Validation of Cut-Points for Evaluating the Intensity of Physical Activity with Accelerometry-Based Mean Amplitude Deviation (MAD)

Purpose

Our recent study of three accelerometer brands in various ambulatory activities showed that the mean amplitude deviation (MAD) of the resultant acceleration signal performed best in separating different intensity levels and provided excellent agreement between the three devices. The objective of this study was to derive a regression model that estimates oxygen consumption (VO2) from MAD values and validate the MAD-based cut-points for light, moderate and vigorous locomotion against VO₂ within a wide range of speeds.

Methods

29 participants performed a pace-conducted non-stop test on a 200 m long indoor track. The initial speed was 0.6 m/s and it was increased by 0.4 m/s every 2.5 minutes until volitional exhaustion. The participants could freely decide whether they preferred to walk or run. During the test they carried a hip-mounted tri-axial accelerometer and mobile metabolic analyzer. The MAD was calculated from the raw acceleration data and compared to directly measured incident VO₂. Cut-point between light and moderate activity was set to 3.0 metabolic equivalent (MET, 1 MET = 3.5 ml · kg^-1 · min^-1) and between moderate and vigorous activity to 6.0 MET as per standard use.

Results

The MAD and VO₂ showed a very strong association. Within individuals, the range of r values was from 0.927 to 0.991 providing the mean r = 0.969. The optimal MAD cut-point for 3.0 MET was 91 mg (milligravity) and 414 mg for 6.0 MET.

Conclusion

The present study showed that the MAD is a valid method in terms of the VO₂ within a wide range of ambulatory activities from slow walking to fast running. Being a device-independent trait, the MAD facilitates directly comparable, accurate results on the intensity of physical activity with all accelerometers providing tri-axial raw data.     

Importance of GluA1 subunit-containing AMPA glutamate receptors for morphine state-dependency

In state-dependency, information retrieval is most efficient when the animal is in the same state as it was during the information acquisition. State-dependency has been implicated in a variety of learning and memory processes, but its mechanisms remain to be resolved. Here, mice deficient in AMPA-type glutamate receptor GluA1 subunits were first conditioned to morphine (10 or 20 mg/kg s.c. during eight sessions over four days) using an unbiased procedure, followed by testing for conditioned place preference at morphine states that were the same as or different from the one the mice were conditioned to. In GluA1 wildtype littermate mice the same-state morphine dose produced the greatest expression of place preference, while in the knockout mice no place preference was then detected. Both wildtype and knockout mice expressed moderate morphine-induced place preference when not at the morphine state (saline treatment at the test); in this case, place preference was weaker than that in the same-state test in wildtype mice. No correlation between place preference scores and locomotor activity during testing was found. Additionally, as compared to the controls, the knockout mice showed unchanged sensitization to morphine, morphine drug discrimination and brain regional μ-opioid receptor signal transduction at the G-protein level. However, the knockout mice failed to show increased AMPA/NMDA receptor current ratios in the ventral tegmental area dopamine neurons of midbrain slices after a single injection of morphine (10 mg/kg, s.c., sliced prepared 24 h afterwards), in contrast to the wildtype mice. The results indicate impaired drug-induced state-dependency in GluA1 knockout mice, correlating with impaired opioid-induced glutamate receptor neuroplasticity.     

Specific absorption rate and electric field measurements in the near field of six mobile phone base station antennas

In this article, the exposure to radio frequency electromagnetic fields was studied in close proximity (distances of 10, 100, 300, and 600 mm) to six base station antennas. The specific absorption rate (SAR) in 800 mm × 500 mm × 200 mm box phantom as well as unperturbed electric field (E) in air was measured. The results were used to determine whether the measurement of local maximum of unperturbed electric field can be used as a compliance check for local exposure. Also, the conservativeness of this assessment method compared to the ICNIRP basic restriction was studied. Moreover, the assessment of whole‐body exposure was discussed and the distance ranges presented in which the ICNIRP limit for local exposure could be exceeded before the limit for whole‐body SAR. These results show that the electric field measurement alone can be used for easy compliance check for the local exposure at all distances and for all antenna types studied. However, in some cases when the local peak value of E was compared directly to the ICNIRP reference level for unperturbed E, the exposure was overestimated only very slightly (by factor 1.1) compared to the basic restriction for localized SAR in a human, and hence these results can not be generalized to all antenna types. Moreover, it was shown that the limit for localized exposure could be exceeded before the limit for the whole‐body average SAR, if the distance to the antenna was less than 240 mm. Bioelectromagnetics 30:307–312, 2009. © 2009 Wiley‐Liss, Inc.     

trkB-Receptor Activation Contributes to the Kainate-Induced Increase in BDNF mRNA Synthesis

1. The expression of brain-derived neurotrophic factor (BDNF) mRNA is induced by neuronal activity through increased intracellular calcium. As BDNF also increases intracellular calcium levels through trkB activation, we have examined here whether BDNF also regulates the synthesis of its own mRNA.2. Neurotrophin mRNA expression was induced with kainic acid administration in transgenic mice overexpressing the dominant-negative form of BDNF receptor trkB and wild-type littermates.3. Kainate strongly induced BDNF mRNA expression in both genotypes, but the upregulation was significantly lower in transgenic mice.4. These data suggest that the synthesis of BDNF mRNA is at least partly mediated by BDNF release and the activation of trkB receptors. The present findings further suggest that the BDNF signaling system in brain is regulated by positive feedback.     

ECOLOGICAL VERSUS PHYLOGENETIC DETERMINANTS OF TROPHIC ASSOCIATIONS IN A PLANT–LEAFMINER–PARASITOID FOOD WEB

Specialized trophic interactions in plant–herbivore–parasitoid food webs can spur “bottom–up” diversification if speciation in plants leads to host‐shift driven divergence in insect herbivores, and if the effect then cascades up to the third trophic level. Conversely, parasitoids that search for victims on certain plant taxa may trigger “top–down” diversification by pushing herbivores into “enemy‐free space” on novel hosts. We used phylogenetic regression methods to compare the relative importance of ecology versus phylogeny on associations between Heterarthrinae leafmining sawflies and their parasitoids. We found that: (1) the origin of leafmining led to escape from most parasitoids attacking external‐feeding sawflies; (2) the current enemies mainly consist of generalists that are shared with other leafmining taxa, and of more specialized lineages that may have diversified by shifting among heterarthrines; and (3) parasitoid–leafminer associations are influenced more by the phylogeny of the miners’ host plants than by relationships among miner species. Our results suggest that vertical diversifying forces have a significant—but not ubiquitous—role in speciation: many of the parasitoids have remained polyphagous despite niche diversification in the miners, and heterarthrine host shifts also seem to be strongly affected by host availability.     

The Structure of the NTPase That Powers DNA Packaging into Sulfolobus Turreted Icosahedral Virus 2

Biochemical reactions powered by ATP hydrolysis are fundamental for the movement of molecules and cellular structures. One such reaction is the encapsidation of the double-stranded DNA (dsDNA) genome of an icosahedrally symmetric virus into a preformed procapsid with the help of a genome-translocating NTPase. Such NTPases have been characterized in detail from both RNA and tailed DNA viruses. We present four crystal structures and the biochemical activity of a thermophilic NTPase, B204, from the nontailed, membrane-containing, hyperthermoacidophilic archaeal dsDNA virus Sulfolobus turreted icosahedral virus 2. These are the first structures of a genome-packaging NTPase from a nontailed, dsDNA virus with an archaeal host. The four structures highlight the catalytic cycle of B204, pinpointing the molecular movement between substrate-bound (open) and empty (closed) active sites. The protein is shown to bind both single-stranded and double-stranded nucleic acids and to have an optimum activity at 80°C and pH 4.5. The overall fold of B204 places it in the FtsK-HerA superfamily of P-loop ATPases, whose cellular and viral members have been suggested to share a DNA-translocating mechanism.