Laboratory Animals
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The document discusses animal models commonly used in biomedical research. It notes that mice and rats are the most widely used species, making up 74% and 7% of animals in pharmacological research, respectively. These rodents are preferred due to their low cost, short lifespans, and similarities to human biology like reproductive and nervous systems. The document also describes how transgenic mice engineered to express human genes are valuable for modeling human diseases. Overall, the selection of animal models aims to use phylogenetically close and relevant species to best study biological processes and safely test new drugs.
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Laboratory Animals
- 2. INTRODUCTION Selection of animal model Use of an animal phylogenetically closer to man Use of an animal in which the process under investigation is as close as possible
- 3. BIOLOGICAL NAMES • Genus: which have common characteristics and which can be divided into subordinate kinds. E.g. Rattus • Species: similar individuals capable of exchanging genes or interbreeding to produce offsprings . E.g. Rattus rattus or norvegicus • Breed: morphological differences in form or function, and therefore tend to be external and visible. E.g. beagles and mongrels in dogs • Strain: share a presumed common ancestry and have clear- cut physiological diff. that are often internal and invisible. E.g Wistar or Sprague Dawley rats
- 6. • They have similar reproductive and nervous systems to humans, and suffer from same diseases such as cancer, diabetes and even anxiety • Adv: – Short gestation period (19-21 days) – Short lifespan (1.5-2.5yrs) – Small size – Low cost of maintenance
- 7. EXPERIMENTAL USES • Toxicological studies • Teratogenicity studies • Bioassay of insulin, screening of analgesic and anticonvulsant drugs • Screening of chemotherapeutic agents • Studies related to genetics and cancer research
- 8. TRANSGENIC MICE • A transgenic animal is one that carries a foreign gene that has been deliberately inserted into its genome • In 1970, Palmiter introduced the human GH gene into mouse zygotes by pronuclear microinjection and transgenic offspring demonstrated dramatic growth • Genetically modified mice are used extensively in research as models of human disease
- 9. METHODS OF PRODUCING TRANSGENIC MICE • Transforming embryonic stem cells (ES cells) growing in tissue culture with the desired DNA • Injecting the desired gene into the pronucleus of a fertilized mouse egg
- 11. • Small Size • Greater Sensitivity to most drugs • Sturdy, Can withstand long periods of experimentation under anesthesia
- 12. Wistar rat Sprague Dawley rat
- 13. Baby Rats vs Mice • Baby rat – blunt & broad large head. Mice have triangular small head. • Baby rat has small ears, mice have larger ears. • Baby rat hind paw: body ratio larger than mice. • Baby rat tail is thick, shorter than body length. Mice have tail thin, larger/same length (to body)
- 14. EXPERIMENTAL USES • Study of analgesics and anticonvulsants • Study of oestrus cycle, mating behaviour and lactation • Gastric acid secretion • Hepatotoxicity studies • Bioassay of various hormones, such as insulin, oxytocin, vasopressin • Toxicology studies • Rat brain tissue is extensively employed in radio-receptor ligand studies
- 18. EXPERIMENTAL USES • Vaccines for diphtheria, TB, etc • Hypersensitivity studies • Anaphylactic shock • Evaluation of bronchodilators • Evaluation of local anaesthetics • Terminal portion of ileum used for screening spasmodic and anti spasmodic agents • Nutritional studies (Ascorbic acid metabolism)
- 27. EXPERIMENTAL USES • Pyrogen testing • Testing Topical agents as skin is sensitive • Bioassay of anti-diabetic drugs , insulin, curaremimetic drugs • Studies related to antifertility agents • It has simple cardiac tissue free of connective tissue and hence is the animal of choice for cardiac studies • Screening embryotoxic agents and teratogens
- 28. • TESTING OF COSMETICS USING DRAIZE TEST – • Rabbits are commonly used in testing for cosmetics and other chemicals • This test involves the substance being placed on the rabbit's eyes or skin, which are then observed for redness, irritation or any other damage
- 29. PARAMETER MOUSE RAT GUINEA PIG RABBIT Typical adult wt. (gm) 20-40 250 800 1500-5000 Average life span (yrs) 1.5-2.5 2-3 3-5 4-6 Avg age for expt. 3 wks 6wks 3 mths 6mths Gestation period (days) 21 (3 wks) 21 (3wks) 68 (2 mths) 31 (1 mth) Avg litter size 6-12 8-10 3-4 6-8 No. of litters per year 8 6 4 4 HR (beats/min) 350-750 300-500 250-400 130-300 BP 113/81 116/90 77/47 110/80 BIOLOGICAL & PHYSIOLOGICAL DATA
- 35. Mongrel Beagle
- 41. • Zebra fish mutants are currently used to model many human diseases, including Alzheimer’s disease, congenital heart disease, polycystic kidney disease , cancers and development of the nervous system
- 43. • The study of frog muscles in the 1920's led to the discovery of neurotransmitter ACh • Used in the study of action of drugs on CNS, heart, neuromuscular junction Studying embryonic development • African clawed frog (Xenopus laevis) used for studying early events, such as the formation of the neural plate
- 48. SUMMARY • Mice(74%) and rats(7%) being extensively used in pharmacological research • Use of transgenic animals will help us to better understand human disease & improve health care
- 49. THANK YOU
Editor's Notes
- Nude mouse – a hairless genetic mutant that lacks a thymus (Deficient in T- Lymphocytes) – less susceptible to cancer as possess normal number of natural killer cells Beige Mouse – lack killer cells, susceptible to cancer.
- 1. Injection of ES cells into blastocyst-stage embryos Embryonic stem cells (ES cells) are derived from the inner cell mass of blastocysts (early embryos). These cells are pluripotent, which means that they can develop into almost any type of tissue. ES cells are used for more precise modifications of the mouse genome. This technique makes it possible to insert as well as remove or modify DNA sequences. Knock-out, knock-in and conditional mutant mice can be produced with this method. The first step is the removal of ES cells from a blastocyst. After transfection of the ES cells, selection, cloning and screening methods make it possible to detect ES cell clones that demonstrate the desired, site-specific recombination. After microinjection of the genetically modified ES cells into blastocyst-stage embryos the ES cells divide and become part of the embryo. The following chimeric animals will subsequently transmit the recombinant genotype to their offspring, if the ES cells have contributed to their germ cells. 2.Microinjection of DNA into the pronucleus The pronuclear microinjection method of producing a transgenic animal is based on the introduction of linear DNA sequences into the chromosomes of fertilized eggs. The foreign DNA must be integrated into the genome prior to the doubling of the genetic material that precedes the first cleavage in order for the animal to be born with a copy of this new information in every cell. For several hours following the entry of the sperm into the oocyte, the male and the female pronuclei can still be seen individually under a normal light microscope and they have not fused yet into a so called zygote. The foreign DNA may be injected into either pronuclei with no difference in results; however, the DNA is typically injected into the male pronucleus because it is slightly larger and closer to the oocyte surface. These oocytes are subsequently transferred into the uterus of pseudopregnant recipient animals. The offspring is screened to confirm a successful integration of the gene of interest for use in further studies.
- Docile Resembles man in that it has to be given Vit C exogenously Histamine : susceptible to anaphylaxis, bronchoconstriction Dopamine decreases blood pressure in GP Uterus stimulated by adrenaline Penicillin is 100 to 1000 times toxic to GP than in mouse
- New Zealand white rabbits Atropinesterase gene influences color of fur (black) – light reflex not abolished Withdrawing blood from ear veins Dopamine decreases blood pressure in GP Uterus stimulated by adrenaline
- The rabbit has provided an
- Table from Ghosh 5th Edition Recall 2 uses each
- Used for BP, diabetes (as there is discrete pancreas)
- Employed in experiments for studying blood pressure Contractions of nictitating membrane for ganglionic blocking action of drugs More suitable to study compounds that can cause methemoglobinemia like acetanilide.
- Because they are transparent Have short life span Teratogenecity/ embryotoxicity studies
- Otto Loewi – Vagusstoff Other uses – retinal toxicity of drugs (prevention of resynthesis of bleached rhodopsin)