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1.
Glia ; 72(9): 1572-1589, 2024 09.
Artículo en Inglés | MEDLINE | ID: mdl-38895764

RESUMEN

The velocity of axonal impulse propagation is facilitated by myelination and axonal diameters. Both parameters are frequently impaired in peripheral nerve disorders, but it is not known if the diameters of myelinated axons affect the liability to injury or the efficiency of functional recovery. Mice lacking the adaxonal myelin protein chemokine-like factor-like MARVEL-transmembrane domain-containing family member-6 (CMTM6) specifically from Schwann cells (SCs) display appropriate myelination but increased diameters of peripheral axons. Here we subjected Cmtm6-cKo mice as a model of enlarged axonal diameters to a mild sciatic nerve compression injury that causes temporarily reduced axonal diameters but otherwise comparatively moderate pathology of the axon/myelin-unit. Notably, both of these pathological features were worsened in Cmtm6-cKo compared to genotype-control mice early post-injury. The increase of axonal diameters caused by CMTM6-deficiency thus does not override their injury-dependent decrease. Accordingly, we did not detect signs of improved regeneration or functional recovery after nerve compression in Cmtm6-cKo mice; depleting CMTM6 in SCs is thus not a promising strategy toward enhanced recovery after nerve injury. Conversely, the exacerbated axonal damage in Cmtm6-cKo nerves early post-injury coincided with both enhanced immune response including foamy macrophages and SCs and transiently reduced grip strength. Our observations support the concept that larger peripheral axons are particularly susceptible toward mechanical trauma.


Asunto(s)
Axones , Animales , Axones/patología , Axones/metabolismo , Axones/fisiología , Ratones , Ratones Noqueados , Modelos Animales de Enfermedad , Ratones Endogámicos C57BL , Células de Schwann/metabolismo , Células de Schwann/patología , Vaina de Mielina/metabolismo , Vaina de Mielina/patología , Nervio Ciático/lesiones , Nervio Ciático/patología , Traumatismos de los Nervios Periféricos/patología , Traumatismos de los Nervios Periféricos/metabolismo , Traumatismos de los Nervios Periféricos/fisiopatología
2.
Ann Neurol ; 93(4): 856-870, 2023 04.
Artículo en Inglés | MEDLINE | ID: mdl-36565265

RESUMEN

OBJECTIVE: Changes in the normal-appearing white matter (NAWM) in multiple sclerosis (MS) may contribute to disease progression. Here, we systematically quantified ultrastructural and subcellular characteristics of the axon-myelin unit in MS NAWM and determined how this correlates with low-grade inflammation. METHODS: Human brain tissue obtained with short postmortem delay and fixation at autopsy enables systematic quantification of ultrastructural characteristics. In this study, we performed high-resolution immunohis tochemistry and quantitative transmission electron microscopy to study inflammation and ultrastructural characteristics of the axon-myelin unit in MS NAWM (n = 8) and control white matter (WM) in the optic nerve. RESULTS: In the MS NAWM, there were more activated and phagocytic microglia cells (HLA+ P2RY12- and Iba1+ CD68+ ) and more T cells (CD3+ ) compared to control WM, mainly located in the perivascular space. In MS NAWM compared to control WM, there were, as expected, longer paranodes and juxtaparanodes and larger overlap between paranodes and juxtaparanodes. There was less compact myelin wrapping, a lower g-ratio, and a higher frequency of axonal mitochondria. Changes in myelin and axonal mitochondrial frequency correlated positively with the number of active and phagocytic microglia and lymphocytes in the optic nerve. INTERPRETATION: These data suggest that in MS NAWM myelin detachment and uncompact myelin wrapping occurs, potassium channels are unmasked at the nodes of Ranvier, and axonal energy demand is increased, or mitochondrial transport is stagnated, accompanied by increased presence of activated and phagocytic microglia and T cells. These subclinical alterations to the axon-myelin unit in MS NAWM may contribute to disease progression. ANN NEUROL 2023;93:856-870.


Asunto(s)
Esclerosis Múltiple , Sustancia Blanca , Humanos , Esclerosis Múltiple/complicaciones , Vaina de Mielina , Axones , Encéfalo , Inflamación/complicaciones , Progresión de la Enfermedad , Imagen por Resonancia Magnética
3.
Glia ; 71(3): 509-523, 2023 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-36354016

RESUMEN

Healthy myelin sheaths consist of multiple compacted membrane layers closely encasing the underlying axon. The ultrastructure of CNS myelin requires specialized structural myelin proteins, including the transmembrane-tetraspan proteolipid protein (PLP) and the Ig-CAM myelin-associated glycoprotein (MAG). To better understand their functional relevance, we asked to what extent the axon/myelin-units display similar morphological changes if PLP or MAG are lacking. We thus used focused ion beam-scanning electron microscopy (FIB-SEM) to re-investigate axon/myelin-units side-by-side in Plp- and Mag-null mutant mice. By three-dimensional reconstruction and morphometric analyses, pathological myelin outfoldings extend up to 10 µm longitudinally along myelinated axons in both models. More than half of all assessed outfoldings emerge from internodal myelin. Unexpectedly, three-dimensional reconstructions demonstrated that both models displayed complex axonal pathology underneath the myelin outfoldings, including axonal sprouting. Axonal anastomosing was additionally observed in Plp-null mutant mice. Importantly, normal-appearing axon/myelin-units displayed significantly increased axonal diameters in both models according to quantitative assessment of electron micrographs. These results imply that healthy CNS myelin sheaths facilitate normal axonal diameters and shape, a function that is impaired when structural myelin proteins PLP or MAG are lacking.


Asunto(s)
Sistema Nervioso Central , Proteína Proteolipídica de la Mielina , Vaina de Mielina , Glicoproteína Asociada a Mielina , Animales , Ratones , Axones/metabolismo , Sistema Nervioso Central/metabolismo , Ratones Noqueados , Microscopía Electrónica de Rastreo , Proteínas de la Mielina/metabolismo , Vaina de Mielina/metabolismo , Glicoproteína Asociada a Mielina/genética , Proteína Proteolipídica de la Mielina/genética
4.
J Comp Neurol ; 530(15): 2782-2801, 2022 10.
Artículo en Inglés | MEDLINE | ID: mdl-35700405

RESUMEN

The central complex in the brain of insects provides a neural network for sensorimotor processing that is essential for spatial navigation and locomotion and plays a role in sleep control. Studies on the neurochemical architecture of the central complex have been performed especially in the fruit fly Drosophila melangoaster and the desert locust, Schistocerca gregaria. In several insect species, myoinhibitory peptides (MIPs) are involved in circadian control and sleep-wake regulation. To identify neurons that might underlie these functions, we investigated the distribution of MIPs in the central complex of the locust. In silico transcript analysis suggests the presence of eight different MIPs in the desert locust. Through immunolabeling, we identified five systems of central-complex neurons that express MIP-like peptides. Two systems constitute columnar neurons of the protocerebral bridge and the lower division of the central body, while the other three systems are columnar neurons (two systems) and tangential neurons (one system) of the upper division of the central body. The innervation pattern and cell count of two systems of columnar neurons revealed the existence of 18 instead of 16 columns of the protocerebral bridge. Immunostaining of preparations containing intracellularly stained single cells allowed us to further specify subtypes of labeled columnar neurons. Double-label experiments showed that three systems of MIP-immunostained columnar neurons are also locustatachykinin-immunoreactive. No colocalization was found with serotonin immunostaining. The data provide novel insights into the architecture of the locust central complex and suggest that MIPs play a prominent role within the central-complex network.


Asunto(s)
Saltamontes , Neuropéptidos , Animales , Encéfalo/metabolismo , Química Encefálica/fisiología , Saltamontes/fisiología , Neuronas/metabolismo , Neuropéptidos/metabolismo , Péptidos
5.
Life (Basel) ; 11(2)2021 Feb 11.
Artículo en Inglés | MEDLINE | ID: mdl-33670172

RESUMEN

Although myelinated nervous systems are shared among 60,000 jawed vertebrates, studies aimed at understanding myelination have focused more and more on mice and zebrafish. To obtain a broader understanding of the myelination process, we examined the little skate, Leucoraja erinacea. The reasons behind initiating studies at this time include: the desire to study a species belonging to an out group of other jawed vertebrates; using a species with embryos accessible throughout development; the availability of genome sequences; and the likelihood that mammalian antibodies recognize homologs in the chosen species. We report that the morphological features of myelination in a skate hatchling, a stage that supports complex behavioral repertoires needed for survival, are highly similar in terms of: appearances of myelinating oligodendrocytes (CNS) and Schwann cells (PNS); the way their levels of myelination conform to axon caliber; and their identity in terms of nodal and paranodal specializations. These features provide a core for further studies to determine: axon-myelinating cell communication; the structures of the proteins and lipids upon which myelinated fibers are formed; the pathways used to transport these molecules to sites of myelin assembly and maintenance; and the gene regulatory networks that control their expressions.

6.
J Comp Neurol ; 529(15): 3533-3560, 2021 10.
Artículo en Inglés | MEDLINE | ID: mdl-34216020

RESUMEN

The lateral complexes (LXs) are bilaterally paired neuropils in the insect brain that mediate communication between the central complex (CX), a brain center controlling spatial orientation, various sensory processing areas, and thoracic motor centers that execute locomotion. The LX of the desert locust consists of the lateral accessory lobe (LAL), and the medial and lateral bulb. We have analyzed the anatomical organization and the neuronal connections of the LX in the locust, to provide a basis for future functional studies. Reanalyzing the morphology of neurons connecting the CX and the LX revealed likely feedback loops in the sky compass network of the CX via connections in the gall of the LAL and a newly identified neuropil termed ovoid body. In addition, we characterized 16 different types of neuron that connect the LAL with other areas in the brain. Eight types of neuron provide information flow between both LALs, five types are LAL input neurons, and three types are LAL output neurons. Among these are neurons providing input from sensory brain areas such as the lobula and antennal neuropils. Brain regions most often targeted by LAL neurons are the posterior slope, the wedge, and the crepine. Two descending neurons with dendrites in the LAL were identified. Our data support and complement existing knowledge about how the LAL is embedded in the neuronal network involved in processing of sensory information and generation of appropriate behavioral output for goal-directed locomotion.


Asunto(s)
Encéfalo/citología , Encéfalo/diagnóstico por imagen , Imagenología Tridimensional/métodos , Red Nerviosa/citología , Red Nerviosa/diagnóstico por imagen , Animales , Encéfalo/fisiología , Química Encefálica , Femenino , Saltamontes , Masculino , Red Nerviosa/química , Neurópilo/química , Neurópilo/citología
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