Effects of neonatal ovarian X-irradiation in the Chinese hamster. I. Correlation between the age of irradiation and the fertility span.

The fertility span between the first and the last estrus was compared among female Chinese hamsters exposed to 1 Gy X-rays on neonatal day 0, 2, 4, 6, 8, 10 and 14. The fertility span changed dramatically according to the age at the time of irradiation. The females irradiated on day 4, 6 and 8 showed a definite delay in sexual maturation and a very early cessation of the estrous cycles, while those irradiated on day 10, 2 and 14 (in this order) showed a much longer, nevertheless significantly shortened, fertility span. Reduction in the number of juvenile oocytes by acute killing was responsible for this shortened reproductive life. The present study indicated again that the sensitivity of the oocytes to the lethal effects of X-rays is unquestionably meiotic stage-dependent.

Vole infant development is influenced perinatally by maternal photoperiodic history.

Vole pups were maintained from the time of conception in the same short-day (SD) photoperiod (10 h light/day, LD 10:14); groups differed only with respect to SD photoperiodic histories of dams before gestation, which simulated those experienced by dams breeding in autumn (SD-2, 2 wk of short days), midwinter (SD-21), or late winter (SD-26). Compared with SD-2 pups, offspring born to SD-26 dams matured more rapidly with respect to body size and reproductive status. Several other somatic and behavioral measures indicated that winter preparedness was greatest in pups whose dams had experienced 2 wk and least in those that had experienced 26 wk of SD treatment before conception. A cross-fostering design, in which pups gestated in long (LD 14:10) or short photoperiods were reared postnatally in the same or opposite day length, indicated that several photoresponsive traits are influenced predominantly by prenatal photoperiod, others by postnatal day length, and others by both photoregimens. Information is communicated to fetuses about the length of time dams have been exposed to short day lengths before mating as well as about the day length prevailing during gestation. The changes induced by the mother in her pups pre- and postnatally likely facilitate adaptation of newly weaned voles to seasonally varying environmental conditions.

Health effects of low-level irradiation during development: experimental design and prenatal and early neonatal mortality in beagles exposed to 60Co gamma rays.

As part of a long-term study of the effects of irradiation during development, prenatal and early neonatal mortality were evaluated for beagles exposed in utero at 8 days postcoitus (dpc), 28 dpc, 55 dpc, or 2 days postpartum. Mean doses used were 0,0.16, or 0.83 Gy. A decrease in whelping rates was observed for female breeders irradiated at 8 dpc. There was a significant decrease in litter sizes from female breeders irradiated at 8 and 28 dpc. Both of these findings are indicative of increased embryonic mortality. There was a significant decrease in the percentage of females born after exposures given at 28 dpc, indicating a differential radiosensitivity by sex. A significant increase in early neonatal mortality up to 14 days of age was observed for beagles exposed 8 or 28 dpc, again with an excess mortality in females.

The effect of prenatal or early postnatal irradiation on the production of anti-arsonate antibodies and cross-reactive idiotypes.

Preliminary studies on the long-term effects of prenatal and early postnatal irradiation on the immune response to arsonate were performed using A/J mice. Pregnant mice were irradiated (0.5 Gy, X-rays) or sham-irradiated on a single occasion during gestation (between day 5 and 18 post-conception). Alternatively, newborn mice received the same treatment between day 2 and 7 after birth. Mice were immunized with keyhole limpet haemocyanin-arsonate (KLH-Ars) in adjuvant from 2 months after birth. The levels of specific antibodies to arsonate (anti-Ars) were measured by radioimmunoassay. In addition, the Ars-related cross-reactive idiotype (CRIA) was measured by the haemagglutination technique. In the primary response the titre of anti-Ars was reduced in animals that had been irradiated between day 12 and 15 of gestation. In the second response, in contrast, they had increased levels of anti-Ars. After immunization with KLH-Ars, high levels of CRIA were observed in all groups. However, in mice irradiated 18-20 days after conception the level of CRIA was often much higher than the level of anti-Ars, indicating that a large proportion of the CRIA-positive molecules were not specific for Ars. Thus, in this particular case, some specificity of the immune response was lost after irradiation. The expression of recurrent idiotypes may be a sensitive indicator of immunological perturbations after irradiation.

Thermoregulatory responses of the immature rat following repeated postnatal exposures to 2,450-MHz microwaves.

This study was designed to determine the changes that occur in the thermoregulatory ability of the immature rat repeatedly exposed to low-level microwave radiation. Beginning at 6-7 days of age, previously untreated rats were exposed to 2,450-MHz continuous-wave microwaves at a power density of 5 mW/cm2 for 10 days (4 h/day). Microwave and sham (control) exposures were conducted at ambient temperatures (Ta) which represent different levels of cold stress for the immature rat (ie, "exposure" Ta = 20 and 30 degrees C). Physiological tests were conducted at 5-6 and 16-17 days of age, in the absence of microwaves, to determine pre- and postexposure responses, respectively. Measurements of metabolic rate, colonic temperature, and tail skin temperature were made at "test" Ta = 25.0, 30.0, 32.5, and 35.0 degrees C. Mean growth rates were lower for rats exposed to Ta = 20 degrees C than for those exposed to Ta = 30 degrees C, but microwave exposure exerted no effect at either exposure Ta. Metabolic rates and body temperatures of all exposure groups were similar to values for untreated animals at test Ta of 32.5 degrees C and 35.0 degrees C. Colonic temperatures of rats repeatedly exposed to sham or microwave conditions at exposure Ta = 20 degrees C or to sham conditions at exposure Ta = 30 degrees C were approximately 1 degrees C below the level for untreated animals at test Ta of 25.0 degrees C and 30.0 degrees C. However, when the exposure Ta was warmer, rats exhibited a higher colonic temperature at these cold test Ta, indicating that the effectiveness of low-level microwave treatment to alter thermoregulatory responses depends on the magnitude of the cold stress.

Behavioral changes in preweaning and adult rats exposed prenatally to low ionizing radiation.

Seven behavioral tests were used to evaluate the postnatal behavior of rats after exposure on gestational Day 15 to 0, 25, 50, 75, or 125 r, whole body irradiation of the pregnant rat. Three tests were administered in the first 2 postnatal weeks (righting reflex, negative geotaxis, and reflex suspension); three tests were administered on postnatal Day 21 (modified open field, spatial maze, and continuous corridor). As adults, the rats were retested with the same tests as at 21 days and also in the running wheel. Dose-response decreases in body weight were greater in the younger rats. Some behavioral tests were not altered by irradiation, while others showed clear dose-response relationships, starting as low as 25 r. The early changes were characterized by light body weight, delays in behavioral development and hypoactivity, followed by recovery of some parameters with maturation. Eventually hyperactivity developed in adult rats after gestational irradiation. However, it cannot be concluded that either morphological or behavioral tests are more sensitive than neonatal body weight change for detection of damage from gestational irradiation.

Influence of pre- and postnatal exposure of rats to 2.45-GHz microwave radiation on neurobehavioral function.

Rats exposed to microwaves prenatally (2,450 MHz, 10 mW/cm2, 3 h/day, days 5-20 of gestation) or perinatally (same as above plus days 2-20 postnatally) were examined by a neurobehavioral test battery on postnatal days 30 and 100. Body mass, locomotor activity, startle to acoustic and air-puff stimuli, fore- and hindlimb grip strength, negative geotaxis, reaction to thermal stimulation, and swimming endurance were assessed. The prenatally and the perinatally exposed rats (male and female) weighted more than sham-exposed rats at 30, but not at 100, days of age. In addition, the perinatally exposed animals had less swimming endurance at 30, but not at 100, days of age relative to sham-exposed rats. For the other measures, only the air-puff startle response was altered and was limited to the prenatally exposed female pups; ie, at postnatal day 30, the startle response was increased in magnitude, and at postnatal day 100, the response was decreased. No other reliable effects were observed. In a second experiment, rats treated as described above were examined for alterations in body mass, locomotor activity, reaction to air-puff stimuli, reaction to thermal stimulation, and swimming endurance at postnatal days 30-36. Again, perinatally exposed rats were larger in body mass and had less swimming endurance compared with sham-exposed rats. The latency to the air-puff startle response was longer in female pups exposed prenatally. These data indicate that altered endurance and gross motor activity result from perinatal exposure to microwave irradiation.

Phototherapy-induced hypocalcemia in newborn rats: prevention by melatonin.

When young rats are exposed to white fluorescent light the concentration of calcium in their serum decreases. This effect is prevented by shielding the occiput, by inhibiting corticosterone synthesis, and by exogenous melatonin. Furthermore, the expected hypocalcemic response to cortisol injection is prevented by melatonin. Light-induced hypocalcemia may result from increased calcium uptake by bone when the blocking effect of melatonin decreases after pineal inhibition by transcranial illumination.