Zenon J. Sienkiewicz

Low‐level exposure to pulsed 900 MHz microwave radiation does not cause deficits in the performance of a spatial learning task in mice

There is some concern that short-term memory loss or other cognitive effects may be associated with the use of mobile cellular telephones. In this experiment, the effect of repeated, acute exposure to a low intensity 900 MHz radiofrequency (RF) field pulsed at 217 Hz was explored using an appetitively-motivated spatial learning and working memory task. Adult male C57BL/6J mice were exposed under far field conditions in a GTEM cell for 45 min each day for 10 days at an average whole-body specific energy absorption rate (SAR) of 0.05 W/kg. Their performance in an 8-arm radial maze was compared to that of sham-exposed control animals. All behavioral assessments were performed without handlers having knowledge of the exposure status of the animals. Animals were tested in the maze immediately following exposure or after a delay of 15 or 30 min. No significant field-dependent effects on performance were observed in choice accuracy or in total times to complete the task across the experiment. These results suggest that exposure to RF radiation simulating a digital wireless telephone (GSM) signal under the conditions of this experiment does not affect the acquisition of the learned response. Further studies are planned to explore the effects of other SARs on learned behavior. Bioelectromagnetics 21:151-158, 2000. Published 2000 Wiley-Liss, Inc.

Deficits in spatial learning after exposure of mice to a 50 Hz magnetic field

A series of four experiments was performed to determine the effect of exposure to a 50 Hz magnetic field on memory-related behaviour of adult, male C57BL/6J mice. Experimental subjects were exposed to a vertical, sinusoidal magnetic field at 0.75 mT (rms), for 45 min immediately before daily testing sessions on a spatial learning task in an eight-arm radial maze. Control subjects were only exposed to a background time-varying field of less than 50 nT and the ambient static field of about 40 microT. In each experiment, exposure significantly reduced the rate of acquisition of the task but did not affect overall accuracy. This finding is consistent with the results of another study that found that prior exposure to 60 Hz magnetic fields affected spatial learning in rats.

Biological effects of electromagnetic fields and radiation

There is much debate and controversy surrounding the effects of low intensity electromagnetic fields and radiation. A few subtle biological effects have been observed in experiments using animals and volunteers, but there is no convincing evidence to suggest that exposure to the fields commonly encountered in the environment will cause any significant adverse health effect in humans.

Prenatal Irradiation and Spatial Memory in Mice: Investigation of Dose-response Relationship

Pregnant CD1 mice were exposed on gestational day 18 to 250 kV X-rays at 0.1, 0.25, 0.35 and 0.5 Gy. The performances of 10 adult male offspring from each exposure condition were investigated on a spatial discrimination learning task in a radial arm maze. An impairment in the performance of this task was found which showed a correlation with dose. Compared with sham exposed control mice, performance was not significantly affected with irradiation at 0.1 Gy and was slightly but non-significantly reduced at 0.25 Gy. Irradiation at 0.35 Gy caused a significant impairment in performance, and exposure at 0.5 Gy resulted in a still larger impairment. The overall association between dose and behavioural impairment was best described by a linear relationship without a threshold, although at doses lower than about 0.25 Gy any impairment would appear to be too small to be detectable.

50 Hz magnetic field effects on the performance of a spatial learning task by mice

Intense magnetic fields have been shown to affect memory-related behaviours of rodents. A series of experiments was performed to investigate further the effects of a 50 Hz magnetic field on the foraging behaviour of adult, male C57BL/6J mice performing a spatial learning task in an eight-arm radial maze. Exposure to vertical, sinusoidal magnetic fields between 7.5 microT and 7.5 mT for 45 min immediately before daily testing sessions caused transient decreases in performance that depended on the applied flux density. Exposure above a threshold of between 7.5 and 75 microT significantly increased the number of errors the animals made and reduced the rate of acquisition of the task without any effect on overall accuracy. However, the imposition of a 45-minute delay between exposure at 0.75 mT and behavioural testing resulted in the elimination of any deficit. Similarly, exposure to fields between 7.5 microT and 0.75 mT for 45 min each day for 4 days after training had no amnesic effects on the retention and subsequent performance of the task. Overall, these results provide additional evidence that 50 Hz magnetic fields may cause subtle changes in the processing of spatial information in mice. Although these effects appear dependent on field strength, even at high flux densities the field-induced deficits tend to be transient and reversible.

Single, brief exposure to a 50 Hz magnetic field does not affect the performance of an object recognition task in adult mice.

A number of studies have shown that power frequency magnetic fields may affect spatial memory functions in rodents. An experiment was performed using a spontaneous object recognition task to investigate if nonspatial working memory was similarly affected. Memory changes in adult, male C57BL/6J mice were assessed by measuring the relative time within which the animals explored familiar or novel stimulus objects. Between initial testing and retesting, the animals were exposed for 45 min to a 50 Hz magnetic field at either 7.5 microT, 75 microT or 0.75 mT. Other animals were sham-exposed with ambient fields of less than 50 nT. No significant field-dependent effects on the performance of the task were observed at any flux density (for all measures, P > 0.05). These data provide no evidence to suggest that nonspatial working memory was affected in mice by acute exposure to an intense 50 Hz magnetic field.

Differential learning impairments produced by prenatal exposure to ionizing radiation in mice

PURPOSE To investigate the behavioural effects of prenatal irradiation on different days of gestation on the performance of two learning tasks by adult mice. MATERIALS AND METHODS CD1 mice were exposed in utero to 1 Gy of 250 kV X-rays on gestational days 13, 15 or 18. Other animals were sham-exposed. Male mice were tested as adults in a radial arm maze on two learning tasks considered dependent upon either spatial memory or visual associative memory. RESULTS Performance of the animals on the tasks was a function of the day on which exposure occurred. Compared with sham-exposed animals, exposure on day 18 produced a highly significant deficit in performance on the spatial task, and a small improvement in the visually cued task. Exposure on day 15 produced no deficit in performance on the spatial task, but a highly significant deficit in the cued task. Exposure on day 13 produced no significant deficits on either task. CONCLUSIONS These differential effects on performance appear to be consistent with radiation-induced insult to different memory systems within the developing mouse brain. These and further studies will help provide better estimates of the risks of radiation at different times during gestation on cognitive function in humans.

PRENATAL EXPOSURE TO A 50 HZ MAGNETIC FIELD HAS NO EFFECT ON SPATIAL LEARNING IN ADULT MICE

Male CD1 mice were exposed in utero to a 50 Hz sinusoidal magnetic field at 5 mT (rms) for the period of gestation and were raised subsequently without applied fields. At 82-84 days of age, they began a radial-arm-maze experiment that was designed to test for deficits in spatial learning and memory. Mice exposed in utero and sham-exposed mice exhibited no statistically significant differences in performances.

Magnetic Fields and Spatial Learning in Mice

There is growing evidence that acute exposure to low frequency magnetic fields may cause subtle changes in nervous system function and affect memory-related behaviours, especially those requiring processing of spatial information. For example, changes have been observed in the behaviour of rats performing a spatial memory task in a radial arm maze with exposure to specific combinations of static and time-varying fields1,2 while the performance of voles and deer mice in a Morris water maze may be altered using sinusoidal fields alone3,4. In addition, Lai5 has recently demonstrated that exposure of rats for 45 minutes to a 60 Hz field at 0.75 mT before daily training sessions in a 12 arm maze produced highly significant deficits in learning, with field-exposed animals consistently making more errors in the maze than sham-exposed animals. In addition, it was suggested5 that changes in central cholinergic transmission were responsible for these effects, since pre treatment with the choline agonist physostigmine was able to reverse the deficits in learning. The present series of experiments was conducted to explore these effects further and to describe the effects of acute exposure to 50 Hz magnetic fields on spatial learning in mice.

Mobile Communications Safety

Within a few years of the introduction of personal telecommunications, rumours began circulating about the safety of using cellular telephones. It was alleged that exposure to the radiation from the handsets and base stations was causing headaches or even brain tumours and other cancers. National and international regulatory and advisory bodies assured the public that such feats were unfounded: a large body of evidence existed describing the effects of radiofrequency and microwave (RF) radiation and there was no conclusive proof of any adverse effect from this radiation in the absence of heating. However, these worries continued to be voiced and resulted in a substantial amount of new research, funded largely by the telecommunications industry itself. This book presents a good summary and compendium of this research to the end of 1995. It is organised into five sections. The first presents a very brief summary of the technology of mobile cellular telephony. The second section is far more substantial and covers the dosimetry, electromagnetic compatibility, biology and epidemiology. The third section presents a summary of current research activities in North America, Europe, China, Japan and Australia, while the fourth section presents the regulatory and standards activities in these areas. The final section offers a critique on how to assess the relevance of reported effects, since many effects have been reported with RF radiation but few have been confirmed by independent laboratories. The book as a whole makes excellent reading, but it is rather like meeting an unknown guest at a party: during conservation the guest is both erudite and thought provoking, but you are never introduced and you have to leave unexpectedly before your discourse is finished. So it is with this book. There are plenty of details and controversial ideas presented but there is a lack of a general overview to give a historical perspective to these opinions, although various chapters attempt this to some extent from their own standpoint. Perhaps more importantly, there is no final summary which brings together all the different strands of past and current research, and clearly states what effects occur consistently, and what the consequences may be for human exposure. With amplitude-modulated RF radiation, in particular, many biological effects have been claimed in animals and cells, but none of these appears to have a clear, functional significance. A final summary could also point out deficiencies or inconsistencies in the data to indicate the directions that future research should take. I appreciate that there can be no definitive answers yet, otherwise no more research would be needed, but a few broad generalisations would have been most welcome. Another problem with any review is that the information it presents quickly dates. This is especially true when research is being described as it is being conducted, but as a snapshot of current research throughout the world, this is a very useful book. I only hope that the studies described that were in progress, are published in the peer-reviewed literature once they have been completed. I would not necessarily recommend buying this book, unless the controversy surrounding the effects of RF radiation is your particular speciality, but I would strongly recommend it to anyone interested in a contemporary viewpoint of the subject.