Cryogenic Procedures Research Articles

SIMS MICROSCOPY: METHODOLOGY, PROBLEMS AND PERSPECTIVES IN MAPPING DRUGS AND NUCLEAR MEDICINE COMPOUNDS

Secondary ion mass spectrometry (SIMS) microscopy, a mass spectrometry method designed in the 1960s, offers new analytical capabilities, high sensitivity (ppm to ppb region), high specificity and improved lateral resolution, thus facilitating insight into many physiological and biomedical questions. Apart from the sample preparation and the physical characteristics of the detection, the biological model must also be considered.SIMS analysis of diffusible ions and molecules requires strict cryogenic procedures which always begin by a flash-freeze fixation. Cellular integrity can be checked by mapping the major element distributions since intra and extracellular ions are redistributed only in damaged cells. Cryofixing may be followed either by a freeze-fracture methodology or by cryoembedding and dry-cutting. Chemical sample preparation is only used for ions or molecules bound to fixed cell structures.The use of scanning procedures ameliorates the lateral resolution and chromosome imaging has been reported with probe size of below 50nm. Absolute quantification can be derived for embedded specimen by using internal references included in tissue equivalent resins. The sensitivity is limited by the ionization yield of the tag element and may be further impaired when working at high mass resolution (≥5000) to eliminate interfering cluster ions.SIMS drug mapping is usually performed afterin vitroadministration of a molecule to cell culture systems. Drug detection is accomplished indirectly by detecting a tag isotope naturally present or introduced by labelling, mainly with halogens,15N and14C. Molecular imaging with TOF-SIMS is an appealing alternative especially for heavier compounds. We stress some biological problems through a critical review of published SIMS drug studies. SIMS proved useful in assessing the targeting specificity of nuclear medicine pharmaceutics, even afterin vivoadministration. The first microscopic evidence of a thionamide induced follicular blockade of the iodine organification process is presented in a human sample.

Cryopreservation of encapsulated shoot primordia induced in horseradish (Armoracia rusticana) hairy root cultures.

Shoot primordia induced inArmoracia rusticana Gaertn. Mey. et Scherb. (horseradish) hairy root cultures were successfully cryopreserved by two cryogenic procedures. Encapsulated shoot primordia were precultured on solidified Murashige-Skoog medium supplemented with 0.5M sucrose for 1 day and then dehydrated with a highly concentrated vitrification solution (PVS2) for 4 h at 0°C prior to a plunge into liquid nitrogen. The survival rate of encapsulated vitrified primordia amounted to 69%. In a revised encapsulation-dehydration technique, the encapsulated shoot primordia were precultured with a mixture of 0.5M sucrose and 1M or 1.5M glycerol for 1 day to induce dehydration tolerance and then subjected to air-drying prior to a plunge into liquid nitrogen. The survival rate of encapsulated dried primordia was more than 90%, and the revived primordia produced shoots within 2 weeks after plating. A long-term preservation of shoot primordia was also achieved by the technique. Thus, this revised encapsulation-dehydration technique appears promising as a routine method for the cryopreservation of shoot primordia of hairy roots.

Distribution, Sources and Sinks of Atmospheric Halogenated Compounds

Based on two comprehensive field studies conducted in California, background concentration (parts per trillion) of N/sub 2/O (296.0 x 10/sup 3/), SF/sub 6/ (0.16), CCl/sub 2/F/sub 2/ (180.8), CCl/sub 3/F (103.8), CCl/sub 2/FCClF/sub 2/ (16.3), CCl/sub 4/ (114.2), CH/sub 3/Cl (952.9), CHCl/sub 3/ (23.4), CH/sub 3/I (2.4), CH/sub 3/CCl/sub 3/ (84.0), CCl/sub 2/CCl/sub 2/ (43.1), CHClCCl/sub 2/ (14.5) and CH/sub 3/Br (-) have been reported. These trace constituents were identified using retention data on eight GC columns, their electron attachment properties, and their EC thermal response. All but CHClCCl/sub 2/ and CH/sub 3/BR were measurable 100% of the time at both sites. Cryogenic procedures for SF/sub 6/ ambient measurements were developed and successfully used. By an analysis of worldwide emissions of these trace constituents, their ambient levels, and their atmospheric lifetimes, it was possible to determine their origin (natural or anthropogenic). Our results indicate that 27% of organic chlorine contribution to the troposphere comes from fluorocarbons as opposed to a 73% contribution from the chlorocarbons. Further, the anthropogenic organic content in the troposphere was found to be about twice the natural content. Very high CHCl/sub 3/ concentrations in onshore ocean waters were measured. Ambient data supporting the anthropogenic origin ofmore » CCl/sub 4/ have been presented.« less

EARTH CONDUCTIVITY DETERMINATIONS EMPLOYING A SINGLE SUPERCONDUCTING COIL

A low‐frequency airborne electromagnetic prospecting method has been developed which exploits the inherent low resistance of a superconducting coil. Changes in the input resistance of this coil are monitored in the presence of the conducting earth. The response of the system, the change in the input resistance, is proportional to the quadrature secondary magnetic field at the transmitter, although unlike two‐coil systems, the response does not decrease with increasing frequency. This research has demonstrated that superconducting wires, large scale nonmetallic cryostats, the requisite measurement circuitry, and an appropriate data acquisition system are realizable in a practical flight configuration. The unicoil presents the following significant advantages in electromagnetic prospecting: 1) The measurement sensitivity is not limited by the relative coil motion experienced by two‐coil systems. 2) Ample field strength may be supplied to override ambient noise. 3) Optimum frequencies for specific geologic sections are easily implemented in the range of 10 to 2000 Hz. 4) Maps of ground conductivity may be obtained because precise thermal stability is maintained and the measurement, therefore, is absolute. 5) The point source observation minimizes analytic complexity. 6) The combination of the foregoing features with multiple frequency operation, yields a system of potentially high sensitivity and unprecedented depth of exploration. The unicoil system also possesses some disadvantages: 1) An operational complexity results from the cryogenic procedures required in the field, and 2) the heavy sensor requires a large helicopter.

Long-term results with cryosurgery for Meniere's disease.

Long-term follow-ups (one to four years) of 72 cryosurgical procedures for Meniere's disease revealed that surgery either completely eliminated the vertigo or substantially reduced the frequency and severity of the attacks in 76% of the cases. Cryosurgery appears to have no effect on hearing. If the hearing was stable prior to surgery, then it remained at the same level during the follow-up period. If hearing fluctuated prior to surgery, however, it generally continued to fluctuate afterwards. Of the 110 cryogenic procedures performed since May 1966, facial nerve complications occurred seven times. Total paralysis occurred twice and both patients recovered without treatment in six weeks. Five patients developed facial weakness nine to ten days after surgery and recovered spontaneously within two weeks.

Effect of Warming Rates on the Viability of Frozen Fungous Spores

The successful application of ultra-low temperatures to the preservation of a broad range of living materials (1, 3, 4, 7, 9, 17, 19) has stimulated interest in the use of cryogenics as an alternative to freezedrying for the preservation of fungous cultures. Alternatives to freezedrying are needed, inasmuch as some fungi do not sporulate sufficiently to be handled by this method, and others simply fail to survive the freeze-dry process (5). Hwang (8) reported the successful use of cryogenic procedures for the preservation of a wide variety of fungous cultures, and, more recently, Wellman and Walden (21) and Hwang (unpublished) have found that the mycelium and hyphal tips of fungi will survive freezing and thawing. Successful preservation of the normally short-lived rust urediospores and pycniospores in liquid nitrogen has also been reported (1, 11), with the result that a collection of plant rusts has been initiated at the American Type Culture Collection (ATCC) (10). Based on the studies of Hwang (8, and unpublished), low-temperature preservation is being used increasingly at the ATCC for the longterm maintenance of fungi that do not sporulate or that otherwise fail to survive the freeze-dry process. In developing an expanded program for preservation of fungi by cryogenic methods, investigations on various aspects of the freezing procedure are needed to determine factors affecting the survival and recovery of fungi from the frozen state. Studies by Mazur (14, 16, 17, 18), Smith (19) and others (12, 13, 20) have shown that injury to biological systems can occur during both the freezing and thawing processes. Best results in preserving living material by freezing have generally been achieved when slow cooling at approximately 1 C per minute has been followed by rapid warming.1