Comparative biology of rat and human

Rodent Biology, Comparation between rats and humans

1. Rodent Biology Pradeep Singh [email protected]

2. Contents Taxonomic classification Introduction History Difference between mouse and rats Difference between laboratory rats and wild rats Comparison of rat and human ages Common inbred and outbred strains Sexing, Reproduction and Pups development Comparative anatomy of rats and humans

3. General Features Rat Human Class Mammalia Mammalia Order Rodentia Primata Family Muridae Hominidae Genus and Species Rattus norvegicus Homo sapiens Chromosome number (2n) 42 46 Sexual maturity 4-7 weeks 10-15 years Life span 2.5 – 3.0 years ~ 70 years Gestation period 21-24 days ~ 40 weeks Mammary glands 12 (6 pairs) 2 discrete, pectoral Male nipples Absent Present

4. Taxonomic Classification Kingdom : Animalia Phylum : Chordata Class : Mammalia Order : Rodentia Family : Muridae Genus : Rattus Species : norvegicus

5. Introduction Found worldwide except Antarctica Binomial Nomenclature : Rattus norvegicus ( Berkenhout , 1769) Common Names : Brown Rat, Sewer Rat, Norway Rat, Wharf Rat, Common Rat, Hanover Rat, Norwegian Rat, etc. R. norvegicus was one of the first mammalian species domesticated for scientific purposes. Replaced the less aggressive R. rattus in most parts of the world except warmer areas.

6. History Rattus norvegicus (2N=42): thought to have originated in temperate Asia. It expanded into Europe in the 8th Century and eventually into the Americas in the late 1700’s. By now it spread worldwide. The name of “Norway rat” has no particular geographic significance, although they are believed to have migrated to Western Europe via the Norwegian Peninsula Rattus rattus (2N=38): spread from Southeast Asia into Europe around the 12th Century, reaching the Americas in the 16th Century. Largely responsible for the spread of Bubonic plague (“Black death”) to Europe in the 14th century (it killed about a quarter of the European population).

7. Use in Laboratory (since mid 1800s) Philipeaux studied adrenalectomized white rats in France in 1856 with published reports of nutritional and breeding research. Neuroanatomical studies by Henry Donaldson at the University of Chicago in the early 1890’s represented the first known experimental use of rats in the USA. He later established Wistar Institute in Philadelphia that will have a major role in the development of the rat as an important laboratory animal similar to the impact the Jackson laboratory had on the development of the laboratory mouse. The Wistar bloodline has contributed more strains of rats than any other line.

8. Mouse Smaller (12-20 cms ) Triangular snout with long whiskers Produce 40-100 droppings/day Long, thin, hairless tail Rat Larger (about 40 cms ) More blunt snout Produce 20-50 droppings/day Thick tail, usually hairless and scaly

9. Difference between Laboratory Rats and Wild Rats Lab rats have smaller adrenal glands, especially the cortex. Ovaries, testes, and secondary sex glands are the same size but mature earlier and function continuously (no seasonal cycle) in lab rats. Better fecundity. Shorter life span (2-3 years for lab rat compared to 4-5 years for wild rats). • Laboratory rats overall have smaller body size.

10. Behaviour Nocturnal animals with most activity occurring during night time and early morning Typically non-aggressive, inquisitive and easily trainable Frequent handlings encourage their non-aggressive nature as they adapt to new environments or experimental situations Improper handling, nutritional deficiencies can evoke fear responses Feel most comfortable in small, dark, confined spaces Coprophagic behaviour - Important for obtaining Vitamin B produced by bacterial action in the colon • In general, males are less likely to fight when housed together than are male mice. P ost parturient females may fight amongst themselves.

11. Comparison of Rat and Human Ages

12. Correlation of days or years of rat age with humans

13. Common Inbred Strains

14. Common Outbred Strains

15. Sexing Sexing of rodents is based upon ano -genital distance Males have a greater distance between the anus and urogenital opening than females. An opposite sex comparison is advisable initially. http://neurocndm.mcgill.ca/uploads/file/Handout%20Rat%20Module%201.pdf http://diakonoi.org/sexing-baby-rats/

16. Reproduction S.No . Reproduction Rats Humans 1. Puberty 6-8 weeks Girls- 11 Boys- 12 2. Estrous cycle 4-5 days 28 days 3. Gestation 21-23 days 280 days 4. Size of litter 8-14 pups Not present 5. Birth weight 5-6 gm 3.5 kg http://ratguide.com/health/basics/vital_statistics_in_rats.php

17. Carnegie Stage 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Human Days 1 2-3 4-5 5-6 7-12 13-15 15-17 17-19 20 22 24 28 30 33 36 40 42 44 48 52 54 55 58 Mouse Days 1 2 3 E4.5 E5.0 E6.0 E7.0 E8.0 E9.0 E9.5 E10 E10.5 E11 E11.5 E12 E12.5 E13 E13.5 E14 E14.5 E15 E15.5 E16 Rat Days 1 3.5 4-5 5 6 7.5 8.5 9 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 Comparative rate of Early Embryo development

18. Pups Development The first four weeks of a rat’s life are filled with dramatic changes. At birth the pup is naked, blind, and completely dependant upon its mother for everything. Week 1 No fur, only slight whiskers and eyelids sealed By day 4, colors and patterns start showing. Ears starts to develop. The babies get more active as the first week progresses. All of their needs at this age are supplied by the mother. She feeds them, cleans them, stimulates them to urinate and have bowel movements, keeps them warm, and protects them. Fingers and toes are lengthening and separating, and by the end of the first week, facial features become more prominent. Sex can be determined. http://ratguide.com/breeding/baby_development/birth_to_weaning.php

19. Week 2 Babies are covered with light fuzz, starts to crawl, ears become separated from the head. Pup rat still cannot hear, although it can sense vibrations. Ear canal opens, allowing the them to hear. They begin to emerge from the nest and walk, although a bit unsteadily at first. Mother is still feeding the babies. Some of the babies’ eyes have started to open. But the vision is blurred. Fur completely covers their bodies, female pups develop nipples. Week 3 At this age the babies are able to run. Babies are old enough to drink without a nipple. As their appearances become more distinctive so do their individual personalities.

20. Week 4 Wrestling and eating are the two preferred activities. Mom is nursing them less often. The babies are now using the water bottle, eating lab block and seed mix, and joining mom in eating snacks. Babies often go through a molt at about this time and may have strange color or texture “patterns” in the coat as new hair comes in. Handle the babies every day to socialize and get them ready for their new homes. The babies are now weaned. Their basic personalities are pretty well established, and each day they show increased individuality.  Pup rats mature quickly.  Remember to separate the males and the females by the time they are 5 weeks old to prevent any pregnancies.  You can leave the females in with their mother. The boys will need their own cage.

21. Age in days Age in weeks/months  Development stages Birth  Hairless, toothless, closed eyes and ears relies on smell of mother/siblings 4 days 4 Days Hair begins to appear 10 days 1.5 weeks Covered with hair 13 days Almost 2 weeks  Eyes and ears open 40-50 days 5 weeks to 7 weeks   Weaned at 5 to 6 weeks Sexual maturity 72 days 2.5 months  Young adult  250-300 days 8 – 10 months Young adult  1000-1300 days 32 – 42 months (2.7 to 3.5 years) end of normal lifespan Full grown; males larger than females http://diakonoi.org/sexing-baby-rats/

22. Vital Statistics S. No. Vital statistics Rats Humans 1. Temperature  37.7°C (99.85°F) 36.5–37.5 °C (97.7–99.5 °F) 2. Respiratory rate/minute 71 - 146 12-16 3. Heart rate/minute 250-493 60-100 4. Weight (average adult) Male – 250-550 gm Female- 225- 400 gm 57.7 kg (Asia average) 5. Life span (average) 24-40 months 79 years http://ratguide.com/health/basics/vital_statistics_in_rats.php

23. VISION The animal's perception of its surrounding world is called its  ümvelt . Rats probably perceive just a hint of ultraviolet, blues and greens. Somewhat like humans with red-insensitive color blindness, R etinas have mainly rods and only few cones . Albino rats have unpigmented irises that do not block light well, so their retinas are constantly dazzled with light, leading to retinal degeneration. Hence, the visual acuity of albinos is much worse than normally pigmented rats, around 20/1200. Rats probably use their vision to detect large, moving, distant objects and to orient themselves in space. At close range, rats rely on other senses: whisker touch and smell. http://www.ratbehavior.org/RatVision.html Human vision Normally-pigmented rats have blurry dichromatic vision with a little color Albino rats may see a very blurry, light-dazzled world

24. while the world may look blurry to the rat... his whiskers will provide detailed information about what he can touch as he moves through the landscape. SMELL AND HEARING Over 1% of his DNA is devoted to detecting odours.  humans can hear up to 20 kHz, but rats can hear up to 90 kHz!

25. The rat's tail has a thermoregulatory function: it serves as a heat-loss organ. H as a large surface to volume ratio, and is perfused with many blood vessels, especially at the tail tip and midlength . THERMOREGULATION http://www.ratbehavior.org/RatTails.html Cross section of the base of a rat's tail at two different body temperatures (37º and 40º C). At 40º C, the diameter of the blood vessels (especially the veins) is larger than at 37º C. This larger diameter permits more blood to flow through the tail: 15% more blood flows through the arteries and 125% more flows through the veins at 40º C than at 37º C. Adapted from Vanhoutte et al. 2002.

26. FEEDING Rats are omnivorous, like humans. Lab blocks( contain all the essential vitamins, minerals, amino acids, fatty acids and macronutrients) provide the best nutrition for rats. Having fresh water at all times ensures the rat is not at risk for dehydration.  S igns that rat may be protein-deficient: Chronic infections Stress fractures in bones Hair loss http://ratguide.com/care/nutrition/diet.php

27. COPROPHAGY Coprophagy is the eating of excrement and is a normal nutritional behaviour for rats. Rats will regulate the amount of feces eaten according to their nutritional needs . Thiamin and pantothenic acid deficiencies will cause a marked increase in coprophagy. Preventing rats from eating their feces can lead to deficiencies of vitamin K, complex B vitamins, and biotin and can cause other vitamin deficiencies to develop. when not permitted to ingest their fresh feces show a stunted growth rate.

28. ENVIRONMENT Rats do need periods of total darkness or else they can experience health and even reproductive problems. Temperature: 20-26 degrees Centigrade (68-78.8 Fahrenheit). Ambient temperature for breeding : 24-26 degrees Centigrade (75.2-78.8 degrees Fahrenheit). Relative humidity: 30-70% H ousing area: 40 inch² per 300 gm wt. of rat P roper bedding, hide away areas, toys, and accessories to provide a healthy and stimulating environment for your rat. Cleanliness is a must for rat housing because Ammonia buildup can cause damage to their delicate respiratory systems . http://ratguide.com/care/environment/

29. Dose Conversion Calculations Larger animals have lower metabolic rates. Physiological process of larger animals is slower. HED (mg / kg )=Animal NOAEL (mg / kg) × {Animal Weight(kg)/human Weight(kg)}^1-0.67 0.67 account for difference in metabolic rate, to convert doses between animals and humans. NOAEL : no observed adverse effect levels. LEVEL: Refers to the dosage, generally expressed as mg / kg HED: Human Equivalent dose

30. EXAMPLE: For a newly developed drug molecule, the NOAEL value in rat weighing approximately 150 g is 18 mg/kg . HED mg / kg = 18 ×( 0.15 / 60)^0.33 = 2.5 mg / kg Thus, for a 60 kg human, the dose is 150 mg. This HED value is further divided by a factor value of 10; thus, the initial dose in entry into man studies is 15 mg. Body weight is not the lone factor which influences the scaling for dose calculation . Km= average body weight (kg) / BSA HED mg / kg = Animal dose (mg/kg) × (Animal Km / Human Km) Nair, A., & Jacob, S. (2016). A simple practice guide for dose conversion between animals and human. Journal of Basic and Clinical Pharmacy, 7(2), 27. doi:10.4103/0976-0105.177703 

31. EXAMPLE: Rat dose (50 mg/kg) by 6.2 or multiply by 0.162, the HED is 8.1 mg/kg.

32. Comparative Anatomy

33. Skeletal System

34. Skeletal system Rat Human Vertebrae C 7 T 13 L 6 S 4 C 27-31 C 7 T 12 L 5 S 5 C 4 Osteon (Haversian system) Absent Present Epiphyseal growth plate Persist throughout life Persistent only during growth and development Bone marrow Persistent throughout in axial and appendicular skeleton Persistent only in long bones in adults

35. Nervous System http://www.gensat.org/imagenavigator.jsp?imageID=92969 https://www.researchgate.net/figure/1-An-illustration-of-the-human-brain-with-several-regions-labeled-Source-Heart-and_fig5_291346848

36. Brain Rat Human Lobes defined by external landmarks Absent Present Sulci and Gyri Absent Present Olfactory bulb Very large Small Meninges Thin Thick, well developed Basal ganglia Combined caudate nucleus and putamen Separate caudate nucleus and putamen Spinal Cord Rodent Human Spinal formula C7 T13 L6 S4 Cd27-30 C7 T12 L5 S5 Cd4 Spinal Cord Terminates at the level of the intervertebral disc between L3 and L4 Terminates at the level of the intervertebral disc between L1 and L2 Sciatic nerve origin Rat: L4-L5 L4-S5 Lateral horn Less prominent More prominent

37. Respiratory System

38. Circulatory System

39. Heart Rat Human Heart shape Oval to spherical Conical Heart weight 0.5-2.5 g 200-300 g Heart rate 300-400 beats/min 60-100 beats/min Cardiac output 70-80 ml/min 4.5-5.5L/min Rests on diaphragm No Yes Location of coronary arteries Intramyocardial Extramyocardial

40. Lymphatic System

41. The lymph nodes of rodents are very small compared to human lymph nodes; therefore, histological appearance varies based on the plane of section in rodents more so than for human nodes. Lymph nodes in young rodents do not have well developed germinal centers, whereas germinal centers are seen in humans at all ages. Distribution of B- and T-cells within lymph nodes is the same in all three species (mice, rat and humans). Spleen: Red pulp in the rodent is a site of normal hematopoiesis. In the adult human, significant extramedullary hematopoiesis is not normal. The B-cell zone predominates in the rodent white pulp, whereas the T-cell zone predominates in the human spleen. Tonsils are absent in rodents but present in humans.

42. Digestive System RAT HUMAN

43. Rat Liver Vs Human Liver Comparative Anatomy and Histology: A mouse, Rat and Human Atlas, 2 nd Edition

44. Rat Human Esophagus Well defined upper and lower sphincter Well defined upper sphincter whereas lower sphincter is less well defined Stomach Forestomach: Present Rugae folds: Present Forestomach: Present Rugae folds: Present Small Intestine Length: ~170 cm Length: ~7000 cm Large Intestine Functional cecum is present Cecum is present but not functional

45. Non-Alcoholic Fatty Liver Disease Nonalcoholic fatty liver disease (NAFLD) includes simple fatty infiltration (a benign condition called fatty liver), whereas nonalcoholic steatohepatitis (NASH) is defined as the presence of fat leading to lipotoxicity and inflammatory damage to hepatocytes. Histologically, NASH is indistinguishable from alcoholic hepatitis. Possible mechanisms for steatosis include reduced synthesis of very low density lipoprotein (VLDL) and increased hepatic triglyceride synthesis (possibly due to decreased oxidation of fatty acids or increased free fatty acids being delivered to the liver). Inflammation may result from lipid peroxidative damage to cell membranes. These changes can stimulate hepatic stellate cells, resulting in  fibrosis . If advanced, NASH can cause  cirrhosis  and  portal hypertension . In response to chronic injury, bridging cords of collagen and nodular regeneration characteristic of cirrhosis are readily apparent in the human liver and to a lesser extent in the rat, but rarely occur in the mouse despite enthusiastic claims of “cirrhosis.”

46. Currently, there is no non-invasive biomarker available for the diagnosis of NAFLD and NASH. Rats serve as important disease model to understand the pathophysiology of NAFLD/NASH.

47. Cirrhosis is a late stage of hepatic fibrosis that has resulted in widespread distortion of normal hepatic architecture. Cirrhosis is characterized by regenerative nodules surrounded by dense fibrotic tissue. Symptoms may not develop for years and are often nonspecific ( eg , anorexia, fatigue, weight loss). Late manifestations include portal hypertension, ascites, and, when decompensation occurs, liver failure. Cirrhosis is usually considered irreversible. Rats plays an important model to study the pathophysiology of cirrhosis which mainly include portal hypertension. Cirrhosis

48. Endocrine System

49. Urinary System

50. RAT HUMAN Female Reproductive System

51. Male Reproductive System

52. Routes of Drug Administration in Rats Route Needle size Maximum Volume Intra-muscular 22-30 G 0.3 mL Subcutaneous 22-30 G 5 mL Intradermal (must be done under anaesthesia ) 25-30 G 0.1 mL Intraperitoneal (Lower left/right quadrant of abdomen at 30˚ angle) 22-30 G 5 mL Intravenous (Injection site – Lateral vein) 25-30 G 0.5 mL Oral gavage (Length of the needle from the tip of the nose to the first rib)

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