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Biomedical subjects

K Chung

Publications and source records attributed to K Chung.

At least 145 records · Page 8Linked to original sources
PubMed1987

A light and electron microscopic level analysis of calcitonin gene-related peptide (CGRP) in the spinal cord of the primate: an immunohistochemical study.

In the present study, the distribution of calcitonin gene-related peptide (CGRP)-stained fibers and varicosities are demonstrated in the lumbar spinal cord of the monkey at the light microscopic level. Immunostained fibers and varicosities form a dense plexus in laminae I, IIo, the reticulated region of lamina V, and in the region of the central canal. The intervaricose fibers consistently measured 1 micron or less in diameter suggesting a population of finely myelinated or unmyelinated fibers. At the electron microscopic level, two types of terminals were labeled: a glomerular type where one CGRP-labeled profile was indented by several unlabeled postsynaptic profiles and an axodendritic type with one or sometimes two postsynaptic elements. The most noteworthy cytologic feature of CGRP-labeled profiles was the presence of many relatively large vesicles with dense cores. These findings are steps towards understanding the synaptic interactions of CGRP in the monkey dorsal horn.

Animals↗
PubMed1987

Dorsal root ganglion neurons with central processes in both dorsal and ventral roots in rats.

Axonal transport of fluorescent dyes, Diamidino yellow dihydrochloride (DY) and Fast blue (FB), applied to the cut distal ends of dorsal and ventral roots, respectively, was studied in order to determine whether any dorsal root ganglion (DRG) neurons have processes in both dorsal and ventral roots. A total of 359 DRG neurons are double labeled in 14 ganglia (L6 and S1) from 6 different animals, thus suggesting a possibility of many DRG neurons having multiple central processes. The somata of the double-labeled DRG neurons are small to medium in size with a mean diameter of 29 microns. These data are consistent with findings that the majority of ventral root afferent fibers are unmyelinated or small myelinated axons.

Amidines↗
PubMed1987

Primary afferent and propriospinal fibers in the rat dorsal and dorsolateral funiculi.

The purpose of this study is to determine the numbers of primary afferent and propriospinal fibers in the dorsal and dorsolateral funiculi of the rat. The reason for concentrating on these areas is that they contain large numbers of unmyelinated axons. Our data are axonal numbers from the S2 segment of spinal cord in animals that had unilateral dorsal rhizotomies or spinal cord isolations. The major conclusions are 1) that 23% of the primary afferent fibers in the dorsal funiculus are unmyelinated; 2) that there are approximately 12,500 unmyelinated primary afferent fibers in the dorsolateral funiculus, which is more than the number of primary afferent fibers in the dorsal funiculus and tract of Lissauer combined, and 3) that approximately 25% of the axons in the dorsal funiculus and 44% of the axons in the dorsolateral funiculus are propriospinal. These data modify and extend previous ideas of the organization of spinal white matter.

Afferent Pathways↗
PubMed1986

Postnatal loss of axons in normal rat sciatic nerve.

Myelinated and unmyelinated axons were counted in sciatic nerves of newborn, 5-day-old, 14-day-old, and adult rats. Myelinated axons increase from essentially none at birth to approximately 8,000 in adulthood, but total axon numbers decrease steadily from 33,954 at birth to 22,872 in adulthood. Thus there is a significant postnatal loss of axons from rat sciatic nerve. This loss is, in our opinion, not associated with the death of the cells that give rise to these axons. This is thus an example of a regressive event that probably is of importance in normal neural development, namely the postnatal elimination of axons unaccompanied by death of the neurons that give rise to axons. These findings presumably imply a considerable amount of proximal peripheral axon branching, and the postnatal elimination of axons in the sciatic nerve presumably results from a reduction of this branching. Thus postnatal elimination of processes on, for example, somatic muscle cells may be at least partially the result of long axon elimination rather than local withdrawal of presynaptic processes, as is usually thought to be the case. In addition, an increased number of axons resulting from early postnatal manipulations may indicate cessation of axon loss rather than formation of new axons.

Age Factors↗
PubMed1986

Correlation of cell body size, axon size, and signal conduction velocity for individually labelled dorsal root ganglion cells in the cat.

Measurements of cell body and peripheral and central axon sizes were made for primary sensory neurons outlined by the intracellular injection of HRP. Conduction velocities were also measured on the outlined processes. The sensory neurons were then subdivided into A and C cells on the basis of the conduction velocity of the impulses carried by the processes of these cells. Central processes of both A and C cells are smaller than the peripheral processes, but the size differential is greater for the C cells. For A cells there is a linear relation between the size of the peripheral axon and the conduction velocity of the impulses carried by these axons, but the confidence limits are wide. For C cells there is a linear relation between the size of the central process and conduction velocity of the impulses carried by the processes, but for the peripheral processes two aberrant processes resulted in no correlation between process size and conduction velocity. For A cells, the size of the central and peripheral processes and the conduction velocity of the impulses carried by the peripheral processes are linearly correlated with cell body size. By contrast no such correlations can be demonstrated for C cells. This presumably implies an important difference in that the size of the cell body is correlated with axon size and impulse conduction velocity for A cells but not for C cells. A widely accepted generalization is that large sensory cells give rise to myelinated axons and small sensory cells to unmyelinated axons. In this study, myelinated and unmyelinated are defined on the basis of impulse conduction velocity. For those cells that are clearly large (greater than 50 microns in diameter), the conduction velocity of the impulses carried by their processes is always greater than 2.5 m/s, and for those cells that are clearly small (less than 35 microns in diameter), the conduction velocity is always less than 2.5 m/s. Thus for these cells the above generalization holds. For the intermediate-sized cells (35-50 microns), however, the size of the cell body bears no predictable relation to the conduction velocity of the impulses carried by those processes, and thus to whether the axons are myelinated or unmyelinated. Thus the above generalization does not hold for this intermediate group of cells, and since there are many cells in this size range, we feel that the generalization that large cells give rise to myelinated axons and small cells to unmyelinated axons is an oversimplification.

Action Potentials↗
PubMed1986

Numbers of rat dorsal root axons and ganglion cells during postnatal development.

The present study demonstrates that T4 and S2 rat dorsal root axons decrease significantly from birth to adulthood with almost all of the decrease occurring in the first two weeks of life. Dorsal root ganglion cell numbers do not change during this time period. This is thus an example of postnatal axon elimination not associated with death of the cells that give rise to the axons. Presumably this regressive process is important in the formation of the normal adult nervous system. In addition, these findings raise the possibility that certain types of neonatal denervation may increase adult axon numbers by stopping a regressive process, the loss of axons, rather than initiating a progressive process, the formation of new axons.

Animals↗
PubMed1985

Numbers of myelinated and unmyelinated axons in the dorsal, lateral, and ventral funiculi of the white matter of the S2 segment of cat spinal cord.

The present work determines the numbers of myelinated and unmyelinated axons in the dorsal, lateral, and ventral funiculi of the S2 segment of the cat spinal cord. The major finding is that unmyelinated axons are almost as numerous as myelinated axons in these pathways. The myelinated axons tend to be distributed uniformly, although there is a slight concentration of these fibers in the dorsal part of the lateral funiculus. By contrast, the unmyelinated fibers, although found in significant numbers in all parts of these funiculi, concentrate in the dorsal part of the lateral funiculus and in the dorsal funiculus. Of particular note are the unmyelinated fibers in the dorsal funiculus, because it is highly likely that some of these are sensory. The findings in this study will serve as a basis for experimental studies to determine the numbers, locations, and types of unmyelinated fibers in the white matter of the mammalian cord.

Animals↗
PubMed1985

Ureteral axon damage following subcutaneous administration of capsaicin in adult rats.

Systemic administration of capsaicin to adult rats results in the death of almost 90% of the axons in the ureter. Because of the massive axon loss we presume that sensory and possibly some sympathetic axons are killed. By contrast sensory axons in the dorsal root do not seem to be affected. We speculate that the axons in the ureter die because they are not protected by sleeves of perineurium. This hypothesis will be tested in subsequent work.

Animals↗
PubMed1985

The relation of nucleolus diameter to cell body diameter in mammalian dorsal root ganglion cells.

The present study correlates cell body and nucleolar sizes for dorsal root ganglion cells in the rat. To do this, we measured cell body areas and calculated their diameters and measured nucleolar diameters for 719 cells. These data indicate that there is a correlation in that increasing cell size is associated with increasing nucleolar size. However, there is considerable variability of cell body size for each nucleolar diameter and vice versa. Nevertheless, when nucleolar diameters are grouped, the function 1n D = 1.687 + 0.334 dr, where D is the diameter of the cell body and dr the rounded diameter of the nucleolus, produced an almost straight line. Thus this formula provides a good estimate of the relation of nucleolar and cell body sizes for dorsal root ganglion cells of the rat. In addition, estimates of the variances of cell body size at each nucleolar diameter are provided.

Animals↗
PubMed1985

Acquisition of a 250-word vocabulary through a tactile vocoder.

In a previous experiment [P. L. Scilley, "Evaluation of a vibrotactile auditory prosthetic device for the profoundly deaf," unpublished Masters thesis, Queen's University, Kingston, Canada (1980)] two normal subjects learned to identify 70 and 150 words, respectively, using the Queen's Tactile Vocoder. In the present experiment, the most advanced subject continued word learning until a tactile vocabulary of 250 words was acquired. At this point randomized tests were given to obtain an indication of final performance level. From these data conditional probabilities of correct response for each stimulus word and significant confusions were obtained, which provides insight into the advantages and present limitations of the tactile vocoder.

Communication Devices for People with Disabilities↗
PubMed1984

The postnatal development of the tract of Lissauer in the rat.

This study determined the numbers of axons in the tract of Lissauer of the S2 segment of rat spinal cord during postnatal development. One day after birth there were an average of 39 myelinated and 9,520 unmyelinated axons in this pathway. These numbers changed steadily to the 722 myelinated and 2,759 unmyelinated axons that characterize the adult. Thus there was a 20-fold increase in myelinated axons but a threefold decrease in total axons in this pathway from birth to adulthood. The axonal changes occurred so long after the changes in the number of cells that give rise to these axons that the axonal changes were almost certainly not due to the death of their parent neurons. We do not yet understand the mechanisms that control axonal numbers in this pathway, but in our opinion these mechanisms are as important as those that control neuronal numbers in considerations of the development of the nervous system.

Aging↗
PubMed1984

The ratio of dorsal root ganglion cells to dorsal root axons in sacral segments of the cat.

Processes of dorsal root ganglion cells are depicted as being unbranched until they reach the spinal cord or periphery. This is an important concept because, for example, branching of these processes might be a basis for referred pain. Recently several studies indicate that axons of rat dorsal root ganglion cells branch in or near the ganglion. The present study extends this work by showing that there are approximately 1.4 dorsal root axons for each dorsal root ganglion cell in sacral segments of the adult cat, and these data are interpreted as indicating that many dorsal root axons in this animal also branch. Thus this study provides further evidence to indicate that a revision of our ideas about the organization of primary sensory cells is desirable. In addition, this study provides data to indicate that the numbers of both dorsal root ganglion cells and dorsal root axons differ on the right as compared to the left side of the same segment.

Animals↗
PubMed1984

An estimate of the ratio of propriospinal to long tract neurons in the sacral spinal cord of the rat.

There are, to our knowledge, no estimates of the number of propriospinal and long tract neurons to mammalian spinal cord. The present study uses retrograde transport of horseradish peroxidase from axons transected by cutting the cervical spinal cord as a method for marking long tract neurons in the S2 segment of rat spinal cord. The findings are that long tract neurons make up approximately 1% of the total neurons of the spinal cord. Since motor neurons make up 1-2% of the total number of neurons in this area of cord, the remaining 97% are almost certainly propriospinal cells and thus propriospinal neurons are numerically predominant.

Animals↗
PubMed1984

A study of axonal diameters and areas in lumbosacral roots and nerves in the rat.

There has been debate as to whether there is a size difference between central and peripheral processes of dorsal root ganglion cells. In the present study, the mean areas of myelinated and unmyelinated fibers are measured as 27.8 micron2 and 0.55 micron2, respectively, in peripheral nerves and 13.72 micron2 and 0.14 micron2 in dorsal roots. Thus myelinated central processes of dorsal root ganglion cells have mean areas 50% less than the mean areas of the myelinated sensory axons in the same peripheral nerves, and the mean diameters of the central myelinated axons are 30% less than the peripheral myelinated axons. The mean areas of the unmyelinated sensory axons in the dorsal roots are 25% of the mean areas of the unmyelinated sensory unmyelinated axons are 50% of the mean diameters of the unmyelinated sensory axons in the same peripheral nerves. These data indicate that both myelinated and unmyelinated central processes of dorsal root ganglion cells are smaller than the peripheral processes of these same cells for lumbosacral segments in the rat. It is shown that axonal tapering is not responsible for these striking differences. Finally, documentation of differences in myelinated fiber histograms from dorsal roots of different segments in the rat is provided.

Animals↗
PubMed1984

An empirical method for converting nucleolar counts to neuronal numbers.

Our goal is to estimate neuronal numbers from counts of nucleolar profiles. The primary difficulty is that a simple way to convert the counts to the numbers, especially when multiple nucleoli are present in a nucleus, is not available. In this paper, we propose a solution. The formula is N = n X [N(c.f.)/n(c.f.)] where N = the true number of neurons, n = the number of nucleolar profiles in these neurons, N(c.f.) = the number of neurons used to estimate the correction factor and n(c.f.) = the number of nucleolar profiles found in the neurons that make up N(c.f.). The constraints are that the neurons identified for N(c.f.) be representative of the entire population, N; that the nucleolar profiles be counted by the same criteria when n(c.f.) is determined as when n is determined, and that when the correction factor [N(c.f.)/n(c.f.)] is calculated, the nucleolar profiles in each neuron be counted only once. The advantages are simplicity, and generality; the latter resulting from the empirical nature of the correction factor which can calibrate for multiple nucleoli, split nucleoli, invisible fragments, nucleolar size changes, section thickness differences and any other factors that cause n to deviate from N.

Animals↗
PubMed1984

The determination of an empirical correction factor to deal with the problem of nucleolar splitting in neuronal counts.

Nucleolar counts are the method of choice for determining neuronal numbers. The main problem is the determination of an accurate correction factor for split nucleoli. The difficulties are that small nucleolar fragments are often unrecognizable and that nucleoli may be pushed or rolled rather than cleanly cut by the knife. A widely used method uses an estimate to account for the difficulties, and almost all methods depend on measurements of such things as section thickness and nucleolar diameters. We differ from previous procedures by identifying neurons first and then determining whether the nucleolus in each identified neuron is split or whole. If N is the true number of neurons, n the number of nucleoli counted to estimate N, T the number of nucleoli counted for the correction factor and S the number of nucleoli in T that are split, then N = [(T-S/2)/T] X n. The advantages are that the observations are easily done and that there are no estimates, only a determination of the numbers of whole and split nucleoli for a sample population of neurons.

Animals↗