Experimental brain tumors produced in rats (n = 10) by stereotactic implantation of cells from the F98 anaplastic glioma clone into the right caudate nucleus were studied in vivo using localized proton NMR and in vitro using high-resolution proton NMR, bioluminescent imaging of lactate, ATP and glucose distributions, and fluorescent imaging of regional pH. In vivo spectra from normal brain contralateral to the tumor regions showed resonances assignable to N-acetyl aspartate (NAA), creatines, choline-containing compounds, myo-inositol, glutamate and glucose in a pattern similar to those obtained from normal anaesthetized rats. In vivo tumor spectra were characterized by the almost complete absence of NAA, a substantial reduction of total creatine and glucose, and an increase of cholines. Based on the in vitro spectra the increase of the myo-inositol signal observed in vivo was mainly attributed to glycine. Histological examination as well as bioluminescent and fluorescent imaging indicated two stages of tumor development, i.e., solid vital tumors and tumors with necrosis. However, there was no consistent relationship between proton NMR observations and tumor development.

Experimental brain tumors were produced in cats by xenotransplantation of the rat glioma clone F98 into the white matter of the left hemisphere. One to 4 weeks after implantation, local adenosine triphosphate (ATP), glucose, lactate, and tissue pH were measured via imaging techniques in cryostat sections passing through the center of the tumor and correlated with changes in water and electrolyte content. The tumors exhibited a heterogeneous metabolic pattern, with a tendency for ATP to decrease and lactate to increase during tumor development. Tissue pH was above 7.5 in tumors with high ATP content but it sharply declined at low ATP levels. In peritumoral edema, ATP also decreased and lactate increased but, in contrast to tumor tissue, pH became more alkaline. Metabolic changes were associated with edema formation, as evidenced by the rise in water and sodium content. There was a distinct difference between tumor tissue and peritumoral edema: in tumor tissue, pH declined with increasing water content, whereas in peritumoral edema it increased. These observations are interpreted as follows: 1) in tumor tissue, "lactacidosis" and ATP depletion are attributed to disturbances in blood flow, resulting in metabolic failure and the intracellular "cytotoxic" accumulation of water; 2) in peritumoral edema, "lactalkalosis" is the result of an efflux of (alkaline) lactate salts from the tumor into the expanded extracellular compartment, and the decrease in ATP is the volumetric effect of extracellular "vasogenic" edema fluid and not the result of cellular energy failure. These findings are of importance for the interpretation of volume-selective magnetic resonance spectroscopy and may contribute to the establishment of spectroscopic criteria for the evaluation of therapeutical interventions.

In 8 gerbils (Meriones unguiculatus) focal cerebral ischemia was produced by occlusion of the left common carotid artery and the opposite external carotid artery. After two hours blood flow was measured with iodoantipyrine labeled with carbon 14, and evaluated by means of quantitative autoradiography. Thereafter the same brain sections were stained for regional potassium by means of a histochemical technique. Changes in tissue potassium content were assessed by measuring the differences in optical densities in homotopic brain regions of the stained sections. The correlation between blood flow and tissue potassium level revealed that below a flow threshold of about 0.23 ml/gm/min, a definite potassium loss from the tissue was observed. The combination of autoradiographic methods with a technique for measuring the regional distribution of potassium may be useful in providing additional information on the occurrence of disturbed electrolyte homeostasis after the onset of focal ischemia.

The topical and temporal relationship between neuronal injury and calcium loading was investigated in gerbils following bilateral carotid artery occlusion for 5 or 10 min and recirculation times from 15 min to 7 days. The association of histochemically visible calcium deposits with neuronal death was assessed by combining two calcium stains, alizarin red and arsenazo III, with conventional histological techniques. Neuronal calcium accumulation was evaluated morphometrically in the striatum, the frontoparietal cortex and the CA1 and CA4 sectors of the hippocampus. After 5-min ischemia and 1-2 days of recirculation numerous calcium-containing neurons appeared in the CA4 sector but only a few were present in the CA1 sector. After 4 days of recirculation calcium accumulation was visible in the whole CA1 sector and the dorso-lateral part of striate nucleus. After 10-min ischemia calcium accumulation started in these regions, as well as in the cortex, already after 1 day. In the CA1 sector calcium accumulation followed a typical time course: on day 2 only the lateral parts were affected, while on day 4 the whole CA1 neuronal band was calcium positive. The regional distribution of histological lesions matched that of calcium loading and, furthermore, the lesions appeared after a corresponding delay in the respective regions. Morphometric evaluations of calcium staining and histological lesions in the CA1 sector revealed a high correlation, indicating that calcium accumulation and neuronal death are closely associated both topically and temporally. This suggests that disturbances of calcium homeostasis such as those measured by this histochemical technique are the consequence of and not the reason for ischemic cell death.

The ultrafast inversion recovery snapshot FLASH technique was used to determine the kinetics of the contrast agent manganese (III) tetraphenylporphine sulfonate (MnTPPS) in experimental brain tumors in rats. In the first part of the investigation this technique was validated with the conventional inversion recovery spin-echo method by comparing in vivo T1 data of a normal rat brain. Agreement between T1 values obtained from both techniques was complete, as tested for a large number of pixels in identical coronal slices. In the second part the fast IR snapshot FLASH method was applied to study the effect of the NMR contrast agent MnTPPS on the T1 relaxation time of experimental gliomas in rat brains. T1 of normal brain tissue (1024-1035 ms), tumor (1217 ms), and edema (1199 ms) was determined with the inversion recovery version of the snapshot FLASH imaging technique. After intraperitoneal injection of MnTPPS (0.25 mmol/kg body wt) T1 decreased exponentially to 56% of control in tumor and to 62% in muscle. In normal and edematous brain tissue no significant changes in T1 were observed up to 5 h after injection of the contrast agent. Once the T1 contrast between tumor and peritumoral brain tissue had reached a saturation, the enhancement persisted for several hours to days. Therefore application of this contrast agent resulted in a sharp demarcation between glioma and peri-tumoral edema.