Reed warbler orientation: initiation of nocturnal migratory flights in relation to visibility of celestial cues at dusk.

We used radiotelemetry to investigate the time of migratory flight initiation relative to available celestial orientation cues and departure direction of a nocturnal passerine migrant, the reed warbler, Acrocephalus scirpaceus, during autumn migration. The study was carried out at Falsterbo, a coastal site in southwest Sweden. The warblers initiated migration from times well after local sunset and well into the night, corresponding to sun elevations between -4 degrees and -35 degrees, coinciding with the occurrence of stars at night. They departed in the expected migratory direction towards south of southwest with a few initiating migration in reverse directions towards northeast to east. Flight directions under overcast conditions (7-8/8) were more scattered than under clear sky conditions (0-4/8). There were fewer clouds on departure nights than on nights when the birds did not initiate migration. For birds staying longer than one night at stopover the horizontal visibility was higher and precipitation was less likely on departure nights than on the previous night. The results show that the visibility of celestial cues, and stars in particular, are important for the decision to initiate migration in reed warblers. However, cloud cover, horizontal visibility and precipitation might be correlated with other weather variables (i.e. wind or air pressure) that are also likely to be important for the decision to migrate. Copyright 2001 The Association for the Study of Animal Behaviour.

Effects of low-dose X-irradiation on mouse-brain aggregation cultures.

Biochemical and morphological differentiation in reaggregating mouse-brain cell cultures after low-dose radiation (0.5 Gy) in vitro was studied. Cells were irradiated on culture day 2, corresponding to embryonic day 15-16, and different glial and neuronal markers were followed through development to postnatal day 40. The shape and size of irradiated aggregates were more irregular and smaller compared with controls. Total amounts of DNA and protein were significantly lower in irradiated aggregates than in controls between days 8 and 20. After 30 days in culture activities of the glial markers glutamine synthetase (GS) and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) were lower in X-irradiated aggregates than in controls. However, after 40 days the CNP activity in irradiated aggregates increased to levels above those of the controls. Irradiated and control aggregates did not differ significantly in neuronal marker enzyme activities, i.e. choline acetyltransferase (ChAT), acetylcholine esterase (AChE) and glutamic acid decarboxylase (GAD) measured on a per mg protein basis. On days 20 and 30 the amount of nerve growth factor (NGF) was two-fold higher in irradiated aggregates compared with non-irradiated ones, suggesting that, after irradiation, surviving cells in culture were induced to produce more NGF. After 40 days the amount of NGF in irradiated aggregates had decreased to the level found in the control aggregates.

Effects of glucan on the reticuloendothelial system and on the development of tumors in 90Sr-exposed mice.

A series of experiments was conducted to examine the effect of glucan on the reticuloendothelial system (RES) and on the development of 90Sr-induced osteosarcomas and malignant lymphomas in CBA/S mice. Glucan demonstrated a strong RES-stimulating effect, as evidenced by a dose-related increase in lysozyme levels in the plasma and an enlargement of the liver and spleen. Weekly injections of glucan between 150 and 250 days after exposure to 90Sr suppressed the actuarial appearance of the fibroblastic type of osteosarcomas and stimulated the emergence of malignant lymphomas. Glucan itself had no tumorigenic effect in mice not exposed to 90Sr.

Epistemological problems in assessing cancer risks at low radiation doses.

Historically, biology has not been subjected to any epistemological analysis as has been the case with mathematics and physics. Our knowledge of the effects in biological systems of various stimuli proves to be dualistic in a complementary (although not mutually exclusive) way, which bears resemblance to the knowledge of phenomena in quantum physics. The dualistic "limbs" of biological knowledge are the action of stimuli and the response of the exposed, biological system. With regard to radiogenic cancer, this corresponds to the action of the ionizations and the response of the exposed mammal to that action, respectively. The following conclusions can be drawn from the present analysis: Predictions as to radiogenic cancer seem often if not always to have neglected the response variability (variations in radiosensitivity) in individuals or among individuals in populations, i.e. the predictions have been based exclusively on radiation doses and exposure conditions. The exposed individual or population, however, must be considered an "open statistical system", i.e. a system in which predictions as to the effect of an agent are only conditionally possible. The knowledge is inverse to the size of the dose or concentration of the active agent. On epistemological grounds, we can not gain knowledge about the carcinogenic capacity of very low (non-dominant) radiation doses. Based on the same principle, we can not predict cancer risks at very low (non-dominant) radiation doses merely on the basis of models, or otherwise interpolated or extrapolated high-dose effects, observed under special exposure conditions.

Effect of high 131I doses on the bone uptake and retention of 90Sr and 90Y.

The uptake and retention of 90Sr and 90Y in mouse bones after injections of the two nuclides in equilibrium were examined after heavy thyroid irradiations from 131I deposited in the glands. The radiation doses to the thyroid glands as well as the gross doses to the femurs and humeri of the mice were calculated. The radiation destruction of the thyroid tissues had no effect on the bone weights nor on the skeletal metabolism of 90Sr. The uptake of 90Y was, however, depressed after thyroidal irradiation but reached the same bone concentration as 90Sr at about 30 days after the administration of the nuclides, i.e. at a time when the corresponding equilibrium between 90Sr and 90Y in the bones was reached in mice without a thyroidal irradiation.

Effect of high 131I doses to the thyroid gland on tumorigenicity of 90Sr and 90Y in mice.

The incidence of tumors was studied in mice injected with 90Sr only or with 90Sr in combination with high amounts of 131I. The high 131I-dose to the thyroid gland was necrotizing to the glandular tissue and the main aim of the investigation was the possible effects of the thyroidal destruction on the formation of bone tumors. After correction for competing mortality, no significant difference in the frequency of bone tumors could be found between 90Sr-treated and (90Sr + 131I)-treated mice. The incidence rate of bone tumors, however, was higher in mice with radiogenically destroyed glands than in those with intact glands. The limitations of using the concept of 'actuarial tumor incidence' in correction for competing mortality in animal experiments are discussed. Large numbers of lymphatic tumors were found in all animal groups. The frequencies of such tumors were independent of the radiation doses but their incidence rates were shortened in a dose dependent manner. Other, directly or indirectly radiation induced tumors were observed.

Evidence of C-cell destruction in the thyroid gland of mice exposed to high 131I doses.

The parafollicular cells of the thyroid gland were visualized by means of the Sevier-Munger silver technique in normal mice and in mice receiving 131I in amounts sufficient to completely destroy the thyroid tissue. The destruction of the C-cells was observed in all 131I injected mice, and no histologic signs of recovery were seen during a period of 40 days following the treatment.

Incidence of malignant thyroid tumors in humans after exposure to diagnostic doses of iodine-131. I. Retrospective cohort study.

Between 1952 and 1965, 10,133 patients received an average of 60 mu Cl of 131I for diagnostic examinations of the thyroid gland. The examinations were mainly done on adults, and only 5% of the patients were younger than 20 years at the time of examination. Of the patients, 9 appeared in the Swedish Cancer Registry between 1958 and 1977 with a diagnosis of malignant tumor of the thyroid gland more than 5 years after the administration of 131I. Inasmuch as the expected number of malignant thyroid tumors computed from Swedish cancer incidence figures was 8.3, there was no elevation of the incidence of malignant thyroid tumors in these patients receiving diagnostic doses of 131I. The patients were examined because of a suspected thyroid dysfunction and therefore represented a selected group. The investigation is being continued to analyze further parameters that could have a bearing on these results.

Age and dose related carcinogenicity of 90Sr.

90Sr was given at three different dose levels (29.6, 14.8 and 7.4 kBq/g b.w.) to groups of mice aged 300, 150, 75 and 25 days. It was found that the incidence of osteosarcomas was highest in the 75-day-old-group and lowest in the two oldest age groups. The frequency of lymphoreticular tumours was inversely dose-related (highest incidence in the lower dose series) and not dependent on age at the time of 90Sr injection. The frequencies of soft tissue tumours indicate that these tumours are more related to age than to the dose employed.

Uptake and retention of 133Ba and 140Ba-140La in mouse tissues.

The distribution of barium in the mouse has been determined qualitatively by whole-body autoradiography after i.v. administration of 133BaCl2 solution. The quantitative distribution of 104Ba and 140La has been analyzed after i.p. injections of the two nuclides in equilibrium by measuring the activity in excised organs in a two-channel scintillation counter. Approximate doses to the eyes and different parts of the skeleton have been calculated.