical studies must follow GLP standards ensuring data integrity, proper documentation, and reproducibility.
- 3Common Laboratory Animals – Species and Strains: Mice (Mus musculus): Most widely used. Small, inexpensive, short gestation (19-21 days), well-characterized genetics. Strains: Swiss Albino (outbred, general screening), BALB/c (inbred, immunology), C57BL/6 (inbred, genetics). Rats (Rattus norvegicus): Larger blood volume than mice, easier surgery. Strains: Wistar (outbred, general pharmacology), Sprague-Dawley (outbred, toxicology), SHR (Spontaneously Hypertensive Rats—CVS research). Rabbits: Used for pyrogen testing (rabbit pyrogen test), eye irritation (Draize test), and dermal studies. Guinea Pigs: Gold standard for bronchospasm/asthma models and skin sensitization tests. Other: Hamsters (cancer), Dogs/Non-human primates (advanced pharmacokinetic/toxicity studies).
- 4Transgenic and Mutant Animals: Transgenic Animals: Genetically engineered organisms with a foreign gene (transgene) inserted into their genome. Knockout Mice: Specific genes are deleted (‘knocked out’) to study gene function and model human diseases. Example: ApoE knockout mice (develop atherosclerosis—used for cardiovascular drug testing). Nude Mice (Athymic): Lack a thymus, have no T-cells (severely immunodeficient). Used for xenograft transplantation of human tumors—critical for anticancer drug screening. db/db Mice: Carry a mutation in the leptin receptor gene, causing severe obesity and Type 2 diabetes—used for antidiabetic drug screening. SCID Mice: Severe Combined Immunodeficiency—used for HIV research and tumor implantation.
- 5Routes of Drug Administration in Laboratory Animals: Oral (PO – Per Os): Gavage needle into the stomach. Most common route simulating human oral dosing. Intraperitoneal (IP): Injection into the peritoneal cavity. Rapid absorption. Most common parenteral route in mice/rats. Intravenous (IV): Injection directly into a vein—tail vein (mouse/rat), marginal ear vein (rabbit). 100% bioavailability, immediate effect. Subcutaneous (SC): Injection under the skin—scruff of the neck. Slower absorption, sustained effect. Intramuscular (IM): Injection into thigh muscle. Topical: Applied to shaved skin/eye. Intranasal/Intrathecal: For CNS-targeted delivery. Dose Calculation: Allometric scaling between species using body surface area conversion factors (e.g., mouse dose = human dose × 12.3).
- 6Blood Collection Techniques & Euthanasia: Blood Collection: Retro-orbital Sinus (mice/rats): A capillary tube is inserted behind the eye into the venous plexus—yields 0.2-0.5 mL. Requires anesthesia. Tail Vein (mice/rats): Small volumes via needle prick of lateral tail vein. Cardiac Puncture: A needle inserted directly into the heart—yields maximum blood volume but is a terminal procedure. Saphenous Vein: Minimally invasive, small volumes. Euthanasia (Humane Killing): Methods must cause rapid, painless death. Approved Methods: CO₂ asphyxiation (most common for rodents), Cervical dislocation (mice, with training), Overdose of anesthetics (Pentobarbital IV/IP), Decapitation (only with scientific justification, under anesthesia). All euthanasia must follow AVMA (American Veterinary Medical Association) guidelines.
Learning Objectives
Exam Prep Questions
Q1. Why can’t we use only cell cultures instead of animals?
Cell cultures (in vitro) study drug effects on isolated cells under controlled conditions, but they cannot replicate the complexity of a whole living organism. In vivo systems involve multiple interconnected processes such as absorption, distribution, metabolism (especially liver first-pass effect), excretion, immune responses, and interactions across different organs and biological barriers. These integrated physiological and pharmacokinetic factors are essential for accurately predicting drug safety and efficacy, which cannot be achieved using cell cultures alone.
Q2. What is the difference between an “Inbred” and an “Outbred” strain?
Inbred strains are produced through repeated brother-sister mating over many generations, resulting in genetically uniform animals with minimal variability. This allows for highly reproducible and precise experimental results. Outbred strains, on the other hand, are maintained through random breeding to preserve genetic diversity, making them more representative of human populations. Thus, inbred strains are ideal for controlled studies, while outbred strains are better for generalizing results.
Q3. Why is the Intraperitoneal (IP) route so commonly used in rodents?
The intraperitoneal (IP) route is widely used in rodents because it is technically easier than intravenous injections, especially in small animals like mice. The peritoneal cavity has a large surface area and rich blood supply, allowing for efficient drug absorption and systemic distribution. It also permits administration of relatively larger volumes compared to other routes like subcutaneous or intramuscular injections. However, drugs administered via the IP route may undergo partial first-pass metabolism through the liver.