Male Cotton Rats Research Articles

Spontaneous Altered Hepatocellular Foci (AHF) in Captive Aged Male Cotton Rats ( Sigmodon hispidus)

Spontaneous altered hepatocellular foci (AHF) of basophilic type were observed in adult male cotton rats. The histological features of these foci were similar to those observed in Fischer 344 rats. However, an immunohistochemical technique with antibody to glutathione S-transferase placental form (GST-P) failed to stain these foci. Also normal bile ducts were not immunoreactive for GST-P. The presence of a gall bladder and of non-GST-P immunoreactive liver foci and bile ducts suggests that these cotton rats are phylogenetically closer to mice than rats.

Morphological, biochemical, and histopathological indices and contaminant burdens of cotton rats ( Sigmodon hispidus) at three hazardous waste sites near Houston, Texas, USA

Male cotton rats ( Sigmodon hispidus) were studied at three industrial waste sites near Houston, Texas, to determine whether various morphological, biochemical, and histopathological indices provided evidence of contaminant exposure and toxic insult. Only modest changes were detected in cotton rats residing at waste sites compared with reference sites. No single parameter was consistently altered, except hepatic cytochrome P-450 concentration which was lower (p < 0·05) at two waste sites, and tended to be lower (p = 0·11) at a third waste site. Elevated petroleum hydrocarbon concentrations were detected in rats at one waste site, but contaminant burdens of rats from the other sites were unremarkable. Unlike rats captured in summer, those trapped in winter exhibited hepatocellular hypertrophy and up to a 65% increase in liver: body weight ratio, cytochrome P-450 concentration, and activities of aniline hydroxylase, aryl hydrocarbon hydroxylase, and glutathione S-transferase. Although genotoxicity has been previously documented in cotton rats residing at two of the waste sites, biomarkers in the present study provided little evidence of exposure and damage.

Postnatal Changes in Nerve Cells and Myelinated Fibers in the Pineal Gland of Cotton Rats (Sigmodon hispidus). A Light Microscopic Study.

Intrapineal neurons and intracapsular and intrapineal myelinated fibers were studied by light microscopy in male cotton rats (Sigmodon hispidus) at various postnatal ages. Until 300 days of age, neurons are encountered mainly in the distal third of the organ; neuronal nuclei are largest in this region. The remaining regions contain only a few neurons with smaller nuclei. In all regions, nuclear sizes of the neurons increase, and neuronal numbers reduce by half until 100-200 days. Neurons thus consist of different populations of cells, and the aging changes in neuronal nuclei seem to be related to the differentiation of the organ. The disappearance of neurons and the enlargement of the nuclei of remaining neurons proceed simultaneously with age. Intracapsular and intrapineal myelinated fibers appear at 20 days and their density increases with age. As the myelinated fibers are distributed mainly in the distal region and its capsule, these fibers are related topographically to intrapineal neurons. The intracapsular myelinated fibers continue into bilateral bundles of myelinated fibers found under the transverse sinuses, corresponding to the nervi conarii. Since the intracapsular fibers and the fibers traced between the capsule and the parenchyma bifurcate in a proximal direction, the intracapsular fibers are considered to run proximally, some entering the organ.

Hemostatic Parameters of the Blood of Cotton Rats, Sigmodon hispidus, Infected with Parastrongylus costaricensis (Metastrongyloidea: Angiostrongylidae)

The hemostatic parameters of adult male cotton rats infected with 20-25 third-stage larvae of Parastrongylus costaricensis were compared with those of ageand sex-matched control animals. The normal range for whole blood clotting times was 85-140 seconds. The parasitic infection caused a decrease in these clotting times. The coagulation assays, performed on the plasma of animals infected for 30-40 days, showed decreases in factors VII, X, XI, and XII and an increase in fibrinogen. The activated partial thromboplastin time was elevated; however, the decrease in prothrombin time was not significant. These findings imply that the blood of cotton rats becomes hypercoagulable following infection, and this may be a defence mechanism facilitating repair of the vascular bed of the intestine when damaged by hatching and movement of the larvae. Adult Parastrongylus costaricensis (Morera & Cespedes, 1971) Ubelaker, 1986, a metastrongylid nematode, occur in the subserosal arteries of the cecum or in the ileocecocolic branch of the cranialmesenteric artery of the major host, a cotton rat, (Sigmodon hispidus). Occasionally, they are found in other mammals including humans (Morera & Cespedes, 1971; Tesh et al., 1973; Ubelaker, 1986). The life cycle is indirect, and cotton rats, as well as humans, become infected by ingesting molluscan intermediate hosts or vegetation containing mucus from snails contaminated with infectious third-stage larvae. The larvae then invade mesenteric lymph nodes where they undergo third and fourth molts. Eleven days following infection, the juvenile worms migrate to the adjacent mesenteric arteries and develop to sexual maturity. In the cotton rat, eggs are deposited by the female worms beginning 18 days after infection and the eggs become trapped in the capillary bed of the cecum. In normal hosts, such as cotton rats, the prepatent period is completed by the twenty-fourth day when larvae hatch from the eggs, traverse the intestinal mucosa, and exit the host in the feces. In unnatural hosts, such as humans, the larvae do not hatch and are destroyed by an intense inflammatory reaction (Morera, 1973; Tesh et al., 1973). Blood coagulation abnormalities have been found in animals infected with other parasites that occur in the blood stream. Tsang & Damian (1977) reported 1 The authors express their appreciation to Ms. J. Winford, and Ms. J. Roberts for excellent technical assistance and to Professor Richard Gunst for his interest and assistance in the statistical analysis. 2 Department of Special Hematology, Baylor University Medical Center, Dallas, Texas 75246,

Light microscopic observations on the behavior of silver-stained trivalents in pachytene cells of Sigmodon fulviventer (Rodentia, Muridae) heterozygous for centric fusion.

Silver-stained pachytene cells of male cotton rats, Sigmodon fulviventer, heterozygous for a naturally occurring Robertsonian fusion, were examined by light microscopy. Silver staining clearly revealed synaptonemal complexes of all autosomal bivalents and of the translocation trivalent, as well as X-Y conformations within the sex vesicle. The synaptonemal complex of the trivalent conforms closely in morphology to that observed by electron microscopy in hybrids of other species. In all cases, the proximal telomeric knobs of the two acrocentric elements were paired and projected in the same direction from the metacentric element. The geometry of trivalent pairing in pachytene may predispose to normal disjunction and, therefore, account for the high fertility observed in S. fulviventer heterozygotes.