Fiber tract

Neuroanatomists have taken advantage of the phenomenon of fast retrograde transport to locate remote nerve cell bodies in the CNS of an experimental animal that are connected to an identified axonal fiber tract whose origin is uncertain. The tracer material [purified horseradish peroxidase (HRP) enzyme] is injected in the region of the axon terminals, where it is taken up by endocytosis and then is carried by retrograde axonal transport over a period of several hours to days back to the nerve cell body. The animal is sacrificed, and the enzyme tracer is localized by staining thin sections of the brain for peroxidase activity. 

The excessive electrical discharges can spread to other neurons, either adjacent ones or distant ones connected by fiber tracts. The seizure thus spreads to other areas of the brain, recruiting them into the uncontrolled firing pattern. The neurons involved may not be abnormal themselves, but are diverted from their normal functioning to participate in the wildly excessive discharges. The degree of spread and the location of brain areas involved determine the clinical manifestations of the seizure. 

If there is a systematic (i.e., highly ordered) tissue substructure such as in white matter, diffusion is usually more restricted in one than in another direction, i.e., the molecular mobility of water is not the same in all directions. In white matter, diffusion is less restricted parallel to than perpendicular to fiber tracts. If diffusion is different along various directions, then it is termed anisotropic diffusion. In stroke imaging the avoidance of the confounding effects of anisotropy is a common goal. However,... 

In DTI, diffusion is no longer described by a single diffusion coefficient, but by an array of nine coefficients that fully characterize how diffusion in space varies according to direction (Basser 1995). With this approach, diffusion anisotropy can be exploited to provide details on tissue microstructure and fiber tracts (le Bihan 2003). To obtain sufficient information on the direction of diffusion, the full diffusion tensor needs to be sampled [for a review on theoretical foundations of DTI see Basser and Jones (2002)]. 

Detected by anatomists who dissected the cerebral hemispheres, the main structure of the basal ganglia was defined as corpus striatum by Thomas Willis in the 17th century (Willis, 1664) because of the mixture of gray matter and fiber tracts. Such mixture was... 

Yamykh VL, Yuan C (2004) Cross-relaxadorr imagirrg reveals detailed anatomy of white matter fiber tracts irr dre humarr brairr. Neuroimage 23 409 24. 

Roizen MF, Kopin IJ, Zivin J, Muth EA, Jacobowitz DM. The effect of two anesthetic agents on norepinephrine and dopamine in discrete brain nuclei, fiber tracts, and terminal regions of the rat. Brain Res 1976 110(3) 515-22. 

Fiber tracts in the drawings are outlined by solid lines, and nuclei and cell groups are outlined by broken lines. In general, each abbreviation is placed in the center of the structure to which it relates where this is not possible, the abbreviation is placed alongside the structure and a leader line is used. The abbreviations for fiber tracts and fissures are almost always positioned on the... 

Capital letters represent nudei, and lower case letters represent fiber tracts. Thus, the letter "N" has not been used to denote nuclei, and the letter "t" has not been used to denote fiber tracts. 

The IR and Raman spectra in Figure 3.6 were extracted from the images in Figure 3.5. These represent the fiber tracts (traces A and C) and the mesencephalon (traces B and D). The spectra contain more intense spectral contributions of lipids and cholesterol relative to the protein bands than the spectra of brain tumors in Figure 3.2. This is evident from the IR bands at 1060, 1234, 1382, 1467, 1740,... 

Many different approaches have been used to identify the neurons that use Glu as a transmitter. Biochemical techniques, including analysis of reduced content or uptake of Glu or Glu analogues following lesions, have proved useful in investigations of major projections (e.g. corticofugal fiber tracts Fonnum, 1984 Storm-Mathisen and Ottersen, 1988 Ottersen, 1991), but poor sensitivity hampers analyses of less massive pathways. Detection of many minor glutamatergic projections was made possible by the use of the metabolically inert Glu... 

A common feature of brain damage between early gestation and infancy is destruction of this cerebral white matter, the fiber tracts that connect one part of the brain to other parts or to the spinal cord. A common consequence of large-scale white matter damage is a clinical syndrome in which disturbances of motor control are prominent. Cerebral palsy is such a syndrome. 

MRI studies of adolescent autistic children show increases in thickness of the cerebral cortex (gray matter) in specific areas of the brain coupled with decreases in thickness of fiber tracts (white matter) leading in and out of those and other areas.63 This provokes the idea that a combination of developmentally enlarged cortex and reduced white matter may be the structural basis of autism. But it s also possible that the anatomical differences may be a consequence of autistic behavior rather than a basis, since the development of the brain continues throughout childhood. 

While the formation and long-lasting persistence of a dense plexus of laminin-immunopositive blood vessels has been observed at the lesion site of a transected fiber tract in the adult rat brain, laminin immunoreactivity is not re-expressed in reactive astrocytes following CNS lesions (Stichel and Muller, 1994). 

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