Summary: The effect of somatosensory stimulation on the local CBF (LCBF), CMRglu (LCMRglu), tissue pH, and tissue content of AT P, glucose, and lactate was studied in chloralose-anesthetized rats before and after 30 min of near-complete forebrain ischemia. In nonischemic rats LCBF in primary somatosensory cortex increased by 33%, LCMRglu increased by 55%, tissue glucose content decreased by 21%, and lactate increased by 30%. Local AT P and tissue pH did not change. Functional activation of the intact chloralose-anesthetized rat, in consequence, is associated with the stimulation of "aerobic"glycolysis but does not result in disturbances of energy or acid-base homeostasis. After 30-min ischemia and 3-h recircula-The coupling between neuronal activity, blood flow, and glucose utilization is a well-documented phenomenon that has been extensively studied in the past and that provides the basis for the meta bolic mapping of functional activity of the brain (Sokoloff, 1981). The general concept of metabolic coupling is based on the assumption that the activa tion of neuronal circuits is associated with an in crease of energy and transmitter turnover that has to be fueled by an increased supply of glucose and oxygen. Recently, evidence has been provided that a period of transient cerebral ischemia suppresses the stimulation-evoked increase of glucose utiliza tion for up to several days after the ischemic impact (Dietrich et aI., 1986). The responsiveness of blood flow to changes of Pco2, which is thought to con- tribute to the flow-metabolism couple, is also sup pressed for days, if not months, after ischemia even if spontaneous and evoked electrical activity return to normal (Schmidt-Kastner et aI., 1986).If functional activation of the brain after ischemia requires the same amount of energy as in the intact brain, and if neither blood flow nor glucose con sumption is increased during activation, the brain will have to cover the increased energy demands by utilizing its energy stores. This process should lead to measurable alterations in the regional content of energy metabolites. To test this hypothesis we have studied the effect of functional activation before and after global ischemia of rat brain by combining autoradiographic measurements of local CBF (LCBF) and CMRg\u (LCMRglu) with methods for the pictorial evaluation of energy metabolites and of the acid-base state of the brain ("multiparame tric brain imaging") (Hossmann et aI., 1985).The results obtained demonstrate that following a period of severe forebrain ischemia, activation of blood flow or glucose utilization is completely sup pressed although EEG and evoked potentials re cover. Surprisingly, this dissociation does not cause any disturbances of the regional energy state of the brain, which raises the fundamental question of the

SUMMARY In cats, the early development of Iscbemlc brain edema was studied 1 to 4 noun after transorbital occlusion of the left middle cerebral artery (MCA). Two groups of animals were compared: those in which blood flow in the territory of the MCA decreased below the threshold of 10-15 ml/100 g/mln (critical ischemia) and those in which it remained above this level (non-critical ischemia).In animals with critical ischemia, water content in the cortex of the MCA territory increased from 80.7 ± 0.4 to 83.0 ± 0 3 vol. % (means ± SE) within 4 h. Edema was associated with an increase in tissue osmolality by 16-22 mosm/kg w.w., and a rise of sodium from 262 ± 9 to 454 ± 13 meq/kg d.w. and a decrease of potassium from 442 ± 20 to 305 ± 32 meq/kg d-w. The sodium/potassium ratio rose from 0.60 ± 0.03 to 1.55 ± 0.17. The water and electrolyte disturbances were accompanied by a major shift of extracellular fluid into the intracellular compartment, as evidenced by the increase in cortical impedance from 282 to 660 ohm/cm within 2 h. According to the Maxwell equation, this reflects a narrowing of the extracellular space from 19.8 to 11.4%. Brain volume was continuously monitored using an induction transducer; swelling began within a few minutes of vascular occlusion, and it continued throughout the 4 h observation period. During this time the blood-brain barrier remained intact as evidenced by the absence of Evans blue staining. Edema was associated with disturbances of the energy producing metabolism, but there was DO strict correlation with either lactate or the concentration of high energy phosphates.In animals without critical ischemia, i.e. in which blood flow remained above 10-15 ml/100 g/min, edema was absent despite a distinct deterioration of the energy state of the brain. Edema was also absent in the border zone, in the territory of the posterior cerebral artery and in the contralateral hemisphere of animals with both critical and non-critical ischemia.It is concluded that the early ischemic brain edema following middle cerebral artery occlusion is of the c>totoxic type, that it develops at a flow rate below 10-15 ml/100 g/min, and that it is not strictly correlated with the energy state of the brain.

The evolution of brain infarction after transient focal cerebral ischemia was studied in mice using multiparametric imaging techniques. One-hour focal cerebral ischemia was induced by occluding the middle cerebral artery using the intraluminal filament technique. Cerebral protein synthesis (CPS) and the regional tissue content of adenosine triphosphate (ATP) were measured after recirculation times from 0 hours to 3 days. The observed changes were correlated with the expression of the mRNAs of hsp-70, c-fos, and junB, as well as the distribution of DNA double-strand breaks, visualized by TUNEL. At the end of 1 hour of ischemia, protein synthesis was suppressed in a larger tissue volume than ATP in accordance with the biochemical differentiation between core and penumbra. Hsp70 mRNA was selectively expressed in the cortical penumbra, whereas c-fos and junB mRNAs were increased both in the lateral part of the penumbra and in the ipsilateral cingulate cortex with normal metabolism. During reperfusion after withdrawal of the intraluminal filament, suppression of CPS persisted except in the most peripheral parts of the middle cerebral artery territory, in which it recovered between 6 hours and 3 days. ATP, in contrast, returned to normal levels within 1 hour but secondarily deteriorated from 3 hours on until, between 1 and 3 days, the ATP-depleted area merged with that of suppressed protein synthesis leading to delayed brain infarction. Hsp70 mRNA, but not c-fos and junB, was strongly expressed during reperfusion, peaking at 3 hours after reperfusion. TUNEL-positive cells were detected from 3 hours on, mainly in areas with secondary ATP depletion. These results stress the importance of an early recovery of CPS for the prevention of ischemic injury and suggest that TUNEL is an unspecific response of delayed brain infarction.

The vascular architecture of the brain of C57Black/6 and SV129 mice was studied following microvascular injection of carbon black stained latex. The dorsal brain surface was photographed to determine the number, diameter, and position of pial anastomotic vessels between the middle and anterior cerebral arteries. The mean number and diameter of anastomoses were not significantly different, but the line of anastomoses interconnecting the half way points of anastomotic vessels was located significantly closer to the midline in C57Black/6 mice, demonstrating that the middle cerebral artery had a larger vascular supplying territory than in SV129 mice. This explains the larger infarct volume previously reported in C57Black/6 mice, and raises concerns about the use of C57Black/6 and SV129 mice as parent strains for genetically modified animals in stroke research.

The evolution of brain infarcts during permanent occlusion of the middle cerebral artery (MCA) was studied in mice using multiparametric imaging techniques. Regional protein synthesis and the regional tissue content of ATP were measured on adjacent cryostat sections at increasing intervals after vascular occlusion ranging from 1 hour to 3 days. The observed changes were correlated with the expression of the mRNA of hsp70, c-fos, c-jun, and junB, as well as the distribution of DNA double-strand breaks visualized by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL). One hour after MCA occlusion, the tissue volume with suppressed protein synthesis was distinctly larger than that in which ATP was depleted. With ongoing ischemia time, the ATP-depleted area gradually expanded and, within 1 day, merged with the region of suppressed protein synthesis. Expression of hsp70 mRNA occurred mainly in the penumbra (defined as the region of suppressed protein synthesis but preserved ATP), peaking at 3 hours after vascular occlusion. Expression of the immediate-early genes c-jun, c-fos, and junB increased both in the penumbra and the periinfarct normal tissue already at 1 hour after vascular occlusion, with slightly different regional and temporal patterns for each of these genes. DNA fragmentations were clearly confined to neurons; they appeared after 1 day in the infarct core (defined as the region of suppressed ATP) and never were detected in the penumbra. The late appearance of TUNEL after infarcts had reached their final size and the absence in the penumbra points against a major pathogenetic role of apoptosis. Permanent MCA occlusion in mice thus produces a gradually expanding infarct, the final size of which is heralded by the early inhibition of protein synthesis.