Echinococcus multilocularis: responses to infection in cotton rats (Sigmodon hispidus)

Various aspects of the responses of cotton rats to intraperitoneal infections with Echinococcus multilocularis were examined to determine if they could be related to the progress of the infection. At 14 weeks post-infection, infected animals had enlarged spleens; there was a slight decrease in packed cell volume, but no reticulocytosis. The number of all four types of leukocytes in the peripheral blood (lymphocytes, monocytes, neutrophils and eosinophils) increased during the course of the infection. In the peritoneal fluid, the numbers of neutrophils increased, monocytes and basophils decreased, and lymphocytes and eosinophils remained unchanged. Antibodies to E. multilocularis were detected in the serum of infected cotton rats as early as 2 weeks post-infection. The mean levels of transaminases (SGOT and SGPT) in the serum of infected animals were higher than in controls, and 5'-nucleotidase levels were elevated in heavily infected animals. There were no differences in responses between male and female animals. Comparison with results previously obtained suggest that both the outcome of the infection, and responses to it, may be under host control.     

Effects of social environment on sexual maturation in female cotton rats (Sigmodon hispidus)

Age at sexual maturation among female cotton rats was measured in a variety of intraspecific social environments. Two experiments were conducted. In Experiment I, female cotton rats attained vaginal perforation and first estrus at younger ages and lighter body masses when paired from weaning with a conspecific juvenile male than when caged alone. In Experiment II, these findings were replicated and extended. Females housed with juvenile males matured at the youngest ages, while those housed alone matured at the oldest ages. Females housed with adult males matured at intermediate ages. Presence of a second juvenile female during maturation was significantly associated with early vaginal opening but not with early first estrus. The results of this study are discussed in context of similar social environmental effects on female sexual maturation that have been identified in other rodent species.     

Pathogenesis of adenovirus type 5 pneumonia in cotton rats (Sigmodon hispidus).

Cotton rats (Sigmodon hispidus) were inoculated intranasally with 10(2.0) to 10(10.0) PFU of human adenovirus type 5. The virus replicated to a high titer in pulmonary tissues, with the peak titer being proportional to the input dose. The 50% lethal dose was 10(9.4) PFU. Histopathologic changes were proportional to the infecting inoculum and included the infiltration of interstitial and intra-alveolar areas, moderate damage to bronchiolar epithelium, and cellular infiltration of peribronchiolar and perivascular regions. These changes could be divided into two phases: an early phase (affecting alveoli, bronchiolar epithelium, and peribronchiolar regions) with an infiltrate consisting primarily of monocytes-macrophages and neutrophils, with occasional lymphocytes, and a later phase (affecting peribronchiolar and perivascular regions) with an infiltrate consisting almost exclusively of lymphocytes. In both phases, the predominant process was the response of the host to infection, rather than direct viral damage to infected cells. An infecting inoculum of 10(8.0) PFU or larger caused severe damage to type II alveolar cells, which were swollen, showed a loss of lamellar bodies, and were surrounded by polymorphonuclear leukocytes and macrophages. No evidence of complete viral replication was found in type II alveolar cells.     

Fatal Caryospora bigenetica (Apicomplexa: Eimeriidae) infections in cotton rats, Sigmodon hispidus

Four groups of cotton rats, Sigmodon hispidus, were shown to be suitable secondary hosts for the viperid coccidium, Caryospora bigenetica, following oral inoculation of a mixture of oocysts and sporocysts. Swelling of the face, ears, and scrota and hemorrhagic ears were the predominant clinical signs and some cotton rats died in 3 of 4 experiments. Developmental stages of C. bigenetica were found in connective tissue components of the ear, nose, cheeks, anal skin, scrotum, and penile sheath of all cotton rats in which these tissues were examined. Additionally, developmental stages of C. bigenetica were found in connective tissue components of the following tissues examined from some cotton rats: tongue, lung, testicle, epididymis, rectum, base of the tail, footpad, and bone marrow. The present study shows that C. bigenetica can be pathogenic for cotton rats and demonstrates many new anatomic sites for developmental stages of this parasite in the secondary host.     

Sarcocystis sigmodontis n. sp. from the cotton rat (Sigmodon hispidus)

Sarcocystis sarcocysts were found in 3 of 4 cotton rats (Sigmodon hispidus) from Atlanta, Georgia. Sarcocysts were several centimetres long and were present only in skeletal muscles. The sarcocyst wall appeared thin (less than 1 micron), with minute projections in the light microscope. By transmission electron microscopy, the sarcocyst wall had 0.6-1.0 x 0.21-0.36-micron villar protrusions without microtubules. The metrocytes were 6.5 x 3.8 micron, and the bradyzoites were 8 x 2.7 micron. The sarcocysts were not infectious for dogs and cats. The parasite was named Sarcocystis sigmodontis because it differed from all sarcocysts in rodents.     

Inclusion bodies in pinealocytes of the cotton rat (Sigmodon hispidus)

Pinealocytes of the cotton rat (Sigmodon hispidus) often contain large (2-6 micron diameter) intracytoplasmic inclusions, the function of which is not known. These inclusions may represent nucleolus-like bodies, mineral deposits, secretory products or viral inclusions. In this study these inclusions were classified as type A, B or C inclusions based on the amount of electron-dense material interspersed within the finely granular material comprising the bulk of these inclusions. Each type of inclusion was analyzed by X-ray microanalysis and enzymatic proteinaceous digestion. X-ray microanalysis of these inclusions differed both quantitatively and semiquantitatively from that of human or gerbil pineal concretions, the latter two of which are extracellular deposits. Pronase, a proteolytic enzyme, digested the electron-dense material only after longer times of tissue exposure to this enzyme in contrast to the easily digested, finely granular matrix-like material of these inclusions. Such intrapinealocytic inclusions have only been observed in the cotton rat. Their functional significance remains unknown.     

Hematologic and coagulation studies on cotton rats, Sigmodon hispidus

1. Blood coagulation factor levels and the normal ranges of commonly used coagulation tests were established for Sigmodon hispidus. 2. The white cell, red cell and platelet counts have been determined together with the red cell parameters as measured by the Coulter model S-plus. 3. The relationship between the results reported here and those published for related species are discussed.     

Neuroendocrine (ECL cell) differentiation of spontaneous gastric carcinomas of cotton rats (Sigmodon hispidus).

BACKGROUND AND PURPOSE: Female inbred cotton rats develop adenocarcinomas in the oxyntic mucosa. Since a female preponderance is typical for enterochromaffin-like (ECL) cell tumors, we examined such tumors for ECL cells. Gastrin plays a decisive role in ECL cell tumorigenesis, so blood gastrin concentration and gastric mucosal pH were measured. METHODS: The stomachs from six female cotton rats (6 to 8 months old) were studied histologically, and at euthanasia, gastric mucosal pH was determined. Euthanasia was performed on 15 other female cotton rats of similar age for determination of blood gastrin values by radioimmunoassay (RIA) and gastric mucosal pH. Rats were classified macroscopically to have normal or thick oxyntic mucosa, with or without tumor. RESULTS: Among the six cotton rats studied histologically, two 6-month-old rats had normal and two others had thick gastric mucosa, whereas two 8-month-old rats had thick mucosa with tumors. The ECL cells were markedly hyperplastic in all rats with thick mucosa, and ECL cells were found in the neoplastic parenchyma. All cotton rats with normal-appearing gastric mucosa had pH <2.5, whereas 14 rats with thick mucosa had pH >3.1 and hypergastrinemia. CONCLUSIONS: Gastrin may play a major role in ECL cell hyperplasia and, perhaps, in adenocarcinoma genesis.     

Diversifying animal models: the use of hispid cotton rats (Sigmodon hispidus) in infectious diseases

The hispid cotton rat (Sigmodon hispidus) has been a longstanding laboratory animal model of infectious diseases. In this review, the most common usage of hispid cotton rats as models of infectious diseases is discussed in detail and all organisms, which have been shown to infect cotton rats, are listed. A state of the art overview is given on handling and maintenance of hispid cotton rats as well as experimental techniques such as narcosis and blood withdrawal. Most importantly, through the development of new reagents, the hispid cotton rat can be used to study immune responses against the respective pathogen. Hispid cotton rat cytokine and chemokine genes have been sequenced and cotton rat specific antibodies and cell lines have been produced which in connection with the establishment of immunological methods should facilitate the use of hispid cotton rats as animal models in the pathogenesis of infectious diseases.     

Assessment of space-use patterns in the hispid cotton rat (Sigmodon hispidus)

Summary Ecological interpretation of space use patterns often suffers from two methodological problems: inadequate number of captures per individual and pooling of data over time intervals. Insufficient sample size biases the computation of spatial areas, while pooling data over time intervals may mask shifts in space use due to changes in resource abundance. Radiotelemetry was used to alleviate these problems in an analysis of space use by the hispid cotton rat (Sigmodon hispidus). Home range area was greater for males than females, was largest during summer and winter months, was positively correlated with body hass, and was negatively correlated with population dencity. Exclusivity of home range revealed a high degree of ntolerance (41% exclusivity) and was positively correlated with body mass for males. In addition, like-sex categories (male-male, female-female) were more exclusive than unlike sex categories (male-female).Habitat composition of home ranges of females was significantly different from that of males and from that available. This result suggested home ranges of females were responsive to habitat composition (and quality), while males may respond more to female occurrence than resource availability.Space-use patterns of the hispid cotton rat indicated a solitary existence with greater tolerance of individuals of the opposite sex. Home range size decreased as population size increased, whereas home range overlaps were not affected by population density. These results reinforced the view of a dominance hierarchy in this species and suggested the existence of a polygynous mating system.     

Immune function and hematology of male cotton rats (Sigmodon hispidus) in response to food supplementation and methionine

We examined effects of supplementation of food quantity and quality (=enhanced methionine) on hematologic and immunologic parameters of wild, but enclosed, adult male cotton rats (Sigmodon hispidus) in north-central Oklahoma. Sheet metal enclosures were stocked with a high density of wild-caught cotton rats (160 animals/ha) and randomly assigned a treatment of no supplementation, mixed-ration supplementation or methionine-enhanced supplementation. Aside from small increases in counts of red blood cells and hematocrit levels, most indices of erythrocytic characteristics were not affected by supplementation with the mixed-ration or enhanced methionine. In contrast, platelet counts were highest in mixed-ration and methionine treatments and counts of total white blood cells were highest with methionine supplementation, albeit relative proportions of different leukocytes did not differ among treatments. Immunologically, neither delayed-type hypersensitivity response nor hemolytic-complement activity differed among treatments. Supplementation of food quantity and quality did not broadly affect hematologic parameters and immune function of male cotton rats, but enhanced platelet and leukocyte counts may confer advantages to overall health. Clarification of the role of such effects on population limitation or regulation requires additional research.     

Variation in chromosomes of the cotton rat,Sigmodon hispidus

Chromosomes were analyzed from 38 hispid cotton rats, currently assigned to the species Sigmodon hispidus, from populations in southeastern and western United States. Cotton rats from southeastern United States had a 2N of 52 and an F. N. which varied from 52 to 54. Specimens from Obion County, Tennessee, and Highlands County, Florida, were found to be polymorphic with a varying number of arms on the largest pair of autosomes. Cotton rats from Arizona had a 2N of 22 and an F. N. of 38; each pair of chromosomes is distinguishable, and a numbering system is proposed. The cytological data suggest that cotton rats from the southeastern populations and those from the Arizona populations belong to separate species, though morphological characters do not indicate such a difference.     

Ultrastructure of pinealocytes of the cotton rat,Sigmodon hispidus

Summary Fine structural features of pinealocytes of cotton rats (Sigmodon hispidus) were examined. Golgi complexes, mitochondria, endoplasmic reticulum and polysomes are usual organelles seen in the perikaryonal cytoplasm of pinealocytes. Many non-granulated vesicles (40 to 80 nm in diameter) and a few granulated vesicles (about 100 nm in diameter) are associated with the Golgi cisternae. Occasionally, the cisternae contain granular materials. The perikaryonal cytoplasm of pinealocytes is characterized by the presence of inclusion bodies. These bodies are usually round in shape, not bounded by a limiting membrane and composed of fine granular or filamentous materials of high electron-opacity, which are similar in appearance to the substance seen in the nucleolonema. Pinealocyte processes, filled with abundant non-granulated vesicles and some granulated vesicles, are mainly found within the parenchyma and occasionally in perivascular spaces.Supported in part by NSF grant no. PCM 77-05734 and NIH grant no. HD-10202 (Morphology Core)