Central chromatolysis is a histopathologic change seen in the cell body of a neuron, where the chromatin and cell nucleus are pushed to the cell periphery, in response to axonal injury. [1] [2] This response is associated with increased protein synthesis to accommodate for axonal sprouting. In addition to traumatic injuries, central chromatolysis may be caused by vitamin deficiency (pellagra [3] ).
An axon, or nerve fiber, is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons, such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body, and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons. Nerve fibers are classed into three types – group A nerve fibers, group B nerve fibers, and group C nerve fibers. Groups A and B are myelinated, and group C are unmyelinated. These groups include both sensory fibers and motor fibers. Another classification groups only the sensory fibers as Type I, Type II, Type III, and Type IV.
A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. It is the main component of nervous tissue all animals except sponges and placozoa. Plants and fungi do not have nerve cells. The spelling neurone has become uncommon.
Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological function in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Histamine is involved in the inflammatory response and has a central role as a mediator of itching. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues. It consists of an imidazole ring attached to an ethylamine chain; under physiological conditions, the amino group of the side-chain is protonated.
Wallerian degeneration is an active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury degenerates. A related process of dying back or retrograde degeneration known as 'Wallerian-like degeneration' occurs in many neurodegenerative diseases, especially those where axonal transport is impaired such as ALS and Alzheimer's disease. Primary culture studies suggest that a failure to deliver sufficient quantities of the essential axonal protein NMNAT2 is a key initiating event.
Diffuse axonal injury (DAI) is a brain injury in which scattered lesions occur over a widespread area in white matter tracts as well as grey matter. DAI is one of the most common and devastating types of traumatic brain injury and is a major cause of unconsciousness and persistent vegetative state after severe head trauma. It occurs in about half of all cases of severe head trauma and may be the primary damage that occurs in concussion. The outcome is frequently coma, with over 90% of patients with severe DAI never regaining consciousness. Those who do wake up often remain significantly impaired.
Astrogliosis is an abnormal increase in the number of astrocytes due to the destruction of nearby neurons from central nervous system (CNS) trauma, infection, ischemia, stroke, autoimmune responses or neurodegenerative disease. In healthy neural tissue, astrocytes play critical roles in energy provision, regulation of blood flow, homeostasis of extracellular fluid, homeostasis of ions and transmitters, regulation of synapse function and synaptic remodeling. Astrogliosis changes the molecular expression and morphology of astrocytes, causing scar formation and, in severe cases, inhibition of axon regeneration.
Peripherin is a type III intermediate filament protein expressed mainly in neurons of the peripheral nervous system. It is also found in neurons of the central nervous system that have projections toward peripheral structures, such as spinal motor neurons. Its size, structure, and sequence/location of protein motifs is similar to other type III intermediate filament proteins such as desmin, vimentin and glial fibrillary acidic protein. Like these proteins, peripherin can self-assemble to form homopolymeric filamentous networks, but it can also heteropolymerize with neurofilaments in several neuronal types. This protein in humans is encoded by the PRPH gene. Peripherin is thought to play a role in neurite elongation during development and axonal regeneration after injury, but its exact function is unknown. It is also associated with some of the major neuropathologies that characterize amyotropic lateral sclerosis (ALS), but despite extensive research into how neurofilaments and peripherin contribute to ALS, their role in this disease is still unidentified.
Neurofilaments (NF) are classed as type IV intermediate filaments found in the cytoplasm of neurons. They are protein polymers measuring 10 nm in diameter and many micrometers in length. Together with microtubules (~25 nm) and microfilaments (7 nm), they form the neuronal cytoskeleton. They are believed to function primarily to provide structural support for axons and to regulate axon diameter, which influences nerve conduction velocity. The proteins that form neurofilaments are members of the intermediate filament protein family, which is divided into six types based on their gene organization and protein structure. Types I and II are the keratins which are expressed in epithelia. Type III contains the proteins vimentin, desmin, peripherin and glial fibrillary acidic protein (GFAP). Type IV consists of the neurofilament proteins L, M, H and internexin. Type V consists of the nuclear lamins, and type VI consists of the protein nestin. The type IV intermediate filament genes all share two unique introns not found in other intermediate filament gene sequences, suggesting a common evolutionary origin from one primitive type IV gene.
An axotomy is the cutting or otherwise severing of an axon. Derived from axo- (=axon) and -tomy (=surgery). This type of denervation is often used in experimental studies on neuronal physiology and neuronal death or survival as a method to better understand nervous system diseases.
Spectrin is a cytoskeletal protein that lines the intracellular side of the plasma membrane in eukaryotic cells. Spectrin forms pentagonal or hexagonal arrangements, forming a scaffold and playing an important role in maintenance of plasma membrane integrity and cytoskeletal structure. The hexagonal arrangements are formed by tetramers of spectrin subunits associating with short actin filaments at either end of the tetramer. These short actin filaments act as junctional complexes allowing the formation of the hexagonal mesh. The protein is named spectrin since it was first isolated as a major protein component of human red blood cells which had been treated with mild detergents; the detergents lysed the cells and the hemoglobin and other cytoplasmic components were washed out. In the light microscope the basic shape of the red blood cell could still be seen as the spectrin-containing submembranous cytoskeleton preserved the shape of the cell in outline. This became known as a red blood cell "ghost" (spectre), and so the major protein of the ghost was named spectrin.
Axonal transport, also called axoplasmic transport or axoplasmic flow, is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other organelles to and from a neuron's cell body, through the cytoplasm of its axon called the axoplasm. Since some axons are on the order of meters long, neurons cannot rely on diffusion to carry products of the nucleus and organelles to the end of their axons. Axonal transport is also responsible for moving molecules destined for degradation from the axon back to the cell body, where they are broken down by lysosomes.
Gliosis is a nonspecific reactive change of glial cells in response to damage to the central nervous system (CNS). In most cases, gliosis involves the proliferation or hypertrophy of several different types of glial cells, including astrocytes, microglia, and oligodendrocytes. In its most extreme form, the proliferation associated with gliosis leads to the formation of a glial scar.
A Nissl body, also known as Nissl substance and Nissl material, is a large granular body found in neurons. These granules are of rough endoplasmic reticulum (RER) with rosettes of free ribosomes, and are the site of protein synthesis. It was named after Franz Nissl, a German neuropathologist who invented the Nissl staining method.
Myelin-associated glycoprotein is a type 1 transmembrane protein glycoprotein localized in periaxonal Schwann cell and oligodendrocyte membranes, where it plays a role in glial-axonal interactions. MAG is a member of the SIGLEC family of proteins and is a functional ligand of the NOGO-66 receptor, NgR. MAG is believed to be involved in myelination during nerve regeneration in the PNS and is vital for the long-term survival of the myelinated axons following myelinogenesis. In the CNS MAG is one of three main myelin-associated inhibitors of axonal regeneration after injury, making it an important protein for future research on neurogenesis in the CNS.
Neuroregeneration refers to the regrowth or repair of nervous tissues, cells or cell products. Such mechanisms may include generation of new neurons, glia, axons, myelin, or synapses. Neuroregeneration differs between the peripheral nervous system (PNS) and the central nervous system (CNS) by the functional mechanisms involved, especially in the extent and speed of repair. When an axon is damaged, the distal segment undergoes Wallerian degeneration, losing its myelin sheath. The proximal segment can either die by apoptosis or undergo the chromatolytic reaction, which is an attempt at repair. In the CNS, synaptic stripping occurs as glial foot processes invade the dead synapse.
Glial scar formation (gliosis) is a reactive cellular process involving astrogliosis that occurs after injury to the central nervous system. As with scarring in other organs and tissues, the glial scar is the body's mechanism to protect and begin the healing process in the nervous system.
Uracil nucleotide/cysteinyl leukotriene receptor is a G protein-coupled receptor that in humans is encoded by the GPR17 gene located on chromosome 2 at position q21. The actual activating ligands for and some functions of this receptor are disputed.
Semaphorin-3A is a protein that in humans is encoded by the SEMA3A gene.
Chromatolysis is the dissolution of the Nissl bodies in the cell body of a neuron. It is an induced response of the cell usually triggered by axotomy, ischemia, toxicity to the cell, cell exhaustion, virus infections, and hibernation in lower vertebrates. Neuronal recovery through regeneration can occur after chromatolysis, but most often it is a precursor of apoptosis. The event of chromatolysis is also characterized by a prominent migration of the nucleus towards the periphery of the cell and an increase in the size of the nucleolus, nucleus, and cell body. The term "chromatolysis" was initially used in the 1940s to describe the observed form of cell death characterized by the gradual disintegration of nuclear components; a process which is now called apoptosis. Chromatolysis is still used as a term to distinguish the particular apoptotic process in the neuronal cells, where Nissl substance disintegrates.
Olfactory ensheathing cells (OECs), also known as olfactory ensheathing glia or olfactory ensheathing glial cells, are a type of macroglia found in the nervous system. They are also known as olfactory Schwann cells, because they ensheath the non-myelinated axons of olfactory neurons in a similar way to which Schwann cells ensheath non-myelinated peripheral neurons. They also share the property of assisting axonal regeneration.