Ronald P. Jensh

Ionizing radiation and the developing brain

The unique susceptibility of the central nervous system to radiation exposure is attributable to its extensive period of development, the vulnerability of its neuronal cells, the migratory activity of many of its cells, its inability to replace mature neurons, and the complexity of the system itself. Radiation effects may be due to glial or neuronal cell death, interruption of migratory activity, impaired capacity to establish correct connections among cells, and/or alterations in dendritic development. These structural changes are often manifested as behavioral alterations later in life. Sensitivity to radiation (dose-response) is markedly similar among all mammalian species when developmental periods are compared. This review compares and contrasts human and animal behavioral data. Neonatal and postnatal adult behavioral tests have been shown to be sensitive, noninvasive measures of prenatal radiation exposure, although currently their predictive validity for humans is uncertain. Additional research is needed to determine the presence and significance of postnatal morphologic and functional alterations due to prenatal exposure to low levels of ionizing radiation.

Chronic stress and plasma catecholamine and corticosterone levels in male rats

Rats were exposed repeatedly to an immobilization, light and noise stressor for 3 weeks and re-exposed to the same stressor after a rest period of 3 weeks. At the beginning of each stress period, blood was obtained by a tail vein cut. Norepinephrine (NE), epinephrine (E) and corticosterone (COR) were determined. The stress response of NE or E remained relatively constant throughout 3 weeks of chronic stress. The stress response of COR remained constant for the first 2 weeks but increased markedly thereafter. After a 3-week recovery, repeat stress values of E were the same while those of NE and COR were significantly lower as compared with the last chronic stress value. Marked individual differences among rats were observed. Thus, the initial stress response during chronic stress showed no adaptation but actual sensitization for COR.

Postnatal Neurophysiologic Effects of Prenatal X-irradiation

Histological and neurophysiological effects of in utero irradiation were examined following exposure of pregnant Wistar rat to 2.0 Gy X-irradiation or sham-irradiated on the 17th day of gestation. The 234 newborns were monitored for the age of appearance of four selected physiologic markers and the age of acquisition of five selected reflexes. Offspring were evaluated as young adults using selected behavioural tests. Postnatal growth was monitored weekly. Selected offspring were autopsied to determine the presence of morphologic central nervous system alterations. The results indicated that 2.0 Gy X-irradiation during the foetal period in rat gestation caused permanent alterations in the mature adult organism, which include non-recuperable growth retardation, morphologic changes in the brain such as microcephaly, abnormal cerebellar cortical cellular patterns, and alterations in the cell architecture of the hippocampus; diminished attainment of selected reflexes; alterations in the appearance of selected physiologic markers; and changes in adult test performance indicating significant hyperactivity among the irradiated offspring. Such exposure to X-irradiation during this period results in behavioural and morphologic alterations, which persist throughout life.

Rapid Schedules for Koh Clearing and Alizarin Red S Staining of Fetal Rat Bone

Various schedules for staining fetal rat skeleton with alizarin red S were tested to determine a procedure that would produce a completely cleared and well-stained specimen in a short period of time. A 2 day procedure is presented which can produce specimens that are satisfactory but not completely transparent. A 7 day procedure produces cleared and stained specimens which can be well visualized with a dissecting microscope (30×). Fetal rats of 21 days gestation were fixed in 10% formalin for at least 1 wk. The specimens were skinned and eviscerated and then dehydrated in 2 changes of acetone for 12 hr (8 ml per gram body weight). The specimens were then placed in 1% KOM-alizarin red S (6 mg/liter) or 3 days, followed by 10% KOH-alizarin red S for 3 days. Finally, the specimens were placed in a mixture of benzyl alcohol, ethanol, and glycerol (1:2:2) (4 ml per gram body weight) for 12 hr, and then transferred to pure glycerol for storage.

The Effect of Low-Level Prenatal X-Irradiation on Postnatal Development in the Wistar Rat

The Objective Of This Investigation Was To Determine The Effect Of Low-Dose Prenatal X-Irradiation On Postnatal Growth And Neurobehavioral Development, And Whether Alterations Would Manifest At Dosages Lower Than Those Which Produce Anatomic Malformations From Exposure At The Most Sensitive Period Of Organogenesis. Ninety-Eight Wistar Strain Rats Were Exposed To 0.1, 0.2, Or 0.4 Gy X-Radiation Of Were Sham Irradiated On The 9Th Or 17Th Day Of Gestation. A Conventional Teratologic Evaluation Was Completed On Half Of The Animals (572 Fetuses). The Age Of Appearance Of Four Physiologic Markers And Of Acquistion Of Six Reflexes Was Observed In 372 Offspring. Exposure During Early Organogenesis At These Levels Had No Effect On Any Of These Parameters. Prenatal Exposure To X-Radiation On The 17Th Day Of Gestation At Dosage Levels Greater Than 0.1 Gy Resulted In Alterations In The Appearance Of Three Postnatal Neurophysiologic Parameters. Growth Retardation Throughout The Postpartum Period Also Was Observed In The Offspring. The Induction Of Developmental And Reflex Alterations Had A Comparable Threshold To The Known Threshold For Anatomic Malformations On The 9Th Day. These Results Indicate That All Of The Parameters Studied Had Thresholds Either At Or Above 0.2 Gy Acute Radiation, And That The Postpartum Developmental And Reflex Acquisition Measures Were Not More Sensitive Indicators Of Exposure To X-Radiation Than Growth Parameters.

Teratologic studies of prenatal exposure of rats to 915 MHz microwave radiation.

Thirty-nine pregnant Wistar strain albino rats were used to determine possible teratogenic activity due to chronic exposure with microwave radiation at a field intensity of a 10 mW/ cm2 at a frequency of 915-MHz microwave radiation. Ten rats were irradiated in a fully characterized anechoic chamber from Days 1 to 21 of gestation. The results of preliminary studies using 20 pregnant rats indicated that this power density was the maximal level which did not cause increased rectal temperature. Twenty-nine pregnant females were used as control animals. On the 22nd day of gestation animals were killed and maternal brain, liver, kidneys, and ovaries were removed, examined, weighed, and fixed in buffered formalin. Fetuses and placentae were removed, examined, weighed, and fixed in Bouins fixative. All fetuses were examined for malformations using a cross-section dissection methodology. No significant alterations were observed for the following parameters: maternal body weight and weight gain, term maternal orga...

An evaluation of the teratogenic potential of protracted exposure of pregnant rats to 2450-MHz microwave radiation: I. Morphologic analysis at term.

The present investigation was designed to study the effects of protracted prenatal exposure of rats to a 20-mW/cm2 power density level of microwave radiation at a frequency of 2450 MHz. Preliminary studies using 24 rats indicated that this power density level did not cause a significant increase in maternal body temperature as measured by a rectal thermocouple. Of 75 pregnant rats, 12 were exposed to microwave radiation, 4 sham-irradiated, and 59 used as environmental control animals. Rats were exposed throughout pregnancy for a total exposure time of approximately 270 h. Daily maternal weights were recorded before irradiation. At term animals were killed, selected maternal tissues were removed, and fetal and placental positions and weights were recorded. After fixation for at least 3 wk, 462 term fetuses were dissected and examined for abnormalities. No significant alterations were observed for the following parameters: maternal weight gain during pregnancy, term maternal organ weights (brain, liver, kidneys, ovaries), term fetal weight, resorption rate, or abnormality rate. These results indicate that the protracted exposure of pregnant rats to 2450-MHz microwave radiation at a power density level of 20 mW/cm2 is not embryopathic.

Studies Concerning the Effects of Low Level Prenatal X-irradiation on Postnatal Growth and Adult Behaviour in the Wistar Rat

Fifty-nine pregnant Wistar strain rats were sham irradiated or subjected to a 0.1 or 0.2 Gy exposure of X-radiation on the 9th or 17th day of gestation. Twenty-seven of the females were killed at term for teratologic analysis. The remaining mothers raised their young. At 60 days of age the 252 offsprings were randomly assigned three of six tests: open field, swimming, hanging, activity wheel, water T-maze, or conditioned avoidance response. Male offspring exposed at the 0.2 Gy level exhibited retarded growth only during the first few weeks of postnatal life. Female offspring exposed on the 17th day to 0.2 Gy X-radiation were growth retarded throughout the test period. Postnatal growth rates, however, were not significantly different between the irradiated and control groups. There were no significant alterations in adult behaviour due to prenatal X-irradiation. There were sex differences in activity wheel and forelimb hanging performance, unrelated to radiation exposure. These results indicate that prenatal low level X-irradiation on the 9th or 17th day of gestation does not result in significant alterations in adult behavioural performance in the rat, but prenatal growth retardation persists postnatally. Growth may be a more sensitive indicator of the effects of prenatal exposure to X-radiation than postnatal behaviour.

Intrauterine effects of ultrasound: animal studies.

During the past several decades, the use of ultrasound technology in the clinical setting has greatly increased. Because nearly every pregnant woman receives at least one sonographic procedure today, there has been developing concern about the safety of such procedures. Since ultrasound exposure can result in hyperthermia and other physiological effects, the determination of a threshold or no-effect exposure has become a high-priority goal. Animal research has been important to the study of the effects of various exposures at all stages of pregnancy, since the clinical use of ultrasonography can occur during the preimplantation, organogenic, and fetal stages. Animal experiments using various mammalian species have been able to determine no-effect exposure levels for embryonic loss, congenital malformations and neurobehavioral effects. The preponderance of evidence from these studies indicates that, in the absence of a thermal effect, ultrasonography represents no measurable risk when used at recommended intensity levels.

An evaluation of the teratogenic potential of protracted exposure of pregnant rats to 2450‐MHz microwave radiation. II. postnatal psychophysiologic analysis

The objective of this study was to determine whether protracted prenatal exposure of rats to 2450-MHz microwave radiation at a power density level of 20 mW/cm2 would significantly alter postnatal growth and psychophysiologic development. Of 75 pregnant rats, 12 were exposed to microwave radiation, 4 sham-irradiated, and 59 served as environmental control animals. Forty-five females were allowed to deliver their offspring. The neonates were examined and weighed on d 3 and weekly thereafter until 87 d of age. Neonatal reflex tests were initiated as early as d 3 (surface righting, air righting, auditory startle, visual placing). One physiologic parameter, eye opening, was also observed. Mothers were rebred 10 d after weaning and a morphologic evaluation was completed on the second litter. Behavioral tests were begun at 60 d of age and included water T-maze, conditioned avoidance response, open field, activity wheel, forelimb hanging, and swimming. At 90 d of age offspring were bred within and across groups, and a morphologic teratologic analyses was completed on the offspring. Representative tissue samples were collected and organ weights recorded for the brain, liver, kidneys, and gonads of all animals. Analyses of the data indicated that there were no significant malformations or significant alterations in the neonatal physiologic or reflex test results, body/organ weight ratios, or breeding results in the adult offspring. There were no significant alterations in five of the six adult behavioral tests. There were significant differences in activity among the irradiated and control offspring between the sexes, the irradiated offspring being more active. These results are indicative of possible radiation-induced behavioral alterations. Further studies are needed to explore the possibility of microwave radiation-related alterations in animal behavior.