[Disproportionate eruption of maxillary and mandibular incisors in the long-tailed ground squirrel].

Abstract-The surface of the maxillary and mandibular incisors of Spermophilus undulatus long-tailed ground squirrels, including those born in the current year and those that have hibernated (trapped one month or later after hibernation) is studied. The presence of daily growth on the incisors' surface allows the evaluation of their eruption rate; a specific change in the character of the incisors' eruption corresponds to winter hibernation (hibernation zone), which serves as the time mark. Correlation between the eruption rates of the maxillary and mandibular incisors typical for rodents is found in yearlings and some animals after hibernation. The eruption rate of the mandibular incisors is higher than the eruption rate of the maxillary incisors and can be taken as proportional to their length. In individuals that have hibernated and show proportional eruption of the incisors, the proportion of the total length of the incisor formed before and after hibernation is equal for the maxillary and mandibular incisors. In the individuals that have hibernated and show the correlation of the total length of the maxillary and mandibular incisors typical for rodents, the eruption rate of the mandibular incisor is equal to or less than the eruption rate of the maxillary incisor and the proportion of the incisor formed before hibernation is greater in the mandibular incisor than in the maxillary. This disproportionate pattern of incisor eruption is not typical for rodents and is a result of inequal grinding of the maxillary and mandibular incisors, which ultimately results in the normal ratio of the total length of the maxillary and mandibular incisors.

Dynamics of radionuclide concentrations in calcified tissues of reindeer in the western Russian Arctic.

The specific activities of artificial and natural nuclides were determined in bone and teeth of reindeer that had lived before, during, and after nuclear tests on the Archipelago Novaya Zemlya and of reindeer from the nearby mainland region. In bone of reindeer from Novaya Zemlya, 90Sr and 210Pb are the main source of beta-activity, the 210Po is the main source of the alpha activity. In bone of reindeer that lived on Novaya Zemlya during underground tests, the 90Sr activity was relatively high (0.75 +/- 0.20 Bq/g dry weight). In animals that lived after the tests were banned, the level was significantly lower (0.44 +/- 0.17 Bq/g) and did not differ from the level of the 90Sr activity found in the mainland reindeer bone. On Novaya Zemlya, the concentrations of the natural 210Pb in bone of the recent reindeer (0.57 +/- 0.19 Bq/g) is similar to that which was in the teeth of reindeer a hundred years ago (0.65-0.75 Bq/g) and significantly higher than in the recent mainland reindeer from different regions (0.18-0.17 Bq/g).

Relationships between ESR-evaluated doses estimated from enamel and activity of radionuclides in bone and teeth of reindeer.

Doses of radiation estimated from ESR analysis of tooth enamel were compared with activities of alpha- and beta-emitters in enamel and in bone tissue of mandibles of 77 reindeer from populations with different levels of radiation contamination. Contribution of the radionuclides incorporated into bone (or bone-seeking radionuclides in food) to ESR-evaluated doses was substantial and the contribution of the radionuclides incorporated into enamel itself proved to be relatively small.

[The dynamics of the radiation load on reindeer on Novaya Zemlya]. / Dinamika radiatsionnoi nagruzki na severnykh olenei Novoi Zemli.

The ESR analysis was carried out aiming at studying the activity of radionuclides in the dental enamel, dentin, and mandible bone tissues of reindeer of Novaya Zemlya. Doses of absorbed ionizing radiation were assessed. It was determined that the doses obtained by reindeer during underground nuclear tests were ten times higher and the activity of 90Sr was greater than those for reindeer living after the nuclear tests were suspended. Relatively high values of doses were observed for reindeer living before the nuclear weapons were invented. This fact is accounted for by an elevated level of natural radiation in the region.

Estimation of accumulated dose of radiation by the method of ESR-spectrometry of dental enamel of mammals.

ESR-spectrometry was used to investigate radiation-induced paramagnetic centers in enamel of mammals: carnivores (polar bear and fox), ungulates (reindeer, European bison, moose), and man. Values at half the microwave power saturation of the radiation signal, P1/2, evaluated at room temperature, was found to range from 16 to 26 mW for animals and man. A new approach to discrimination of the radiation induced signal from the total ESR spectrum of reindeer enamel is proposed. 'Dose-response' dependencies of enamel of different species mammals were measured within the dose range from 0.48 up to 10.08 Gy. Estimations of 'radiosensitivity' enamel of carnivores and ungulates showed good agreement with radiosensitivity enamel of man by ESR method.

Radiation dosage accumulated by reindeer from Novaya Zemlya.

ESR spectrometry of tooth enamel revealed a significant difference in accumulated radiation dose between reindeer which lived on Novaya Zemlya when underground nuclear tests were performed there and those which lived there after the tests were stopped.

[New prospects in assessing the absorbed radiation dose by electron paramagnetic resonance]. / Novye vozmozhnosti v otsenke pogloshcheniia radiatsionnoi dozy metodom élektronnogo paramagnitnogo rezonansa.

Spin-lattice relaxation rates of radiation induced and background centers in dental enamel have been investigated by electron spin resonance techniques. It has been found that these centers differ in the value of the saturation half-power and the saturation process. Based on these experimental results a new approach to discrimination of the radiation induced signal from the total ESR spectrum of dental enamel is proposed. Comparison of the current methods of radiation dose estimation by the ESR analysis has been performed using the new approach.

[Cumulative radiation dosage and epidemiological research in the Chernobyl region]. / Dozy radiatsionnykh nagruzok i épidemiologicheskie issledovaniia v Chernobyl'skom regione.

Individual biological dosimetry covering chromosomal analysis and electronic paramagnetic resonance spectrometry has been performed in 1300 subjects exposed to ionizing radiation after the Chernobyl accident. Cumulative radiation doses above 40 ImC were registered in 5%, about 100 ImC in 1% of the examinees. In 1% of cytogenetic investigations there appeared multiaberrant cells indicative of hot particle incorporation. Regional epidemiologists do not record changes in the incidence of hematological diseases. This may be explained by a small percent of the dose carriers, rare occurrence of hematological disorders and the time of radiation-induced oncogenic effects. The above representative group exposed to definite radiation doses may serve the subject of epidemiological surveys on the role of low-dose and low-rate radiation in pathogenesis of human diseases.

[Determining the accumulated dose of gamma radiation in the tooth enamel]. / Opredelenie nakoplennoi dozy gamma-izlucheniia po émali zuba.

Following ideas of Japanese and Canadian scientists the authors tried to develop practical application of dental enamel for dosimetry of gamma-radiation accumulated by an individual. Human teeth were irradiated in vitro with gamma-rays of 60Co and with x-rays, and the amount of free radicals in ++non-caries enamel was measured on an ESR spectrometer. Linear regression ESR signals on dose of radiation within an interval of 0.1-20 Gy were plotted for gamma- and x-rays with regression coefficients 0.276 and 0.693, respectively. These regressions were used for estimation of accumulated doses of gamma-radiation in 85 residents of Byelorussia and 301 residents of the Tomsk region during investigation of teeth that were removed in normal dental practice.

[Diurnal layer formation in the incisor dentin of rodents]. / Formirovanie sutochnykh sloev v dentine reztsov u gryzunov.

The growth of dentin of the constantly growing lower incisors in rodents was studied using tetracycline as a vital marker of the growing parts of bones and teeth. In the common vole in nature the incisors grow in length at a rate of 490 micrometers per day; a basal-apical gradient of growth of the tooth walls in thickness was found: the minimal daily increment at the tooth base and the maximal in the apical third, it decreases again at the very apex. In the peripulp part of dentin of the apical incisor half there are diurnal layers seen both on polished sections and stained slides the formation of which correlates with the diurnal rhythm of skeleton growth. The diurnal dentin layers form in the apical incisor half only. The odontoblasts appear to begin to function rhythmically from the middle of their life on only. A similar phenomenon was found in a natural population of large-toothed redbacked voles. The topography of dentin layers in the laboratory rats is similar to that in the voles but the layers are not distinct and the basal-apical gradient of dentin growth is observed in young animals, rather than in the old ones.