![]() They are born hairless and their eyes open after 10-12 days. The young are born incompletely developed (altricius). Proestrus lasts 3-12 hours and has abundant nucleated non-cornified epithelial cells. Diestrus lasts up to 57 hours and there are abundant neutrophils and a few nucleated non-cornified epithelial cells. Metestrus lasts 21 h and usually has many neutrophils in the smear and scattered squamous epithelial cells. Estrus lasts up to 12 h and is indicated by the presence of large cornified cells in the vaginal smear. Giemsa or Diff-Quick® can also be used to stain the cells. Fixed specimens are then stained using Papanicolaou stain for best results and examined using a light microscope under low power. This material is then applied onto a microscope slide and processed as above. 25 ml of vaginal fluid a short time later. Samples for making a vaginal smear can also be collected by introducing 1.0 ml of saline into the vaginal cavity using a blunt tipped disposable pipette, and recovering. Air drying or dipping the slides in 100% alcohol does not produce but the very good cytologic preparation of rat vaginal smears. ![]() The specimen is spray fixed using 95% ethanol. The moist swab is then rolled onto a clean glass microscope slide. The swab should be applied gently against the vaginal wall and rolled slightly before withdrawing. ![]() Samples for making a vaginal smear can be collected by inserted a cotton tipped swab moistened with phosphate buffered saline into the vaginal cavity of a rat. Plugs persist for 16-24 hours and may last as long as 48 hours. Mating leads to formation of a vaginal plug. Such females will adopt a rigid posture with the hindquarters raised. Receptive females exhibit lordosis when a downward pressure is applied to the pelvis. Ovulation occurs at the end of metestrus. The stage of the estrous cycle can be determined by vaginal cytology. Rats have a four to five-day estrous cycle, divided into characteristic phases: proestrus, estrus, metestrus and diestrus. Mammary tissue is widely distributed and may extend to the lateral and dorsal areas of the abdomen. Rats have an os penis or os clitoridis associated with external genitalia. The inguinal canal remains patent throughout life. There is a vaginal closure membrane, which is lost at puberty. There are separate urethral and vaginal openings. Rats have two distinct cervices and uterine bodies. Rats can inflict severe bite wounds and must be handled gently and with care to avoid biting. They are nocturnal animals but adapt to their environments. ![]() Rats are burrowers and take advantage of that whenever the opportunity presented. Males can be co housed as fighting rarely occurs among adults. Young are raised communally with shared nursing responsibilities. The amount of secretions increases during stress and appears as 'red crusts' around the eyes and nostrils. Secretions from the gland contain varying amount a reddish-brown porphyrin pigment depending on the physiologic state, age, strain and sex of the rat. Rats have a large horseshoe-shaped Harderian gland deep within the orbit. The only treatment is to trim the teeth every 2-3 weeks, if malocclusion persists. There is no permanent cure for overgrown teeth. Malocclusion can be hereditary or follow trauma, disease or inappropriate diet and/or soft food. Due to this continuous growth of the incisors rats can have problems with incisor overgrowth when the upper and lower incisors do not meet properly (malocclusion). ![]() Molars are permanently rooted while the incisors have an open root and grow continuously. Rats have a pair of incisors and three pairs upper and lower of molars. Rattus norvegicus (brown rat) has a short tail compared to Rattus rattus (black rat), which has a much longer tail. Albino rats have poor eyesight and depend on facial vibrissae and olfaction for sensory input. The rat has short hair, a long naked tail, rounded erect ears, protruding eyes, a pointed snout with long whisker (vibrissae) and five toes on each foot. Strains were developed to study neuroanatomy, nutrition, endocrinology, genetics and behavior. Rats were first used for experimental purposes in the mid 1800s. The laboratory rat, Rattus norvegicus, belongs to the order Rodentia and family Muridae. ![]()
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