Abstract-The effect of methotrexate (MTX) on local cerebral blood flow (I-CBF) was studied with autoradiographic[14C]-iodoantipyrine methods in normal con scious rats. I-CBF was reduced by 30-57% in the rats given MTX (100 mg or 200 mg/body) as compared to that in the saline injected control group, but no dose dependent effect was observed. The mechanism of I-CBF reduction by MTX was discussed.The administration of high-dose metho trexate (MTX) is now widely used in the treatment of osteogenic sarcoma and child hood brain tumors (1). However, this treat ment may lead to severe neurotoxicity such as acute encephalopathy (2). To examine the mechanisms of MTX neurotoxicity, Phillips et al. (3) developed a model of acute high-dose MTX encephalopathy in the rat and found that MTX reduced cerebral glucose me tabolism in the absence of systemic organ toxicity. Silverstein and Johnston (4) re ported that MTX produced histopathologic changes in the brain and it disrupted the syntheses of some neurotransmitters, or af fected the metabolism in the rat. However, the effect of MTX on the cerebral circulation has not been studied. In the present study, we have examined the effect of MTX on local cerebral blood flow (I-CBF) in normal con scious rats.CBF was measured by an autoradiographic technique (5). Male Sprague-Dawley rats weighing from 300 to 460 g were anesthetized with halothane and N20, and polyethylene catheters were inserted into the femoral artery and vein for arterial blood sampling and for drug infusion, respectively. The rats were then immobilized by loosely fitted plaster casts. After recovering from anesthesia, low dose MTX (LD-MTX) rats (n=5) were infused intravenously with 100 mg of MTX in 6 ml of saline for 2 hr. Similarly, high dose MTX (HD MTX) rats (n=4) were infused with 200 mg of MTX, and control rats (n=4) were infused with 6 ml of saline. For the measurement of I-CBF, [14C]-iodoantipyrine was infused intravenously for 1 min, and the animals were then sacrificed by intravenous injection of 1 ml of saturated KCI solution. During the 1 min infusion period, 18-20 arterial samples were collected for measurement of 14C activity. The tissue activity was determined in 33 defined brain structures with quantitative autoradiography. Plasma MTX concentrations were measured 2 hr after the start of MTX infusion by a dihydrofolate reductase inhi bition assay (Methotrexate® kit, Lederle). Mean arterial blood pressure (MABP) was continuously monitored, and PaC02, Pa02, pH and hematocrit values were measured im mediately before I-CBF measurement. Sta tistically significant differences were deter mined using one-way analysis of variance

A strong hyperperfusion was reported in transient ischemic tissue between 48 and 72 hours after middle cerebral artery occlusion (MCAO). Cerebral blood flow (CBF) estimated by continuous arterial spin labeling (CASL) with short delay after tagging was sensitive to cerebral blood volume (CBV) change. The delayed hyperperfusion may indicate a CBV increase after MCAO. For confirmation of the delayed hyperperfusion, we investigated a transit-time dependency in CASL at two days after MCAO. We also acquired CBF using the dynamic susceptibility contrast (DSC) at the same day. We have confirmed the CBF in transient ischemic tissue is quite higher (179.1+/-21.6 ml/100g/min) than normal tissue (121.0+/-6.9 ml/100g/min) with CASL using tagging delay of 0.4 sec. CBF estimated by DSC also show delayed hyperperfusion in transient ischemic tissue. These results confirm existence of physiological delayed hyperperfusion in transient ischemic area.

The distribution of functionally active monoamine oxidase type A (MAO-A) was investigated by in vivo quantitative autoradiography using [14C]clorgyline in normal, conscious rat brain. [14C]clorgyline was synthesized by the methylation reaction of N-desmethylclorgyline using [14C]methyliodide. Sixty minutes after [14C]clorgyline administration (1.58 MBq/animal i.v.), the brains were removed and prepared for autoradiography by washing the brain sections with 5% trichloroacetic acid solution to remove the nonbinding free tracer. The amount of MAO-A was calculated from the regional acid-insoluble tissue radioactivity and the specific activity of the tracer. The highest amount of MAO-A (5.84 nmol/g tissue) was found in the locus coeruleus. The interpeduncular nucleus, habenular nucleus, fasciculus retroflexus, and solitary tract nucleus possessed over 1.6 nmol/g tissue of MAO-A. Among 23 regions of interest, the lowest amount of MAO-A (0.37 nmol/g tissue) was found in the globus pallidus. The findings of this study suggest that the pattern of MAO-A parallels both in neuroanatomical distribution and in density that of norepinephrine and serotonin innervation. The MAO-A concentration was, however, relatively low in the dopamine-related areas. This corresponded to the previous results obtained by histochemical analysis. In addition, among the white matter structures, a high amount of MAO-A was found specifically in the fasciculus retroflexus.

Japan SUMMARY I5O-H2O2 is thought t o be a candidate o f attractive injectable tracers for the study of oxygen metabolism with PET. A simple synthetic method yielding I5O-H 0 in saline solut' n by the autoxidation of 2-ethylanthrahydroquinol with gaseous "0-0, produced by cyclotron target system is described.