Steve Mihok

Bioconcentration of fallout 137Cs by fungi and red-backed voles (Clethrionomys gapperi)

Cesium-137 and 40K concentrations were measured in vegetation and in red-backed voles (Clethrionomys gapperi) in southeastern Manitoba, Canada, following the Chernobyl accident in 1986. Voles from wet coniferous habitats contained concentrations of 137Cs twenty- to fiftyfold higher than voles from deciduous habitats. Maximum 137Cs values were observed in autumn. Voles captured in a spruce bog at this time contained an average body burden of about 11 Bq. Concentrations in vegetation samples were similar to those found by other researchers. Overall, there was only minimal evidence of contamination attributable to Chernobyl in either vegetation or voles. The primary source of 137Cs in voles appeared to be dietary, particularly mushrooms that contained up to 74 Bq g-1 ash. Based on physiological constraints, mushrooms were the only plausible source of 137Cs in autumn diets. Elevated values at other times in coniferous areas may have been related to the consumption of epiphytic lichens. These findings suggest that fungi, or the animals that consume them, can serve as sensitive indicators of 137Cs contamination in the environment.

Anemia at the onset of winter in the meadow vole (Microtus pennsylvanicus)

1. From 1981 to 1986, 6120 meadow voles (Microtus pennsylvanicus) were sampled for hematological indices in southeastern Manitoba, Canada. This survey revealed the sporadic occurrence of anemia in early winter at mean temperatures below about -5 degrees C. 2. Anemia was associated with leukocytosis and circulating normoblasts, suggesting a sudden, large blood loss. Individuals became anemic quickly, with no obvious predisposing factors. 3. Attempts were made to induce anemia by exposing voles in traps to various temperatures. Temperatures characteristic of most trapping sessions failed to induce anemia in both wild and laboratory-born voles. 4. Short-term exposure to more extreme temperatures (-20 to -30 degrees C) induced anemia. Voles lost blood through erosions of the epithelium of the glandular stomach, and developed other pathological lesions characteristic of hypothermia. 5. Although there was a strong association between cold weather and anemia, we could find no clear relationship between winter survival and winter weather. However, in 1984, extraordinarily cold temperatures were associated with anemia and a subsequent population decline. These events suggest a threshold mean daily temperature of about -15 degrees C, below which vole survival is grossly affected. 6. Deteriorating protein levels and energy reserves of small mammals in winter may make them particularly susceptible to cold stress. Hence, sporadic bouts of sustained cold may be responsible for some of the enigmatic winter declines seen in northern small mammals.

Artificial induction of azurocytes in the meadow vole (Microtus Pennsylvanicus)

Abstract 1. Meadow voles ( Microtus pennsylvanicus ) were manipulated with various biological response modifiers to develop a protocol for artificial induction of azurocytes (AZ). Only progestin hormones, and interferon inducers such as polyinosinc polycytidilic acid or Reovirus-3, initiated AZ maturation. A synthetic progestin, medroxyprogesterone acetate (MPA) was the most effective agent. 2. Following a single injection of 5 mg MPA, AZ appeared in the blood on day 3 or 4. Cells peaked at about 10 9 cells/1 on days 7 through 10. Numbers declined sharply afterwards, suggesting a lifespan for the cell of about 1–2 weeks. 3. Splenectomy of MPA-treated voles had no effect on the number of AZ induced. Attempts at indirect induction through transfer of tissues from MPA-treated voles early in the induction process were unsuccessful. 4. Induction of AZ with MPA was accompanied by severe lymphopaenia. Lymphopaenia was also observed when AZ were induced with polyinosinic polycytidilic acid, but it was not observed during natural pregnancy. Lymphopaenia was not observed in MPA-treated splenectomized voles, despite the induction of large numbers of AZ.

Origins and maturation patterns of azurocytes in the meadow vole (Microtus pennsylvanicus)

1. The origins, maturation sequence, and traffic patterns of azurocytes (AZ) were studied in vivo in the meadow vole (Microtus pennsylvanicus) with the aid of various biological response modifiers. 2. AZ originated from lymphocyte-like precursors in the bone marrow. These precursors entered into intense mitotic activity in the bone marrow following progestin treatment. 3. While still in the bone marrow, AZ precursors differentiated into granulated cells with some of the histochemical properties of AZ. 4. At this time, maturation could be blocked completely with cyclophosphamide. Hydroxyurea and cyclosporin A inhibited maturation significantly, but did not block it. 5. Estradiol, hydrocortisone, prostaglandin E2, and conditioned medium had no effect on the numbers of cells induced. 6. Transitional stages between a granulated bone marrow precursor and an AZ were rarely observed, suggesting rapid synthesis of AZ inclusions upon terminal differentiation. 7. After release from the bone marrow, AZ were common in the blood only. Modest numbers of cells were also found in the red pulp of the spleen, and the thymic cortex. 8. AZ in the thymus were sometimes found in clusters, and were often associated with septa. Very low numbers of mature AZ were detected in the bone marrow. 9. AZ were absent from lymph nodes and Peyers patches, and were never observed in the B-lymphocyte areas of the spleen. 10. Based on experiments with dextran sulphate, AZ and their precursors never entered the recirculating lymphocyte population. AZ in the blood or tissues were never observed in mitosis, and were never observed degranulating. 11. Cyclophosphamide or hydrocortisone had no effect on AZ numbers when administered at the peak of their occurrence in the blood. 12. Although no clear function of the AZ was elucidated, experiments confirmed a high degree of similarity between its properties and those of cytotoxic cells found in other mammals.