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.

Propriospinal fibers in the rat

Segments of rat spinal cord were isolated by transecting in two places and sectioning all dorsal roots between the transections. Following this procedure, the areas of the gray and white matter are decreased by approximately 50% compared to normal. We feel, for reasons elaborated in the discussion, that the white matter of the isolated segments contains almost exclusively propriospinal axons. If this is accepted, then the axonal counts in this paper provide estimates of the numbers of propriospinal axons in rat spinal cord. In the isolated segments, the lateral funiculi contain 21,000 myelinated and 31,000 unmyelinated axons and the ventral funiculi 10,500 myelinated and 1,500 unmyelinated axons. The number of these fibers is approximately 33% of the number in unoperated spinal cords. Thus approximately one-third of the axons in rat sacral lateral and ventral funiculi are propriospinal, a lower figure than would have been predicted from classical work. The ratio of myelinated to unmyelinated fibers is higher for propriospinal fibers than for the other axons in these funiculi. Thus the propriospinal axons, as a group, are slightly larger than the other axons in these funiculi. This is against currently accepted thinking which generally regards the propriospinal fibers as the finest in the white matter of the cord. Finally, the quantification of propriospinal systems in these funiculi allows more precision in our thinking about the organization of the spinal cord.

Numbers of axons in lateral and ventral funiculi of rat sacral spinal cord

The present study determines the numbers of myelinated and unmyelinated axons in the ventral and lateral funiculi of rat sacral spinal cord. On average, there are 55,000 myelinated and 110,000 unmyelinated axons in the lateral funiculus and 26,000 myelinated and 9,000 unmyelinated axons in the ventral funiculus at these levels. These figures combined with data from earlier studies of the posterior funiculus and the tract of Lissauer give approximate figures of 88,500 myelinated and 131,500 unmyelinated axons for the entire white matter of one side of the rat sacral spinal cord. Thus unmyelinated axons predominate in the white matter of the rat sacral spinal cord. The majority of axons, particularly the unmyelinated axons, are located in the lateral funiculus. The axons are concentrated in the dorsolateral part of the lateral funiculus, and so the dorsal part of the lateral funiculus, often referred to as the dorsolateral funiculus, contains more than half the fibers in the white matter of the spinal cord. A small nick in the dorsal and lateral part of the lateral funiculus, which is often done for various experimental reasons, could thus remove 40% of the axons in the white matter of rat sacral spinal cord. The data reported in the present paper will serve as a basis for future studies on the white matter of the isolated spinal cord.

Quantitation of propriospinal fibers in the tract of Lissauer of the rat

The present study uses a spinal cord isolation procedure to remove extrinsic axons but leave intrinsic axons intact. The isolation is done by sectioning the spinal cord in two places and then cutting all dorsal roots between the two sections. The axons that survive the isolation procedure are thought to be propriospinal axons. Following isolation, approximately one-third of the axons in sacral tracts of Lissauer in the rat survive. Thus approximately one-third of the axons in sacral tracts of Lissauer in the rat are propriospinal. Proportionately more myelinated than unmyelinated axons are lost. There are approximately equal numbers of surviving axons in the medial as opposed to the lateral part of the tract. This implies that there is, as yet, no morphological basis for dividing the tract into medial and lateral halves. The fact that the number of propriospinal axons in the tract of Lissauer has been quantitated offers more precision in our thinking about the organization of the dorsal horn.

Primary afferent axons in the tract of Lissauer in the monkey

The main thrust of the present study was to determine the numbers of primary afferent fibers in the tract of Lissauer in the monkey. The findings are that approximately 40% of the axons in the tract of Lissauer are primary afferent axons from a single segment, and approximately another 40% are primary afferents from segments cranial and caudal to the segment under consideration. Presumably, the remaining 20% are propriospinal axons. There is relatively little difference in the proportions of primary afferents in medial as opposed to lateral parts of the tract, and in this respect the monkey differs somewhat from the rat and cat. Thus in the monkey the tract of Lissauer should probably be regarded as a primary afferent pathway with the propriospinal forming a distinct but relatively minor component of the tract.

Ultrastructure of HRP-identified sympathetic preganglionic neurons in cats

Electron microscopic studies were conducted on cat sympathetic preganglionic neurons which were labeled using retrograde transport of horseradish peroxidase from the injection site in the stellate ganglion to somas in the thoracic spinal cord. Based on size, the identified somas were divided into two groups: large multipolar somas (25-35 micron), usually having three dendrites with a mean diameter of 8 micron, and small fusiform somas (12-24 micron), with two primary dendrites with a mean diameter of about 4 micron. The ultrastructures of the perikarya and dendrites were similar to other spinal neurons. Three types of terminals were identified: 1) round asymmetric terminals, 2) pleomorphic symmetric terminals, and 3) round symmetric terminals. On the soma, pleomorphic terminals were more numerous than round asymmetric terminals. On the dendrites, the density of round asymmetric terminals was similar to pleomorphic symmetric terminals. Round symmetric terminals represent only a small percent on either the soma or dendrites. Because of the greater total density of terminals on the dendrites than soma, pleomorphic symmetric and round asymmetric terminals are primarily located on the dendrites. Very few dense-core vesicles characteristic of monomamine terminals were observed, perhaps due to the fixative used.

The anatomical localization of descending pressor pathways in the cat spinal cord

Functional evidence suggests the location of descending pressor pathways in the bilateral dorsolateral funiculus (DLF). To investigate the anatomical course of these pathways, orthograde degeneration studies were conducted following unilateral lesions of the DLF at the C6-C7 spinal level. Degenerating fiber tracts were localized exclusively in the ipsilateral DLF. Degeneration was also demonstrated in the central portion of the intermediate spinal gray matter, but little or no degeneration in the intermediolateral cell column. This evidence suggests that these descending pathways do not terminate on sympathetic preganglionic cell bodies or their proximal dendrites, but perhaps upon their more distal dendrites or interneurons.

Primary afferent axons in the tract of Lissauer in the cat

The present study is concerned with the numbers of primary afferent axons in the tract of Lissauer in the cat. The data show that approximately 27% of the axons in mid-thoracic and lumbosacral tracts are primary afferent fibers from the segment in question and another 20% of the axons are primary afferent fibers that come from nearby segments. In addition the data show that approximately 80% of the axons in the tract are unmyelinated and that there is a slightly higher proportion of unmyelinated as opposed to myelinated primary afferents. There is also a higher proportion of primary afferents in the medial as opposed to lateral parts of the tract, but there are significant numbers of primary afferents in lateral parts of the tract. Thus it seems clear that the tract contains more primary afferent fibers than was previously believed and if these data are confirmed, the conclusions will have a bearing on considerations of the primary afferent input into the dorsal horn.

Sympathetic neurons in the cat spinal cord projecting to the stellate ganglion

Horseradish peroxidase (HRP) was injected into the stellate ganglia of anesthetized cats. After a 2-day survival time the spinal cord was processed for the HRP reaction to study the distribution of the preganglionic neurons which project to the stellate ganglia. HRP-labeled neurons in the cord were located exclusively on the side ipsilateral to the injected stellate ganglia and were concentrated in four distinct areas: (1) intermediolateral cell column (78.2%), (2) lateral funiculus (18.5%), (3) intercalated area and (4) central autonomic area (3.3%) for the latter 2 areas). Their distribution pattern in the very rostral pole of the thoracic sympathetic preganglionic cell column was different from the typical thoracic pattern in that a greater proportion of the cells were located in the lateral funiculus, and a few labeled cells were observed in the ventral horn. Longitudinally, a wide range (C8-T8) of spinal cord levels projected to the stellate ganglia, with a peak at the T2 level. These observations infer that a large population of axonal processes of sympathetic preganglionic neurons traveled several segments of the spinal cord through an intraspinal pathway before exiting a particular ventral root.

Primary afferent fibers in the tract of Lissauer in the rat

More than two-thirds of the axons in the tract of Lissauer at mid-thoracic and lumbosacral levels of the rat spinal cord are primary afferent fibers. The proportions of primary afferents in the tract are approximately the same at the two spinal levels. A slightly higher percentage of the unmyelinated, as opposed to the myelinated, fibers are primary afferents. There is a somewhat greater percentage of primary afferent axons in medial parts of the mid-thoracic levels, but all areas of the tract that were examined contain a majority of primary afferent fibers. The primary afferent axons appear to travel less than a segment in the tract at mid-thoracic levels but for several segments in the tract at lumbo-sacral levels. These data indicate that the tract of Lissauer is predominately a primary afferent fiber system in these segments of the rat.

Regulation of internodal lenght by peroxidase enzymes in grain sorghum

A relationship between height genes (dw locus) and perioxidase was demonstrated by extracting and determining peroxidase specific activity in internode tissue from different height isogenic lines of sorghum Sorghum bicolor (L.) Moench]. Tall plants (2 dwarf) had less peroxidase per gram tissue than their short counterparts (3 dwarf); their F1 offspring internodes were closer but had more peroxidase than the tall parent. Peroxidase in the F2 offspring was inversely related to their height and followed a simply-inherited pattern similar to that for height.Among different tissues analyzed, peroxidase concentration in roots was higher than in leaves and internodes, whole internode higher than in pith, and seed embryo higher than in endosperm. Peroxidase activity of nonviable seeds was negligible.Isoelectric focusing provided a more detailed peroxidase zymogram than did gel electrophoresis. Differences in peroxidase bands among tall and short parental plants, F1 and F2 segregating groups all appear to be reflected by intensity differences rather than by position or number of bands.Activities of nitrate reductase and acid phosphatase did not correlate with height. That finding provides a control and suggests that peroxidase activity is not associated with height by chance but may have a functional relationship.

Acupuncture analgesia in dentistry: an analysis of studies from the People's Republic of China

Studies conducted on the use of acupuncture analgesia for dental procedures in the People's Republic of China have not provided sufficient evidence to indicate that acupuncture analgesia can replace conventional drugs as the preferred anesthetic. However, studies currently in progress in China and in the United States may be successful in finding ways to reduce the failure rate and in determining the operative benefits of acupuncture.