Mechanical feedback and robustness of apical constrictions in Drosophila embryo ventral furrow formation.

Formation of the ventral furrow in the Drosophila embryo relies on the apical constriction of cells in the ventral region to produce bending forces that drive tissue invagination. In our recent paper we observed that apical constrictions during the initial phase of ventral furrow formation produce elongated patterns of cellular constriction chains prior to invagination and argued that these are indicative of tensile stress feedback. Here, we quantitatively analyze the constriction patterns preceding ventral furrow formation and find that they are consistent with the predictions of our active-granular-fluid model of a monolayer of mechanically coupled stress-sensitive constricting particles. Our model shows that tensile feedback causes constriction chains to develop along underlying precursor tensile stress chains that gradually strengthen with subsequent cellular constrictions. As seen in both our model and available optogenetic experiments, this mechanism allows constriction chains to penetrate or circumvent zones of reduced cell contractility, thus increasing the robustness of ventral furrow formation to spatial variation of cell contractility by rescuing cellular constrictions in the disrupted regions.

Susceptibility-Weighted MRI Approximates Intraoperative Microelectrode Recording During Deep Brain Stimulation of the Subthalamic Nucleus for Parkinson's Disease.

BACKGROUND: Deep brain stimulation of the subthalamic nucleus (STN-DBS) for Parkinson's disease can be performed with intraoperative neurophysiological and radiographic guidance. Conventional T2-weighted magnetic resonance imaging sequences, however, often fail to provide definitive borders of the STN. Novel magnetic resonance imaging sequences, such as susceptibility-weighted imaging (SWI), might better localize the STN borders and facilitate radiographic targeting. We compared the radiographic location of the dorsal and ventral borders of the STN using SWI with intraoperative microelectrode recording (MER) during awake STN-DBS for Parkinson's disease. METHODS: Thirteen consecutive patients who underwent placement of 24 STN-DBS leads for Parkinson's disease were analyzed retrospectively. Preoperative targeting was performed with SWI, and MER data were obtained from intraoperative electrophysiology records. The boundaries of the STN on SWI were identified by a blinded investigator. RESULTS: The final electrode position differed significantly from the planned coordinates in depth but not in length or width, indicating that MER guided the final electrode depth. When we compared the boundaries of the STN by MER and SWI, SWI accurately predicted the entry into the STN but underestimated the length and ventral boundary of the STN by 1.2 mm. This extent of error approximates the span of a DBS contact and could affect the placement of directional contacts within the STN. CONCLUSIONS: MER might continue to have a role in STN-DBS. This could potentially be mitigated by further refinement of imaging protocols to better image the ventral boundary of the STN.

Bilateral Deep Brain Stimulation of the Ventral Intermediate Nucleus of the Thalamus Improves Objective Acoustic Measures of Essential Vocal Tremor.

BACKGROUND AND OBJECTIVES: Deep brain stimulation of the ventral intermediate nucleus of the thalamus (VIM-DBS) is an established treatment for medically refractory essential tremor. However, the effect of VIM-DBS on vocal tremor remains poorly understood, with results varying by method of vocal tremor assessment and stimulation laterality. This single-center study measures the effect of bilateral VIM-DBS on essential vocal tremor using blinded objective acoustic voice analysis. METHODS: Ten patients with consecutive essential tremor with comorbid vocal tremor receiving bilateral VIM-DBS underwent voice testing before and after implantation of DBS in this prospective cohort study. Objective acoustic measures were extracted from the middle one second of steady-state phonation including cepstral peak prominence, signal-to-noise ratio, percentage voicing, tremor rate, extent of fundamental frequency modulation, and extent of intensity modulation. DBS surgery was performed awake with microelectrode recording and intraoperative testing. Postoperative voice testing was performed after stable programming. RESULTS: Patients included 6 female and 4 male, with a mean age of 67 ± 6.7 years. The VIM was targeted with the following coordinates relative to the mid-anterior commissure:posterior commissure point: 13.2 ± 0.6 mm lateral, 6.2 ± 0.7 mm posterior, and 0.0 mm below. Mean programming parameters were amplitude 1.72.0 ± 0.6 mA, pulse width 63.0 ± 12.7 µs, and rate 130.6 ± 0.0 Hz. VIM-DBS significantly improved tremor rate from 4.43 ± 0.8 Hz to 3.2 ± 0.8 Hz (P = .001) CI (0.546, 1.895), jitter from 1 ± 0.94 to 0.53 ± 0.219 (P = .02) CI (-0.124, 1.038), cepstral peak prominence from 13.6 ± 3.9 to 18.8 ± 2.9 (P = .016) CI (-4.100, -0.235), signal-to-noise ratio from 15.7 ± 3.9 to 18.5 ± 3.7 (P = .02) CI (-5.598, -0.037), and articulation rate from 0.77 ± 0.2 to 0.82 ± .14 (P = .04) CI (-0.097, 0.008). There were no major complications in this series. CONCLUSION: Objective acoustic voice analyses suggest that bilateral VIM-DBS effectively reduces vocal tremor rate and improves voicing. Further studies using objective acoustic analyses and laryngeal imaging may help refine surgical and stimulation techniques and evaluate the effect of laterality on vocal tremor.

The effect of preoperative ibuprofen on tooth sensitivity caused by in-office bleaching.

This study determined the effect of Ibuprofen on tooth sensitivity from in-office bleaching with 38% hydrogen peroxide. A double-blind, randomized-controlled clinical trial was performed on healthy non-smoker patients who retain all anterior teeth (N=31). Patients with anterior restorations, calculus or heavy stain, and those who were taking medications or desensitizer products were excluded. After signing the informed consent, the patients were randomly divided into a Placebo group (n=16) that received a placebo (tinted oil in clear capsule) (Health Dimensions Inc, Compound Pharmacy, Farmington Hills, MI, U.S.A.) or an Ibuprofen group (n=15) that received a 600 mg, PO single dose of Ibuprofen (Advil Liquid Gel, Wyeth, Madison, NJ, USA). The patients were watched while taking the capsules 30 minutes prior to treatment. A single operator applied the 38% hydrogen peroxide (Opalescence Xtra Boost, Ultradent Products Inc) for 20 minutes on 12 anterior teeth. The hydrogen peroxide solution was then rinsed, the teeth were gently dried and the cycle was repeated, for a total application time of 40 minutes. A Visual Analog Scale (VAS) was used to evaluate the level of sensitivity 30 minutes before treatment, immediately after treatment, then 1 hour and 24 hours post-bleaching. The patients graded their maximum sensitivity levels during each period on a scale from 0 to 100 (0=no sensitivity, 100=unbearable sensitivity). The VAS scores were statistically analyzed to compare the groups' scores at different times and to compare the scores within each group at various times (Wilcoxon rank sum tests). The mean score and standard deviation of the Ibuprofen group immediately after bleaching was 5.0 +/- 9.9, at 1 hour--31.5 +/- 32.1 and at 24 hours--25.8 +/- 30.8; the placebo group at the time of treatment was 26.6 +/- 31.0, at 1 hour--30.9 +/- 30.5 and at 24 hours--31.1 +/- 32.6. When comparing the two groups at different times, the Ibuprofen group showed statistically significantly lower sensitivity scores immediately post-bleaching than the placebo group (p = 0.0216) but not at 1 hour (p = 0.84) or 24 hours post-bleaching (p = 0.54). When comparing times within the Ibuprofen group, the mean VAS score immediately after bleaching was significantly lower than 1 hour post-bleaching (p = 0.0024) and 24-hours post-bleaching (p = 0.0110), but the mean VAS score at 1 hour post-bleaching and 24-hours post-bleaching were not significantly different (p = 0.64). For the placebo group, the intragroup time effect was not significant. Within the limitations of the current study, the authors concluded that the use of an analgesic may help to reduce tooth sensitivity during in-office bleaching. In the current study, Ibuprofen (600 mg, PO single dose) reduced tooth sensitivity during but not after the treatment period.