Fine structure of the retino-optic nerve junction in dogs

In most mammals, the optic nerve fibers are myelinated in its extraocular part (EON) but not in its intraocular part (ION) and also in the retina. Transitional zone from the myelinated to unmyelinated optic nerve usually lies in the central part to the lamina cribrosa. It has been known that dogs contain exceptionally myelinated fibers in ION by light microscopy. The aim of this study was to investigate electron microscopically the retino-optic nerve junction in dogs and re-evaluate the barrier to migration of oligodendroblasts into ION. Fourteen adult dogs were used. EON was largely myelinated. In ION the percentage of myelinated fibers decreased gradually toward the retina. A narrow area of ION adjoining the retina was completely unmyelinated. In most mammalian optic nerves, oligodendrocytes are not found in ION. It has been suggested that oligodendroblasts are prevented from migrating from EON into ION; that is to say, there is a barrier to migration of oligodendroblasts. The lamina cribrosa, a dense meshwork of fibrous astrocytic processes, and a defect in the blood optic nerve barrier have been proposed as a candidate for the barrier to migration. Our results suggest, however, that these factors, at least in dogs, would be not involved in the formation of a barrier to migration of oligodendroblasts.     

Congenital hypomyelinating polyneuropathy in two golden retriever littermates

Serial peripheral nerve biopsies from two golden retriever littermates with chronic neurologic disease were taken for morphologic and morphometric evaluation. Teased nerve preparations were difficult to interpret due to the lightness of myelin staining. Light and electron microscopic findings were characterized by the following: reduced number of myelinated axons, presence of myelinated sheaths inappropriately thin for the caliber of the fiber, poor myelin compaction, increased numbers of Schwann cell nuclei, increased concentration of neurofilaments in myelinated axons, many Schwann cells with voluminous cytoplasm, and increased perineurial collagen. Onion bulb formation was not seen. In contrast to control data, a poor correlation was seen between numbers of myelin lamellae (ML) and axonal circumference (AC). The frequency distribution of ML ranged from 5 to 55 lamellae in affected animals (mean, 28 lamellae) compared to 20 to 140 lamellae in controls (mean, 66 lamellae). The ML/AC ratio was significantly reduced (P less than 0.001) in nerves of affected dogs. Morphometric results indicated that fibers of all calibers were hypomyelinated.     

Spectral domain optical coherence tomography (SD-OCT) assessment of the healthy female canine retina and optic nerve

Objective To provide normative data for canine whole retinal thickness (WRT), nerve fiber layer thickness (NFL), photoreceptor layer thickness (PR), and outer nuclear layer thickness (ONL) using spectral domain optical coherence tomography. Animal studied: Twelve healthy adult intact female beagles. Procedure Horizontal volume scans through the area dorso‐temporal from the optic nerve (superior retina), and the area ventro‐temporal from the optic nerve (inferior retina) were used to evaluate the thickness of retinal NFL, PR, ONL, and WRT. Peripapillary circular scans were used to evaluate NFL thickness. Statistical analyses were performed to compare the thickness of the individual layers between the superior and inferior retina (paired t‐test). One‐way analysis of variance (ANOVA) was used to compare the thickness of peripapillary NFL between the superior, inferior, temporal and nasal quadrants of the circle scan. Results The WRT, PR, and NFL thickness were greater in the superior than in the inferior retina (198.7 ± 9.6 μm vs. 164.4 ± 6.4 μm, P < 0.0001; 95.5 ± 6.5 μm vs. 78.8 ± 7.4 μm, P < 0.0001; and 26.4 ± 1.6 μm vs. 25.0 ± 1.9 μm, P = 0.0236, respectively). No statistical difference was found between the ONL thickness of the superior and inferior retina (50.1 ± 6.4 μm vs. 44.3 ± 3.6, P = 0.0578). Peripapillary NFL thickness showed a similar tendency as the linear scans, with the superior quadrant having the greatest thickness (91.26 ± 7.0 μm) and the inferior quadrant being the thinnest (76.42 ± 9.2 μm) (P < 0.001). Conclusions Results of our in vivo studies showed significant differences between thickness values for the superior (tapetal) and inferior (nontapetal) retinal regions.     

Morphologic and morphometric study of the facial nerve in clinically normal adult dogs.

A morphologic and morphometric study was carried out on the facial nerve: to determine normal histologic data in myelinated fibers of clinically normal young adult dogs; to establish reference values for mean fiber diameter, and to delineate the relative diameter frequency distribution curve. Few degenerative changes were observed in single teased-nerve fibers and semithin cross-sectional nerve preparations. Statistical difference was not observed between left and right facial nerves. The distribution of fiber diameters in the facial nerve was unimodal. Mean (+/- SD) fiber diameter of the facial nerve was 3.92 +/- 1.18 microns. Approximately 89% of fibers in the facial nerve had diameter between 3 and 6 microns. Fiber diameter ranged from 2 to 12 microns; however, less than 1% of fibers had diameter greater than 8 microns.     

Sensory nerve conduction and nociception in the equine lower forelimb during perineural bupivacaine infusion along the palmar nerves

The purpose of this investigation was to study lateral palmar nerve (LPN) and medial palmar nerve (MPN) morphology and determine nociception and sensory nerve conduction velocity (SNCV) following placement of continuous peripheral nerve block (CPNB) catheters along LPN and MPN with subsequent bupivacaine (BUP) infusion. Myelinated nerve fiber distribution in LPN and MPN was examined after harvesting nerve specimens in 3 anesthetized horses and processing them for morphometric analysis. In 5 sedated horses, CPNB catheters were placed along each PN in both forelimbs. Horses then received in one forelimb 3 mL 0.125% BUP containing epinephrine 1:200 000 and 0.04% NaHCO(3) per catheter site followed by 2 mL/h infusion over a 6-day period, while in the other forelimb equal amounts of saline (SAL) solution were administered. The hoof withdrawal response (HWR) threshold during pressure loading of the area above the dorsal coronary band was determined daily in both forelimbs. On day 6 SNCV was measured under general anesthesia of horses in each limb's LPN and MPN to detect nerve injury, followed by CPNB catheter removal. The SNCV was also recorded in 2 anesthetized non-instrumented horses (sham controls). In both LPN and MPN myelinated fiber distributions were bimodal. The fraction of large fibers (>7 μm) was greater in the MPN than LPN (P < 0.05). Presence of CPNB catheters and SAL administration did neither affect measured HWR thresholds nor SNCVs, whereas BUP infusion suppressed HWRs. In conclusion, CPNB with 0.125% BUP provides pronounced analgesia by inhibiting sensory nerve conduction in the distal equine forelimb.     

Early Embryonic Development of the Camel Lumbar Spinal Cord Segment

The lumbar spinal cord segment of the camel embryo at CVRL 2.4 to 28 cm was examined. Major changes are occurring in the organization of the lumbar spinal cord segments during this early developmental period. At the CVRL 2.4, 2.7 and 3.6 cm the three primary layers, ependymal cells layer, mantle cells layer, marginal cells layer in the developing lumber spinal cord segment were demonstrated. The mantle layer is the first to show striking differentiation, while the marginal layer is represented by thin outer rim. Proliferation and differentiation of the neuroepithelial cells in the developing spinal cord produce the thick lateral walls, thin roof and floor plates. The spinal ganglion and dorsal root of the spinal nerve are differentiated. At 2.7 cm CVRL differential thickening of the lateral walls produces a shallow longitudinal groove called sulcus limitans , which separates the dorsal part (alar plate) from ventral part (basal plate). The ventral root of the spinal nerve, the spinal cord and ganglion are embedded in loose mesenchyme, which tends to differentiate into spinal meninges. At 3.6 cm CVRL the basal plate, which is the future ventral gray horn, seem to be quite voluminous and the dorsal and ventral roots unite to form the beginning of the spinal nerve. At 5.5 cm CVRL the alar plates enlarge forming the dorsal septum. At 8.4 cm to 10.5 cm CVRL the basal plates enlarge, and bulge ventrally on each side of the midline producing the future ventral medium fissure, and the white and gray matters can be recognized. At 28 cm CVRL the lumen of the spinal cord is differentiated into the central canal bounded dorsally and ventrally by dorsal and ventral gray commissures, and therefore the gray matter takes the appearance of a butterfly.The lumber spinal nerve and their roots are well distinguished.     

An ultrastructural study of spinal nerve roots and dorsal root ganglia in aging rats with spontaneous radiculoneuropathy

The spinal nerve roots and dorsal ganglia of 104- to 135-week-old rats with spontaneous radiculoneuropathy were examined by light and electron microscopy. Demyelination was common in myelinated fibers of various diameters of both ventral and dorsal roots. The most striking alteration was wide distention of myelin sheaths, which extended throughout the entire internode. The spaces formed between separated lamellae frequently were invaded by macrophages. Subsequent vesicular degeneration of myelin seemed to be mediated by invading macrophages. These processes caused complete myelin destruction, but most axons showed no degenerative changes except for obvious reduction in diameter. Occasionally, there were clumping and partial degradation of neurofilaments and ruptured axolemma in the severely demyelinated axons. A few fibers also were undergoing wallerian-type degeneration, perhaps secondary to the severe demyelinative changes. Remyelinating fibers in various phases of repair were coexistent with markedly demyelinated ones. Demyelinative changes described above also developed within some of these remyelinated internodes. There were no remarkable changes in neurons of the dorsal root ganglia, though accumulation of lipofuscin was common. Our findings suggest that the changes in the nerve roots are essentially a primary segmental demyelination in aging rats with radiculoneuropathy.     

Anatomical Studies of the Accessory Nerve in the Indian Buffalo (Bubalus bubalis)*

This is a study of the origin, formation, course, distribution, the fascicular number, their area and arrangement, total fibre count, density and diameterspectra of the accessory nerve in the Indian buffalo. The radices spinales are located from the level of C₁ to midlevel of C₆cord segments. The radices craniales arise in series from the medulla oblongata caudal to those of the vagus nerve. The accessory nerve contains 7931 myelinated fibres arranged in 31 fascicles. Of these 41 % have an external diameter of 10–12 μm. The greatest density of fibres viz. 1781/mm² is obtained in the anastomosing ramus from the second cervical spinal nerve. The least value (377/mm²) is found in its ventral ramus. However, the dorsal ramus appears to have a larger cross-sectional area.     

猪延髓中微血管及静脉注射呕吐毒素后阳性细胞的分布

应用组织学方法对猪延髓微血管及静脉注射呕吐毒素(DON)后在猪延髓的分布进行了初步观察.结果显示,进入延髓的动脉有较厚的弹性纤维膜,平滑肌层厚度为弹性膜的一半,向背侧延伸的分支,管壁薄,仅见内皮细胞和周细胞.在网状结构与纤维束间见有微血管,管壁未见弹性纤维.电镜免疫组化染色结果显示,延髓最后区毛细血管内皮细胞间有的部位有紧密连接,而有些部位缺失,内皮细胞与胶质细胞之间有较宽的空隙,有些部位缺少周细胞.D()N免疫阳性反应为棕褐色或棕黄色颗粒,主要分布于延髓微动脉管壁及最后区毛细血管周边神经元细胞质中,细胞核内量少或无反应.结果表明,猪延髓内不同部位的微血管的分布及结构均有差异,为猪的中枢神经系统脑血管的组织学增加了内容.     

Morphologic and morphometric studies of the vagus and recurrent laryngeal nerves in clinically normal adult dogs

Morphologic and morphometric studies were performed on the vagus nerve and its major branch, the recurrent laryngeal nerve (RLN): (1) to determine normal histologic data in myelinated fibers of clinically normal young adult dogs, (2) to establish reference values for mean fiber diameter in the vagus nerve and in the proximal and distal portions of the RLN, and (3) to delineate relative frequency distribution curves for each nerve. Few degenerative changes were observed in single teased-nerve fiber preparations. There was no statistical difference between left and right sides of the vagus nerve or between the proximal and distal portions of the RLN (right and left sides). In contrast to the unimodal distribution of fibers in the vagus nerve and the proximal portion of the RLN, the distribution of fibers in the distal portion of the RLN was bimodal. Mean (+/- SD) fiber diameters of the vagus nerve and in the proximal portion of the RLN (3.02 +/- 1.44 microns and 3.63 +/- 1.49 microns, respectively) were not significantly different, despite a shift to large-diameter fibers in the latter. However, mean fiber diameters of distal and proximal portions of the RLN (5.56 +/- 1.88 microns and 3.63 +/- 1.49 microns, respectively) were significantly (P less than 0.001) different. Approximately 86% of fibers in the vagus nerve and 76% of fibers in the proximal portion of the RLN, had a diameter less than 5 microns, and about 70% of fibers in the distal portion of the RLN had a diameter greater than 5 microns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional Specialisation of the Ganglion Cell Density in the Retina of the Native Duck (Anas platyrhynchos) of Bangladesh

In this study, retinal whole‐mount specimens were prepared and stained with 0.1% cresyl violet for the ganglion cell study in the native duck (Anas platyrhynchos). The total number, distribution and size of these cells were determined in different retinal regions. The mean total number of ganglion cells was 1 598 501. The retinal area centralis had the highest ganglion cell density with 11 200 cells/mm². Number of ganglion cell bodies was the highest in temporal area, followed by dorsal, nasal and ventral areas. Ganglion cell size ranged from 5.25 to 80 μm². In the temporal and nasal region, most of the cells were ranged from 15 to 25 μm², and in the dorsal and ventral region, most of the cells were ranged from 12 to 25 μm². There was a marked trend for the retinal ganglion cell size to increase as the population density decrease towards the periphery. A population of small ganglion cells persisted into the central area just above the optic disc and the largest soma area was in the ventral zone of the retina. Thus, the specialisation of ganglion cell densities and their sizes support the notion that the conduction of visual information towards the brain from all regions of the retina is not uniform, and the central area is the fine quality area for vision in native duck.     

Peripheral hypomyelinization in two golden retriever littermates

Peripheral hypomyelinization was found in 2 Golden Retriever littermates that had pelvic limb ataxia, depressed postural reactions, and depressed segmental reflexes. Diagnostic findings included infrequent denervation potentials, reduced or absent evoked potentials, and markedly diminished motor nerve conduction velocities. Light and electron microscopy of peripheral nerves revealed fewer than normal myelinated axons, myelinated sheaths inappropriately thin for the caliber of the fiber, poor myelin compaction, greater than normal numbers of Schwann cell nuclei, many Schwann cells with voluminous cytoplasm, and greater than normal amount of perineural collagen. Findings were compatible with a peripheral hypomyelinization process; a defect in Schwann cell function was suspected.     

Number and density of retinal photoreceptor cells with emphasis on oil droplet distribution in the Mallard Duck (Anas platyrhynchos var. domesticus)

This study was intended to determine the number and regional distribution of photoreceptor cells and different colored oil droplets in the retina of the Mallard Duck (Anas platyrhynchos var. domesticus). To estimate the number and density of photoreceptor cells, adult ducks were killed and both eyes were enucleated under deep anesthesia to prepare Nissl‐stained retinal whole‐mount samples. Different colored oil droplets were counted from color microphotographs of the freshly prepared retina. The mean number of retinal photoreceptors was approximately 6 308 828 ± 521 927, with a peak density of 33 573/mm² in the central retina. The density was similar in the nasal, temporal, ventral and dorsal areas of the retina. Five types of oil droplets were identified on the basis of color: red, orange, greenish‐yellow, yellow and clear. The mean density of oil droplets was highest in the central retina (17 639/mm²) and gradually declined towards the nasal, temporal, ventral and dorsal areas. The size of oil droplets gradually increased with retinal eccentricity and varied even within an area. The greenish‐yellow oil droplets were most abundant across the retina. Taken together, these results demonstrate the differential retinal distribution of photoreceptor cells and oil droplets in duck retina. We conclude that the area of high photoreceptor cell density, which is matched by high neuron densities of the ganglion cell layer, corresponds to the site of acute vision in duck retina.     

Topography of ganglion cells in the retina of the duck (Anas platyrhynchos var. domesticus)

The purpose of this study was to define ganglion cell density, size and topography in the retina of the mallard duck. After killing adult mallard ducks (Anas platyrhynchos var. domesticus), their eyes were removed using pentobarbital (30 mg/kg). The retinas were isolated, whole mount specimens were prepared by staining with 0.1% cresyl violet and then fixing the tissues for study. The retinal ganglion cells were counted, mapped and measured. The mean total number of ganglion cells was estimated at approximately 1.7 × 10⁶ and the retinal area centralis had the highest ganglion cell density with 15 820 cells/mm². The number of ganglion cell bodies was highest in the temporal area, followed by the nasal, dorsal and ventral areas. Ganglion cell size ranged from 56 to 406 μm². A population of small ganglion cells persisted into the central area just above the optic disc and the largest soma area was in the ventral zone of the retina. This localization of ganglion cells suggests that the quality of vision is not equal in all the areas of the duck retina and the central part may have the highest vision quality as a function of the retinal ganglion cells.     

Retinal vascular patterns in domestic animals

In this paper a morphological study of the retinal vascular patterns in various species of domestic animals is reported. A classification of these patterns into four well-defined groups is described. In the domestic ruminants, pigs and carnivores the retina contains a compact plexus of blood vessels located in the major part of the light-sensitive portion of the retina (euangiotic or holangiotic pattern). In other domestic animals blood vessels are present only in a smaller part of the retina. In the rabbit, vessels are confined to a broad horizontal band coincident with the area of dispersion of the myelinated nerve fibres. The larger of these vessels are readily visible macroscopically (merangiotic pattern). In the horse and the guinea pig the retinal blood vessels are minute and restricted to the direct neighbourhood of the optic disc (paurangiotic pattern). The avian retina is completely avascular (anangiotic pattern), but a densely vascularised pecten oculi is attached to the linear optic nerve head and protrudes far into the inferior part of the vitreous body.     

羊垂体前叶降钙素基因相关肽(CGRP)与P物质(SP)免疫反应神经纤维

应用免疫组化ＡＢＣ法发现羊垂体前叶有降钙素基因相关肽免疫反应神经纤维存在,这些纤维呈串球状分布于结节部及远侧部前２／３区域。纤维形态多样,细长者穿行于腺细胞之间;短小弯曲者围绕于腺细胞周围;反复分支折叠盘曲缠绕成团簇状者将腺细胞成堆的网络其中。神经纤维及串珠与腺细胞关系密切,提示有可能对腺细胞分泌起直接支配作用。在纤维分布区域可见散在的免疫反应细胞,形态不规则,大部分与神经纤维无接触关系,但有少数可位于纤维的网络之中。Ｐ物质免疫反应神经纤维及细胞在羊垂体前叶分布稀疏,且多位于结节部,远侧部很少。     

IMAGING DIAGNOSIS–SCLEROSING ENCAPSULATING PERITONITIS IN A DOG

An approximately 5‐month‐old American Staffordshire terrier was presented with a history of recurrent peritoneal effusion. Abdominal radiographs and ultrasound showed a loculated effusion in the ventral abdomen with dorsal displacement of abdominal organs, hepatomegaly and rounding of liver and splenic margins. Computed tomography demonstrated centrally located gastrointestinal segments surrounded by a thin soft tissue band and a thickened peritoneal lining. At necropsy a fibrous membrane continuous with liver and splenic capsules encapsulated all abdominal organs. Microscopically the abdominal wall and fibrous capsule consisted of an irregular thick layer of hypocellular connective tissue. The final diagnosis was sclerosing encapsulating peritonitis.     

Sensory and motor neuropathy in a Border Collie

A 5-month-old female Border Collie was evaluated because of progressive hind limb ataxia. The predominant clinical findings suggested a sensory neuropathy. Sensory nerve conduction velocity was absent in the tibial, common peroneal, and radial nerves and was decreased in the ulnar nerve; motor nerve conduction velocity was decreased in the tibial, common peroneal, and ulnar nerves. Histologic examination of nerve biopsy specimens revealed considerable nerve fiber depletion; some tissue sections had myelin ovoids, foamy macrophages, and axonal degeneration in remaining fibers. Marked depletion of most myelinated fibers within the peroneal nerve (a mixed sensory and motor nerve) supported the electrodiagnostic findings indicative of sensorimotor neuropathy. Progressive deterioration in motor function occurred over the following 19 months until the dog was euthanatized. A hereditary link was not established, but a littermate was similarly affected. The hereditary characteristic of this disease requires further investigation.     

Anatomical Evidence of Electroreception in the Coelacanth (Latimeria chalumnae)

Serial sections of an immature female Latimeria brain were studied to describe the octavolateral area. Sections were stained with cresyl violet (for cell bodies) and with Klüver-Barrera method for myelinated fibers. The presence of a well-developed dorsal nucleus of the octavolateral area suggests that Latimeria probably possesses the electroceptive capacity with ampullary organs.