Behavioral sensitivity of rats to extremely-low-frequency magnetic fields.

Work in our laboratory has revealed autonomic and/or behavioral sensitivity of mice, rats, and a domestic fowl to extremely-low-frequency (ELF) or nominally static magnetic (B) fields at flux densities between 250 and 1700 microT (rms). To extend our work, an automated exposure and data-acquisition system was used with the technique of conditional suppression to assess behavioral sensitivity to time-varying B fields. Each of five rats was exposed aperiodically to a B field during 3 min warning periods that terminated in a brief electric shock. The difference between rates of lever pressing during B-field warning periods and rates during immediately antecedent, 3 min control periods was analyzed at frequencies of 7, 16, 30, 60, and 65.1 Hz. To produce equivalent induced voltages in the rat at each frequency, graded flux densities were established that ranged from 1900 microT at 7 Hz to 200 microT at 65.1 Hz. Analysis of differences in lever-pressing rates revealed that in a given session of testing the rats would increasingly suppress responding when exposed to a B field, but this trend was independent of frequency. This experiment provides evidence of behavioral sensitivity by a mammal to an ELF magnetic field.

Ototoxicity of intraventricularly administered gentamicin in adult rabbits.

To determine whether daily intraventricular injection of gentamicin sulfate is ototoxic, adult male rabbits were given 0.2 ml of saline (group 1; n = 8) or 0.25 mg/kg of gentamicin sulfate in 0.2 ml of saline (group 2; n = 7) by intraventricular infusion once a day for 21 d. All rabbits were also given intramuscular gentamicin sulfate, 2 mg/kg, twice daily. Before and after antibiotic treatment, brainstem auditory evoked responses (BAERs) were recorded. During the experimental period, neurologic examinations were performed on all rabbits. After treatment, the animals were euthanized; brain tissue and cochleas were then removed for histopathologic examination. The ratios of neurologic abnormalities observed in group 1 and 2 animals, respectively, were 0/8 and 5/7; of abnormal BAERs, 0/8 and 5/7; of abnormal brain morphology, 2/5 and 6/6; and of abnormal cochlear morphology, 0/6 and 7/7. The electrophysiologic evidence of auditory deficit and the structural evidence of ototoxic insult are significantly associated (p less than or equal to 0.006) with intraventricularly administered gentamicin sulfate. These data suggest that intraventricular gentamicin should be used with caution.

Temperature gradients in the microwave-irradiated egg: implications for avian teratogenesis.

Five experiments were performed on a total of 60 non-fertile eggs of Gallus gallus to determine the spatial character, persistence, and physical basis of thermal gradients after a 300-s exposure to the intense, multipath, 2.45-GHz yield of a multimode cavity (dose rates: approximately 80 to 120 mW/g). After irradiation of an intact egg that was first equilibrated to the ambient temperature, a 3-mm diameter Plexiglas rod, which was fitted with junctions of four microwire thermocouples at 10-mm intervals, was inserted to place the distal junction in the approximate center of the yolk, the most proximal junction in peripheral thin white. Temperatures measured immediately after irradiation revealed a highly reliable linear gradient of mean temperatures from central yolk to peripheral white (P less than 0.001). The gradient was also highly persistent: Mean temperatures of central yolk exceeded those of outer thin white by more than 4 degrees C 5 minutes after irradiation, and by more than 2 degrees C 60 minutes afterward. In contrast, when an egg's contents were mixed before irradiation, the gradient was effectively eliminated. A previous report of athermally induced (field-specific) teratogenesis in chick embryos is placed under an interpretive cloud by the present findings: Terata emerged from eggs that were structurally intact during microwave irradiation, but estimates of maxima of embryonic temperatures were based on thermal measurements of non-fertile eggs the contents of which had been mixed by a thermal probe before irradiation.

Photic cuing of escape by rats from an intense microwave field.

A total of 16 female hooded rats was first observed for baseline behaviors and then they received 25 2-min trials of training, five trials per day, under one of four stimulus conditions (all ns = 4): exposure to a highly intense 918-MHz field (dose rate, 60 mW/g); exposure to photic stimulation (approximately 350 1x); exposure to the field in synchrony with photic stimulation; or exposure to faradic shock (approximately 800 micro A rms). During conditioning trials, which were separated by 2-min intertrial intervals, entry by a rat into a safe area of a multimode cavity resulted in immediate and complete cessation of stimulation; exit, in resumption. Acquisition of the escape response was rapid and highly efficient for shocked animals and was less rapid and efficient but was reliably demonstrated by irradiated animals that were also signaled by light. In the absence of microwave irradiation, cessation of light did not reliably motivate escape behavior. Although there was weak evidence of escape learning by rats subjected only to microwave irradiation, their performance failed to differ reliably from those of rats in the light-only condition. These data confirm and extend those of Carroll et al, which indicate that potentially lethal, deeply penetrating, nonpulsed microwaves in a multipath field lack the sensory quality to motivate efficient aversive behavior by the rat.

A comparative study of human sensory thresholds: 2450-MHz microwaves vs far-infrared radiation.

Three male and female adults individually placed the ventral surface of the right and upright forearm against a 15-cm-diameter aperture in a wall of microwave-absorbent material. Ten-second exposures occurred to E-vector-vertically polarized, 2450-MHz-CW microwave (MW) fields. Comparable exposure to infrared (IR) waves was repeated with four of the six observers. Thresholds of detection of just-noticeable warming by MW and IR radiation were determined by the double-staircase psychophysical method. Although the exposed surface areas of male observers' arm were larger than those of female observers, thresholds of warming by either source of energy overlapped; the pooled means of irradiance at threshold are 26.7 mW/cm2 (MW) and 1.7 mW/cm2 (IR). Dosimetric measures on saline models indicated virtually perfect absorption of the incident IR, but nearly two-thirds of the MW energy was scattered. Accordingly, the 15-fold difference in means of MW and IR thresholds resolves to a 5-fold difference in threshold quantities of absorbed energy. In the light of the high correlation between thresholds of IR and MW irradiation (r = .97), it is concluded that the same set of superficial thermoreceptors was being stimulated, only less efficiently so, by the more deeply penetrating, more diffusely absorbed MW energy.

Failure of rats to escape from a potentially lethal microwave field.

Ocularly pigmented rats, all mature females of the Long-Evans strain, were repeatedly presented an opportunity to escape from an intense 918-MHz field (whole-body dose rate = 60 mW/g) to a field of lower intensity (40, 30, 20, or 2 mW/g) by performing a simple locomotor response. Other rats could escape 800-microamperemeter faradic shock to the feet and tail by performing the same response in the same milieu, a multimode cavity. None of 20 irradiated rats learned to associate entry into a visually well-demarcated area of the cavity with immediate reduction of dose rate, in spite of field-induced elevations of body temperature to levels that exceeded 41 degrees C and would have been lethal but for a limit on durations of irradiation. In contrast, all of ten rats motivated by faradic shock rapidly learned to escape. The failure of escape learning by irradiated animals probably arose from deficiencies of motivation and, especially, sensory feedback. Whole-body hyperthermia induced by a multipath field may lack the painful or directional sensory properties that optimally promote the motive to escape. Moreover, a decline of body temperature after an escape-response-contingent reduction of field strength will be relatively slow because of the large thermal time constants of mammalian tissues. Without timely sensory feedback, which is an essential element of negative reinforcement, stimulus-response associability would be imparied, which could retard or preclude learning of an escape response.

Limits to conceptual rule-learing by schizophrenic patients.

Two studies of conceptual rule-learning by 36 hospitalized psychiatric patients revealed that (a) while all were clinically diagnosed as schizophrenic, they differed widely in their ability to discover abstract rules; (b) the Whitaker Index of Schizophrenic Thinking (WIST) strongly predicted the patients' ability to learn and to apply a conceptual rule; and (c) regardless of severity of conceptual impairment, the patients were unaffected by modest levels of externally generated irrelevant information as presented through the modality of vision. Deficits in abstractive ability, when they exist, are believed to be due to a schizophrenic patient's inability to prevent task-irrelevant information that originates in long-term memory from spilling into and despoiling the operations of working memory.

Teratology, survival, and reversal learning after fetal irradiation of mice by 2450-MHz microwave energy.

In the first of two factorially designed studies, 80 primigravid mice of the C3H-HeJ strain were subjected to 2450-MHz sinusoidally modulated microwave radiation or to sham radiation (with or without an accompanying injection of 5 mg of cortisone as a teratological marker) on the 11th, 12th, 13th or 14th day of gestation. The radiation treatment consisted of a single intense dosing of microwave energy (38 mW/g for 600 sec.= 22.8 J/g) in a multi-mode cavity. On the 19th day of gestation fetuses were taken via Caesarean section and were observed for gross structural abnormalities. While radiation of dams failed reliably to increase the incidence of fetal mortality or morbidity above that of controls, the dams treated with cortisone gave birth to reliably greater numbers of stillborn and deformed fetuses. In the second experiment and during their 14th day of gestation 60 primigravid mice received the radiation of sham-radiation treatment, half with, half without, the accompanying injection of cortisone. A virtually complete failure to survive to weaning characterized the pups born of the sham-radiated cortisone-treated group of dams, but the incidence of cortisone-induced mortality was reliably reduced in pups whose dams were also radiated by microwave energy. Pups sampled from all but the depleted group were observed later as young adults for competency in mastering a series of reversal habits in a water maze. No differences in maze performances were observed in the mice as a function of their placement in the control or the radiation condition, but offspring of cortisone-treated, radiated dams made reliably more errors. Careful measurement of elevations of colonic temperatures of radiated dams shortly after treatment with cortisone revealed an averaged deltaT that is close to that observed in a comparably radiated volume of water of equivalent mass. If the finding has generality beyond the gravid mouse-it, that is, cortisone effectively and reversibly renders the mammal ectothermic-an important advance in biological dosimetry of non-ionizing radiation may be at hand.