The magnetic retina: light-dependent and trigeminal magnetoreception in migratory birds

Recent advances have brought much new insight into the physiological mechanisms and required characteristics of the sensory molecules that enable birds to use magnetic fields for orientation. European robins almost certainly have two magnetodetection senses, one associated with the ophthalmic branch of the trigeminal nerve, and one based on light-dependent radical-pair processes in both eyes. The first brain areas processing magnetic information from each of these two senses have been identified. It has been experimentally verified that Earth-strength magnetic fields can affect photo-induced chemical reactions and that these reactions can respond to magnetic field direction. Diagnostic behavioural experiments have provided clues to identify putative magnetoreceptive molecules in the retina. We discuss the implications of these and other recent findings and outline crucial open questions with an emphasis on the light-dependent mechanism.     

Two common invertebrate predators show varying predation responses to different types of sentinel prey

Sentinel prey (an artificially manipulated patch of prey) are widely used to assess the level of predation provided by natural enemies in agricultural systems. Whilst a number of different methodologies are currently in use, little is known about how arthropod predators respond to artificially manipulated sentinel prey in comparison with predation on free‐living prey populations. We assessed how attack rates on immobilized (aphids stuck to cards) and artificial (plasticine lepidopteran larvae mimics) sentinel prey differed to predation on free‐moving live prey (aphids). Predation was assessed in response to density of the common invertebrate predators, a foliar‐active ladybird Harmonia axyridis (Coleoptera: Coccinellidae), and a ground‐active beetle Pterostichus madidus (Coleoptera: Carabidae). Significant increases in attack rates were found for the immobilized and artificial prey between the low and high predator density treatments. However, an increased predator density did not significantly reduce numbers of free‐living live aphids included in the mesocosms in addition to the alternate prey. We also found no signs of predation on the artificial prey by the predator H. axyridis. These findings suggest that if our assessment of predation had been based solely on the foliar artificial prey, then no increase in predation would have been found in response to increased predator density. Our results demonstrate that predators differentially respond to sentinel prey items which could affect the level of predation recorded where target pest species are not being used.     

Behavioural responses of piglets to different types of music

Music or other background sounds are often played in barns as environmental enrichment for animals on farms or to mask sudden disruptive noises. Previous studies looking at the effects of this practice on non-human animal well-being and productivity have found contradictory results. However, there is still a lack of discussion on whether piglets have the ability to distinguish different types of music. In this study, we exposed piglets to different music conditions to investigate whether the piglets preferred certain music types, in which case those types would have the potential to be used as environmental enrichment. In total, 30 piglets were tested for music type preference to determine whether growing pigs respond differently to different types of music. We used music from two families of instruments (S: string, W: wind) and with two tempos (S: slow, 65 beats/min (bpm); F: fast, 200 bpm), providing four music-type combinations (SS: string-slow; SF: string-fast; WS: wind-slow; WF: wind-fast). The piglets were given a choice between two chambers, one with no music and the other with one of the four types of music, and their behaviour was observed. The results showed that SS and WF music significantly increased residence time (P<0.01) compared with the other music conditions. Compared with the control group (with no music), the different music conditions led to different behavioural responses, where SS music significantly increased lying (P<0.01) and exploration behaviour (P<0.01); SF music significantly increased tail-wagging behaviour (P<0.01); WS music significantly increased exploration (P<0.01); and WF music significantly increased walking, lying, standing and exploration (all P<0.01). The results also showed that musical instruments and tempo had little effect on most of the behaviours. Fast-tempo music significantly increased walking (P=0.02), standing (P<0.01) and tail wagging (P=0.04) compared with slow-tempo music. In conclusion, the results of this experiment show that piglets are more sensitive to tempo than to musical instruments in their response to musical stimulation and seem to prefer SS and WF music to the other two types. The results also suggest a need for further research on the effect of music types on animals.     

Biological effects of 6 mT static magnetic fields: a comparative study in different cell types

The present work was a comparative study of the bio-effects induced by exposure to 6 mT static magnetic field (MF) on several primary cultures and cell lines. Particular attention was dedicated to apoptosis. Cell viability, proliferation, intracellular Ca(2+) concentration and morphology were also examined. Primary cultures of human lymphocytes, mice thymocytes and cultures of 3DO, U937, HeLa, HepG2 and FRTL-5 cells were grown in the presence of 6 mT static MF and different apoptosis-inducing agents (cycloheximide, H(2)O(2), puromycin, heat shock, etoposide). Biological effects of static MF exposure were found in all the different cells examined. They were cell type-dependent but apoptotic inducer-independent. A common effect of the exposure to static MF was the promotion of apoptosis and mitosis, but not of necrosis or modifications of the cell shape. Increase of the intracellular levels of Ca(2+) ions were also observed. When pro-apoptotic drugs were combined with static MF, the majority of cell types rescued from apoptosis. To the contrary, apoptosis of 3DO cells was significantly increased under simultaneous exposure to static MF and incubation with pro-apoptotic drugs. From these data we conclude that 6 mT static MF exposure interfered with apoptosis in a cell type- and exposure time-dependent manner, while the effects of static MF exposure on the apoptotic program were independent of the drugs used.     

Two different types of apoptosis in thymocytes

Thymocyte cell death was investigated after UVA-irradiation (365 nm) of the primary thymocyte culture in vitro. To determine the mode of cell death two fluorescent DNA-binding dyes (Acridine Orange and Ethidium Bromide) were used along with flow cytometry. Thymocytes undergo apoptosis spontaneously, but a percentage of apoptotic cells was seen to increase in a dose dependent manner after thymocytes exposition to 1-100 J/m2 UVA. These doses are lower than those commonly used for apoptosis induction in other lymphoid cells. Using flow cytometry, we demonstrated that UVA-irradiation induced two different types of apoptosis. The one referred to as the "fast" apoptosis was recorded within 1-4 h following irradiation, whereas the other one, called the "delayed" apoptosis occurred within 3-24 h after irradiation. After UVA-irradiation, the activation of the former prevented the development of the latter; whereas the inhibition of delayed apoptosis brought about the induction of the fast apoptosis in thymocytes. The interrelation between the fast and delayed types of apoptosis in thymocytes can be modulated by cycloheximide, an inhibitor of protein synthesis.     

Two light-dependent conductances in Lima rhabdomeric photoreceptors

Light-dependent membrane currents were recorded from solitary Lima photoreceptors with the whole-cell clamp technique. Light stimulation from a holding voltage near the cell's resting potential evokes a transient inward current graded with light intensity, accompanied by an increase in membrane conductance. While the photocurrent elicited by dim flashes decays smoothly, at higher stimulus intensities two kinetically distinct components become visible. Superfusion with TEA or intracellular perfusion with Cs do not eliminate this phenomenon, indicating that it is not due to the activation of the Ca-sensitive K channels that are present in these cells. The relative amplitude of the late component vs. the early peak of the light response is significantly more pronounced at -60 mV than at -40 mV. At low light intensities the reversal potential of the photocurrent is around 0 mV, but with brighter lights no single reversal potential is found; rather, a biphasic response with an inward and an outward component can be seen within a certain range of membrane voltages. Light adaptation through repetitive stimulation with bright flashes diminishes the amplitude of the early but not the late phase of the photocurrent. These observations can be accounted for by postulating two separate light-dependent conductances with different ionic selectivity, kinetics, and light sensitivity. The light response is also shown to interact with some of the voltage-sensitive conductances: activation of the Ca current by a brief conditioning prepulse is capable of attenuating the photocurrent evoked by a subsequent test flash. Thus, Ca channels in these cells may not only shape the photoresponse, but also participate in the process of light adaptation.     

Effect of homogeneous magnetic fields on responses to toxic stimulation in spirostomum ambiguum

Effects of DC magnetic fields, up to 125,000 G, on the survival of the ciliated protozoan Spirostomum ambiguum exposed to the toxic substance 2,2′-dipyridyldisulfide are reported. The magnetic field diminishes the ability of the organism to survive the drug, and lengthens the extension phase of the contraction cycle. It is proposed that the magnetic field alters the regulation of intracellular (C²⁺) transients.     

Nitric oxide modulates the responses of osteoclast formation to static magnetic fields

Nitric oxide (NO) is involved in osteoclast differentiation. Our previous studies showed that static magnetic fields (SMFs) could affect osteoclast differentiation. The inhibitory effects of 16 T of high SMF (HiMF) on osteoclast differentiation was correlated with increased production of NO. We raised the hypothesis that NO mediated the regulatory role of SMFs on osteoclast formation. In this study, 500 nT of hypomagnetic field (HyMF), 0.2 T of moderate SMF (MMF) and 16 T of high SMF (HiMF) were utilized as SMF treatment. Under 16 T, osteoclast formation was markedly decreased with enhanced NO synthase (NOS) activity, thus producing a high level of NO. When treated with NOS inhibitor N-Nitro-L-Arginine Methyl Ester (L-NAME), NO production could be inhibited, and osteoclast formation was restored to control group level in a concentration-dependent manner. However, 500 nT and 0.2 T increased osteoclast formation with decreased NOS activity and NO production. When treated with NOS substrate L-Arginine (L-Arg) or NO donor sodium nitroprusside (SNP), the NO level in the culture medium was obviously elevated, thus inhibiting osteoclast differentiation in a concentration-dependent manner under 500 nT or 0.2 T. Therefore, these findings indicate that NO mediates the regulatory role of SMF on osteoclast formation.     

Aversive responses of captive sandbar sharks Carcharhinus plumbeus to strong magnetic fields

This experimental study focused on the possible deterrent effect of permanent magnets on adult sandbar sharks Carcharhinus plumbeus. Results showed that the presence of a magnetic field significantly reduced the number of approaches of conditioned C. plumbeus towards a target indicating that adult C. plumbeus can be deterred by strong magnetic fields. These data, therefore, confirm that the use of magnetic devices to reduce shark by‐catch is a promising avenue.     

Characteristics of the background fields in multichannel-recorded magnetic field responses

We have studied the background fields in the auditory evoked magnetic field responses recorded with a 37-channel SQUID magnetometer. The background fields were found to have a main contribution from the spontaneous fields, which originate in the neural activities of the brain. The spontaneous fields had strong spatial correlation across the recording sites even after averaging over 100 epochs. The spatial distribution of the spontaneous field consisted of 3 main components of single extremum pattern, dipolar pattern, and a dipolar pattern with some distortion. Computer simulations of the localization of a single dipole source of the evoked field response showed that the spontaneous background field could bring about large location errors in an unpredictable manner, as compared with the location errors caused by a spatially random Gaussian noise field.     

Hormonal and inflammatory responses to different types of sprint interval training

We evaluated the effect of different types of sprint interval sessions on the balance between anabolic and catabolic hormones and circulating inflammatory cytokines. Twelve healthy elite junior handball players (17-25 years) participated in the study. Exercise consisted of increasing distance (100 m, 200 m, 300 m, 400 m) and decreasing distance (400 m, 300 m, 200 m, 100 m) sprint interval runs on a treadmill (at random order), at a constant work rate of 80% of the personal maximal speed (calculated from the maximal speed of a 100 m run). The total rest period between the runs in the different interval sessions were similar. Blood samples were collected before, after each run, and after 1-hour recovery. Both types of sprint interval trainings led to a significant (p < 0.05) increase in lactate and the anabolic factors growth hormone, insulin-like growth factor-I (IGF-I), IGF binding protein-3 (IGFBP-3), and testosterone levels. Both types of sprint interval sessions led to a significant (p < 0.05) increase in the circulating pro- and anti-inflammatory mediators IL-1, IL-6, and IL1ra. IL-6 remained elevated in both sessions after 1-hour recovery. Area under the curve was significantly greater (p < 0.05) for lactate and growth hormone (GH) in the decreasing distance session. In contrast, rate of perceived exertion was higher in the increasing distance session, but this difference was not statistically significant (p = 0.07). Changes in anabolic-catabolic hormones and inflammatory mediators can be used to gauge the training intensity of anaerobic-type exercise. Changes in the GH-IGF-I axis and testosterone level suggest exercise-related anabolic adaptations. Increases in inflammatory mediators may indicate their important role in muscle tissue repair after anaerobic exercise. The decreasing distance interval was associated with a greater metabolic (lactate) and anabolic (GH) response but not with a higher rate of perceived exertion. Coaches and athletes should be aware of these differences, and as a result, of a need for specific recovery adaptations after different interval training protocols.     

Orientation responses of American eels, Anguilla rostrata, to varying magnetic fields

1. The locations of freshwater yellow eels in an eight-chambered octagonal behavior tank were videotaped during six-day intervals while the animals were being subjected to normal and experimental magnetic fields. 2. The earth's magnetic field (0.5 g) was utilized for two control periods at the start and completion of each run for each animal. 3. During each run, the sequence of applied magnetic fields was +1.0, 0.0, -0.5 and -1.0 g, each being applied for a period of 24 hr. 4. Under the influence of the earth's magnetic field, the eels showed a preference for a northeast direction (27.01%). During the second control period (i.e. after being subjected to variations in the magnetic field), the animals showed a dual preference for north and northwest directions (23.02% and 25.9%, respectively). 5. In a 0.0 g field, the eels preferred the north chamber (24.43%) and the vestibule of the behavior tank (19.46%); a preference for north was also obtained with a field of +1.0 g (25.95%). 6. The preferred direction with the -0.5 and -1.0 g fields was southeast (20.93 and 26.71%, respectively).     

Two structurally different types of rabbit light chains

Disulphide bonds of rabbit γ-G-globulin and the antibody of the γ-G-globulin type against the 2,4-dinitrophenyl group were split both by the oxidative sulphitolysis at pH 8.6 and by the reduction with 2-mercaptoethanol followed by carboxymethylation. The fractionation was carried out in 0.05 m formic acid containing 6m urea, in 1m propionic acid or in 6m guanidine hydrochloride. Both heavy (H) and light) (L) chains are released from the I+J fraction preceding on an elution diagram H chains when rechromatographed in a stronger desaggregation medium. A small amount of the L chains is also released on rechromatography of the H chains (isolated from 1m propionic acid) in 6m guanidine hydrochloride. The separation of the degraded γ-G-globulin in 0.05m formic acid containing 6m urea or in 6m guanidine hydrochloride showed a separation of the L chains to two fractions differing by electrophoretic properties, peptide maps and N-terminal amino acids. However, these chains exhibit a similar molecular weight, immunoelectrophoretic behaviour and similar properties on reactivation of the antibody H chain.     

Two different molecular types of rat mitochondrial DNAs

Experiments with restriction endonucleases showed that Sprague-Dawley strain rats have two types of mitochondrial DNAs (mtDNAs), named α- and β-types, which differ in primary structure. Individual rats have only one type. Individuals of other strains, such as Wistar, Fischer, and Donryu, also all have one of these types of mtDNA. Thus irrespective of their strain, all rats can be classified into one of two groups according to the type of their mtDNA.     

Two ecologically-divergent generalist predators have different responses to landscape fragmentation

We conducted three replicated field experiments to test the population response of two ecologically-divergent wolf spider species ( Hogna helluo and Pardosa milvina ) to three correlates of landscape fragmentation: area reduction, spatial subdivision, and increased edge to core ratio. We selected these two species because they differ in vagility and habitat selectivity. Hogna helluo is relatively large, averse to disturbed substrata, and has poor colonization abilities. Conversely, Pardosa is small, vagile, and will use barren, disturbed areas. In a test for the effect of area reduction on populations of the two wolf spiders, we destroyed 0%, 20% or 80% of randomly selected habitat islands in replicated experimental landscapes. We found that population densities of Hogna declined significantly, even at the lowest level of area reduction (20%), and that there was an increase in numbers of Pardosa . In a test for the response to an increase in landscape subdivision, we created four levels of habitat fragmentation in replicate plots. We found a significant decline in Hogna populations with increasing fragmentation. Pardosa populations did not respond to the fragmentation. In the third experiment we kept landscape area and subdivision constant, but manipulated the edge-to-core ratio. We found that populations of Hogna declined sharply with increasing edge, and that populations of Pardosa did not respond. These two syntopic wolf spiders have distinctly different responses to landscape fragmentation.     

Cytogenetic effects of 50 Hz magnetic fields of different magnetic flux densities

Cytogenetic investigations were performed in human peripheral blood lymphocytes following exposure to 50 Hz magnetic fields alone or in combination with the chemical mutagen mitomycin C or with X-rays. It was found that magnetic fields up to 2500 microT did not significantly influence the chromosome aberration and sister chromatid exchange frequency. Also, the combined treatments failed to indicate the presence of any synergistic, potentiating, or antagonistic effect between the ELF magnetic fields and the mutagens. However, there were two exceptions: Cells exposed to 504 microT magnetic fields before and during cultivation displayed a statistically significant decrease in sister chromatid exchange frequency. Also, when cells were cultivated in the presence of 88.4 microT magnetic fields following X-ray exposures there was a significant increase in chromosome aberration frequency compared to X-ray exposure alone.     

A comparison between different treeline types shows contrasting responses to climate fluctuations

Treeline position is mainly determined by growth season temperature, but the response of treelines to climate warming is not uniform worldwide. We compared treeline structure, dynamics and thermal profile in nearby areas with different treeline type, species composition and bioclimatic conditions. We performed a detailed survey of different treeline types in three areas of Italian Alps and northern Apennines. Every tree individual was recorded along altitudinal transects from the closed forest to the species limit. Treeline structure and dynamics were described through altitudinal limits of tree height, density and age. Data were elaborated by principal components analysis. Temperature regime of the three sites was assessed from homogeneous historical climatic data. Treeline was different in the three areas for species composition, shape and dynamics. Both Alpine sites showed diffuse treeline, but only one showed advancing dynamics. Apennine treeline was abrupt and static, with higher temperature at the tree limit. Our study showed the variable dynamics of treelines within a relatively restricted area and the connection between treeline shape and dynamics. An important role is played by species composition, determined by bioclimatic and historical features. These factors should be taken into account when modelling future treeline dynamics at global scale.     

Two different types of dynorphin-A-immunoreactive terminals in rat substantia nigra

Summary The opioid peptide dynorphin A (1–17) is the third transmitter identified in the striatonigral projection, the other two being gamma-aminobutyric acid (GABA) and substance P. The ultrastructural features of the dynorphinergic terminals in substantia nigra/pars reticulata were studied using pre-embedding immunocytochemistry with the classical peroxidase-antiperoxidase-diaminobenzidine-method; these features were compared with GABAergic boutons visualized with an immunogold method. Two distinct types of dynorphin-A-immunoreactive boutons could be identified: (1) type A (81%) possessing characteristics similar to the GA-BAergic nerve endings in this region, i.e., large pleomorphic vesicles and symmetric synaptic contacts, (2) type B (19%) displaying asymmetric synaptic zones and small, mostly round vesicles. These results are in agreement with physiological studies suggesting a dual action of dynorphin A in substantia nigra.