Inconsistent suppression of nocturnal pineal melatonin synthesis and serum melatonin levels in rats exposed to pulsed DC magnetic fields

Random Effects in Magnetobiology and a Way to Summarize Them

In magnetobiology, it is difficult to reproduce the nonspecific (not associated with specialized receptors) biological effects of weak magnetic fields. This means that some important characteristic of the data may be missed in standard statistical processing, where the set of measurements to be averaged belongs to the same population so that the contribution of fluctuations decreases according to the Central Limit Theorem. It has been shown that a series of measurements of a nonspecific magnetic effect contains not only the usual scatter of data around the mean but also a significant random component in the mean itself. This random component indicates that measurements belong to different statistical populations, which requires special processing. This component, otherwise called heterogeneity, is an additional characteristic that is typically overlooked, and which reduces reproducibility. The current method for studying and summarizing highly heterogeneous data is the random-effect meta-analysis of absolute values, i.e., of magnitudes, rather than the values themselves. However, this estimator-the average of absolute values-has a significant positive bias when it comes to the small effects that are characteristic of magnetobiology. To solve this problem, an improved estimator based on the folded normal distribution that gives several times less bias is proposed. We used this improved estimator to analyze the nonspecific effect of the hypomagnetic field in the Stroop test in 40 subjects and found a statistically significant meta-effect with a standardized average of magnitudes of about 0.1. It has been shown that the proposed approach can also be applied to a single study. © 2021 Bioelectromagnetics Society.

Effect of occupational EMF exposure from radar at two different frequency bands on plasma melatonin and serotonin levels

OBJECTIVE

To delineate the effect of chronic electromagnetic field (EMF) exposure from radar on plasma melatonin and serotonin levels in occupationally exposed military personnel.

SUBJECTS AND METHODS

A total of 166 male military personnel participated in the study out of which only 155 joined for blood draw. They were divided into three sets: Control group (n = 68), exposure group I (n = 40) exposed to 8-12 GHz and exposure group II (n = 58) working with radar at 12.5-18 GHz frequency. The three groups were further split into two groups according to their years of service (up to 10 years and > 10 years) in order to investigate the effect of years of exposure from radar. Melatonin and serotonin levels were estimated by enzyme immunoassay in fasting blood samples collected from 06:00-07:00 h. EMF measurements were recorded at different locations using Satimo EME Guard 'Personal Exposure Meter' and Narda 'Broad Band Field Meter'.

RESULTS

The group I exposed population registered a minor though not significant decrease in plasma melatonin concentration while the other group II exposed population registered statistically significant decline in melatonin concentration when compared with controls. Highly significant increase in plasma serotonin levels was found in exposure group II when compared to control whereas marginal non-significant rise was also registered in exposure group I in comparison to control. Exposure in terms of length of service up to 10 years did not produce any significant effect in the indoleamine levels in both the exposure groups when they were compared with their respective control groups. Whereas, length of service greater than 10 years was observed to decrease and increase respectively the melatonin and serotonin concentration significantly in exposure group II but not in exposure group I. However, correlation test did not yield any significant association between years of service and melatonin or serotonin levels respectively in both the exposure sets I and II. No significant association was observed between melatonin and serotonin levels as well.

CONCLUSION

The study showed the EMF ability to influence plasma melatonin and serotonin concentration in radar workers, significantly in 12.5-18 GHz range with service period greater than 10 years.

Influence of electric, magnetic, and electromagnetic fields on the circadian system: current stage of knowledge

One of the side effects of each electrical device work is the electromagnetic field generated near its workplace. All organisms, including humans, are exposed daily to the influence of different types of this field, characterized by various physical parameters. Therefore, it is important to accurately determine the effects of an electromagnetic field on the physiological and pathological processes occurring in cells, tissues, and organs. Numerous epidemiological and experimental data suggest that the extremely low frequency magnetic field generated by electrical transmission lines and electrically powered devices and the high frequencies electromagnetic radiation emitted by electronic devices have a potentially negative impact on the circadian system. On the other hand, several studies have found no influence of these fields on chronobiological parameters. According to the current state of knowledge, some previously proposed hypotheses, including one concerning the key role of melatonin secretion disruption in pathogenesis of electromagnetic field induced diseases, need to be revised. This paper reviews the data on the effect of electric, magnetic, and electromagnetic fields on melatonin and cortisol rhythms—two major markers of the circadian system as well as on sleep. It also provides the basic information about the nature, classification, parameters, and sources of these fields.

The effects of extremely low-frequency magnetic fields on melatonin and cortisol, two marker rhythms of the circadian system

In the past 30 years the concern that daily exposure to extremely low-frequency magnetic fields (ELF-EMF) (1 to 300 Hz) might be harmful to human health (cancer, neurobehavioral disturbances, etc) has been the object of debate, and has become a public health concern. This has resulted in the classification of ELF-EMF into category 2B, ie, agents that are “possibly carcinogenic to humans” by the International Agency for Research on Cancer. Since melatonin, a neurohormone secreted by the pineal gland, has been shown to possess oncostatic properties, a “melatonin hypothesis” has been raised, stating that exposure to EMF might decrease melatonin production and therefore might promote the development of breast cancer in humans. Data from the literature reviewed here are contradictory. In addition, we have demonstrated a lack of effect of ELF-EMF on melatonin secretion in humans exposed to EMF (up to 20 years' exposure) which rebuts the melatonin hypothesis. Currently, the debate concerns the effects of ELF-EMF on the risk of childhood leukemia in children chronically exposed to more than 0.4 μT. Further research is thus needed to obtain more definite answers regarding the potential deleterious effects of ELF-EMF.

Effects of electromagnetic radiation from 3G mobile phone on heart rate, blood pressure and ECG parameters in rats

Effects of electromagnetic energy radiated from mobile phones (MPs) on heart is one of the research interests. The current study was designed to investigate the effects of electromagnetic radiation (EMR) from third-generation (3G) MP on the heart rate (HR), blood pressure (BP) and ECG parameters and also to investigate whether exogenous melatonin can exert any protective effect on these parameters. In this study 36 rats were randomized and evenly categorized into 4 groups: group 1 (3G-EMR exposed); group 2 (3G-EMR exposed + melatonin); group 3 (control) and group 4 (control + melatonin). The rats in groups 1 and 2 were exposed to 3G-specific MP’s EMR for 20 days (40 min/day; 20 min active (speech position) and 20 min passive (listening position)). Group 2 was also administered with melatonin for 20 days (5 mg/kg daily during the experimental period). ECG signals were recorded from cannulated carotid artery both before and after the experiment, and BP and HR were calculated on 1st, 3rd and 5th min of recordings. ECG signals were processed and statistically evaluated. In our experience, the obtained results did not show significant differences in the BP, HR and ECG parameters among the groups both before and after the experiment. Melatonin, also, did not exhibit any additional effects, neither beneficial nor hazardous, on the heart hemodynamics of rats. Therefore, the strategy (noncontact) of using a 3G MP could be the reason for ineffectiveness; and use of 3G MP, in this perspective, seems to be safer compared to the ones used in close contact with the head. However, further study is needed for standardization of such an assumption.

Emerging synergisms between drugs and physiologically-patterned weak magnetic fields: implications for neuropharmacology and the human population in the twenty-first century

Synergisms between pharmacological agents and endogenous neurotransmitters are familiar and frequent. The present review describes the experimental evidence for interactions between neuropharmacological compounds and the classes of weak magnetic fields that might be encountered in our daily environments. Whereas drugs mediate their effects through specific spatial (molecular) structures, magnetic fields mediate their effects through specific temporal patterns. Very weak (microT range) physiologically-patterned magnetic fields synergistically interact with drugs to strongly potentiate effects that have classically involved opiate, cholinergic, dopaminergic, serotonergic, and nitric oxide pathways. The combinations of the appropriately patterned magnetic fields and specific drugs can evoke changes that are several times larger than those evoked by the drugs alone. These novel synergisms provide a challenge for a future within an electromagnetic, technological world. They may also reveal fundamental, common physical mechanisms by which magnetic fields and chemical reactions affect the organism from the level of fundamental particles to the entire living system.

Circadian phase and sex effects on depressive/anxiety-like behaviors and HPA axis responses to acute stress

Circadian dysregulation in sleep pattern, mood, and hypothalamic-pituitary-adrenal (HPA) axis activity, often occurring in a sexually dimorphic manner, are characteristics of depression. However, the inter-relationships among circadian phase, HPA function, and depressive-like behaviors are not well understood. We investigated behavioral and neuroendocrine correlates of depressive/anxiety-like responses during diurnal ('light') and nocturnal ('dark') phases of the circadian rhythm in the open field (OF), elevated plus maze (EPM), forced swim (FST), and sucrose contrast (SC) tests. Plasma corticosterone (CORT) was measured after a) acute restraint and OF testing and b) FST. Both phase and sex significantly influenced behavioral responses to stress. Males were more anxious than females on the EPM in the light but not the dark phase. Further, the open:closed arm ratio was lower in the dark for females, but not males. By contrast, in the FST, females showed more "despair" (immobility) when tested in the dark, while phase did not affect males. Acute restraint stress increased OF activity in the light, but not the dark, phase. CORT levels were increased in both sexes following the FST, and in males and light phase females post-OF. As expected, females had higher CORT levels than males, even at rest, and this effect was more pronounced in the dark phase. Together, our data highlight the sexually dimorphic influences of circadian phase and stress on behavioral and hormonal responsiveness.

Effects of a 50 Hz electric field on plasma lipid peroxide level and antioxidant activity in rats

The effects of exposure to extremely low frequency electric fields (ELF EFs) on plasma lipid peroxide levels and antioxidant activity (AOA) in Sprague-Dawley rats were studied. The test was based on comparisons among rats treated with a combination of the oxidizing agent, 2,2'-azobis(2-aminopropane) dihydrochloride (AAPH) and 50 Hz EF of 17.5 kV/m intensity for 15 min per day for 7 days, AAPH alone, EF alone or no treatment. EF significantly decreased the plasma peroxide level in rats treated with AAPH, similar to treatment by ascorbic acid or the superoxide dismutase. Ascorbic acid increased AOA; however, EF and superoxide dismutase did not change AOA compared with sham exposure in stressed rats. No influence on the lipid peroxide level and AOA in unstressed rats was observed with EF exposure alone. Although the administration of AAPH decreased AOA, this decrease did not change when EF was added. These data indicate that the ELF EF used in this study influenced the lipid peroxide level in an oxidatively stressed rat.

Zinc Supplementation Ameliorates Electromagnetic Field-Induced Lipid Peroxidation in the Rat Brain

Extremely low-frequency (0-300 Hz) electromagnetic fields (EMFs) generated by power lines, wiring and home appliances are ubiquitous in our environment. All populations are now exposed to EMF, and exposure to EMF may pose health risks. Some of the adverse health effects of EMF exposure are lipid peroxidation and cell damage in various tissues. This study has investigated the effects of EMF exposure and zinc administration on lipid peroxidation in the rat brain. Twenty-four male Sprague-Dawley rats were randomly allocated to three groups; they were maintained untreated for 6 months (control, n = 8), exposed to low-frequency (50 Hz) EMF for 5 minutes every other day for 6 months (n = 8), or exposed to EMF and received zinc sulfate daily (3 mg/kg/day) intraperitoneally (n = 8). We measured plasma levels of zinc and thiobarbituric acid reactive substances (TBARS), and levels of reduced glutathione (GSH) in erythrocytes. TBARS and GSH levels were also determined in the brain tissues. TBARS levels in the plasma and brain tissues were higher in EMF-exposed rats with or without zinc supplementation, than those in controls (p < 0.001). In addition, TBARS levels were significantly lower in the zinc-supplemented rats than those in the EMF-exposed rats (p < 0.001). GSH levels were significantly decreased in the brain and erythrocytes of the EMF-exposed rats (p < 0.01), and were highest in the zinc-supplemented rats (p < 0.001). Plasma zinc was significantly lower in the EMF-exposed rats than those in controls (p < 0.001), while it was highest in the zinc-supplemented rats (p < 0.001). The present study suggests that long-term exposure to low-frequency EMF increases lipid peroxidation in the brain, which may be ameliorated by zinc supplementation.

N-acetyltransferase is not the rate-limiting enzyme of melatonin synthesis at night

Circadian melatonin production in the pineal gland and retina is under the control of serotonin N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase. Because NAT activity varies diurnally, it has been considered both the melatonin rhythm-generating enzyme and the rate-limiting enzyme of melatonin synthesis. In rats with dramatically reduced NAT activity due to a H28Y mutation in NAT, melatonin levels remained the same as in wildtype controls, suggesting that NAT does not determine the rate of melatonin production at night. Using a combination of molecular approaches with a sensitive in vivo measurement of pineal diurnal melatonin production, we demonstrate that (i) N-acetylserotonin (NAS), the enzymatic product of NAT, is present in vast excess in the night pineals compared with melatonin; (ii) the continuous increase in NAT protein levels at late night does not produce a proportional increase in melatonin; and (iii) an increase in NAS in the same animal over several circadian cycles do not result in corresponding increase in melatonin output. These results strongly suggest that NAT is not the rate-limiting enzyme of melatonin formation at night.

Oxidative Damage in the Kidney Induced by 900-MHz-Emitted Mobile Phone: Protection by Melatonin

BACKGROUND

The mobile phones emitting 900-MHz electromagnetic radiation (EMR) may be mainly absorbed by kidneys because they are often carried in belts. Melatonin, the chief secretory product of the pineal gland, was recently found to be a potent free radical scavenger and antioxidant. The aim of this study was to examine 900-MHz mobile phone-induced oxidative stress that promotes production of reactive oxygen species (ROS) on renal tubular damage and the role of melatonin on kidney tissue against possible oxidative damage in rats.

METHODS

The animals were randomly grouped as follows: 1) sham-operated control group and 2) study groups: i) 900-MHz EMR exposed (30 min/day for 10 days) group and ii) 900-MHz EMR exposed+melatonin (100 microg kg(-1) s.c. before the daily EMR exposure) treated group. Malondialdehyde (MDA), an index of lipid peroxidation), and urine N-acetyl-beta-d-glucosaminidase (NAG), a marker of renal tubular damage were used as markers of oxidative stress-induced renal impairment. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities were studied to evaluate the changes of antioxidant status.

RESULTS

In the EMR-exposed group, while tissue MDA and urine NAG levels increased, SOD, CAT, and GSH-Px activities were reduced. Melatonin treatment reversed these effects as well. In this study, the increase in MDA levels of renal tissue and in urine NAG and also the decrease in renal SOD, CAT, GSH-Px activities demonstrated the role of oxidative mechanism induced by 900-MHz mobile phone exposure, and melatonin, via its free radical scavenging and antioxidant properties, ameliorated oxidative tissue injury in rat kidney.

CONCLUSIONS

These results show that melatonin may exhibit a protective effect on mobile phone-induced renal impairment in rats.

Do magnetic fields cause increased risk of childhood leukemia via melatonin disruption?

Epidemiological studies have reported associations between exposure to power frequency magnetic fields and increased risk of certain cancer and noncancer illnesses. For childhood leukemia, a doubling of risk has been associated with exposures above 0.3/0.4 microT. Here, we propose that the melatonin hypothesis, in which power frequency magnetic fields suppress the nocturnal production of melatonin in the pineal gland, accounts for the observed increased risk of childhood leukemia. Such melatonin disruption has been shown in animals, especially with exposure to electric and/or rapid on/off magnetic fields. Equivocal evidence has been obtained from controlled laboratory magnetic field exposures of volunteers, although the exposure conditions are generally atypical of neighborhood exposures. In contrast, support for the hypothesis is found in the body of studies showing magnetic field disruption of melatonin in human populations chronically exposed to both electric and magnetic fields associated with electricity distribution. Further support comes from the observation that melatonin is highly protective of oxidative damage to the human haemopoietic system. Aspects of the hypothesis are amenable to further investigation.

Evaluation of Residential Exposure to Intermediate Frequency Magnetic Fields

The authors measured the exposure to intermediate-frequency (IF: 10 kHz to 30 MHz) electromagnetic fields (EMF) in residential environments. They developed a system to acquire and record waveforms of IF magnetic fields (MFs) and set 5 nanotesla (nT) for the trigger level of acquisition. They operated the system near power lines, railroads, and electrical appliances as possible sources of IF-MFs. Most of the maximum values of magnetic flux density and the time derivative for each wave were below the upper limit of the measurable range of our system (i.e., 53 nT and 10 T/s); these values were much lower than the minimum amplitudes that can theoretically induce heating or membrane excitation within biological systems. Moreover, the amplitudes of the IF-MFs were not related to those of extremely low frequency (ELF) MF measured simultaneously, indicating that IF-MFs do not underlie the associations, observed in several epidemiological studies, between residential exposure to ELF-EMF and childhood cancer.

Circularly polarised MF (500 micro T 50 Hz) does not acutely suppress melatonin secretion from cultured Wistar rat pineal glands

Magnetic fields (MF, 50 Hz) have been proposed to affect melatonin production in mammals; however, there is very little data about the mechanism by which this possible interaction may occur. Here we describe results from the first study in which circularly polarised 50 Hz MF have been administered to isolated pineals in highly controlled conditions. Melatonin release from isolated Wistar rat pineal glands, dissected 2 h after light onset ZT 2, was measured in a flow through culture system, during and after exposure to a 4 h MF similar in nature and magnitude to that produced in extremely close proximity to a high voltage power line (500 micro T 50 Hz circularly polarised). Melatonin release from isolated pineals was comparable to that observed in previous studies, plateauing to approximately 100 pg/ml/30 min. No significant alterations in pineal melatonin release were caused by exposure to the MF when compared to sham exposure (< 1 micro T). These results suggest that if the circadian system is acutely responsive to MF exposure of this nature, an intact circadian axis may be necessary in order to observe an effect on the production on melatonin from the pineal gland

Effects of electromagnetic radiation of mobile phones on the central nervous system

With the increasing use of mobile communication, concerns have been expressed about the possible interactions of electromagnetic radiation with the human organism and, in particular, the brain. The effects on neuronal electrical activity, energy metabolism, genomic responses, neurotransmitter balance, blood-brain barrier permeability, cognitive function, sleep, and various brain diseases including brain tumors are reviewed. Most of the reported effects are small as long as the radiation intensity remains in the nonthermal range, and none of the research reviewed gives an indication of the mechanisms involved at this range. However, health risks may evolve from indirect consequences of mobile telephony, such as the sharply increased incidence rate of traffic accidents caused by telephony during driving, and possibly also by stress reactions which annoyed bystanders may experience when cellular phones are used in public places. These indirect health effects presumably outweigh the direct biological perturbations and should be investigated in more detail in the future.

Acute exposure to 50 Hz magnetic fields with harmonics and transient components: lack of effects on nighttime hormonal secretion in men

The purpose of this study was to examine whether low frequency magnetic field (MF) influences nighttime secretion of hormones, particularly melatonin. Ten healthy males stayed in the experimental room (2.7 m cube with 3 axis Merritt coils) on two separate nights. On one night, subjects were exposed to linearly polarized 50 Hz, 20 microT sinusoidal MF with the third (30%) and the fifth (10%) harmonics and repetitive transient waves (1 burst/s of 1 kHz waves, exponentially attenuated with a duration of 50 ms; initially 100 microT peak), and the other night was for blind control. During the nights (2000-0800 h, including sleeping time, 2300-0700 h), blood samples were collected from the subjects at 1 h intervals for determining the levels of plasma hormones (melatonin, growth hormone (GH), cortisol, prolactin) and at 10 min intervals from 2200 to 0200 h for observing the GH surge induced by sleep. Statistical analyses revealed no significant difference between the 2 nights in the profiles of the four hormones, and the result suggested that extremely low frequency (ELF) or intermediate frequency (IF) MF to which humans are exposed residentially has no acute effect on nighttime secretion of hormones, particularly melatonin.

Effects of electromagnetic radiation from a cellular telephone on the oxidant and antioxidant levels in rabbits

The number of reports on the effects induced by electromagnetic radiation (EMR) in various cellular systems is still increasing. Until now no satisfactory mechanism has been proposed to explain the biological effects of this radiation. Oxygen free radicals may play a role in mechanisms of adverse effects of EMR. This study was undertaken to investigate the influence of electromagnetic radiation of a digital GSM mobile telephone (900 MHz) on oxidant and antioxidant levels in rabbits. Adenosine deaminase, xanthine oxidase, catalase, myeloperoxidase, superoxide dismutase (SOD) and glutathione peroxidase activities as well as nitric oxide (NO) and malondialdehyde levels were measured in sera and brains of EMR-exposed and sham-exposed rabbits. Serum SOD activity increased, and serum NO levels decreased in EMR-exposed animals compared to the sham group. Other parameters were not changed in either group. This finding may indicate the possible role of increased oxidative stress in the pathophysiology of adverse effect of EMR. Decreased NO levels may also suggest a probable role of NO in the adverse effect.

The effect of melatonin on morphological changes in liver induced by magnetic field exposure in rats

In this study, we aimed to investigate the possible effect of melatonin on morphological changes in liver induced by magnetic fields exposure. Thirty albino young male Wistar Albino rats were used in the study. They were divided into 3 groups. Control group (C) (n: 10) received daily intraperitoneal injections of saline (0.1 ml/100 g) containing 5% ethanol for two weeks. Only magnetic field exposed (MF) group (n: 10); only magnetic field exposed had daily intraperitoneal injections of physiologic saline (0.1 ml/100 g) containing 5% ethanol for two weeks. Magnetic field exposed and melatonin treated (MF+m) group (n: 10); melatonin was dissolved in ethanol with further dilution in physiological saline. The animals in this group were exposed magnetic fields for two weeks. The magnetic fields exposed animals had intraperitoneal single dose of 4 mg/kg melatonin (0.1 ml/100 g) at 10:00 o'clock daily for two weeks following magnetic fields exposure. We used commercial CB handheld portable transceiver, Midland (USA) labelled, of 4 Watts, 40 channel. This channel frequency has been measured 27.17 MHz with frequency counter. According to the IRPA exposure standards; for 27 MHz, for 6 min, exposure limit is 0.2 mW/cm2. This value is for General Public. For occupational exposure limit is 1 mW/cm2. We have to consider General Public exposure limit. Therefore our limit is 0.2 mW/cm2. In other words; in this study; our exposure is always over the recommended limit. All the animals were decapitated. Liver samples were fixed in buffered neutral formalin. Paraffin sections were dyed with hematoxylen-eosin. Sections were examined under light microscopy. In MF group; sinusoidal dilatations, mixed cell infiltrations noticed in the periportal area, necrosis and vacuoler degeneration were determined in liver samples. However, parenchymal and stromal structures were observed to be prevented partially from effects of magnetic fields in melatonin treated group. In conclusion, it is suggested that melatonin has a mild preventive effect on magnetic field exposed changes in liver tissue in the rats.

No effects of pulsed radio frequency electromagnetic fields on melatonin, cortisol, and selected markers of the immune system in man

There is growing public concern that radio frequency electromagnetic fields may have adverse biological effects. In the present study eight healthy male students were tested to see whether or not radio frequency electromagnetic fields as used in modern digital wireless telecommunication (GSM standard) have noticeable effects on salivary melatonin, cortisol, neopterin, and immunoglobulin A (sIgA) levels during and several hours after exposure. In a specifically designed, shielded experimental chamber, the circularly polarized electromagnetic field applied was transmitted by an antenna positioned 10 cm behind the head of upright sitting test persons. The carrier frequency of 900 MHz was pulsed with 217 Hz (average power flux density 1 W/m2). In double blind trials, each test person underwent a total of 20 randomly allotted 4 hour periods of exposure and sham exposure, equally distributed at day and night. The results obtained show that the salivary concentrations of melatonin, cortisol, neopterin and sIgA did not differ significantly between exposure and sham exposure.

The influence of long-term exposure of mice to randomly varied power frequency magnetic fields on their nocturnal melatonin secretion patterns

Disruption of the normal melatonin rhythm has many implications in health and disease. Exposure to magnetic fields is alleged to suppress nocturnal melatonin production, which could implicate magnetic fields in the development of, for example, breast cancer. Magnetic fields of overhead powerlines allegedly pose a risk in the development of childhood leukemia, and the question arises whether changed pineal function could play a role here. In this study two strains of mice were exposed to a rms 50-Hz magnetic field which varied randomly between 0.5 and 77 microT with an average of 2.75 microT and compared to sham-exposed groups. The male mice were exposed for 24 h per day from conception until adult age. Nighttime plasma melatonin values were determined using radioimmunoassay (n=9 for each time point). Statistical comparison was done by nonparametric 95% confidence intervals for median differences to determine nocturnal elevated melatonin values. Although a shortcoming of the study was the small sample size, no statistically significant difference in the nocturnal median elevated melatonin values between exposed and sham-exposed groups could be demonstrated. Long-term and continuous exposure to simulated powerline magnetic fields did not result in a decreased nocturnal melatonin secretion in mice.

Varying responses to the rat forced-swim test under diurnal and nocturnal conditions

The paradox that experiments in behavioural pharmacology employing nocturnal rodent species are carried out almost exclusively in the resting phase of the animals' circadian cycle has remained largely unexamined and unquestioned. This is despite the fact that all major physiological systems in the body are intrinsically aligned with its natural circadian rhythm. The forced-swim test (FST) is a rodent model that is used extensively as a screening test for antidepressant activity. The objectives of the present study were to examine the behaviour of rats in the FST under diurnal and nocturnal conditions and, in addition, to profile the response of neurochemical, neuroendocrine, and cellular indices of stress at time points up to 120 min following exposure to the FST. The time spent in escape-oriented activity was significantly less when animals were tested in the dark phase. The profile of serum corticosterone and adrenal ascorbic acid concentrations indicates that the animals were less stressed by the test situation during the active (i.e., dark) phase of their circadian cycle. Similarly, increases in blood enzymatic markers of stress-induced cellular damage were less marked following FST exposure in the nocturnal period. Characteristic stress-induced increases in 5-HT turnover in the frontal cortex and amygdala observed in the diurnal phase were reversed in the nocturnal period. In conclusion, circadian differences in behaviour in the FST may be related to parallel alterations in the ability of animals to adapt to exposure to stress.