Demyelination Axon degeneration

Chicken (Leghorn) 5 d 1 x/d (GO) 240 F (axonal degeneration and demyelination in peripheral nerves and spinal cord white matter) Gaworski et al.. 1986 Durad MP280... 

Pale coat color, axonal degeneration -motor and sensory, limited segmental demyelination pit (71-73)... 

When myelin is lost, axonal function is rapidly affected. Conduction velocity slows in proportion to the degree of demyelination and, in extreme situations, conduction can be blocked. Loss of the myelin may also lead to loss of the axon. Axons can generally survive some demyelination, but extensive loss of myelin can result in axonal degeneration. Because myelin-forming cells can proliferate, they generally reestablish a myelin sheath around an axon once the demyelinating stimulus is removed. 

Although the sensory ganglia and roots are the primary affected area in SN, demyelination and axonal degeneration combined with inflammatory infiltrates consisting of CD8+ cells and macrophages also extend to peripheral nerves [102]. Simultaneous affection of the CNS and autonomic ganglia is common [42]. 

The neuron and the Schwann cell are the principal cell types in the PNS. There are great morphological, biochemical, and functional differences between neurons and Schwann cells, and this is reflected in the considerable variation in their vulnerability to toxic injury. Some toxic neuropathies are characterized primarily by injury of the neuron, its axon, or its terminal, as evidenced by the presence of axonal degeneration in peripheral nerve, while other toxic neuropathies are characterized primarily by Schwann cell injury, as evidenced by the presence of demyelination. Those neuropathies characterized by axonal injury are often categorized as axonal neuropathies, whereas those characterized by demyelination are categorized as demyelinating neuropathies. ... 

The vast majority of neurotoxic agents that affect the PNS preferentially cause axonal injury rather than Schwann cell injury. Axonal injury is usually manifested as axonal degeneration, a pathologic process characterized by complete dissolution of the axon. If the degeneration involves a myelinated axon, then the myelin sheath enveloping the degenerating axon also breaks down. This myelin breakdown, which occurs in the context of axonal degeneration, is not considered demyelination, since demyelination refers to loss of the myelin sheath from an intact axon. 

Guillain-Barre Syndrome, Chronic Inflammatory Demyelinating Polyradiculoneuropathy, and Axonal Degeneration and Regeneration... 

Huglies R, Atkinson P, Coates P, Hall S, Leibowitz S (1992) Sur al nerve biopsies in Guillain-Bane syndr ome Axonal degeneration and macrophage-associated demyelination and absence of cytomegalovirus genome. Muscle Nerve 15 568—575. 

Axonal variants Unlike AIDP, axonal variants of GBS show primary axonal injury without substantial T-cell inflammation or demyelination (Griffin et al., 1995, 1996a). In AMAN, axonal degeneration predominantly involves the motor axons, whereas in AMSAN sensory axons are also involved. It has been postnlated that AMAN and AMSAN represent a pathologic spectrum and that AMSAN actually represents a more severe form of AMAN. 

Figure 20.1. Hypothetical scheme of the immune response in acute inflammatory demyelinating polyradiculoneuropathy (AIDP) Inflammatory cells migrate from the systemic immune compartment through the damaged blood-nerve barrier into the endoneurium. Inflammatory infiltrates, which contain T-lymphocytes and macrophages cause marked segmental demyelination and secondary axonal degeneration (B B-cell T T-cell M4> Macrophage).

A 36-year-old man developed peripheral polyneuropathy after chronic perianal use of an ammoniated mercury ointment. He had very high blood and urine mercury concentrations. Sural nerve biopsy showed mixed axonal degeneration/demyelination. His symptoms improved progressively over 2 years after withdrawal of the ointment, but neurophysiological recovery was incomplete. 

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