Maarten R. Drost

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Determination of mouse skeletal muscle architecture using three-dimensional diffusion tensor imaging

Muscle architecture is the main determinant of the mechanical behavior of skeletal muscles. This study explored the feasibility of diffusion tensor imaging (DTI) and fiber tracking to noninvasively determine the in vivo three‐dimensional (3D) architecture of skeletal muscle in mouse hind leg. In six mice, the hindlimb was imaged with a diffusion‐weighted (DW) 3D fast spin‐echo (FSE) sequence followed by the acquisition of an exercise‐induced, T2‐enhanced data set. The data showed the expected fiber organization, from which the physiological cross‐sectional area (PCSA), fiber length, and pennation angle for the tibialis anterior (TA) were obtained. The values of these parameters ranged from 5.4–9.1 mm2, 5.8–7.8 mm, and 21–24°, respectively, which is in agreement with values obtained previously with the use of invasive methods. This study shows that 3D DT acquisition and fiber tracking is feasible for the skeletal muscle of mice, and thus enables the quantitative determination of muscle architecture. Magn Reson Med 53:1333–1340, 2005.

DTI-based assessment of ischemia-reperfusion in mouse skeletal muscle

Diffusion tensor imaging (DTI) is frequently applied to characterize the microscopic geometrical properties of tissue. To establish whether and how diffusion MRI responds to transient ischemia of skeletal muscle, we studied the effects of ischemia and reperfusion using DTI and T2‐weighted MRI before and during ischemia and up to 24 hr after reperfusion. Ischemia was induced by 50 min of hindlimb occlusion with or without dorsal flexor stimulation. During ischemia the apparent diffusion coefficient (ADC) tended to decrease (up to 15%), whereas the fractional anisotropy (FA) and T2 showed a varied response depending on the protocol and muscle type. During reperfusion the ADC and T2 initially increased and subsequently renormalized for the occlusion protocol. For the occlusion plus stimulation (OS) protocol, the FA was decreased by 13% and the ADC and T2 were increased by 20% and 57%, respectively, after 24 hr in the stimulated muscle complex. In the latter tissue the three DTI eigenvalues gradually increased upon reperfusion. The smallest eigenvalue (λ3) showed the largest relative increase. Changes in DTI indices in the reperfusion phases followed a similar time course as the changes in T2. The changes in MR indices after 24 hr correlated with the tissue damage quantified with histology. The highest correlation was observed for λ3 (R2 = 0.81). This study shows that DTI can be used to assess ischemia‐induced damage to skeletal muscle. Magn Reson Med, 2006.

Diffusion‐tensor MRI reveals the complex muscle architecture of the human forearm

To design a time‐efficient patient‐friendly clinical diffusion tensor MRI protocol and postprocessing tool to study the complex muscle architecture of the human forearm.

Skeletal muscle wasting and contractile performance in septic rats

We investigated the temporal effects of sepsis on muscle wasting and function in order to study the contribution of wasting to the decline in muscle function; we also studied the fiber‐type specificity of this muscle wasting. Sepsis was induced by injecting rats intraperitoneally with a zymosan suspension. At 2 h and at 2, 6, and 11 days after injection, muscle function was measured using in situ electrical stimulation. Zymosan injection induced severe muscle wasting compared to pair‐fed and ad libitum fed controls. At 6 days, isometric force‐generating capacity was drastically reduced in zymosan‐treated rats. We conclude that this was fully accounted for by the reduction of muscle mass. At day 6, we also observed increased activity of the 20S proteasome in gastrocnemius but not soleus muscle from septic rats. In tibialis anterior but not in soleus, muscle wasting occurred in a fiber‐type specific fashion, i.e., the reduction in cross‐sectional area was significantly smaller in type 1 than type 2A and 2B/X fibers. These findings suggest that both the inherent function of a muscle and the muscle fiber‐type distribution affect the responsiveness to catabolic signals. Muscle Nerve, 2005

Confined compression of canine annulus fibrosus under chemical and mechanical loading

Uniaxial confined compression and swelling experiments on cylindrical specimens taken either in an axial or in a radial direction from a canine lumbar annulus fibrosus are presented. The loading protocol consisted of a combination of stepwise mechanical and chemical loading. Swelling and consolidation curves of normalized displacement versus square root of normalized time did not show a dependence on site or orientation of the specimen. All stages in which height increases, namely, conditioning, swelling, and desolidation show only slight differences in these normalized curves. Consolidation is initially faster, and later slower. The transport coefficient for axial specimens is higher than for radial specimens, for consolidation e.g., 3.14 +/- 1.56 10(-10) m2s(-1) and 1.11 +/- 0.33 10(-10) m2s(-1) respectively, the biphasic aggregate moduli are 1.01 +/- 0.31 MPa and 0.66 +/- 0.30 MPa, respectively.

The control of two-element, reciprocal aiming movements: Evidence for chunking

Abstract This study evaluates the chunking hypothesis in the context of two-element, reciprocal aiming movements. The chunking hypothesis assumes that movements toward small targets require a movement stop while movements toward large targets require a movement reversal . According to the chunking hypothesis, a movement reversal allows for a functional coupling or linkage between the forward and backward movement such that braking energy generated by antagonist activity in the forward movement is stored as elastic energy and re-utilized as acceleration energy in the backward movement (Guiard, 1993). An experiment is reported which examined movement kinematics of left-right reversal movements using four different target combinations; small-small, small-large, large-large, and large-small, for left and right targets, respectively. The results accommodated predictions derived from the chunking hypothesis. Several implications for motor control theory are discussed.

Muscle changes detected with diffusion-tensor imaging after long-distance running

PURPOSE To develop a protocol for diffusion-tensor imaging (DTI) of the complete upper legs and to demonstrate feasibility of detection of subclinical sports-related muscle changes in athletes after strenuous exercise, which remain undetected by using conventional T2-weighted magnetic resonance (MR) imaging with fat suppression. MATERIALS AND METHODS The research was approved by the institutional ethics committee review board, and the volunteers provided written consent before the study. Five male amateur long-distance runners underwent an MR examination (DTI, T1-weighted MR imaging, and T2-weighted MR imaging with fat suppression) of both upper legs 1 week before, 2 days after, and 3 weeks after they participated in a marathon. The tensor eigenvalues (λ1, λ2, and λ3), the mean diffusivity, and the fractional anisotropy (FA) were derived from the DTI data. Data per muscle from the three time-points were compared by using a two-way mixed-design analysis of variance with a Bonferroni posthoc test. RESULTS The DTI protocol allowed imaging of both complete upper legs with adequate signal-to-noise ratio and within a 20-minute imaging time. After the marathon, T2-weighted MR imaging revealed grade 1 muscle strains in nine of the 180 investigated muscles. The three eigenvalues, mean diffusivity, and FA were significantly increased (P < .05) in the biceps femoris muscle 2 days after running. Mean diffusivity and eigenvalues λ1 and λ2 were significantly (P < .05) increased in the semitendinosus and gracilis muscles 2 days after the marathon. CONCLUSION A feasible method for DTI measurements of the upper legs was developed that fully included frequently injured muscles, such as hamstrings, in one single imaging session. This study also revealed changes in DTI parameters that over time were not revealed by qualitative T2-weighted MR imaging with fat suppression.

A modified PAS stain combined with immunofluorescence for quantitative analyses of glycogen in muscle sections.

Simultaneous analyses of glycogen in sections with other subcellular constituents within the same section will provide detailed information on glycogen deposition and the processes involved. To date, staining protocols for quantitative glycogen analyses together with immunofluorescence in the same section are lacking. We aimed to: (1) optimise PAS staining for combination with immunofluorescence, (2) perform quantitative glycogen analyses in tissue sections, (3) evaluate the effect of section thickness on PAS-derived data and (4) examine if semiquantitative glycogen data were convertible to genuine glycogen values. Conventional PAS was successfully modified for combined use with immunofluorescence. Transmitted light microscopic examination of glycogen was successfully followed by semiquantification of glycogen using microdensitometry. Semiquantitative data correlated perfectly with glycogen content measured biochemically in the same sample (r2=0.993, P<0.001). Using a calibration curve (r2=0.945, P<0.001) derived from a custom-made external standard with incremental glycogen content, we converted the semiquantitative data to genuine glycogen values. The converted semiquantitative data were comparable with the glycogen values assessed biochemically (P=0.786). In addition we showed that for valid comparison of glycogen content between sections, thickness should remain constant. In conclusion, the novel protocol permits the combined use of PAS with immunofluorescence and shows valid conversion of data obtained by microdensitometry to genuine glycogen data.

Reproducibility of diffusion tensor imaging in human forearm muscles at 3.0 T in a clinical setting

The aim of the present study was to evaluate a fast clinical protocol to enable diffusion tensor imaging of the human forearm and assess the reproducibility of six diffusion tensor imaging parameters, i.e., the tensor eigenvalues (λ1, λ2, and λ3), mean diffusivity, fractional anisotropy, and ellipsoid eccentricity. The right forearms of 10 healthy volunteers were scanned twice, with a 1‐week interval. Reproducibility of the diffusion tensor imaging parameters was interpreted using Bland‐Altman plots, coefficient of repeatability, repeatability index, and the intraclass correlation coefficient. Analysis was done for three regions of interest: the whole muscle volume, flexor digitorum profundus, and extensor digitorum. The Bland‐Altman analysis showed that there is good agreement between the two measurements. Based on the intraclass correlation coefficients, agreement was substantial (0.59 < intraclass correlation coefficient < 0.92) for all six parameters of the whole muscle volume and flexor digitorum profundus but only fair (0.18 < intraclass correlation coefficient < 0.64) for the extensor digitorum. Using a 7 min 40 sec scan protocol, which was well tolerated by the volunteers, the reproducibility of diffusion tensor imaging parameters was demonstrated. However, repeatability varies, depending on the region of interest and diffusion tensor imaging parameters. This should be taken into account when a longitudinal study is designed. Magn Reson Med, 2010.