| Abstract No.: | C-A3010 |
| Country: | Canada |
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| Title: | SEVERED ADULT MAMMALIAN BRAIN ARCHITECTURE HEALS VIGOROUSLY |
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| Authors/Affiliations: | 1 Anne Foerster*; 1 Michael Holmes;
1 McMaster University, Hamilton, ON, Canada
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| Content: | Objectives: The objective was to ask whether brain’s cut tissue can heal so perfectly that its injury could escape notice later on, by re-examining the histological results of lowering fine wire cutting devices through it which made precise disconnections. Implanting the device allowed the width of its cutting crosswire to be permanently marked, in horizontal sections, by the two holes that had contained its parallel supports. Orderly axonal detours rapidly and progressively re-connected severed pathways around the lesion. When a device had been withdrawn and implanted elsewhere to mark the original lesion’s width, the obvious scar, narrower than the lesion had been, had no detours around it; instead, the tissue appeared normal and often made a small a small bulge into the line of lesion (Foerster, 1982). Now we sought capabilities and consequences of detours, histological markers of their new axon elongation, and whether restorative healing had indeed produced normal-appearing tissue adjacent to those short scars.
Materials and Methods: Series of horizontal sections from 65 rats (survival 18-230 days) and two monkeys (Macaca mulatta) (3 weeks), prepared between 1970–1982, were comprehensively stained (block pyridine silver, Luxol Fast Blue, Nuclear Fast Ruby) to reveal neurons and axons, indicate myelin (normal and degenerate) and glia, and give an overview of normal and altered brain architecture.
Results One marker of restorative healing was – nothing. Re-located axon populations could have normal diameters, myelin, argyrophilia and glia; they could produce a normal-appearing filling of the distal portions of severed one-way tracts. Growth-indicating abnormalities near the lesion included terminal enlargements, new patternings, changed diameter or argyrophilia and regular undulations typical of developing brain. Detours were precise, able to reconstitute hippocampal strata (e.g. CA3, including the pyramidale) around one end of the cut while their adjacent alveus detoured en masse around the other end. Selectivity in the re-directing signal was indicated when the proximal portions of intermingling parallel axons of medial lemniscus and Forel’s Field H1, cut while ascending through the subthalamus, became segregated and orthogonally interwoven en route to opposite ends of the cut beyond which, as is typical of distal components of detouring one-way tracts, each curved smoothly into its appropriate target. Perikaryal rescue was indicated when thalamic neurons, re-connected to the cortex via thalamic radiation detours, showed no sign of disappearance or abnormality. Shortened scars of unmarked lesions were not attributable to brain shrinkage. The “normal-appearing brain” next to them, on educated re-inspection, bore indications of having been newly created. Its protrusions into the ends of the scar contained many signs of new axonal growth, as if second-intention healing had been zipping the severed tissue back together. There were also examples of first-intention healing across the scar.
Results: The monkey results, obtained during early days of using the cutting-device technique, were robust and supported those obtained with rat.
Conclusion: Brain incisions trigger a healing process whose accuracy (e.g. Foerster and Holmes, 1999) suggests an |
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