White matter tract

S1P5 Brain, white matter tracts Gj/o. G12/13 Proliferation, cell rounding... 

A marked increase in apolipoprotein D immunoreactivity is observed in hippocampus following neurotoxicity induced by KA (Table 6.3) (Ong et al., 1997). This increase in apolipoprotein D immunoreactivity occurs on the first day after KA injection, mainly in the cell bodies and dendrites of neurons (Fig. 6.3 A, 3B). Unlike the gray matter, no increase is observed in white matter tracts (Ong et al., 1997a). The significance of this upiegulation of apolipoprotein D remains unknown. However, apolipoprotein D binds to arachidonic acid (Morais Cabral et al., 1995), which is released by PLA2 stimulation. This could be a protective mechanism to limit the oxidative products from arachidonic acid, e.g. 4-HNE, after kainate injection. 

Demyelination. The role of myelin in the nervous system is to aid in signal transduction. Myelin acts like an electrical insulator by preventing loss of ion current, and intact myelin is critical for the fast saltatory nerve conduction discussed above. Neurotoxicants that target the synthesis or integrity of PNS myelin may cause muscle weakness, poor coordination, and paralysis. In the brain, white matter tracts that connect neurons within and between hemispheres may be destroyed, in a syndrome known as toxic leukoencephalopathy. A multifocal distribution of brain lesions is reflected in mental deterioration, vision loss, speech disturbances, ataxia (inability to coordinate movements), and paralysis. 

Rinse the sample thoroughly (>12 h) in water and process for paraffin embedding (dehydrate through at ethanol series and then to xylene, do not allow nervous system samples to sit longer than necessary in ethanol or white matter tracts will look like Swiss cheese). 

Gillard JH, Papadakis NG, Martin K, Price CJ, Warburton EA, Antoun NM et al (2001) MR diffusion tensor imaging of white matter tract disruption in stroke at 3 T. Br J Radiol 74 642-647... 

Lim KO, Hedehus M, Moseley M, de Crespigny A, Sullivan EV, et al. 1999. Compromised white matter tract integrity in schizophrenia inferred from diffusion tensor imaging. Arch Gen Psychiatry 56 367-374. 

Diffuse axonal injury is one of the most common and devastating types of traumatic brain injury it refers to the extensive lesions in white-matter tracts and is one of the major causes of unconsciousness and persistent vegetative state after head trauma. 

A very exciting and innovative application of DTI and tractography that will have profound clinical application is analysis of brain lesions. There has already been early work defining tumor growth and metastases within major white matter tracts (Witwer et al., 2002 Yu et al., 2005 Hlatky et al.. 

This application will provide measures of white matter tract displacement and tumor invasion that will be defined with great specificity. Previously estimates of white matter tract invasion could only be made by gross estimates of where the white matter tracts were expected to lie based on cross-sectional MRI or CT studies. However, cuiTent mothods of DTI tractography can not reproducibly demonstrate the the true size of fiber bundles (Kinoshita et al., 2005). 

More advanced quantitation methods for MT MRI have been showm to be sensitive to white matter tracts and axonal density (Yamykh and Yuan, 2004) as well as being sensitive to the earliest events in stroke lesions (Jiang et al., 2001) including early detection of ruptures in the blood-brain barrier which may be susceptible to hemorrhagic transformation (Knight et al., 2005). 

Figure 3.4. Cellular components of the central nervous system. (A) Neurons impregnated with Golgi silver satin, (C) Calbindin immunoreactive intemeurons in the neocortex, (G) astrocytes immunoreactive with an antibody against GFAP, (H) peri-vascular astrocytes components of the BBB, (I) oligodendrocytes and white matter tracts stained with luxol fast blue, (F) ependimal cells around the periventricular zone.

Witwer BP, Moftakhar R, Hasan KM, Deshmukh P, Haughton V, Field A, Arfanakis K, Noyes J, Moritz CH, Meyerand ME, Rowley HA, Alexander AL, Badie B (2002) Diffusion-tensor imaging of white matter tracts in patients with cerebral neoplasm. J Neurosurg 97 568-575. 

---