Rat Anatomy and Biology

1. Rat Anatomy and Biology

2. Introduction • Rattus norvegicus (“Norway rat”) • Laboratory rat • Pet rats • Came from Asia to Europe at the beginning of 1700’s • Rattus rattus (“black rat”) • Many strains (inbred- brother/sister matings for 20 generations) and stocks (outbred) used in research • Outbred stocks used as pets

3. Norway Rat Albino Wild

4. Black Rat (Rattus rattus) has faded away

5. Strains & Stocks • Common outbred rat stocks: • Wistar, Sprague-Dawley, Holtzman (albino) • Long-Evans (“hooded”) • Smart, sociable, docile, trainable • Excellent pets if handled gently

6. Hooded Rat • Wistar Wistar

7. Terminology • Dorsal - the back or upper surface • Ventral - the belly or lower surface • Lateral - the side • Anterior - the front or head end • Posterior - the hind or tail end • Medial - toward the midline of the animal • Proximal - closer to the midline of the body • Distal - farther from the midline of the body • Superficial - near the surface • Deep - a distance below the surface

8. External Features • Vibrissae - These are groups of very long hairs found just behind the nose and above the eyes. They are tactile organs very useful to a nocturnal animal • Ear - The long flexible fold of the ear is called the pinna. It is composed of cartilage covered with skin. • Eyes - Notice that the eyes are placed anteriorly in the skull. The central area through which light enters the eye is the pupil. • External nares - Look for this pair of openings near the tip of the snout. Air can be drawn through these openings into the respiratory system

9. Skeletal System • The skeletal system supports the body against gravity and provides a protective encasement for some of the vital organs such as the brain and heart. • There are two main parts to the vertebrate skeleton: -The axial skeleton, which is composed of the skull, mandible, vertebral column, ribs, and sternum; - The appendicular skeleton, which is composed of the limbs and the pectoral and pelvic girdles

10. Rat Skeleton

11. Most of the rodents share a dental formula of: 2 (I 1/1, C 0/0, P0/0, M 3/3) The incisors are open rooted and grow continuously; the molars don’t. Incisors will develop a yellow-orange color as the animal age.

12. Anatomy & Physiology • Hypsodontic incisors (grow continuously) • Brachiodontic molars • Harderian gland- porphyrin production: oversecretion (chromodacryorrhea) when stressed or sick • Brown fat- thermogenic

13. Porphyrin from Harderian Gland

14. Brown Fat Function: Stores Glycogen Regulate Temperature

15. Anatomy & Physiology • Stomach anatomy (limiting ridge) prevents vomiting • No gallbladder

16. Rat Stomach Rodents are monogastric with their Stomach divided in two areas; One glandular portion One nonglandular portion

17. Coprophagy • Rats and mice eat their own feces. • Important for obtaining vitamin B produced by bacterial action in the colon. • Directly from anus – grid floor does not prevent. • Preventing coprophagy decreases growth by 10-20%. • Important in pharmacology with per OS administration.

18. Reproductive Anatomy • Inguinal canals remain open • Bicornuate uterus (duplex) • 6 pair of mammary glands: 3 thoracic, 3 inguinal • Sexing: urogenital distance (Males > Females • Scent glands (male accessory sex gland)

19. Sexing Male Female

21. Reproductive Physiology • Puberty ~2-3 mo. (strain variation) • Maximal fertility 3.5-10 months of age • Estrous cycle length: 4-5 days • Copulatory plug left by male • Can palpate pregnancy by 12 days of gestation • Gestation length 19-23 days (avg=21)

22. Parturition • Nest-building ~ 5 days prepartum • 1.5-4 hrs prepartum = fluid discharge • Parturition takes 1-2, to several hrs. • Dystocia is rare • Average litter size is 6-12 pups • Cannibalism in rats means dam is stressed

23. Parturition and Neonatal Life • Pups are altricial (helpless), hairless, and nidicolous (blind) • In utero maternal antibody transfer and via milk until around day 21 of age

24. More rats!!! • Females go into heat between about 10 and 24 hours after giving birth. Specifically, females go into heat on the first evening that is at least 10 hours after giving birth (Gilbert et al. 1985). This phenomenon of coming into heat shortly after giving birth is called postpartum estrus.

25. Timed Pregnacies • Vaginal smears • Groups of females housed with a male and monitored • Rats usually mate at night • After mating (post coitus) a vaginal plug forms and falls out in about 24 hrs. • Place a dark paper on cage floor and look for the plug to confirm mating • Then remove male

26. Rat Pup Development • Incisors erupt at 6-8 days • Fully haired by 7-10 days • Eyes open at 10-12 days • Weaning at 21 days • Lifespan: 2.5 - 3 years • Adult weights: • Female ~ 250-300g • Male ~ 300-600g

27. Behavior and Handling • Docile, easily trained • Nocturnal • Coprophagic • Males are more sociable than females mice • Males prefer company but tolerate single housing

28. No musty odor like mice • Males can be housed together • Females can be housed together, post parturient females may fight among.

29. Housing & Husbandry • Most rats are housed in shoebox cages composed of polypropylene (opaque) or polycarbonate material (clear) with a wire bar lid used to hold the water bottle and feed. • Bedding is placed directly into the shoe box cage allowing the absorption of urine and the animal to burrow. • This type of cage will hold 1-3 adult rats depending on the size of the cage

30. Housing & Husbandry • Caging: “Shoe-box” • Germ free • SPF (specific pathogen free) • Conventional • Solid floor

31. Housing & Husbandry • Optimal temperature range: 65-79 °F • Keep humidity >40% to prevent ringtail • Water requirement: • 10 ml water/100g BW/24 hrs • Medicating water may reduce intake

32. Pelleted natural ingredient diets are used to feed all rodents and are composed primarily of cereal grains which are supplemented with additional protein, vitamins and minerals • Balanced all-in-one pelleted diet • 5 g food/100g BW/24 hrs • Do not supplement: obesity Need hard diet to wear teeth down

33. Commercial Diets