Experimental animals

it describes the animals commonly used in experimental pharmacology

1. Dr.K.Sathishbabu IInd year PG Department of Pharmacology 07.05.2020 EXPERIMENTAL ANIMALS

2. OVERVIEW Introduction Classification Animals Summary References

3. INTRODUCTION To study the effect of newly developed drug we need experimental animals for safety and efficacy measurement Selection of an animal model – most important step in any experimental pharmacological studies

4. Objectives for selection of animal model ;- Phylogenetically closer to man The process under investigation is as close as possible to that in a man Anatomy, Physiology and Biochemistry are considered to be similar

5. Classification Rodents : Eg : Mouse, Rat, Guinea pig, Gerbil, Hamster etc. Non - rodents : Eg : Rabbit, Monkey, Dog, Cat, Pig etc. 3. Misellaneous : Eg : Frog, Pigeon, Zebra fish, Chicken etc.

6. MOUSE

7. MOUSE ( Mus musculus ) Smallest laboratory animal Uniform bred, Cheap and easy to handle Sensitive to very small doses of substance Strains : - Commonly used : Swiss Albino mice - Other strains : DBA/2, Balb /C and C-57

8. Large similarity in mice and human genome – provides good model for genetic studies Knock out mice : selective gene is taken out from the mice Knock in mice : gene of interest is introduced in the mice Knocked down – genes are silenced by pieces of RNA

9. Nude mice : Hairless genetic mutant which lacks thymus gland – used for tissue immunity and transplantational research Biege mice : lack of NK cells and are susceptible to cancer – used for cancer studies Biege mice Nude mice

10. Used in Acute toxicity studies Assay of Insulin and analgesics Screening of chemotherapeutic and teratogenic agents Cancer and genetic research Isolated preparation - Vas deferens , ileum

11. RAT

12. RAT (Rattus norvegicus) Most commonly used Small size ; greater sensitivity to most drugs Most standardized of all lab animals Very sturdy to withstand long periods of experimentation under anaesthesia Common strains : Wistar & Sprague - Dawley rats

13. Wistar rats : Moderately prolific strain ; resistant to infection Low incidence of spontaneous tumors Wide head; long ears; tail length < body length Sprague – Dawley rats : More prolific ; rapidly growing; less resistant to infection Long & narrow head ; tail length = body length

14. Lack of vomiting centre, tonsils, gall bladder Strong LES ; Extremely diffuse pancreas Stomach – two parts (Secretory & Non secretory) Secretory part – continuous spontaneous secretion Coprophagic animals Rat uterus – inhibited by adrenaline Physiologically, 24 hr old rat = 6 month old infant.

15. VC - So, they don’t vomit Gall bladder – continuous entrance of bile into the intestine leads to strong gastric secretogogue Diffuse pancreas – pancreatectomy is difficult to produce diabetes Stomach – divided by transverse ridge : upper 2/5 th is non secretory – translucent & thin Lower 3/5th is glandular secretory portion – this part is analogous to the human portion of the stomach anatomically & functionally Special care needs during gastric secretion studies; coprophagic Uterus – inhibited by adrenaline, which forms a basis of bioassay methods of adrenaline 24h old rat = 6m infant ; used to evaluate the compounds used in this age group

16. Used in Evaluation of Psychopharmacological agents Teratogenic and Carcinogenic Activity Anti Ulcer & Liver Physiological Studies Assay of Hormones & Acute/ Chronic analgesics Antihypertensive Effects Isolated Preparation- Uterus, Fundus Strip, Colon

17. Psychopharmacological studies – can be trained properly for various types of work performances including development of condition reflexes Used especially for chronic studies, because of the drug can be administered and effects observed throughout their short life span of 3 yrs Shay rat method – used for anti ulcer agent screening method by pyloric ligation Normal rat BP is 130/90 mmHg; used for anti hypertensive drug studies Liver physiological studies – following partial hepatectomy the organ regenerates almost completely with in a week

18. GUINEA PIG

19. GUINEA PIG ( Cavia porcellus ) Most useful and docile laboratory animal Newborn GP can eat solid food by 5 th day Young GP best mated after 3 months – polygamous mating Maturation is slow in males than in females Not able to synthesize the required vitamin C daily

20. Highly sensitive to histamine & penicillin Very susceptible to mycobacterial infection and anaphylactic shock Uterus - inhibited by adrenaline Serum contains asparginase – anti-leukemic action In this species, dopamine causes fall in BP

21. Used in Evaluation of bronchodilator (Anti-Asthmatic) Sensitization Studies - Egg Albumin and Horse Serum. Study of local anesthetics Bioassay of Digitalis, Histamines, and acetyl choline Study of Vitamin C metabolism & anti-TB drugs

22. Sensitive cochlea – suitable for hearing experiments More resistant to hypoxia – suitable for oxygen consumption experiments Isolated preparation of Ileum - Screening of spasmodic and anti-spasmodic compounds Other isolations – tracheal chain, vas deferens etc.

23. GERBIL

24. GERBIL ( Meriones unguiculatus ) Mongolian gerbil – small laboratory animal ; length in between rat and mice – “ Sand rat” Originally developed in japan as lab animals Ease in handling, mild and quiet in nature Used in the field of stroke, epilepsy, auditory studies, parasitic & bacterial infections and lipid metabolism & heart disease studies

25. HAMSTER Syrian hamster Chinese hamster European hamster

26. HAMSTER ( Mesocricetus auratus ) 3 rd most commonly used animal in biomedical research Strains : Syrian hamster (Golden) Chinese hamster (striped back) European hamster & Armenian hamster (Gray)

27. Syrian hamsters : free from spontaneous disease and susceptible to many pathogens Used in virology, cancer, genetics, toxicology and reproductive physiology studies European hamsters : larger than other hamsters Suitable – highly concentrated and prolonged smoke inhalation studies

28. Armenian hamsters : more specific for mutagenic and carcinogenic studies Chinese hamsters : Has lowest no. of chromosomes compared to other lab animals; Useful for cytogenetic studies Defective β cells in pancreas – used in diabetic studies

29. Advantages Availability and Ease in reproduction Anatomical and physiological features with unique potential for study Rapid development with short life cycles Cheek pouch : lack of lymphatic drainage ; ideal site for tissue transplants such as tumors and grafts Pouch isolation - Assay of Prostaglandin E& F

30. RABBIT

31. RABBIT ( Oryctolagus cuniculus ) Very docile Newzealand white rabbit – most common strain Homologous to humans to react similarly to diseases and medications Cannot vomit and sensitive to histamine like rodents Has an ability to taste water - absent in rodents

32. Dopamine causes fall in BP Presence of atropinesterase – degrades atropine Doesn’t have adrenergic vasodilator nerves – no vasomotor reversal phenomenon Has huge caecum and long appendix Ear veins – convenience for injection & blood withdrawal

33. Only known mammal from which tubules of the kidney can be dissected with basement membrane intact Absence of CYP3A4 Lack of melanin – ‘ Albinism’ Uterus – stimulated by adrenaline

34. Used in Pyrogen Testing Anti Diabetic Study & Topical agents study Bioassay of Insulin, curare and sex hormones Capillary Permeability Study Embryo Toxic and Reproductive studies Isolated preparation : heart, duodenum, ileum

35. MONKEY

36. MONKEY ( Macaca mulatta ) Rhesus species – commonly used Structure and function – closely resemble to man Uterus resembles human & exhibiting regular menstrual periods Metabolic pattern & Brain structure – same as man Require regular check up & timely immunization

37. Used in Infertility studies Virology, Parasitology & Immunological studies Immunosuppressant & Nutrition related studies Ideal model for pharmacokinetic studies Best for studying drugs acting on CNS, CVS and GIT

38. SQUIRREL MONKEY Most commonly used neotropical primates in US Plasmodium species are host specific - important animal model for malaria vaccine development studies One of the most susceptible non - human primate species to experimental infection with Creutzfeldt - Jakob disease & spongiform encephalopathies

39. DOG

40. DOG ( Canis familiaris ) Most preferred large experimental animal Can be easily trained for behavioral activity Stomach and intestinal tract resembles human Distinct structure of pancreas May develop spontaneous Diabetes &Hypertension

41. Cervical sympathetic and vagal nerves run together inseparable – vagal stimulation causes reflex variations in blood pressure Animal of choice for studies on gastric secretion and digestion Preferred for Anti hypertensive, cardiovascular, Diabetes and anti ulcer experiments.

42. CAT

43. CAT ( Felis catus ) Similar physiological features with humans Ease of collecting blood samples – useful in studying the transmission of vitamins & minerals to the fetus Thick nictiating membrane – used in screening of ganglionic blocking drugs Able to produce methemoglobinemia – suitable for toxicity studies

44. Cats are used for the studies where stable BP is required Morphine produces excitation in CNS Adrenaline – stimulates the pregnant uterus & inhibits the null uterus Essential in the study of the nerve centres in the brain

45. PIG

46. PIG ( Sus scrofa domestica ) Similar in Human physiology Less hairy skin – preferred for skin related studies Small lungs – susceptible to bronchitis & pneumonia Alimentary tract resembles human – used in digestive system studies Important model – Cardiovascular research such as MI, atherosclerosis etc.

47. ZEBRA FISH

48. ZEBRA FISH ( Danio rerio ) Dr.George streisinger – Father of zebra fish research Optically translucent embryos Clear eggs – developed outside the mother’s body ; allows watching a egg grow into a newly formed fish in 2-4 days Length is 5-6 cm ; Life span is approx. 5 years

49. Advantages : Cheaper to maintain than other animals Suitable model for vertebrate development and genetic studies Drawback : Not closely related to humans Glofish : Genetically modified florescent fish - Tool for examining the erythrocyte development & circulation defects in embryo

50. FROG

51. FROG ( Rana tigrina ) Only tailless experimental amphibian Frog and toad – differentiated by their appearance only ; Heart contain 3 chambers Vagal response – varies by species & seasonal Adrenaline – neurotransmitter in sympathetic system Important substances – obtained from various species

52. Used in Used for determining the retinal toxicity of drugs Used in study of the action of drugs on the CNS, CVS, Neuromuscular junction and pregnancy assays Cloning and embryological researches

53. CHICKEN

54. CHICKEN (Gallus domesticus) Widely used due to easy availability and maintenance Only model – studying avian diseases Studies related to breeding, genetics, performance testing, embryology, fertility, toxicology etc. Important models – chick comb method, scleroderma models, autoimmune thyroiditis etc.

55. PIGEON

56. PIGEON (Columbia livia ) Mainly preferred for screening of anti emetic activity Spontaneous arteriosclerosis – cardiovascular studies Apomorphine induces stereotypic behavior Standardization of cardiac glycosides Screening of intravenous anesthetics Pigeon crop method – prolactin bioassay

57. SUMMARY Animal selection – based on how it is closer to human Mice & Rats – commonest experimental model for various studies Guinea pig – very docile; requires vitamin C daily Gerbil – auditory studies Rabbit – able to taste water; pyrogen testing

58. Hamster – presence of cheek pouch – site for tissue transplant & graft studies Monkey – very closer to human ; metabolic studies Dog – GI drug studies; nerve conduction studies Pig – skin related studies Frog – pregnancy assays; chemicals isolation Pigeon – screening model for anti emetics