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Myelin contributes to the parallel orientation of axonal growth on white matter in vitro.

Pettigrew DB, Crutcher KA - BMC Neurosci (2001)

Bottom Line: These neurons also extended neurites that were not constrained to a parallel orientation.Moreover, preincubation with NGF and treatment with cAMP analogs, manipulations that attenuate overall myelin-mediated inhibition of neurite growth, also led to a reduced parallel orientation of neurite growth.The present studies suggest that some of the relevant factors that constrain axonal growth on white matter are not haptotactic in nature and appear to be partly mediated by factors that are associated with myelin and may involve myelin-associated "inhibitors".

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept. of Neurobiology and Anatomy University of Texas-Houston Health Science Center, USA. David.Pettigrew@uth.tmc.edu

ABSTRACT

Background: Brain and spinal cord white matter can support extensive axonal growth. This growth is generally constrained to an orientation that is parallel to the longitudinal axis of the fiber tract. This constraint is presumably due to permissive and non-permissive substrates that are interleaved with each other and oriented in parallel within the tract.

Results: Embryonic chick sympathetic neurons were cultured on cryostat sections of rat brain and the orientation of neurite growth on white matter was assessed. To determine if haptotaxis is sufficient to guide parallel neurite growth, neurons were cultured under conditions designed to interfere with interactions between growing neurites and factors that act as biochemical contact guidance cues but not interactions with haptotactic cues. Under these conditions, neurites extending on white matter were not exclusively oriented in parallel to the fiber tract, suggesting that biochemical cues are involved. To assess the role of myelin in guiding parallel neurite growth, neurons were cultured on myelin-deficient corpus callosum. These neurons also extended neurites that were not constrained to a parallel orientation. Moreover, preincubation with NGF and treatment with cAMP analogs, manipulations that attenuate overall myelin-mediated inhibition of neurite growth, also led to a reduced parallel orientation of neurite growth.

Conclusions: The present studies suggest that some of the relevant factors that constrain axonal growth on white matter are not haptotactic in nature and appear to be partly mediated by factors that are associated with myelin and may involve myelin-associated "inhibitors".

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Neurites extending on fixed and unfixed corpus callosum or on unfixed corpus callosum treated with polyornithine. A, Fluorescein-labelled neurons cultured for one week on unfixed corpus callosum (edges of the fiber tract are indicated by open arrows). The neurites extending from these neurons were mostly unfasciculated and generally extended in parallel with the longitudinal axis of the fiber tract. B, Neurons cultured for one week on fixed corpus callosum. These neurons were mostly clustered (white asterisks) and many of the neurites extending on the fixed fiber tract were fasciculated (white arrows). From one neuron cluster (white arrowhead), unfasciculated neurites radiated outward in all directions over the fixed fiber tract. C, D, Phase-contrast micrographs of the underlying anatomy of panels A and B, respectively. E, A fluorescein-labelled explant attached on the corpus callosum (cc; edges are indicated by open arrows) in an unfixed tissue section that had been mounted on an untreated culture dish. The neurite outgrowth halo (after 6 days in culture) was oriented in parallel with the underlying fiber tract. F, An explant attached on the corpus callosum in an unfixed tissue section that had been mounted on a polyornithine-treated culture dish. The neurite outgrowth halo (after 3 days in culture) extended radially with no parallel orientation. cc, corpus callosum; ctx, neocortex; cg, cingulum. Scale bars: A, B, C, D, 200 μm; E, F, 100 μm.
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Figure 1: Neurites extending on fixed and unfixed corpus callosum or on unfixed corpus callosum treated with polyornithine. A, Fluorescein-labelled neurons cultured for one week on unfixed corpus callosum (edges of the fiber tract are indicated by open arrows). The neurites extending from these neurons were mostly unfasciculated and generally extended in parallel with the longitudinal axis of the fiber tract. B, Neurons cultured for one week on fixed corpus callosum. These neurons were mostly clustered (white asterisks) and many of the neurites extending on the fixed fiber tract were fasciculated (white arrows). From one neuron cluster (white arrowhead), unfasciculated neurites radiated outward in all directions over the fixed fiber tract. C, D, Phase-contrast micrographs of the underlying anatomy of panels A and B, respectively. E, A fluorescein-labelled explant attached on the corpus callosum (cc; edges are indicated by open arrows) in an unfixed tissue section that had been mounted on an untreated culture dish. The neurite outgrowth halo (after 6 days in culture) was oriented in parallel with the underlying fiber tract. F, An explant attached on the corpus callosum in an unfixed tissue section that had been mounted on a polyornithine-treated culture dish. The neurite outgrowth halo (after 3 days in culture) extended radially with no parallel orientation. cc, corpus callosum; ctx, neocortex; cg, cingulum. Scale bars: A, B, C, D, 200 μm; E, F, 100 μm.

Mentions: After 3 days in culture, neurites continued to extend freely on both fixed and unfixed sections. On the unfixed corpus callosum, scattered neurons continued to extend neurites parallel to the tract, forming dense plexi of neurites attached firmly to the underlying substrate. On the fixed corpus callosum, however, many of the neurons had migrated together forming small clusters that extended neurites in all directions across the fiber tract. Many of these neurites grew in close association, appearing to use each other as a substrate. While the growth cones of these neurites remained firmly attached to the underlying substrate, the proximal segments often detached from the substrate and straightened under the tension applied by the outward migrating growth cone. After one week in culture dense parallel plexi of firmly-attached neurites were found on the unfixed corpus callosum (Fig. 1A). Neurites extending on the fixed corpus callosum (Fig. 1B) formed a web of loosely attached neurites radiating in all directions across the fiber tract.


Myelin contributes to the parallel orientation of axonal growth on white matter in vitro.

Pettigrew DB, Crutcher KA - BMC Neurosci (2001)

Neurites extending on fixed and unfixed corpus callosum or on unfixed corpus callosum treated with polyornithine. A, Fluorescein-labelled neurons cultured for one week on unfixed corpus callosum (edges of the fiber tract are indicated by open arrows). The neurites extending from these neurons were mostly unfasciculated and generally extended in parallel with the longitudinal axis of the fiber tract. B, Neurons cultured for one week on fixed corpus callosum. These neurons were mostly clustered (white asterisks) and many of the neurites extending on the fixed fiber tract were fasciculated (white arrows). From one neuron cluster (white arrowhead), unfasciculated neurites radiated outward in all directions over the fixed fiber tract. C, D, Phase-contrast micrographs of the underlying anatomy of panels A and B, respectively. E, A fluorescein-labelled explant attached on the corpus callosum (cc; edges are indicated by open arrows) in an unfixed tissue section that had been mounted on an untreated culture dish. The neurite outgrowth halo (after 6 days in culture) was oriented in parallel with the underlying fiber tract. F, An explant attached on the corpus callosum in an unfixed tissue section that had been mounted on a polyornithine-treated culture dish. The neurite outgrowth halo (after 3 days in culture) extended radially with no parallel orientation. cc, corpus callosum; ctx, neocortex; cg, cingulum. Scale bars: A, B, C, D, 200 μm; E, F, 100 μm.
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Related In: Results  -  Collection

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Figure 1: Neurites extending on fixed and unfixed corpus callosum or on unfixed corpus callosum treated with polyornithine. A, Fluorescein-labelled neurons cultured for one week on unfixed corpus callosum (edges of the fiber tract are indicated by open arrows). The neurites extending from these neurons were mostly unfasciculated and generally extended in parallel with the longitudinal axis of the fiber tract. B, Neurons cultured for one week on fixed corpus callosum. These neurons were mostly clustered (white asterisks) and many of the neurites extending on the fixed fiber tract were fasciculated (white arrows). From one neuron cluster (white arrowhead), unfasciculated neurites radiated outward in all directions over the fixed fiber tract. C, D, Phase-contrast micrographs of the underlying anatomy of panels A and B, respectively. E, A fluorescein-labelled explant attached on the corpus callosum (cc; edges are indicated by open arrows) in an unfixed tissue section that had been mounted on an untreated culture dish. The neurite outgrowth halo (after 6 days in culture) was oriented in parallel with the underlying fiber tract. F, An explant attached on the corpus callosum in an unfixed tissue section that had been mounted on a polyornithine-treated culture dish. The neurite outgrowth halo (after 3 days in culture) extended radially with no parallel orientation. cc, corpus callosum; ctx, neocortex; cg, cingulum. Scale bars: A, B, C, D, 200 μm; E, F, 100 μm.
Mentions: After 3 days in culture, neurites continued to extend freely on both fixed and unfixed sections. On the unfixed corpus callosum, scattered neurons continued to extend neurites parallel to the tract, forming dense plexi of neurites attached firmly to the underlying substrate. On the fixed corpus callosum, however, many of the neurons had migrated together forming small clusters that extended neurites in all directions across the fiber tract. Many of these neurites grew in close association, appearing to use each other as a substrate. While the growth cones of these neurites remained firmly attached to the underlying substrate, the proximal segments often detached from the substrate and straightened under the tension applied by the outward migrating growth cone. After one week in culture dense parallel plexi of firmly-attached neurites were found on the unfixed corpus callosum (Fig. 1A). Neurites extending on the fixed corpus callosum (Fig. 1B) formed a web of loosely attached neurites radiating in all directions across the fiber tract.

Bottom Line: These neurons also extended neurites that were not constrained to a parallel orientation.Moreover, preincubation with NGF and treatment with cAMP analogs, manipulations that attenuate overall myelin-mediated inhibition of neurite growth, also led to a reduced parallel orientation of neurite growth.The present studies suggest that some of the relevant factors that constrain axonal growth on white matter are not haptotactic in nature and appear to be partly mediated by factors that are associated with myelin and may involve myelin-associated "inhibitors".

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept. of Neurobiology and Anatomy University of Texas-Houston Health Science Center, USA. David.Pettigrew@uth.tmc.edu

ABSTRACT

Background: Brain and spinal cord white matter can support extensive axonal growth. This growth is generally constrained to an orientation that is parallel to the longitudinal axis of the fiber tract. This constraint is presumably due to permissive and non-permissive substrates that are interleaved with each other and oriented in parallel within the tract.

Results: Embryonic chick sympathetic neurons were cultured on cryostat sections of rat brain and the orientation of neurite growth on white matter was assessed. To determine if haptotaxis is sufficient to guide parallel neurite growth, neurons were cultured under conditions designed to interfere with interactions between growing neurites and factors that act as biochemical contact guidance cues but not interactions with haptotactic cues. Under these conditions, neurites extending on white matter were not exclusively oriented in parallel to the fiber tract, suggesting that biochemical cues are involved. To assess the role of myelin in guiding parallel neurite growth, neurons were cultured on myelin-deficient corpus callosum. These neurons also extended neurites that were not constrained to a parallel orientation. Moreover, preincubation with NGF and treatment with cAMP analogs, manipulations that attenuate overall myelin-mediated inhibition of neurite growth, also led to a reduced parallel orientation of neurite growth.

Conclusions: The present studies suggest that some of the relevant factors that constrain axonal growth on white matter are not haptotactic in nature and appear to be partly mediated by factors that are associated with myelin and may involve myelin-associated "inhibitors".

Show MeSH
Related in: MedlinePlus