Development of a live tissue microtome: reflections of an amateur machinist.

Live circular tissue slices of nearly identical diameter and thickness can be generated from most tissues by the use of two instruments; a coring tool to cut cylindrical tissue cores which are subsequently sliced by a microtome into thin circular sections 5-8 mm in diameter and 50-300 microns thick. The sections are of very similar geometry permitting direct comparisons without normalization. Both instruments operate submerged in a cold isotonic medium that caries the cut slices outside the microtome. The slices are cut by a rapidly oscillating disposable Gillette blade mounted at an angle of 20 degrees to the vertical main axis of the tissue core. The latter is advanced against the oscillating blade by a weighted plunger pushing it against a screw adjustable limit plate that defines the desired slice thickness. Both instruments can be sterilized and slices can be obtained at a rate of approximately one every ten seconds.

C677T methylene-H4-folate-reductase variant decreases binocular accommodation.

PURPOSE: The C677T polymorphism of methylene tetrahydrofolate reductase (MTHFR) lowers the activity of this enzyme, producing moderate elevation of blood levels of homocysteine (Hcy) and lowering the levels of 5-methyl-tetrahydro-folic acid (5-MeTHFA), methionine (Meth), and S-adenosylmethionine (SAM). In this study we examined 100 apparently normal subjects of both sexes (average age 25.6 +/- 4.25) for the genotypic presence of the T allele and its association with accommodative amplitude (AA). METHODS: The amplitude of accommodation was measured by the subjective "push-up" technique. DNA from buccal cells was genotyped for the C677T polymorphism of MTHFR by a PCR-restriction fragment length polymorphism genotyping assay. Descriptive statistics were obtained by frequency distribution and univariate analysis. Comparisons between monocular and binocular AA were obtained by t-test statistics or ANOVA. Associations between genotype and phenotype were analyzed using regression models. RESULTS: The C677T polymorphism was associated with decreased binocular AA (p = 0.0087). Monocular AA was not associated with the MTHFR genotype. CONCLUSIONS: Our results suggest a role for the C677T polymorphism in damaging the neural aspects of binocular vergence accommodation. The postulated neural damage could be due to the decreased formation of 5-MeTHFA and the defective synthesis of Meth, SAM and neurotransmitters or other methyl acceptors in nervous tissue of bearers of the C677T polymorphism. The differential effect upon monocular and binocular accommodation is hypothetically explained by a greater involvement of methylation reactions in vergence accommodation. A similar mechanism is proposed to explain the prevalent insufficient accommodation of Down's syndrome in which the blood levels of Meth and SAM are reduced.