This article is from the Jan./Feb. 1996 AFRMA Rat & Mouse Tales news-magazine.

By Carmen Jane Booth, D.V.M.

From C. J. Booth, D.V.M.
RE: Head Tilt/Red Eye Discharge
Ms. Royer did a great job answering questions; what follows is additional or expanded relevant information.

The internal ear is the organ for both hearing and equilibrium (balance) and consists of fluid-filled ducts and sacs (semicircular canals and cochlea) within a bony labyrinth that conduct impulses (information) via the eighth cranial nerve (Vestibulocochlear) regarding the orientation of the body in space and hearing to the brain. If there is abnormal pressure in the inner ear (as may occur in a severe bacterial infection), incorrect impulses are sent to the brain regarding the body's position. This causes the animal to tilt its head, circle, or even roll to try and orientate itself. This may also occur if there is pressure or inflammation (as from a tumor) anywhere along the Vestibulococular nerve on its path into the brain or in the hearing centers in the brain itself. This can be a difficult area to treat as many oral and topical antibiotics have difficulty reaching the inner ear. Oftentimes, even if the infection is resolved, there is so much damage in the inner ear that the abnormal behavior continues.

Behind each eye in rats is the Harderian gland. This gland is larger than the eyeball itself, secretes a lipid (fat) and red (porphyrin-rich) secretion that lubricates the eye and lids. Illness or stress from any cause can cause these red tears to overflow and stain the face and nose. The dried, red-porphyrin crusts contain little or no blood.

There are few parasites that can infest both rats and humans and are extremely rare in domestic rats. Many people who work with or have rodents as pets develop an allergic/hypersensitivity reaction over time. Hypersensitivity reactions include nasal congestion, runny nose, itchy eyes, asthma, and a variety of skin manifestations. The most common allergen is the urine. Since domestic rats often have needle sharp toenails, they can abrade the skin and exacerbate the problem. Rats and mice by the nature of their normal behavior tend to have urine on their feet and in their hair. Bathing them occasionally, housing them on wire bottom cages, keeping their nails trimmed, and minimizing direct skin contact may help minimize problems. Some people develop severe reactions. Anyone who is concerned should contact their physician for suggestions on appropriate treatment or medication.

This past year at the annual meetings of The American Veterinary Medical Association and The American Association of Laboratory Animal Science, there was a lecture concerning pain medication for rodents given by the same veterinarian. Her conclusions were that most medications were ineffectual outside of certain controlled substances, such as morphine, given frequently (every two hours) because of the high metabolic rate of rodents.

Bantam Medical Dictionary definition: any one of a group of disorders of brain function characterized by recurrent attacks that have a sudden onset. Idiopathic epilepsy is not associated with structural damage to the brain. It includes *grand mal and *petit mal, which can be controlled by the use of different *anticonvulsant drugs.

Focal (or symptomatic) epilepsy is a symptom of structural disease of the brain, and the nature of the seizure depends upon the location of the disease in the brain. In jacksonian epilepsy the epileptic discharge spreads over the cerebral cortex, with the resulting manifestations spreading throughout the body. In a Jacksonian motor seizure, the convulsive movements might spread from the thumb to the hand, arm, and face (this spread of symptoms is called the march). Temporal lobe (or psychomotor) epilepsy is caused by disease in the cortex in the temporal lobe or the adjacent parietal lobe of the brain. Its symptoms include *hallucinations of smell, taste, sight, and hearing, paroxysmal disorders of memory, and *automatism. Throughout an attack, the patient is in a state of clouded awareness and afterward he may have no recollection of the event.

In the past two issues of Rat and Mouse Tales, Pamela Sorrentino has been telling us of her pet rat “Porkchop” and the ordeal she faced with epilepsy. In this issue is the conclusion of the story; the necropsy results are as follows:

From Pamela Sorrentino, Sciutate, MA

Lungs okay—mycoplasma was kept out of the lungs due to the intensive antibiotic therapy. There was a mass around the pituitary and middle ear (this was what was causing the seizures). The liver was enlarged and yellow, internal tissues yellowed. The adrenal glands had a fatty area around them.

Liver: Section of liver characterized by extensive peripheralobular (pertaining to/located on lobes) and sinusoidal (curvatious) infiltrates (accumulation) of broad sheets of a population of large, highly pleomorphic (many structural forms) round cells. These contained irregular round to oval to clefted heterochromatic (different colored) nuclei with a high mitotic (division) rate and variable amounts of eosinophilic (easily accepts eosin dye) cytoplasm. Many cells contained giant often bizarre and multiple nuclei. There was an extensive effacement (obliteration) of hepatocellular parenchyma (liver tissue cells).

Other organs: Similar populations of neoplastic round cells diffusely infiltrate the spleen, peribronchiolar (around lung bronchi) and interalveolar (between/among lung alveoli) interstitium of the lung, adrenal glands, meninges and neurpil of the cerebral cortex and tympanic bulla.

** Note that the tissue necropsy showed that organs that looked completely normal in the gross necropsy, were actually diseased. This goes to show that a gross necropsy is just not enough if you really want to know what happened; tissue necropsys are necessary to truly diagnose.

Diagnosis: Liver, spleen, lung, adrenal, brain, bulla: Histiocytic Sarcoma.

Kidneys were normal.

Pathologist comment: This variant of myeloproliferative disease in rodents is considered spontaneous and not thought to be associated with any of the mouse oncogenic viruses.

Neoplasms of this nature most often found in animals over 12 months of age with no obvious sex predisposition. The cell of origin in histiocytic sarcoma is thought to be a component of the mononuclear phagocyte system (bacterial defense system), possibly the tissue macrophage. One of the major products secreted by these macrophages is lysozyme (destroys the bacteria). In the rat lysozyme has been identified in the cells of the histiocytic sarcomas and the enzyme has been proposed as a reliable and specific tumor marker for this tumor type.

The liver involvement is typical of histiocytic sarcoma and provides impetus to select that diagnosis over others. Histiocytic sarcomas are most commonly localized to the uterus and/or ovaries of female mice, and/or the liver of both sexes. In mice, Histiocytic sarcomas has been found in high incidence in mice subjected to prolonged antigenic stimulation (the antigen or bacteria. In Porkchop's case this would have been the mycoplasma. The constant presence of the bacteria would have caused a constant immunological response; the macrophages/WBC constantly being mobilized to fight off the bacteria).

If the causative agent is antigenic stimulation, then perhaps if more people had their rats necropsied (tissue necropsied) we would see a higher incidence of this. The cancer was a big surprise to both me and my vet. It just goes to show that the only way we can ever totally know about disease and life is to study the cause of death. What you think happened is not always what did, and so little is known about rats that the only way we are going to be able to prolong life is to find out about the problems that shorten them, and the only way we will know this is to necropsy. Also be aware that inbreeding, while producing beautiful colors/markings also can have an effect on the physical well-being of any animal, decreasing resistance to disease. I wonder maybe that since Porkchop was a rather rare breed (Blue Satin Hooded) if maybe she had a predisposition to anything.

Back to top