Hamsters Hamsters Biology and Anatomy Biology and Anatomy

Syrian HamsterSyrian HamsterMesocricetus auratusMesocricetus auratus

TaxonomyTaxonomy

The Syrian or golden The Syrian or golden hamster belongs to hamster belongs to the order the order RodentiaRodentia, , family family CricetidaeCricetidae. Its . Its genus and species genus and species designation is designation is Mesocricetus Mesocricetus auratus.auratus. The Syrian The Syrian hamster is a desert hamster is a desert rodent, indigenous rodent, indigenous to northwest Syria to northwest Syria (orange area on this (orange area on this map of the map of the Mediterranean). Mediterranean).

Natural HistoryNatural History

This drawing depicts This drawing depicts the type the type of deep of deep chambered burrows chambered burrows Syrian hamsters dig in Syrian hamsters dig in the wild.the wild. Note that Note that there are separate there are separate chambers for food and chambers for food and for the nest. An actual for the nest. An actual burrow may extend 8 burrow may extend 8 feet underground and feet underground and may have additional may have additional chambers and chambers and entrances. Adult entrances. Adult hamsters usually live hamsters usually live alone and are very alone and are very aggressive and aggressive and territorial. territorial.

AdaptationsAdaptations

Syrian hamsters have made several Syrian hamsters have made several physiologic adaptations to their desert physiologic adaptations to their desert habitat. Like the gerbil, habitat. Like the gerbil, Syrian hamsters Syrian hamsters have a lower daily waterhave a lower daily water requirement than requirement than other laboratory rodents. They conserve other laboratory rodents. They conserve water by water by decreasing water excretion decreasing water excretion through the kidneysthrough the kidneys, lungs, and colon. They , lungs, and colon. They also developed the ability to also developed the ability to hibernatehibernate in in order to survive long periods of cold and order to survive long periods of cold and depletion of natural food supplies in the depletion of natural food supplies in the environment.environment.

DescriptionDescription

The Syrian hamster The Syrian hamster has a short stocky has a short stocky body body 15 to 20 cm long. Adult 15 to 20 cm long. Adult hamsters weigh from hamsters weigh from 110 to 140 g, with 110 to 140 g, with females slightly larger females slightly larger than malesthan males. Growth . Growth curves and adult body curves and adult body weights vary among weights vary among different commercial different commercial breeding stocks.. breeding stocks..

Typically, the haircoat is reddish-gold Typically, the haircoat is reddish-gold over the dorsum and sides with a gray-over the dorsum and sides with a gray-white ventrum. There are, however, color white ventrum. There are, however, color variations that range from albino to very variations that range from albino to very dark brown among stocks and strains, as dark brown among stocks and strains, as a result of genetic mutation a result of genetic mutation

Male Flank GlandsMale Flank Glands

The arrows in this The arrows in this image show the location image show the location of the of the flank glands, one flank glands, one of the unique anatomic of the unique anatomic characteristics of Syrian characteristics of Syrian hamstershamsters. Both male . Both male and female hamsters and female hamsters have complex flank have complex flank glands composed of glands composed of sebaceous glands, sebaceous glands, terminal hairs terminal hairs (indicated by the (indicated by the arrow), and pigment arrow), and pigment cells. cells.

ReproductionReproduction

Flank glands, this sebaceous glands Flank glands, this sebaceous glands are brown in color and are brown in color and play a part in play a part in mating behavior and territorial mating behavior and territorial marking behaviormarking behavior

Cheek pouchesCheek pouches

Hamsters have Hamsters have well-well-developed buccaldeveloped buccal or or cheek pouches cheek pouches beneath the skin on beneath the skin on the lateral sides of the lateral sides of the head, which can the head, which can expand to expand to 20 mm 20 mm wide when filled and wide when filled and measure 30 to 40 mm measure 30 to 40 mm long and 4 to 8 mm long and 4 to 8 mm wide when emptywide when empty

Gastrointestinal TractGastrointestinal Tract Cheek pouches- extended back to the Cheek pouches- extended back to the

scapula. These pouches can distend to quite scapula. These pouches can distend to quite a large size, allowing the hamster to a large size, allowing the hamster to transfer food and bedding from one point to transfer food and bedding from one point to

anotheranother

The cheek pouches have The cheek pouches have been called been called immunologically immunologically privileged sitesprivileged sites,, because because tumors from man or other tumors from man or other animals can be animals can be transplanted to them and transplanted to them and not be readily rejected by not be readily rejected by the hamster immune the hamster immune system. The reason why system. The reason why tumors can remain and tumors can remain and grow in the hamster grow in the hamster cheek pouches is not fully cheek pouches is not fully understood understood

The dental formula The dental formula for hamsters is 2(I for hamsters is 2(I 1/1 C 0/0 PM 0/0 M 1/1 C 0/0 PM 0/0 M 3/3) = 16.3/3) = 16. In other In other words, the Syrian words, the Syrian hamster has 2 upper hamster has 2 upper and 2 lower incisors, no and 2 lower incisors, no canines, no premolars, canines, no premolars, and 6 upper and 6 lower and 6 upper and 6 lower molars for a total of 16 molars for a total of 16 teeth. As with other teeth. As with other rodents, hamsters have rodents, hamsters have open-rooted incisors open-rooted incisors

Abdominal VisceraAbdominal Viscera

The liver is the dark, red-brown organ filling the The liver is the dark, red-brown organ filling the body cavity on the left. The liver is composed of body cavity on the left. The liver is composed of four lobes, with the gallbladder located in the four lobes, with the gallbladder located in the ventral medial lobe ventral medial lobe

Gastrointestinal TractGastrointestinal Tract Hamsters are monogastric with their Hamsters are monogastric with their

stomach divided in two portions one stomach divided in two portions one glandular & one nonglandular stomachglandular & one nonglandular stomach

NonglandularforestomachGlandular

Rodents can not regurgitate and the practice of coprophagy is believed to assimilate certain nutrients such as B vitamins The nonglandular forestomach acts like rumen and has higher pH than the glandular stomach

The cecum is The cecum is large and slightly large and slightly sacculated, with sacculated, with apical and basal apical and basal portions. portions. The The colon is relatively colon is relatively long compared to long compared to other rodents,other rodents, suggesting an suggesting an adaptation for adaptation for water retention.water retention.

Sexing Hamsters Sexing Hamsters

Sexual identification Sexual identification in hamsters is in hamsters is similar to other similar to other rodents. rodents. The The anogenital distance anogenital distance in the male is in the male is greater than in the greater than in the female (female (1). In the 1). In the male, the penis is male, the penis is retracted when the retracted when the animal is not mating animal is not mating

Sexing Hamsters Sexing Hamsters

Dorsal ViewDorsal View

Differentiation Differentiation between adult male between adult male and female hamsters and female hamsters is relatively simple. is relatively simple. The adult female has The adult female has a blunt posterior, a blunt posterior, while the male has a while the male has a bulge associated bulge associated with the scrotal sac with the scrotal sac

Sexing PupsSexing Pups Sexing of hamster Sexing of hamster

pups is somewhat pups is somewhat more difficult, but the more difficult, but the principle is the sameprinciple is the same—the animal with the —the animal with the longer anogenital longer anogenital distance is the male. distance is the male. Also notice in this Also notice in this image, that the image, that the mammary glands are mammary glands are much more distinct in much more distinct in the female pupthe female pup, which , which is on the left.is on the left.

Female Urogenital TractFemale Urogenital Tract

This image This image demonstrates the demonstrates the arrangement of the arrangement of the female urogenital female urogenital system, after the other system, after the other abdominal viscera abdominal viscera have been removed. have been removed. The ovaries are The ovaries are dorsolateral to the dorsolateral to the kidneys, 3 to 4 mm kidneys, 3 to 4 mm long, oval, and long, oval, and completely enclosed in completely enclosed in a bursa a bursa

Male Urogenital SystemMale Urogenital System

Large fat bodies or Large fat bodies or pads cover the pads cover the proximal portion of proximal portion of the testicles and the testicles and the epididymis the epididymis

Accessory sex Accessory sex glands include the glands include the large branched large branched vesicular glands vesicular glands

Brown fatBrown fat Brown adipose tissue or brown fat (between arrows) is Brown adipose tissue or brown fat (between arrows) is

primarily located ventral to and between the scapulae primarily located ventral to and between the scapulae or shoulder blades from the lower cervical spine to the or shoulder blades from the lower cervical spine to the mid-thorax. mid-thorax. In cold-acclimating, hibernating, or In cold-acclimating, hibernating, or neonatal animals, brown fat plays an important role in neonatal animals, brown fat plays an important role in thermogenesis or heat production by heating the blood thermogenesis or heat production by heating the blood passing through it. passing through it.

PHYSIOLOGYPHYSIOLOGY

Normative DataNormative Data Syrian hamsters have a normal life Syrian hamsters have a normal life

span of 18 to 24 months. span of 18 to 24 months. Normal body temperatures range Normal body temperatures range

from 98.6° to 100.4 ° F. from 98.6° to 100.4 ° F. The normal heart rate is 250 to 500 The normal heart rate is 250 to 500

beats per minute. beats per minute. Normal respiration is 33 to 135 Normal respiration is 33 to 135

breaths per minute, averaging 72. breaths per minute, averaging 72. (page 132)(page 132)

UrineUrine

Hamster urine is Hamster urine is milky white because milky white because it contains it contains calcium calcium carbonatecarbonate. The urine . The urine is highly is highly concentrated and concentrated and alkaline, with a alkaline, with a normal pH of 8. normal pH of 8. Because it is highly Because it is highly concentrated and concentrated and alkaline, the urine alkaline, the urine adheres to cage adheres to cage surfaces. surfaces.

Food and Water Food and Water Average food Average food

consumption is 8 to 12 consumption is 8 to 12 g of commercialg of commercial pelleted rodent food pelleted rodent food per day for adult per day for adult hamsters. Hamsters hamsters. Hamsters drink approximately drink approximately 8-8-10 ml of water per 100 10 ml of water per 100 g of bodyg of body weight per weight per day. This rate of water day. This rate of water consumption is similar consumption is similar to the gerbil, another to the gerbil, another rodent species rodent species indigenous to the indigenous to the desert. desert.

HibernationHibernation

Hibernation is a physiologic adaptation of Hibernation is a physiologic adaptation of many hamster species to harsh winter many hamster species to harsh winter environments. Hamsters are permissive environments. Hamsters are permissive hibernators who may avoid hibernation if hibernators who may avoid hibernation if there are insufficient food stores in the there are insufficient food stores in the burrow or may arouse from hibernation if the burrow or may arouse from hibernation if the temperature temporarily rises. temperature temporarily rises.

Cold exposure is considered an important Cold exposure is considered an important factor in inducing hibernation. factor in inducing hibernation. Hamsters may Hamsters may hibernate if the hibernate if the temperature falls below temperature falls below 48°F (8°C).48°F (8°C). Testicular regression or atrophy Testicular regression or atrophy due to decreasing photoperiod or daylight due to decreasing photoperiod or daylight predisposes male hamsters to hibernate predisposes male hamsters to hibernate

ReproductionReproduction Although the female hamster can be Although the female hamster can be

sexually mature as sexually mature as young as 4 to 6 weeksyoung as 4 to 6 weeks of age, breeding should not be allowed of age, breeding should not be allowed until the optimal age until the optimal age of 8 to 10 weeks. of 8 to 10 weeks.

The hamster has a The hamster has a 96 h or 4 day estrous 96 h or 4 day estrous cyclecycle

Ovulation occurs during estrus—about Ovulation occurs during estrus—about 18-19 h into day 1. 18-19 h into day 1.

During estrus, the female hamster is During estrus, the female hamster is receptive to the male receptive to the male

Post-Ovulatory DischargePost-Ovulatory Discharge

This image shows the This image shows the post-ovulatory post-ovulatory discharge, which is discharge, which is drawn into a long drawn into a long string. The end of string. The end of estrus and start of estrus and start of diestrus is marked by diestrus is marked by the appearance of this the appearance of this discharge, which fills discharge, which fills the vagina and even the vagina and even extrudes through the extrudes through the vaginal orifice. vaginal orifice.

Gestation and Parturition Gestation and Parturition

Gestation is from Gestation is from 15 to 16 days15 to 16 days duration, duration, usually averaging 16 days. usually averaging 16 days.

Imminent parturition is indicated by Imminent parturition is indicated by restlessness, increased respiratory rates, restlessness, increased respiratory rates, bloody discharge prior to delivery, and active bloody discharge prior to delivery, and active licking of the perineal area. licking of the perineal area.

Litter size usually ranges from Litter size usually ranges from 5 to 9 pups5 to 9 pups. . The short gestation period, 16 days The short gestation period, 16 days

compared to 21 days for rats and mice; and compared to 21 days for rats and mice; and the large litter size make hamsters an the large litter size make hamsters an excellent model for use in teratology or the excellent model for use in teratology or the study of the causes of fetal defects study of the causes of fetal defects

Postpartum Postpartum This is a picture of This is a picture of

7- to 10-day-old 7- to 10-day-old pups with their pups with their dam. dam. The dam and The dam and her pups should be her pups should be disturbed as little as disturbed as little as possible for the first possible for the first 7 to 10 days7 to 10 days. This is . This is especially true if especially true if she is primiparous, she is primiparous, as she may as she may cannibalize or cannibalize or abandon the litter. abandon the litter.

WeaningWeaning

The pups can be The pups can be weaned at 21 days of weaned at 21 days of ageage. Postpartum estrus . Postpartum estrus in the Syrian hamster in the Syrian hamster is infertile; the female is infertile; the female hamster will return to hamster will return to estrus when the litter estrus when the litter is weaned. is weaned.

A female hamster can A female hamster can produce from 4 to 6 produce from 4 to 6 litterslitters during her during her reproductive life span.reproductive life span.

Newborn hamsters weigh Newborn hamsters weigh from 2 to 3 g, and are from 2 to 3 g, and are hairlesshairless, with eyes and , with eyes and ears closed. The incisor ears closed. The incisor teeth are erupted. The teeth are erupted. The ears open on day 5, and ears open on day 5, and eyes open on day 15. In eyes open on day 15. In the female hamster, the the female hamster, the vagina opens at 10 days vagina opens at 10 days of age. By 21 days of age, of age. By 21 days of age, hamsters weigh 35 to 40 hamsters weigh 35 to 40 g; at 6 to 8 weeks of age, g; at 6 to 8 weeks of age, they approach adult they approach adult weights—the males will weights—the males will weigh from 85 to 110 g, weigh from 85 to 110 g, and females will weigh and females will weigh from 95 to 120 g from 95 to 120 g

RESEARCH USE OF SYRIAN RESEARCH USE OF SYRIAN HAMSTERSHAMSTERS

Use in researchUse in research Hamsters are the fifth most commonly used Hamsters are the fifth most commonly used

animal in researchanimal in research, behind mice, rats, rabbits, and , behind mice, rats, rabbits, and guinea pigs guinea pigs

Most of the hamsters used in research are Most of the hamsters used in research are outbred stocks used, for example, in outbred stocks used, for example, in cancer cancer research, infectious disease research, and research, infectious disease research, and behavioral studiesbehavioral studies. .

Inbred strains of hamsters have been developed Inbred strains of hamsters have been developed for specific research use, including for specific research use, including immunogenetics and genetic models of human immunogenetics and genetic models of human diseases.diseases.

Cancer researchCancer research

Syrian hamsters are valuable Syrian hamsters are valuable in cancer in cancer research, because they have a relatively research, because they have a relatively low incidence of naturally occurring low incidence of naturally occurring tumors when compared to other rodentstumors when compared to other rodents. . Hamsters are highly susceptible to viral Hamsters are highly susceptible to viral oncogenesis by experimental inoculation oncogenesis by experimental inoculation of viruses from other species. For of viruses from other species. For example, several human adenoviruses example, several human adenoviruses produce undifferentiated sarcomas at produce undifferentiated sarcomas at the site of inoculation in hamsters. the site of inoculation in hamsters.

Cheek pouchCheek pouch The cheek The cheek

pouches have pouches have been termed been termed immunologically immunologically privileged privileged sites sites because tumors because tumors can be can be transplanted or transplanted or inducedinduced and not and not readily rejected readily rejected by the hamster’s by the hamster’s immune system. immune system.

Infectious diseaseInfectious disease

Hamsters are utilized in infectious Hamsters are utilized in infectious disease research because they are disease research because they are susceptible to a wide variety of susceptible to a wide variety of bacterial, viral, and parasitic agents. bacterial, viral, and parasitic agents. The hamster has served as a model The hamster has served as a model of mycoplasma infection in man as of mycoplasma infection in man as well as a model of leishmaniasis well as a model of leishmaniasis (protozoan parasites) and (protozoan parasites) and toxoplasmosis.toxoplasmosis.

EpilepsyEpilepsy

The BlO86.93The BlO86.93szsz/Bio strain of hamster is a /Bio strain of hamster is a genetic model of epilepsy that has both a genetic model of epilepsy that has both a genetically determined proneness to genetically determined proneness to seizureseizure and an intrinsic trigger to induce and an intrinsic trigger to induce seizures. seizures.

Spontaneous seizures can occur in Spontaneous seizures can occur in hamsters from 30 to 60 days of agehamsters from 30 to 60 days of age and and may be induced by mild stress such as may be induced by mild stress such as changing cages. Seizures last from 2 to 5 changing cages. Seizures last from 2 to 5 hours hours

TeratologyTeratology

The Syrian hamster is valuable in The Syrian hamster is valuable in experimental teratology because of experimental teratology because of the ease of obtaining timed matings, the ease of obtaining timed matings, rapid embryonic development, rapid rapid embryonic development, rapid differentiation of the embryo at day differentiation of the embryo at day 8 of development, and low rate of 8 of development, and low rate of spontaneous malformations spontaneous malformations

Type of hamsters Type of hamsters

The image below shows a Chinese The image below shows a Chinese hamster (left), an Armenian hamster hamster (left), an Armenian hamster (middle), and a Syrian hamster (right). (middle), and a Syrian hamster (right).

ACLAM creditsACLAM credits

This program was developed for the This program was developed for the American College of Laboratory Animal American College of Laboratory Animal Medicine.Medicine.C. W. McPherson, DVM ChairC. W. McPherson, DVM ChairJ. E. Harkness, DVMJ. E. Harkness, DVMJ. F. Harwell, Jr, DVMJ. F. Harwell, Jr, DVMJ. M. Linn, DVMJ. M. Linn, DVMB. J. McGough, BS Medical CommunicationB. J. McGough, BS Medical CommunicationA. F. Moreland, DVMA. F. Moreland, DVMG. L. Van Hoosier, Jr, DVMG. L. Van Hoosier, Jr, DVM