Updates on local anaesthetics.

This article draws from a book entitled: "A practical approach to hazards of local anaesthetic injections" by DP Barnard.

A 360 degrees single-axis tilt stage for the high-voltage electron microscope.

A new type of specimen stage that permits more than 180 degrees of tilting about the axis of a side-entry rod has been developed for a high-voltage electron microscope (HVEM). Roughly cylindrical specimens, with radial dimensions of less than a few micrometers, that can be mounted on the tip of a microneedle or micropipette are applicable. For glass micropipettes, the energy of the 1-MeV beam of the HVEM is sufficient to image specimens through both walls. The stage employs a spindle mechanism that holds these needles or micropipettes coaxial with the tilt axis, allowing the specimen to be rotated without restriction. This arrangement, along with the cylindrical form of the specimen, is an important development for single-axis tomography, because it permits a complete 180 degrees set of projections to be recorded. The angular accuracy of the stage was demonstrated to be within +/- 0.20 degrees, with a cumulative error of less than 1.0 degrees over a 180 degrees span. The new stage was tested using puffball spores mounted on a micropipette. A 180 degrees tilt series was recorded and processed to yield a tomographic three-dimensional reconstruction which was displayed both as a cross-sectional view perpendicular to the tilt axis, and as a shaded surface viewed from different directions. The same computations were repeated using subsets of the tilt series to assess the effect of various amounts of missing information. Visual inspection of a selected cross-section from these reconstructions indicated that limiting the angular range to 160 degrees produced results nearly as good as the full data set. Limiting the range to 140 degrees, however, produced a noticeable geometric distortion, which became increasingly severe with ranges of 120 degrees and 100 degrees.

High-precision tilt stage for the high-voltage electron microscope.

The high-voltage electron microscope is used to study thick samples (0.25 to several micrometers) to obtain three-dimensional information at ultrastructural resolution. Three-dimensional image reconstructions are often employed to extract, process and display this information. The sets of images used to form reconstructions must be recorded for precisely known specimen-beam orientations, especially if tomographic methods are employed. The design and operation of a precision (+/- 0.06 degrees) single-tilt stage to support this type of imaging is reported. All motions including two translations, height adjustment and tilting are accomplished via a single objective lens entry port. The specimen rod is supported on two rubber gaskets for vibration isolation, and motorized precision micrometers with encoder readouts for position monitoring drive the motions. The stage is stable to 0.6 nm for at least 16 s and is capable of tilt angles of +/- 70 degrees.