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Axonal Neuropathy
Published in Maher Kurdi, Neuromuscular Pathology Made Easy, 2021
One of the best methods to examine AD is through epoxy-embedded toluidine sections. The histological features are dependent on the disease stage. Acute axonal degeneration is commonly characterized by myelin ovoids and axonal swelling. This process immediately occurs after the nerve injury. The hallmark feature of chronic type degeneration is partial or complete loss of myelin sheaths that surround the axons (Figure 26.2a). It is sometimes difficult to appreciate axonal degeneration in histological sections; however, ultrastructural examination is considered a golden confirmatory technique. In early stages, the myelin disintegrates and shrinks forming axoplasmic pallor or osmophilic materials. Later, the axoplasm turns dark and may contain lipid droplets. These are typically called myelin figures or debris. They are commonly accompanied with macrophages containing lipids, collagen pockets, and flattened Schwann cells (Figure 26.3a–c). Aggregated organelles, Schwann cell lipid droplets, absent axons, myeloid bodies, and tubulovesicular profiles in axoplasm are rarely seen. Mitochondrial abnormalities are other rare findings and can be identified in vitamin E deficiency and some toxic neuropathies.
Comparative Anatomy, Physiology, and Biochemistry of Mammalian Skin
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Meissner’s corpuscles are located in the papillary layer of the dermis of glabrous skin. These corpuscles were first described in 1852 and are also known as Wagner-Meissner corpuscles, Dogiel’s end-bulb, or as Ruffini’s end-bulbs in older literature.117 Each corpuscle is oval and approximately 100 μm long and 50 μm in diameter. Large myelinated nerve fibers (two to nine) enter the corpuscle at its base and along the sides, lose their myelin sheath, and then branch. The axoplasm is loaded with mitochondria and vesicles. These nonmyelinated axons spiral and form a bulbous ending among the flattened Schwann cells and collagen fibers. Surrounding this arrangement of expanded nerve endings and flattened cells is a connective tissue capsule which is continuous with the endoneurial sheaths of the afferent nerve fibers. The capsule is bound by elastic fibrils to the basal projections of the epidermis. The Meissner’s corpuscle is a mechanoreceptor which responds to touch116,117,137,219,249
Vagal Receptor Transport
Published in Sue Ritter, Robert C. Ritter, Charles D. Barnes, Neuroanatomy and Physiology of Abdominal Vagal Afferents, 2020
A variety of neurotransmitters or neuromodulators are released from vagal fibers and the vagus has been demonstrated to contain neurotransmitter and peptide receptors. Since there is no synthesis of proteins in nerve terminals, some neurotransmitter molecules or receptor proteins must be synthesized at the cell body and transported to the locations where they will exert some physiological function. There are axoplasmic transport mechanisms responsible for the delivery of large and small molecules to and from nerve endings. This chapter will focus on the transport of receptors within the vagus, identify the mechanisms by which this transport is carried out, and review the available information on which receptor populations are contained and transported in both the efferent and afferent limbs of the vagus nerve.
Histopathological effects of topical coenzyme q 10 + Vit E TPGS in experimental ischemic optic neuropathy
Published in Ultrastructural Pathology, 2022
Oğuzhan Oruz, Kemal Yar, Dilek Şaker, Arbil Açıkalın, Yusuf Kenan Dağlıoğlu, Sait Polat
In the electron microscopic examination of optic nerve sections of the EG in which ischemia was created and no treatment was applied, it was observed that the lamellar structure of the myelin sheath was disrupted and the myelin sheath lamellae were separated from each other in some areas. It was found that the myelin sheath was invaginated into the axon in most areas and evaginated toward the outside of the axon in some areas. It was also noted that vacuoles formed between the axon and the myelin sheath and there were degenerative changes in the organelles located within the axon. It was observed that the neurotubules and neurofilaments in the axoplasm were dispersed. In some nerve fibers, it was noted that oligodendrocytes surrounding the axon increased heterochromatin in the nucleus and vacuolization in the cytoplasm (Figure 3a,b).
Multimodal Imaging Characteristics of a Rare Co-occurrence of Optic Nerve Head Drusen and Peripapillary Myelinated Retinal Nerve Fibres
Published in Neuro-Ophthalmology, 2021
Dilek Top Karti, Hasan Mahmut Arcagok, Omer Karti
Optic nerve head drusen (ONHD) are made up of calcified aggregates of extracellular materials including hyaline, calcium, and other proteins at the optic disc. Retinal ganglion cell nerve fibre degeneration or alterations in axoplasmic flow have been associated with their pathogenesis. ONHD, whose incidence ranges from 0.4% to 2.4%, are bilateral in 75% to 86% of cases.1–4 Though it is mostly benign and asymptomatic, they can sometimes be associated with several complications including ischaemic optic neuropathy, central retinal artery, and vein occlusion.5–7 In addition, visual field defects including nasal step defect, peripheral depression, arcuate defect, and enlarged blind spot can also be detected.3 Visual field defects arising from disc drusen are considered to be the result of the pressure caused by the calcific material on the retinal nerve fibre layer.8 In the present case, we demonstrate multimodal imaging of a 47-year-old healthy woman who had visual field defects associated with the disc drusen hidden by peripapillary myelinated retinal nerve fibres (MRNF).
Histological and ultrastructural study of AflatoxinB1 induced neurotoxicity in Sciatic nerve of adult male Albino rats
Published in Ultrastructural Pathology, 2020
Ultrastructurally, the control sciatic nerve revealed normal myelinated nerve fibers with Schwann cells. Groups of non-myelinated nerve fibers were observed surrounded by Schwann cell (Figure 5). The Schwann cell exhibited euchromatic nucleus and electron-lucent cytoplasm containing few mitochondria and rough endoplasmic reticulum. The myelin sheath appeared more electron dense, formed of compact several layers of Schwann cell membrane and surrounded an electron-lucent axoplasm containing neurofilaments and mitochondria. Treatment with Aflatoxin B1 (AFB1), the sciatic nerves revealed that the myelin sheath showed Wallerian degeneration. Some nerve fibers appeared smaller in size with destruction in their myelin sheath (Figures 6 and 7). Signs of edema were also observed between the degenerated fibers. Other nerve fibers appeared normal. Macrophages containing myelin debris and neutrophils were observed between the nerve fibers (Figures 7 and 8). The macrophages appeared to infiltrate the degenerated nerve fiber and help to clear the myelin debris. The axoplasm of some nerve fibers appeared rarified from organelles (Figure 8).