Morphometric Nerve Fiber Analysis and Aging Process of the Human Abducent Nerve

Abstract

Summary: Myelinated nerve fibers of the human abducent nerve were analyzed with a new staining method that permits simultaneous observation of the axon and surrounding myelin sheath. The following equipment was employed for the measurements: an image-analyzing digitizer, a microscope equipped with a drawing tube (or camera lucida), and a computer for data storage and statistical analysis. The numbers, transverse areas, and circularity ratios of axons were measured in 10 human abducent nerves. The average number was 1,997 with a definite decrease with age, and the Several studies on the number and size of fibers in the human abducent nerve have been conducted, but to our knowledge, these studies have not dealt with age-related changes in the abducent nerve. The aim of the present study was precisely to investigate these changes through an analysis of transverse area, number and shape of axons. Material and MethodsSmall sections of the abducent nerve situated in the subarachnoid space were removed from 10 human cadavers (4 males and 6 females) aged 63-88 years (average age: 74.7 years). The causes of death had no direct or indirect influence on the nervous system, so the abducent nerves were considered to be normal.Fixation: The fixation procedure consisted of two steps as follows: (1) Primary fixation: the material was kept in 3.7% formaldehyde for at least one week. (2) Secondary fixation: the material was immersed in a mixture of 5% potassium dichromate and 5% potassium chromate (1:4 in volume) for three weeks (two weeks at room temperature, and a further week at 37 °C). The volume of fixative was at least ten times the volume of the specimen.Washing: After fixation, tissue blocks fitted with a nylon-mesh bag or a plastic tissue-basket were washed in running water with siphon-operated automatic pipette washer for several hours.Dehydration and celloidin embedding: The tissue blocks were dehydrated with ethanol at 50%, 70%, 90%, 95% and pure, and were then embedded in celloidin. The shrinkage of nerve tissue sections during fixation and embedding amounted to approximately 10% in length.Sections: The blocks were sectioned transversely into 20 p.m thick slices.Staining: The sections were stained with LPH triple stain (Luxol fast blue-periodic acid-Schiffhematoxylin staining). For more details, see the reference section (Goto, 19875)).Morphometry: The systemic sampling method was employed for the measurement of axons. A sampling site at the center of the abducent nerve Correspondence to:

The Human Trochlear and Abducens Nerves at Different Ages - a Morphometric Study

“…The counts in the present study are higher than that reported by Sawabe et al [39] in aged (63-88 years old) subjects, in which the counts ranged from 1473 to 2638. This discrepancy in the findings may be due to the methodological disparity in the two studies, the latter having been done using older morphometric methods using camera lucida drawings and customised programs [39].…”

“…Reports in literature indicate that myelinated fibers predominate in these nerves [7,39]. Our findings ( Table 1 &2) are not quite in agreement with previous studies [33,35] that were on electron microscopic montages, and counting frames were chosen manually, therefore were inherently biased.…”

Unmyelinated Nerve Fiber Analysis of the Human Oculomotor Nerve

“…The methods for fixation, embedding, sectioning, staining and measurement were the same as in our previous reports2, 3,6,7,[9][10][11]14,15). For morphometric measurements, we employed the systemic sampling method.…”

Morphometric evaluations of the human nervous system

“…Myelinated nerve fibers were analyzed in human abducent nerves from 10 cadavers (four males and six females) aged 63–88 (average 74.7) years using the same methods 47 . The average number of fibers was 1997, with a definite decrease with age.…”