Brain radioactivity

An additional benefit of COMT inhibitors can be found in positron emission tomography (PET) studies. In PET, using 6-[18F]-fluoro-L-dopa (6-FD) to visualize the brain dopamine metabolism, the peripheral formation of 3-0-methyl-6-[18F]-fluoro-L-dopa (3-OMFD) by COMT is harmful. 3-OMFD contaminates the brain radioactivity analysed since it is easily transported like 3-OMD to the... 

FIGURE 7 Movement of ( HJBCNU-associated radioactivity through rabbit brain. Radioactivity resulting from [ H]BCNU was measured at various distances from the implantation site following implantation of discs described for Fig. 5 into the brains of rabbits. Details of the experimental procedure are described in the text. 

The FA method involves the intravenous injection or infusion of a radiolabeled albumin-bound FA, then measuring plasma and brain radioactivities. In awake rodents, the... 

SUBSTANCE DOSE AND ROUTE ANIMALS WITH VOCALISATION / TREATED ANIMALS CHANGES IN BRAIN RADIOACTIVITY... 

Positron emission tomography studies using "C-toluene in nonhuman primates and mice showed a rapid uptake of radioactivity into striatal and frontal brain regions (Gerasimov et al. 2002). Maximal uptake of the radiotracer by these structures occurred 1 minutes after intravenous administration. Subsequently, clearance of the radiotracer from the striatal and frontal areas occurred rapidly, with a clearance half-life from peak uptake of 10—20 minutes. Radiotracer clearance from white matter appears to be slower... 

The difference in rates of release of BCNU from wafers produced by the trituration or solution methods is also seen in vivo (11,14), as is shown in Fig. 6. Wafers of PCPP-SA 20 80 were prepared by either the solution or trituration methods, as described above, and were implanted into the brains of rabbits. The animals were sacrificed at various times after implantation and the brains were removed, fixed, and processed for quantitative autoradiography. To quantitate the percentage of the brain exposed to BCNU released from these wafers, the following calculation was performed. The percentage of the brain in which the radioactivity from the tritiated BCNU released from the wafers exceeded the background counts by at least two standard deviation units was plotted as a function of time following implantation in Fig. 6. A control set of rabbits had a solution of BCNU injected directly into the same location in the... 

Since these studies utilized autoradiographic techniques, it was important to determine the chemical nature of the material measured using radiochemical procedures. Using punch biopsies of the brain slices which were measured autoradiographically, it was shown using thin-layer chromatography that about 30% of the radioactivity was associated with unchanged BCNU (14). It was therefore concluded that the measurements described above accurately reflect brain concentrations of BCNU. 

Figure 9. Anti-PbTx antiserum inhibition of [ H]PbTx-3 binding to its receptor site in rat brain membrane preparations. Labeled toxin (0.5 nM in 1 ml PBS) was incubated with rat brain membranes (125 fig total protein) and increasing amounts of anti-PbTx antiserum (- -) or pre-immune serum (- -) for 1 hr at 4 C. Membrane-bound radioactivity was then measured in a centrifugation assay as previously described (8),...

A PET scan requires a substance called a tracer. A suitable tracer must accumulate in the target organ, and it must be modified to contain unstable radioactive atoms that emit positrons. Glucose is used for brain imaging, because the brain processes glucose as the fuel for mental and neural activities. A common tracer for PET brain scans is glucose modified to contain radioactive fluorine atoms. Our molecular inset shows a simplified model of this modified glucose molecule. 

The radioactive source need not aiways be introduced into the body. Inoperable brain tumors can be treated with y rays from an extemai source, usuaiiy a sampie of cobait-60. The patient is placed in a position where the y-ray beam passes through the tumor. The patient is moved so that the y rays irradiate the tumor from several angles. In this manner the tumor receives a much higher dose of radiation than the dose received by any surrounding tissues. 

Biochemical results (A", in nM) obtained in binding assays of radioactively labeled brain receptors [57] from the same 17 neuroleptics shown in Table 37.9. 

Twenty-four hours after application of 2.094 g TOCP labeled with radioactive phosphorus to a 15x20 cm area of clipped and depilated abdominal skin, radioactivity was detected in the following tissues in a dog, listed in order of decreasing concentration (counts per gram of tissue) skin and facia at site of application, liver, omental fat, blood, kidney, lung, muscle (triceps femoris), spinal cord, heart, spleen = brain = sciatic nerve, and bone (femur) (Hodge and Sterner 1943). 

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