A NEW METHOD OF POLARIZATION MICROSCOPIC ANALYSIS : I. Scanning with a Birefringence Detection System

A new method of polarized light analysis is described in which a highly sensitive electronic detector specific for birefringence is used to identify the crystalline axes of an object and then measure its phase retardation due to birefringence. The microscopic system employed in the method consists of an electronic birefringence detection system (BDS), a microscope with strain-free lenses, and a driven stage for passing the specimen at appropriate velocities across the image of an aperture placed at the field stop and imaged in the specimen plane by the condenser. The detector registers retardations directly as voltage at a constant deflection sensitivity of ca. 1.1 v per angstrom unit over a range of 120 angstrom units. The basal rms noise level is 0.002 A for a spot 36 µ in diameter formed by a 95 x, N. A. 1.25 objective pair, and increases in proportion to the reciprocal of the diameter of the scanning spot. The increase in noise with high resolution scanning can be offset by increasing the instrumental time constant, which is adjustable in decades between 0.004 and 0.4 seconds. A number of difficult problems in high extinction polarization microscopy are avoided by the use of modulated light and a rapid electronic detector. For example: (a) The measured distribution of birefringence is unaffected by the usual diffraction anomaly; therefore polarization rectifiers are not required. (b) The detector is selective for birefringence, so that there is no problem in separating contrast due to different optical properties (e.g. dichroism, light scattering). (c) The speed and sensitivity are both increased by between one and two orders of magnitude over that attainable by visual or photographic methods, thereby rendering a vast number of weakly birefringent, light-scattering, and motile objects readily analyzable for the first time with polarized light.     

GENETICS OF STERILITY IN HYBRIDS BETWEEN TWO SUBSPECIES OF DROSOPHILA

Hybrids between D. pseudoobscura bogotana and D. pseudoobscura pseudoobscura are fertile except for males produced in one of the two reciprocal crosses. As there is no premating isolation between these subspecies, nonreciprocal male sterility represents the first step in speciation. Genetic analysis reveals two causes of hybrid F₁ sterility: a maternal effect and incompatibilities between chromosomes within males. The maternal effect appears to play the greatest role in hybrid sterility. The X chromosome has the largest effect on fertility of any chromosome, a ubiquitous result in analyses of hybrid sterility and inviability in Drosophila. This effect is entirely attributable to a region comprising less than 30% of the X chromosome. These results are compared to those from a similar study of D. pseudoobscura-D. persimilis hybrids, an older and more reproductively isolated species pair in the same lineage. Such comparisons may allow one to identify the genetic changes characterizing the early versus late stages of speciation.     

An analysis of repeated sequence heterogeneity

High-resolution thermal denaturation was used to measure the heterogeneity within repeated DNA sequences. An analysis of combined denaturation/redenaturation experiments on mouse satellite DNA suggests the existence of two minor components, one of which does not appear in the prepared EcoRII monomer. The resolving power of the denaturation/redenaturation experiment is estimated and contrasted with that of the reassociation experiment, often used to estimate repeated sequence heterogeneity. A mathematical model of the redenaturation experiment was developed and applied to mouse satellite data; the results suggest that only one-fourth of the mismatched base pairs are energetically significant in the reduction of heteroduplex stability.     

A missense mutation (G197→A) in theα-l-fucosidase gene of fucosidosis patients leads to loss ofα-l-fucosidase

Fucosidosis is an autosomal recessive lysosomal storage disease resulting from the absence of -l-fucosidase activity. Two natural missense mutations (G¹⁹⁷A) and (A⁸⁶⁰G) within the -l-fucosidase gene have been reported to be homozygous in four patients with fucosidosis. Expression of wild-type and mutated -l-fucosidase cDNAs in COS-1 cells revealed complete deficiency of -l-fucosidase for the G¹⁹⁷A transition and a normal level of enzyme for A⁸⁶⁰G. We therefore conclude that the change of G¹⁹⁷A is responsible for fucosidosis in the patients while A⁸⁶⁰G is a normal polymorphic variant of -l-fucosidase.     

Determination of betaxolol, a new beta-blocker, by gas chromatography mass spectrometry: application to pharmacokinetic studies

Betaxolol, a beta selective adrenoceptor antagonist recently approved for the treatment of hypertension, was determined by monitoring in chemical ionization mode with ammonia the [MH]+ ions of the trimethylsilyl derivatives of the drug and of its internal standard [2H5)betaxolol). Its pharmacokinetic profile obtained following administration of a 20 mg oral dose was characterized by a half-life of 22 h and a bioavailability of 85%. The main acid metabolite formed by elimination of the isopropylamino group may also be determined as the methyl TMS derivative but methylation with BF3-methanol should be used with caution since it may induce the opening of the cyclopropyl group. The routine electron capture determination procedure was compared to this mass spectrometric method and an excellent correlation was found (r = 0.9974). Both procedures have the same sensitivity (1 ng ml-1). Finally it was observed that under electron impact mode betaxolol trimethylsilyl side chain rearranged to lose TMS-O-CH=CH2; this elimination was confirmed by deuterium labelling studies.     

Changes in serum trace element levels following local irradiation of a solid tumor.

The changes in concentrations of a number of trace elements have been determined by neutron activation analysis in tumor, liver, and blood serum of host animals, following local irradiation of a solid tumor (3924A Morris hepatoma). These trace element changes are compared to the changes observed in a parallel study of the effects of the chemotherapeutic agent 5-fluorouracil on the same tumor. Since the changes in some of the trace elements parallel the changes in pathological and biochemical factors resulting from the insult of radiation on the tumor, these trace elements may be valuable markers in the clinical evaluation of therapeutic response and as monitors of the long term effects of cancer therapy.