Effects of exposure to a 50 Hz sinusoidal magnetic field during the early adolescent period on spatial memory in mice

Adolescence is a critical developmental stage during which substantial remodeling occurs in brain areas involved in emotional and learning processes. Although a robust literature on the biological effects of extremely low frequency magnetic fields (ELF‐MFs) has been documented, data on the effects of ELF‐MF exposure during this period on cognitive functions remain scarce. In this study, early adolescent male mice were exposed from postnatal day (P) 23–35 to a 50 Hz MF at 2 mT for 60 min/day. On P36–45, the potential effects of the MF exposure on spatial memory performance were examined using the Y‐maze and Morris water maze tasks. The results showed that the MF exposure did not affect Y‐maze performance but improved spatial learning acquisition and memory retention in the water maze task under the present experimental conditions. Bioelectromagnetics 34:275–284, 2013. © 2012 Wiley Periodicals, Inc.     

Effects of 50‐Hz magnetic field exposure on hormone secretion and apoptosis‐related gene expression in human first trimester villous trophoblasts in vitro

Evidence from epidemiological and animal studies showed that exposure to extremely low frequency magnetic fields (ELF‐MF) could produce deleterious effects on reproduction. In order to investigate the possible mechanism of MF exposure on reproductive effects, first trimester human chorionic villi at 8–10 weeks' gestation were obtained, and trophoblasts were isolated, cultured, and exposed to a 50‐Hz MF for different durations. The human chorionic gonadotropin (hCG) and progesterone in the culture medium was measured by electrochemiluminescence immunoassay. The mRNA levels of apoptosis‐related genes bcl‐2, bax, caspase‐3, p53, and fas in trophoblasts were analyzed using real‐time RT‐PCR. The results showed that exposure of trophoblasts to MF at 0.2 mT for 72 h did not affect secretion of hCG and progesterone from these cells. There was also no significant change in secretion of these hormones when trophoblasts were exposed to a 0.4 mT MF for 48 h. However, MF significantly inhibited hCG and progesterone secretion of trophoblasts after exposure for 72 h at 0.4 mT. Results of apoptosis‐related gene expression analysis showed that, within 72 h of exposure at 0.4 mT, there was no significant difference between MF exposure and control on the expression pattern of each gene. Based on results of the present experiment, it is suggested that exposure to MF for a longer duration (72 h) could inhibit secretion of hCG and progesterone by human first trimester villous trophoblasts, however, the effect might not be related to trophoblast apoptosis. Bioelectromagnetics 31:566–572, 2010. © 2010 Wiley‐Liss, Inc.     

Disruption of imprinting by memory inhibitors

Several amnestic drugs were administered intracranially to day-old chicks at selected times around a 10-min exposure to an imprinting stimulus. The drugs used were monosodium glutamate, ouabain, cycloheximide and amino-iso-butyrate. The chicks were tested for 10 min in the same apparatus two days later, and the time spent following the stimulu was recorded., The index of memory retention was the difference between the time spent following on test and the time spent following on the initial exposure. When compared with saline-injected control, glutamate administered 5 min before the beginning of the initial exposure was effective in producing a reduction in following times and hence amnesia. Ouabian was effective when injeced before the beginning and immediately after the end of the initial exposure; while cycloheximide was effective when administered as late as 5 min after the initial exposure. The effective times of administration for the drugs to produce a reduction in following times were similar to that observed for amnesia in passive avoidance memory tasks. The increase in following shown by the control chicks was not a developmental effect due to the increae in age on test. Experiments involving a choice of stimuli on test support the invovement of a memoryrelated phenomenon in these experiments.     

Effect of exposure to 50 Hz magnetic field with or without insulin on blood–brain barrier permeability in streptozotocin‐induced diabetic rats

We investigated the effect of long‐term exposure to modulation magnetic field (MF), insulin, and their combination on blood–brain barrier (BBB) permeability in a diabetic rat model. Fifty‐three rats were randomly assigned to one of six groups: sham, exposed to no MF; MF, exposed to MF; diabetes mellitus (DM), DM induced with streptozotocin (STZ); DM plus MF (DMMF); DM plus insulin therapy (DMI); and DM plus insulin therapy plus MF (DMIMF). All the rats underwent Evans blue (EB) measurement to evaluate the BBB 30 days after the beginning of experiments. The rats in MF, DMMF, and DMIMF groups were exposed to MF (B = 5 mT) for 165 min every day for 30 days. Mean arterial blood pressure (MABP), body mass, and serum glucose level of the study rats were recorded. The extravasation of brain EB of the MF, DM, DMMF, DMI, and DMIMF groups was higher than that of the sham group and the extravasation of right hemisphere of the DMIMF group was highest (P < 0.05). The post‐procedure body mass of the sham and MF groups were significantly higher than those of the DM and DMMF groups (P < 0.05). In the DM, DMMF, DMI, and DMIMF groups, the baseline glucose was significantly lower than the post‐procedure glucose (P < 0.05). DM and MF increase BBB permeability; in combination, they cause more increase in BBB permeability, and insulin decreases their effect on BBB. Improved glucose metabolism may prevent body mass loss and the hypoglycemic effect of MF. DM increases MABP but MF causes no additional effect. Bioelectromagnetics 31:262–269, 2010. © 2009 Wiley‐Liss, Inc.     

Taming parent‐reared orange‐winged Amazon parrots by neonatal handling

Tameness in parrots is often achieved by artificial rearing, in which chicks are typically removed from parents, fed a liquified or semi‐liquified diet by oral gavage and maintained in thermally controlled brooders until they are grown. As an alternate means of rearing birds, we tested whether occasional neonatal human handling of parent‐reared chicks might produce tameness while reducing the risk of sexual imprinting on humans. Orange‐winged Amazon chicks (Amazona amazonica) were incubated and hatched by wild‐caught parents, then were temporarily removed from the nest box, and handled at various times during the nestling period. In Trial 1, handled chicks (n = 6) were handled from days 10 to 39 of age for 10–20 min/day and from 40 days to fledging (days 56–/57) for 20–30 min/day. Nonhandled chicks (n = 4) were handled only to record body weight and provide medication, as needed. After fledging, chicks were evaluated for tameness, e.g., by their willingness to approach the handler, perch on a finger, be touched on the head, and by their respiratory rate in the presence of the handler. Handled birds differed significantly in all indices of tameness. In Trial 2, handled chicks were handled for 30 min, four times/week either from days 15 to 36 (n = 3) or 35 to 56 (n = 3); results were similar to Trial 1. Chicks handled later tended to be slightly tamer than those handled earlier. In both trials, the amount of time that handled chicks were in contact with humans was less than 2% of the time they spent with conspecifics. It is therefore unlikely that these chicks imprinted either filially or sexually on humans, although this has not been experimentally tested. While continued handling is likely necessary to maintain tameness, these results support the concept that neonatal handling of parent‐raised parrots provides a low‐labor and low‐technology alternative to artificial rearing as a means of initially taming birds, thereby improving their adaptation to life in captivity. Zoo Biol 18:177–187, 1999. © 1999 Wiley‐Liss, Inc.     

Phosphatidylinositol 3‐kinase‐mediated regulation of neuronal apoptosis and necrosis by insulin and IGF‐I

We examined effects of two insulin‐like growth factors, insulin and insulin‐like growth factor‐I (IGF‐I), against apoptosis, excitotoxicity, and free radical neurotoxicity in cortical cell cultures. Like IGF‐I, insulin attenuated serum deprivation‐induced neuronal apoptosis in a dose‐dependent manner at 10–100 ng/mL. The anti‐apoptosis effect of insulin against serum deprivation disappeared by addition of a broad protein kinase inhibitor, staurosporine, but not by calphostin C, a selective protein kinase C inhibitor. Addition of PD98059, a mitogen‐activated protein kinase kinase (MAPKK) inhibitor, blocked insulin‐induced activation of extracellular signal‐regulated protein kinases (ERK1/2) without altering the neuroprotective effect of insulin. Cortical neurons underwent activation of phosphatidylinositol (PI) 3‐kinase as early as 1 min after exposure to insulin. Inclusion of wortmannin or LY294002, selective inhibitors of PI 3‐K, reversed the insulin effect against apoptosis. In contrast to the anti‐apoptosis effect, neither insulin nor IGF‐I protected excitotoxic neuronal necrosis following continuous exposure to 15 μM N‐methyl‐d ‐aspartate or 40 μM kainate for 24 h. Surprisingly, concurrent inclusion of 50 ng/mL insulin or IGF‐I aggravated free radical‐induced neuronal necrosis over 24 h following continuous exposure to 10 μM Fe²⁺ or 100 μM buthionine sulfoximine. Wortmannin or LY294002 also reversed this potentiation effect of insulin. These results suggest that insulin‐ like growth factors act as anti‐apoptosis factor and pro‐oxidant depending uon the activation of PI 3‐kinase. © 1999 John Wiley & Sons, Inc. J Neurobiol 39: 536–546, 1999     

Sleep after mobile phone exposure in subjects with mobile phone‐related symptoms

Several studies show increases in activity for certain frequency bands (10–14 Hz) and visually scored parameters during sleep after exposure to radiofrequency electromagnetic fields. A shortened REM latency has also been reported. We investigated the effects of a double‐blind radiofrequency exposure (884 MHz, GSM signaling standard including non‐DTX and DTX mode, time‐averaged 10 g psSAR of 1.4 W/kg) on self‐evaluated sleepiness and objective EEG measures during sleep. Forty‐eight subjects (mean age 28 years) underwent 3 h of controlled exposure (7:30–10:30 PM; active or sham) prior to sleep, followed by a full‐night polysomnographic recording in a sleep laboratory. The results demonstrated that following exposure, time in Stages 3 and 4 sleep (SWS, slow‐wave sleep) decreased by 9.5 min (12%) out of a total of 78.6 min, and time in Stage 2 sleep increased by 8.3 min (4%) out of a total of 196.3 min compared to sham. The latency to Stage 3 sleep was also prolonged by 4.8 min after exposure. Power density analysis indicated an enhanced activation in the frequency ranges 0.5–1.5 and 5.75–10.5 Hz during the first 30 min of Stage 2 sleep, with 7.5–11.75 Hz being elevated within the first hour of Stage 2 sleep, and bands 4.75–8.25 Hz elevated during the second hour of Stage 2 sleep. No pronounced power changes were observed in SWS or for the third hour of scored Stage 2 sleep. No differences were found between controls and subjects with prior complaints of mobile phone‐related symptoms. The results confirm previous findings that RF exposure increased the EEG alpha range in the sleep EEG, and indicated moderate impairment of SWS. Furthermore, reported differences in sensitivity to mobile phone use were not reflected in sleep parameters. Bioelectromagnetics 32:4–14, 2011. © 2010 Wiley‐Liss, Inc.     

Corticosterone responses of hand‐reared and parent‐reared grey‐faced petrel chicks (Pterodroma macroptera gouldi)

Hand‐reared grey‐faced petrel (Pterodroma macroptera gouldi) chicks (Order Procellariformes) that were subjected to a standardised blood sampling protocol immediately before they fledged showed a reduced corticosterone response compared to parent‐raised chicks. Serum corticosterone concentrations were lower in hand‐reared than parent‐reared birds 30 and 60 min after handling was initiated (21.5±6.7 vs. 105.4±7.4 ng/ml at 30 min, and 11.3±3.6 vs. 93.8±11.4 ng/ml at 60 min, respectively). The total integrated corticosterone response and the response corrected for initial corticosterone concentrations were similarly lower in hand‐reared than parent‐reared birds (927±489 vs. 4639±1924 ng/ml.min, and 529±352 vs. 4110±1896 ng/ml.min, respectively). Habituation to handling associated with hand‐rearing, which is expressed as a subdued corticostrone response, is likely to reduce the physiological stress associated with the translocation and reintroduction of these birds. However, the longer‐term consequences of this attenuated response remain unclear. Zoo Biol 0:1–8, 2005. © 2005 Wiley‐Liss, Inc.     

Lack of a co‐promotion effect of 60 Hz circularly polarized magnetic fields on spontaneous development of lymphoma in AKR mice

The present study was conducted to investigate the possible effect of 60 Hz circularly polarized magnetic fields (MFs) as promoters of genetically initiated lymphoma in AKR mice. One hundred sixty female animals were divided into four different groups. They were exposed to four different intensities of circularly polarized MFs. Animals received exposure to 60 Hz circularly polarized MF at field strengths (rms‐value) of 0 µT (sham control, T1, Group I), 5 µT(T2, Group II), 83.3 µT (T3, Group III), or 500 µT(T4, Group IV), for 21 h/day from the age of 4–6 weeks to the age of 44–46 weeks. There were no exposure‐related changes in mean survival time, clinical signs, body weights, hematological values, micronucleus assay, gene expression arrays, analysis of apoptosis, and necropsy findings. At histopathological examination, lymphoma was seen in all the groups. The tumor incidence was 31/40(78%), 30/40(75%), 32/40(80%), and 31/40(78%) in sham control, 5, 83.3, and 500 µT groups, respectively. However, there were no differences in the tumor incidence between the sham control (T1) and circularly polarized MF exposure groups (T2–T4). In conclusion, there was no evidence that exposure to 60 Hz circularly polarized MF strengths up to 500 µT promoted lymphoma in AKR mice. Bioelectromagnetics 31:130–139, 2010. © 2009 Wiley‐Liss, Inc.     

Chronic exposure to an extremely low‐frequency magnetic field induces depression‐like behavior and corticosterone secretion without enhancement of the hypothalamic–pituitary–adrenal axis in mice

An extremely low‐frequency magnetic field (ELF‐MF) is generated by power lines and household electrical devices. Many studies have suggested an association between chronic ELF‐MF exposure and anxiety and/or depression. The mechanism of these effects is assumed to be a stress response induced by ELF‐MF exposure. However, this mechanism remains controversial. In the present study, we investigated whether chronic ELF‐MF exposure (intensity, 3 mT; total exposure, 200 h) affected emotional behavior and corticosterone synthesis in mice. ELF‐MF‐treated mice showed a significant increase in total immobility time in a forced swim test and showed latency to enter the light box in a light–dark transition test, compared with sham‐treated (control) mice. Corticosterone secretion was significantly high in the ELF‐MF‐exposed mice; however, no changes were observed in the amount of the adrenocorticotropic hormone and the expression of genes related to stress response. Quantification of the mRNA levels of adrenal corticosteroid synthesis enzymes revealed a significant reduction in Cyp17a1 mRNA in the ELF‐MF‐exposed mice. Our findings suggest the possibility that high intensity and chronic exposure to ELF‐MF induces an increase in corticosterone secretion, along with depression‐ and/or anxiety‐like behavior, without enhancement of the hypothalamic–pituitary–adrenal axis. Bioelectromagnetics 34:43–51, 2013. © 2012 Wiley Periodicals, Inc.     

Effects of repeated investigator handling of Leach's Storm‐Petrel chicks on growth rates and the acute stress response

Disturbance during development may have lasting effects on the growth rates and stress physiology of birds. Although repeated handling by researchers is often necessary, the possible effects of such handling on the development of semi‐altricial young are unclear. We examined the effect of daily handling on growth rates and plasma corticosterone levels of Leach's Storm‐Petrel (Oceanodroma leucorhoa) chicks on Kent Island in the Bay of Fundy, New Brunswick, Canada, during the 2011 nesting season. From post‐hatch day 7 to post‐hatch days 14–36, birds in the experimental group were extracted from burrows and measured (wing, tarsus, and mass) for ～3 min every day, whereas birds in the control group were left undisturbed. After the treatment period, blood was collected from birds in both groups within 3 min of initially reaching into burrows (baseline) and after a 30‐min restraint stress test to assess the effect of early life disturbance on programming of the hypothalamic‐pituitary‐adrenal (HPA) axis. A second acute restraint stress test was conducted three weeks after the end of the treatment period to investigate possible longer term effects of early life disturbance. Growth rates of wings and tarsi were similar for handled chicks (N = 18) and non‐handled control chicks (N = 21), as were baseline and 30‐min acute restraint stress‐induced corticosterone levels. As also reported in previous studies of other altricial and semi‐altricial species, older chicks (42–64 d old) had higher plasma corticosterone levels than younger chicks (21–43 d old) after acute restraint stress tests, reflecting delayed development of the HPA axis. The age‐related increase in HPA axis sensitivity observed prior to fledging could facilitate foraging and predator avoidance behaviors while minimizing exposure to high levels of corticosterone earlier in development. Overall, we found no evidence that repeated disturbance influenced either growth rates or HPA axis programming of Leach's Storm‐Petrel chicks.     

胚胎期光照和皮质酮处理对日龄小鸡记忆的作用

该实验对胚胎发育后期的鸡胚进行光孵化,暗孵化以及药物注射处理后,采用一次性味觉被动回避行为模式观察它们对出生后小鸡记忆保持的影响并对其作用机制进行了初步探讨,结果表明胚胎期光照可增强小鸡记忆的保持,使用糖皮质激素受体拮抗剂可阻断光照对小鸡记忆的增强作用,对暗孵化鸡胚注射皮质酮可以促进出生后小鸡记忆的保持,因此皮质酮可能能与光照对小鸡记忆的增强过程,蛋白合成抑制剂在一定程度上阻断皮质醇对小鸡记忆的增     

Quantification of three triterpenic acids in dried rosemary using HPLC‐fluorescence detection and 4‐(4,5‐diphenyl‐1H‐imidazole‐2‐yl)benzoyl chloride derivatization

Functional triterpenic acids such as ursolic acid (UA), oleanolic acid (OA) and betulinic acid (BA) are representative ingredients in rosemary that may have health benefits. UA, OA and BA in rosemary extracts were derivatized with 4‐(4,5‐diphenyl‐1H‐imidazole‐2‐yl)benzoyl chloride (DIB‐Cl) and detected using HPLC‐fluorescence (FL). Dried rosemary (50 mg) was ground, added to 3 ml of ethanol, sonicated for 40 min, then the sample solution was added to a mixture of 1% trimethylamine and 1 mM DIB‐Cl in acetonitrile. The mixture was settled for 5 min at room temperature, then the DIB‐triterpenic acid derivatives were separated using a Wakopak Handy ODS column (250 × 4.6 mm, 6 μm) eluted with 25 mM acetate buffer (pH 4.5)/methanol/acetonitrile (= 8:10:82 v/v/v%). The fluorescence intensity of the eluent was monitored at 365 (λ_ex) and 490 nm (λ_em) and the maximum retention time of the derivatives was 30 min. Calibration curves constructed using rosemary extract spiked with standards showed good linearity (r ≥ 0.997) in the range 2.5–100 ng/ml. The detection limits at 3σ for internal BA, UA and OA peaks in rosemary extract were 0.2, 0.4 and 0.5 ng/ml, respectively. This method was used to quantify BA, UA and OA in commercially available dried rosemary products.     

Development of a higher power intermediate‐frequency magnetic field exposure system for in vitro studies

In a previous article we developed an in vitro 23 kHz magnetic field (MF) exposure system that generated an MF of 532 µT_rms. Using this system, the biological effects of 23 kHz MFs on cell functions have been reported. To further clarify the biological effect of intermediate‐frequency (IF) MFs and investigate the dose–response relationship in cell lines, an exposure system that generates stronger MFs is required. To meet this requirement, we developed a 6.25 mT_rms MF exposure system for in vitro study. This level is 1000 times the reference level for the general public in the ICNIRP guidelines. This system provides an MF of 6.25 mT_rms at 23 kHz with a uniformity within ±5%. To verify that in vitro experimental conditions are maintained, we examined the temperature, environmental MF, and MF leakage for a sham exposure system. In addition, we examined the harmonics, coil shape, and heat generated in the medium by the high‐strength MF. As a result, it was confirmed that this system can be used to evaluate the biological effects of IF MFs. This article presents the design and successful construction of the in vitro exposure system. Bioelectromagnetics 31:156–163, 2010. © 2009 Wiley‐Liss, Inc.     

Effects of systemic pancreastatin on memory retention

Pancreastatin, a peptide isolated from the pancreas, was shown to enhance memory retention after peripheral administration in mice when administration following T-maze footshock avoidance training. The effect of pancreastatin on memory retention, one week after training, was time dependent showing enhancement of retention when pancreastatin was administered 0 and 30 min but not 60 min after training. Pancreastatin reversed the amnesia produced by scopolamine. The pancreastatin fragment (33-49) also enhanced memory. Pancreastatin did not increase glucose in vivo. We conclude that peripherally administered pancreastatin modulates memory processing.     

The role of calcium in apoptosis induced by 7β‐hydroxycholesterol and cholesterol‐5β,6β‐epoxide

Oxysterols, such as 7β‐hydroxy‐cholesterol (7β‐OH) and cholesterol‐5β,6β‐epoxide (β‐epoxide), may have a central role in promoting atherogenesis. This is thought to be predominantly due to their ability to induce apoptosis in cells of the vascular wall and in monocytes/macrophages. Although there has been extensive research regarding the mechanisms through which oxysterols induce apoptosis, much remains to be clarified. Given that experimental evidence has long associated alterations of calcium (Ca²⁺) homeostasis to apoptotic cell death, the aim of the present study was to determine the influence of intracellular Ca²⁺ changes on apoptosis induced by 7β‐OH and β‐epoxide. Ca²⁺ responses in differentiated U937 cells were assessed by epifluorescence video microscopy, using the ratiometric dye fura‐2. Over 15‐min exposure of differentiated U937 cells to 30 μM of 7β‐OH induced a slow but significant rise in fura‐2 ratio. The Ca²⁺ channel blocker nifedipine and the chelating agent EGTA blocked the increase in cytoplasmic Ca²⁺. Moreover, dihydropyridine (DHP) binding sites identified with BODIPY‐FLX‐DHP were blocked following pretreatment with nifedipine, indicating that the influx of Ca²⁺ occurred through L‐type channels. However, following long‐term incubation with 7β‐OH, elevated levels of cytoplasmic Ca²⁺ were not maintained and nifedipine did not provide protection against apoptotic cell death. Our results indicate that the increase in Ca²⁺ may be an initial trigger of 7β‐OH–induced apoptosis, but following chronic exposure to the oxysterol, the influence of Ca²⁺ on apoptotic cell death appears to be less significant. In contrast, Ca²⁺ did not appear to be involved in β‐epoxide–induced apoptosis. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:324–332, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20295     

Effects of Lanthanum Chloride Administration in Prenatal Stage on One-Trial Passive Avoidance Learning in Chicks

Lanthanum cations (La 3+) are well known for their inhibitory actions on calcium channels. Prenatal lanthanum exposure may affect the development of embryo and alter the capacity for learning and memory in adults, and the one-trial passive avoidance learning paradigm with day-old chicks is an excellent model to study several mechanisms of memory formation. In the present study, we examined the effects of prenatal lanthanum chloride exposure on memory consolidation using one-trial passive avoidance learning task in day-old chicks. The data suggest that chicks injected with lanthanum chloride (2 mg/kg) daily from E9 to E16 had significantly impaired long-term memory at 120 min after training (p < 0.05) but not the chicks injected with lanthanum chloride (0.1 mg/kg) daily from E9 to E16.     

α8‐Integrins are required for hippocampal long‐term potentiation but not for hippocampal‐dependent learning

Integrins are heterodimeric transmembrane cell adhesion receptors that are essential for a wide range of biological functions via cell–matrix and cell–cell interactions. Recent studies have provided evidence that some of the subunits in the integrin family are involved in synaptic and behavioral plasticity. To further understand the role of integrins in the mammalian central nervous system, we generated a postnatal forebrain and excitatory neuron‐specific knockout of α8‐integrin in the mouse. Behavioral studies showed that the mutant mice are normal in multiple hippocampal‐dependent learning tasks, including a T‐maze, non‐match‐to‐place working memory task for which other integrin subunits like α3‐ and β1‐integrin are required. In contrast, mice mutant for α8‐integrin exhibited a specific impairment of long‐term potentiation (LTP) at Schaffer collateral–CA1 synapses, whereas basal synaptic transmission, paired‐pulse facilitation and long‐term depression (LTD) remained unaffected. Because LTP is also impaired in the absence of α3‐integrin, our results indicate that multiple integrin molecules are required for the normal expression of LTP, and different integrins display distinct roles in behavioral and neurophysiological processes like synaptic plasticity.     

Leisure Activity,Brain β‐amyloid,and Episodic Memory in Adults with Down Syndrome

The present study provided an investigation of associations between leisure activity and early Alzheimer’s disease neuropathology (i.e., brain β‐amyloid) and episodic memory in a sample of 65 adults with Down syndrome (aged 30–53 years), at baseline and follow‐up, approximately three years apart. Findings indicated that leisure activity at baseline was not associated with brain β‐amyloid at baseline or change in brain β‐amyloid from baseline to follow‐up. Greater cognitively stimulating leisure activity at baseline was associated with better episodic memory at baseline, and greater social leisure activity at baseline was associated with less decline in episodic memory from baseline to follow‐up. High (as opposed to low) levels of social and overall leisure activity at baseline moderated the association between increase in brain β‐amyloid and decline in episodic memory, from baseline to follow‐up. Findings suggest that cognitively stimulating and social leisure activity could protect against the effect of Alzheimer’s disease neuropathology on episodic memory in adults with Down syndrome.     

Theoretical evaluation of magnetoreception of power‐frequency fields

Several effects of power‐frequency (50/60 Hz) magnetic fields (PF‐MF) of weak intensity have been hypothesized in animals and humans. No valid mechanism, however, has been proposed for an interaction between PF‐MF and biological tissues and living beings at intensities relevant to animal and human exposure. Here we proposed to consider PF‐MF as disrupters of the natural magnetic signal. Under exposure to these fields, an oscillating field exists that results from the vectorial summation of both the PF‐MF and the geomagnetic field. At a PF‐MF intensity (rms) of 0.5 µT, the peak‐to‐peak amplitude of the axis and/or intensity variations of this resulting field exceeds the related discrimination threshold of magnetoreception (MR) in migrating animals. From our evaluation of the 50/60 Hz responsiveness of the putative mechanisms of MR, single domain particles (Kirschvink's model) appear unable to transduce that oscillating signal. On the contrary, radical pair reactions are able to, as well as interacting multidomain iron–mineral platelets and clusters of superparamagnetic particles (Fleissner/Solov'yov's model). It is, however, not yet known whether the reception of 50/60 Hz oscillations of the natural magnetic signal might be of consequence or not. Bioelectromagnetics 31:371–379, 2010. © 2010 Wiley‐Liss, Inc.