Peripheral nerve injury and myelination: Potential therapeutic strategies

Traumatic peripheral nerve injury represents a major clinical and public health problem that often leads to significant functional impairment and permanent disability. Despite modern diagnostic procedures and advanced microsurgical techniques, functional recovery after peripheral nerve repair is often unsatisfactory. Therefore, there is an unmet need for new therapeutic or adjunctive strategies to promote the functional recovery in nerve injury patients. In contrast to the central nervous system, Schwann cells in the peripheral nervous system play a pivotal role in several aspects of nerve repair such as degeneration, remyelination, and axonal growth. Several non-surgical approaches, including pharmacological, electrical, cell-based, and laser therapies, have been employed to promote myelination and enhance functional recovery after peripheral nerve injury. This review will succinctly discuss the potential therapeutic strategies in the context of myelination following peripheral neurotrauma.     

Thousands of corresponding human and mouse genomic regions unalignable in primary sequence contain common RNA structure

Human and mouse genome sequences contain roughly 100,000 regions that are unalignable in primary sequence and neighbor corresponding alignable regions between both organisms. These pairs are generally assumed to be nonconserved, although the level of structural conservation between these has never been investigated. Owing to the limitations in computational methods, comparative genomics has been lacking the ability to compare such nonconserved sequence regions for conserved structural RNA elements. We have investigated the presence of structural RNA elements by conducting a local structural alignment, using FOLDALIGN, on a subset of these 100,000 corresponding regions and estimate that 1800 contain common RNA structures. Comparing our results with the recent mapping of transcribed fragments (transfrags) in human, we find that high-scoring candidates are twice as likely to be found in regions overlapped by transfrags than regions that are not overlapped by transfrags. To verify the coexpression between predicted candidates in human and mouse, we conducted expression studies by RT-PCR and Northern blotting on mouse candidates, which overlap with transfrags on human chromosome 20. RT-PCR results confirmed expression of 32 out of 36 candidates, whereas Northern blots confirmed four out of 12 candidates. Furthermore, many RT-PCR results indicate differential expression in different tissues. Hence, our findings suggest that there are corresponding regions between human and mouse, which contain expressed non-coding RNA sequences not alignable in primary sequence.     

Ultrasound in preoperative staging of rectal tumours

A dynamic ultrasound sector scanner with 5.0 and 7.5 MHz transducers was used for examination of resected bowel specimens with rectal carcinoma. Pathologic structures, i.e. tumour extension into or beyond the bowel wall, and perirectal lymph nodes, were marked. Corresponding parts of the tissue were embedded in paraffin and a detailed comparison between the findings at ultrasound and those in the histopathological sections was made. There was a good accordance between the histopathologic and ultrasonic findings which makes it possible to perform an exact preoperative staging of rectal carcinomas with ultrasound. Twenty patients with primary tumours of the rectum preoperatively underwent ultrasonography with a prototype transrectal probe with the same type of crystals and frequencies. In the 14 cases, however, where ultrasound findings could be compared with the histopathologic findings only six (43%) were correctly staged at ultrasonography. Certain difficulties were encountered in the preoperative examinations with a rigid probe as used in this study.     

Computed tomography in early diagnosis of local recurrence of rectal carcinoma

Local recurrence is a common problem among patients treated surgically for adenocarcinoma of the rectum and rectosigmoid. When a local recurrence has become clinically manifest, curative therapy is virtually impossible. Asymptomatic local recurrences are difficult to find clinically, especially in patients treated with an abdominoperineal resection. In 177 patients who had undergone locally curative surgery and had had an uneventful recovery, a postoperative follow-up program, including computed tomography (CT), was carried out. In 77 per cent (137/177) a mass was observed in the pelvis at the first postoperative CT. This mass partly represents fibrosis due to radiation therapy. The risk of developing local recurrence cannot be foreseen from a CT image. CT should not be performed by routine but only in patients with symptoms in whom local recurrence cannot be verified by clinical examination, and always with CT-guided needle biopsy of the detected mass.     

Quality assurance of magnetic resonance spectroscopic imaging-derived metabolic data

PURPOSE: Spatially resolved metabolite maps, as measured by magnetic resonance spectroscopic imaging (MRSI) methods, are being increasingly used to acquire metabolic information to guide therapy, with metabolite ratio maps perhaps providing the most diagnostic information. We present a quality assurance procedure for MRSI-derived metabolic data acquired ultimately for guiding conformal radiotherapy. METHODS AND MATERIALS: An MRSI phantom filled with brain-mimicking solutions was custom-built with an insert holding eight vials containing calibration solutions of precisely varying metabolite concentrations that emulated increasing grade/density of brain tumor. Phantom metabolite ratios calculated from fully relaxed 1D, 2D, and 3D MRS data for each vial were compared with calibrated metabolite ratios acquired at 9.4 T. Additionally, 3D ratio maps were "discretized" to eight pseudoabnormality levels on a slice-by-slice basis and the accuracy of this procedure was verified. RESULTS: Regression analysis revealed expected linear relationships between experimental and calibration metabolite ratios with intercepts close to zero for the three acquisition modes. 1D MRS data agreed most with theoretical considerations (regression coefficient, b = 0.969; intercept 0.008). The 2D (b = 1.049; intercept -0.199) and 3D (correlation coefficient r(2) = 0.9978-0.7336 for five slices) MRSI indicated reduced MRS data quality in regions of degraded B(0) and B(1) homogeneity. Pseudoabnormality levels were found to be consistent with expectations within regions of adequate B(0) homogeneity. CONCLUSIONS: This simple phantom-based approach to generate baseline calibration curves for all MRS acquisition modes may be useful to identify temporal deviations from acceptable data quality in a routine clinical environment or for testing new MRS and MRSI acquisition software.     

Spatial and temporal receptive fields of geniculate and cortical cells and directional selectivity

The spatio-temporal receptive fields (RFs) of cells in the macaque monkey lateral geniculate nucleus (LGN) and striate cortex (V1) have been examined and two distinct sub-populations of non-directional V1 cells have been found: those with a slow largely monophasic temporal RF, and those with a fast very biphasic temporal response. These two sub-populations are in temporal quadrature, the fast biphasic cells crossing over from one response phase to the reverse just as the slow monophasic cells reach their peak response. The two sub-populations also differ in the spatial phases of their RFs. A principal components analysis of the spatio-temporal RFs of directional V1 cells shows that their RFs could be constructed by a linear combination of two components, one of which has the temporal and spatial characteristics of a fast biphasic cell, and the other the temporal and spatial characteristics of a slow monophasic cell. Magnocellular LGN cells are fast and biphasic and lead the fast-biphasic V1 subpopulation by 7 ms; parvocellular LGN cells are slow and largely monophasic and lead the slow monophasic V1 sub-population by 12 ms. We suggest that directional V1 cells get inputs in the approximate temporal and spatial quadrature required for motion detection by combining signals from the two non-directional cortical sub-populations which have been identified, and that these sub-populations have their origins in magno and parvo LGN cells, respectively.     

Is medial elbow pain correlated with cubital tunnel syndrome? An electrodiagnostic study

Introduction: Medial elbow pain is often considered to be a symptom associated with ulnar neuropathy at the elbow (UNE). We examined the relationship between medial elbow pain and a positive electrodiagnostic (EDx) test result for UNE. Methods: We performed a retrospective review of 884 patients referred for EDx evaluation of UNE. Regression models were used to determine the odds ratios between clinical findings and a positive EDx result for UNE. Results: Patients reported medial elbow pain in 44.3% of cases. Clinical factors that correlated with a positive EDx study result for UNE included male gender, small and ring finger numbness, ulnar intrinsic weakness, and age. Medial elbow pain was negatively correlated with a positive EDx result. Conclusions: This study demonstrates a negative correlation between medial elbow pain and a positive EDx result for UNE. Medial elbow pain should not be considered a clear diagnostic symptom of UNE. Muscle Nerve 53: 252–254, 2016     

Specific absorption rate studies of the parallel transmission of inner-volume excitations at 7T

PURPOSE: To investigate the behavior of whole-head and local specific absorption rate (SAR) as a function of trajectory acceleration factor and target excitation pattern due to the parallel transmission (pTX) of spatially tailored excitations at 7T. MATERIALS AND METHODS: Finite-difference time domain (FDTD) simulations in a multitissue head model were used to obtain B(1) (+) and electric field maps of an eight-channel transmit head array. Local and average SAR produced by 2D-spiral-trajectory excitations were examined as a function of trajectory acceleration factor, R, and a variety of target excitation parameters when pTX pulses are designed for constant root-mean-square excitation pattern error. RESULTS: Mean and local SAR grow quadratically with flip angle and more than quadratically with R, but the ratio of local to mean SAR is not monotonic with R. SAR varies greatly with target position, exhibiting different behaviors as a function of target shape and size for small and large R. For example, exciting large regions produces less SAR than exciting small ones for R >or=4, but the opposite trend occurs when R <4. Furthermore, smoother and symmetric patterns produce lower SAR. CONCLUSION: Mean and local SAR vary by orders of magnitude depending on acceleration factor and excitation pattern, often exhibiting complex, nonintuitive behavior. To ensure safety compliance, it seems that model-based validation of individual target patterns and corresponding pTX pulses is necessary.