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.

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.

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.

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.

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.

Acute exposure to power-frequency magnetic fields has no effect on the acquisition of a spatial learning task by adult male mice.

A series of four experiments was performed to determine whether acute exposure to a range of 50 Hz magnetic fields had any effect on a learning task in adult male CD1 mice. A radial-arm maze placed within the bore of an electromagnet was used to assess spatial discrimination learning for food reward. Subjects were reduced to 85% of their free-feeding weight and were placed in the maze for up to 15 minutes each day for 10 days. Performance of the task was measured by using maximum likelihood techniques to calculate the probability that an animal would not reenter any given arm of the maze. Experimental subjects were exposed to a vertical, 50 Hz sinusoidal magnetic field at 5 microT, 50 microT, 0.5 mT, or 5.0 mT (rms). Control subjects were exposed only to a background time-varying field of less than 50 nT and the ambient static field of about 40 microT. The variation in the applied magnetic field was less than 5% except at the ends of the arms, where it approached 10%. It was found that all eight groups of subjects (n = 10 in all cases) showed similar increases in performance with testing, and the acquisition curve for each group of experimental subjects was not significantly different from that of their control group (P > 0.05 in all cases). It was concluded that exposure had no effect on learning at any flux density. This result is contrary to the findings of a number of preliminary studies, although other studies have reported that magnetic fields do not affect spatial learning in adult male rodents. It is possible that differences between experimental conditions might explain some of this apparent discrepancy.

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.

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.

Effects of prenatal exposure to 50 Hz magnetic fields on development in mice: II. Postnatal development and behavior.

To investigate the potential of magnetic fields to act as a behavioral teratogen, pregnant CD1 mice were exposed or sham-exposed for all of gestation to a 50 Hz/20 mT magnetic field. Maturation of offspring was assessed using a range of standard developmental indices (eye opening, pinna detachment, hair coat, tooth eruption, sexual maturity, and weight) and simple reflexive behaviors (air righting, surface righting, forepaw grasp, cliff avoidance, and negative geotaxis). Activity and coordination levels were explored in juvenile and adult mice using an open field arena, a head-dip board, an accelerating Rotarod, and a residential activity wheel. All assessments were carried out without knowledge of exposure condition. Results from 168 sham-exposed mice from 21 litters and from 184 exposed mice from 23 litters were compared using survival analysis techniques and multivariate regression methods. Three possible field-dependent effects were found: Exposed animals performed the air righting reflex earlier (P < 0.01); exposed males (but not females) were significantly lighter in weight (P = 0.008) at 30 days of age; and exposed animals remained on a Rota-rod for less time as juveniles (P = 0.03). Some of these results have not been reported in other studies and may reflect spurious statistical significance, although some effect of magnetic field exposure cannot be ruled out. Overall, these results suggest that prenatal exposure to a 50 Hz magnetic field does not engender any gross impairments in the postnatal development or behavior of mice. This does not preclude such exposure affecting more subtle aspects of behavior.

Prenatal irradiation and spatial memory in mice: investigation of critical period.

Pregnant CD1 mice were exposed on various gestational or postnatal days to 1 Gy of 250 kV X-rays. Ten adult, male offspring from each exposure condition were tested in a radial arm maze. Compared to sham-exposed control mice, acquisition of spatial information was unimpaired in animals exposed on gestational days 13 or 15, or on postnatal day 10, but animals exposed on gestational day 18 or postnatal day 1 showed sustained deficits in acquisition. These results appear consistent with the known time-course for the proliferation and migration of the dentate granule cells of the hippocampus in the mouse, and are discussed in relation to the dependence on hippocampal integrity of the acquisition and use of spatial information. The results suggest that comparable deficits in mental function might be expected in humans similarly exposed to ionizing radiation during periods of proliferation and migration of the dentate granule cells.

Gustatory responses of single neurons in the caudolateral orbitofrontal cortex of the macaque monkey.

1. In recordings made from 3,120 single neurons, a secondary cortical taste area was found in the caudolateral part of the orbitofrontal cortex of the cynomolgus macaque monkey, Macaca fascicularis. The area is part of the dysgranular field of the orbitofrontal cortex and is situated anterior to the primary cortical taste areas in the frontal opercular and adjoining insular cortices. 2. The responses of 49 single neurons with gustatory responses in the caudolateral orbitofrontal taste cortex were analyzed using the taste stimuli glucose, NaCl, HCl, quinine HCl, water, and blackcurrant juice. 3. A breadth-of-tuning coefficient was calculated for each neuron. This is a metric that can range from 0.0 for a neuron that responds specifically to only one of the four basic taste stimuli to 1.0 for one that responds equally to all four stimuli. The mean coefficient for 49 cells in the caudolateral orbitofrontal cortex was 0.39. This tuning is much sharper than that of neurons in the nucleus of the solitary tract of the monkey, and sharper than that of neurons in the primary frontal opercular and insular taste cortices. 4. A cluster analysis showed that at least seven different groups of neurons were present. For each of the taste stimuli glucose, blackcurrant juice, NaCl, and water, there was one group of neurons that responded much more to that tastant than to the other tastants. The other groups of neurons responded to two or more of these tastants, such as glucose and blackcurrant juice. In this particular region neurons were not found with large responses to HCl or quinine HCl, although such neurons could be present in other parts of the orbitofrontal cortex. 5. On the basis of this and other evidence it is concluded that in the caudolateral orbitofrontal cortex there is a secondary cortical taste area in which the tuning of neurons has become finer than in early areas of taste processing, in which foods, water, and NaCl are strongly represented and where motivation dependence first becomes manifest in the taste system.

Gustatory responses of single neurons in the insula of the macaque monkey.

1. In recordings made from 2,925 single neurons, a region of primary taste cortex was localized to the rostral and dorsal part of the insula of the cynomolgus macaque monkey, Macaca fascicularis. The area is part of the dysgranular field of the insula and is bordered laterally by the frontal opercular taste cortex. 2. The responses of 65 single neurons with gustatory responses were analyzed in awake macaques with the use of the taste stimuli glucose, NaCl, HCl, quinine HCl (QHCl), water, and black currant juice. 3. Intensity-response functions showed that the lowest concentration in the dynamic part of the range conformed well to human thresholds for the basic taste stimuli. 4. A breadth-of-tuning coefficient was calculated for each neuron. This is a metric that can range from 0.0 for a neuron that responds specifically to only one of the four basic taste stimuli to 1.0 for one that responds equally to all four stimuli. The mean coefficient for 65 cells in the taste insula was 0.56. This tuning is sharper than that of neurons in the nucleus of the solitary tract of the monkey, and similar to that of neurons in the primary frontal opercular taste cortex. 5. A cluster analysis showed that at least six different groups of neurons were present. For each of the taste stimuli, glucose, NaCl, HCl, QHCl, water, and black currant juice, there was one group of neurons that responded much more to that tastant than to the other tastants. Other subgroups of these neurons responded to two or more of these tastants, such as glucose and black currant juice, or NaCl and QHCl. 6. On the basis of this and other evidence, it is concluded that the primary insular taste cortex, in common with the primary frontal opercular taste cortex, represents a stage of information processing in the taste system of the primate at which the tuning of neurons has become sharper than that of neurons in the nucleus of the solitary tract, and is moving toward the fineness achieved in the secondary taste cortex in the caudolateral orbitofrontal taste cortex, where motivation-dependence first becomes manifest in the taste system.

Relationship between local temperature and heat transfer through the hand and wrist.

The heat uptake that resulted from immersing the hand and wrist into a water-filled calorimeter maintained at temperatures between 37-40 degrees C was measured under standard conditions in a group of eight subjects of either sex. The rate of heat transfer (W) increased exponentially with temperature and was a function of hand or body size and age, but not sex. The heat transfer rate normalized to hand mass (W.kg-1) was determined by temperature and age: best-fit mean values (and 95% confidence limits of the population) were 6.0 W.kg-1 (3.2-11.2 W.kg-1) at an immersion temperature of 37 degrees C and 25.4 W.kg-1 (13.7-47.0 W.kg-1) at 40 degrees C. The application of these results to limits on specific energy absorption rate induced in the hands and wrists by radiofrequency dielectric heat sealer welders is discussed.

The responsiveness of neurones in the frontal opercular gustatory cortex of the macaque monkey is independent of hunger.

1. In order to determine whether the responsiveness of neurones in the primary gustatory cortex is influenced by hunger, the activity of neurones in the gustatory cortex in the frontal operculum was recorded while macaque monkeys (Macaca fascicularis) were fed to satiety. The responses of single neurones in the gustatory cortex to the prototypical taste stimuli glucose, NaCl, HCl and quinine hydrochloride, and to fruit juice, were measured before, while, and after the monkey was fed to satiety with glucose or fruit juice. 2. While behaviour turned from avid acceptance to active rejection upon repletion, the responsiveness of the neurones to the stimulus array, including the satiating solution, was unmodified. 3. It is concluded that in the gustatory cortex in the frontal operculum, neuronal responses to gustatory stimuli are not influenced by the normal transition from hunger to satiety. This is in contrast to the responses of a population of neurones recorded in the hypothalamus, which only occur to the taste of food when the monkey is hungry. Thus the neurones in the primary gustatory cortex are involved in a motivation-independent analysis of gustatory stimuli, whereas the hypothalamic neurones may be more closely related to the influence of motivational state on behavioural responsiveness to gustatory stimuli.

The responsiveness of neurons in the insular gustatory cortex of the macaque monkey is independent of hunger.

(1) In order to determine whether the responsiveness of neurons in the insular gustatory cortex is influenced by hunger, neuronal activity was analysed in it while macaque monkeys (Macaca fascicularis) were fed to satiety. The responses of single neurons in the insular gustatory cortex to the protypical taste stimuli glucose, NaCl, HCl and quinine HCl, and to fruit juice, were measured before, while, and after the monkey was fed to satiety with glucose or fruit juice. (2) While behavior turned from avid acceptance to active rejection upon repletion, the responsiveness of the neurons to the stimulus array, including the satiating solution, was unmodified. (3) It is concluded that in the insular gustatory cortex, neuronal responses to gustatory stimuli are not influenced by the normal transition from hunger to satiety. This is in contrast to the responses of a population of neurons recorded in the hypothalamus, which only respond to the taste of food when the monkey is hungry. Thus the neurons in the insular gustatory cortex are involved in a motivation-independent analysis of gustatory stimuli, whereas the hypothalamic neurons may be more closely related to the influence of motivational state on behavioral responsiveness to gustatory stimuli.

Gustatory responses in the frontal opercular cortex of the alert cynomolgus monkey.

The responses of 165 single taste neurons in the anterior operculum of the alert cynomolgus monkey were analyzed. Chemicals were deionized water, blackcurrant juice, and the four basic taste stimuli: glucose, NaCl, HCl, and quinine HCl. Taste-evoked responses could be recorded from an opercular region that measured approximately 4.0 mm in its anteroposterior extent, 2.0 mm mediolaterally, and 3.0 mm dorsoventrally. Within this area, taste-responsive neurons were sparsely distributed such that multiunit activity was rarely encountered and neuronal isolation was readily achieved. Intensity-response functions were determined for nine cells. In each case, the lowest concentration of the dynamic response range conformed well to human electrophysiological and psychophysical thresholds for the basic taste stimuli. There was some evidence of chemotopic organization. Cells that responded best to glucose tended to be distributed toward the anterior operculum, whereas most acid-sensitive neurons were located more posteriorly. The proportion of cells responding best to NaCl peaked in the middle of the area, whereas quinine sensitivity was rather evenly distributed throughout. Opercular neurons in the monkey showed moderate breadth of sensitivity compared with taste cells of other species and at other synaptic levels. A breadth-of-tuning coefficient was calculated for each neuron. This is a metric that can range from 0.0 for a cell that responds specifically to only one of the four basic stimuli to 1.0 for one that responds equally to all four stimuli. The mean coefficient for 165 cells in the operculum was 0.67 (range = 0.12-0.99). Efforts were made to determine whether neurons could be divided into a discrete number of types, as defined by their responsiveness to the stimulus array used here. It was concluded that most taste cells may be assigned to a small number of groups, each of which is statistically independent of the others, but within which the constituent neurons are not identical. An analysis of taste quality indicated that the sweet and salty stimuli evoked patterns of activity that were significantly intercorrelated. Similarly, patterns representing HCl, quinine HCl, and water were related.

Gustatory responses in the nucleus tractus solitarius of the alert cynomolgus monkey.

Multiunit and single neuron responses to taste stimuli in the nucleus tractus solitarius (NTS) of alert cynomolgus monkeys were analyzed. Intensity-response functions, including neural thresholds to glucose and quinine HCl, agreed well with psychophysical reports, implying that the cynomolgus monkey and human share the same dynamic range of sensitivity to prototypical taste stimuli. The NTS is chemotopically organized: neurons most responsive to HCl are more common in the posterior gustatory area, whereas those most responsive to glucose and NaCl are located in the anterior NTS. Responsiveness to quinine is more widely distributed but tends toward the anterior. Efforts were made to determine if neurons could be divided into a discrete number of types, as determined by their sensitivities to the prototypical stimuli. The clearest distinction was between those that did or did not respond well to HCl. Beyond this, neuronal categories were not obvious. Individual neurons were quite broadly sensitive to our stimulus array, so that, for the typical NTS cell, no one of the four prototypes evoked a majority of the discharges. This extreme breadth of tuning suggests that taste-quality information in the monkey might be incorporated in relative discharge rates across the neuron population. Correlations among patterns of activity to the four prototypical stimuli indicated that only HCl and quinine HCl have closely related taste qualities.

Satiety does not affect gustatory activity in the nucleus of the solitary tract of the alert monkey.

Feeding to satiety decreases the acceptability of the taste of food. In order to determine whether the responsiveness of gustatory neurons in the nucleus tractus solitarius (NTS) is influenced by hunger, neural activity in the NTS was analyzed while monkeys were fed to satiety. Gustatory neural activity to glucose, fruit juice, NaCl, HCl and quinine HCl was measured before, while and after the monkey was fed to satiety with glucose, fruit juice or sucrose. While behavior turned from avid acceptance to active rejection upon repletion, the responsiveness of NTS neurons to the stimulus array, including the satiating solution, was unmodified. It is concluded that at the first central synapse of the taste system of the primate, neural responsiveness is not influenced by the normal transition from hunger to satiety. This is in contrast to the responses of a population of neurons recorded in the hypothalamus, which only occur to the taste of food when the monkey is hungry. Thus, NTS gustatory activity appears to occur independently of normal hunger and satiety, whereas hypothalamic neuronal activity is more closely related to the influence of motivational state on behavioral responsiveness to gustatory stimuli.