Local cerebral blood flow during and after bilateral carotid artery occlusion in unanesthetized gerbils

Electrochemical monitoring of superoxide anion production and cerebral blood flow: effect of interleukin-1 beta pretreatment in a model of focal ischemia and reperfusion

Conditions associated with systemic infection, such as endotoxinemia, are known to increase the levels of pro-inflammatory cytokines such as interleukin (IL)-1 in the central nervous system. Systemic infection has been shown to be a common preexisting condition in patients with stroke. To examine a possible consequence of systemic infection, we used a novel electrochemical technique, which combines measurement of cerebral blood flow with measurement of superoxide anion concentrations, to examine the effect of pretreatment of pial vasculature with a proinflammatory cytokine, IL-1 beta, on cerebral blood flow and superoxide anion concentration in a rat model of middle cerebral artery occlusion and reperfusion. In addition, neutrophil recruitment was measured using an immunohistochemical technique. Our results indicate that exposure of pial and cerebral vasculature to IL-1 beta significantly accelerates recruitment of neutrophils, reduces cerebral blood flow, and increases superoxide anion concentration at the pial surface during reperfusion. These results support the idea that prior exposure of brain vasculature to IL-1 beta results in acceleration of cerebrovascular injury by accelerating recruitment of neutrophils, which secrete superoxide anion, during reperfusion. This finding has possible implications for the treatment of stroke with reperfusion agents in patients with preexisting infections.

Implementation of quantitative FAIR perfusion imaging with a short repetition time in time-course studies

Flow-sensitive alternating inversion recovery (FAIR) is a pulsed arterial spin labeling magnetic resonance imaging method for perfusion quantification. In its standard implementation for quantification with full longitudinal relaxation between acquisitions, its use in time-course investigations of rapidly changing flow values is limited. The time efficiency can be improved by decreasing the repetition time but quantification becomes problematic. This situation is further complicated if a whole-body radiofrequency transmit coil is not used since fresh blood spins will flow in from outside the coil. To alleviate these problems, the use of global pre-saturation is proposed. The resulting expression for the flow signal depends on the relationship between the imaging parameters and the coil inflow time and can be significantly simplified under certain combinations of these parameters. With this implementation of FAIR, quantitative flow maps of gerbil brains were obtained with a 3 minute time resolution in a study of the effects of reperfusion. The pre-occlusion flow measurements were in good agreement with values obtained by the standard FAIR implementation and by other techniques, but the low values following occlusion were underestimated due to the increased transit times.

Volume expansion during cardiopulmonary resuscitation reduces cerebral no-reflow

Resuscitation of the brain after cardiac arrest requires homogeneous blood recirculation which, however, may be impaired by low reperfusion pressure, intravascular coagulation, increased blood viscosity and endothelial cell swelling. Intravascular volume expansion induced by intravenous infusion of a small volume of hypertonic solution has previously been shown to improve nutritional flow to the brain after severe hemorrhage shock. We therefore investigated whether this therapy also improves cerebral reperfusion after cardiopulmonary resuscitation. Fourteen adult normothermic cats were resuscitated after 15 min of ventricular fibrillation by closed-chest cardiac massage in combination with epinephrine, bicarbonate and DC-defibrillations. Eight animals were submitted to the standard resuscitation protocol. Six cats received additionally 2 ml/kg/10 min 7.5% NaCl/6% hydroxyethyl starch solution for post-ischemic volume expansion. EEG, ECG, CBF, and the aortic, left ventricular, central venous and intracranial pressures were monitored. Reperfusion of the brain was visualized 30 min after cardiac resuscitation by labelling the circulating blood with fluorescein isothiocyanate albumin. Areas of impaired brain reperfusion (no-reflow)-defined by the absence of microvascular filling-were identified by fluorescence microscopy at eight standard coronal levels of the forebrain, and expressed as percent of total sectional area. All animals were successfully resuscitated although volume expansion decreased myocardial and cerebral reperfusion pressure during cardiopulmonary resuscitation. Treatment with hypertonic solution increased serum osmolality transiently and prevented hemoconcentration throughout the experiment. Cerebral no-reflow was significantly reduced from 28 +/- 13% to 15 +/- 6% of total forebrain sectional area. Volume expansion by small volume hypertonic solutions may, therefore, improve recovery of brain function following cardiac arrest.

Resistance to cerebral ischemia in developing gerbils

Two-, three-, four-, five-, and twelve-week-old gerbils were subjected to various periods of bilateral carotid occlusion (BCO). Rectal and cranial temperatures were maintained at 37 degrees C during BCO, and only rectal temperature was monitored for 30 min of reperfusion. Seven days after ischemia, animals were perfusion-fixed and the neuronal densities in the hippocampal CA1 subfields were counted. The extent of cerebral ischemia during BCO was evaluated with [14C]iodoantipyrine autoradiography. The rectal temperature spontaneously fell to 33-34 degrees C during reperfusion in 2-week-old gerbils, although animals over 3 weeks old presented postischemic hyperthermia. Two-week-old animals therefore were divided into three experimental groups: In one group (2-week-old group I) rectal temperature was not regulated during 30 min of reperfusion, while in the other two groups (2-week-old groups II and III) rectal temperature was regulated at 37 and 38 degrees C, respectively, during reperfusion. Five-minute BCO produced almost complete destruction of the CA1 neurons in 12-week-old animals. In contrast, most CA1 neurons survived 30 min of BCO in 2-week-old group I and 15 min of BCO in 2-week-old groups II and III. [14C]Iodoantipyrine autoradiography revealed that BCO produced severe forebrain ischemia in 2-week-old gerbils as well as in 12-week-old gerbils. These findings indicate that developing gerbils have a greater tolerance to cerebral ischemia and that such ischemic tolerance is not due to a collateral network between the vertebrobasilar and the carotid circulations previously reported to develop more abundantly in developing gerbils.

Differential vulnerability in the hindbrain neurons and local cerebral blood flow during bilateral vertebral occlusion in gerbils

Differential vulnerability in the hindbrain neurons was examined immunohistochemically during hindbrain ischemia in the gerbil. Hindbrain ischemia was produced by extracranial occlusion of the bilateral vertebral arteries just before their entry into the transverse foramen of the cervical vertebra. Local cerebral blood flow was measured by quantitative autoradiographic technique after 5 min of ischemia and was reduced to less than 5 ml/100 g per min in the cerebellum, the pons, and the medulla, indicating that severe and reproducible hindbrain ischemia was induced immediately after occlusion. For immunohistochemical investigation, four gerbils each were used for each ischemic period of 5, 10, 15, and 30 min. Immunohistochemical lesions, detected by the reaction for microtubule-associated protein 2, were visible in the lateral vestibular nucleus and the cerebellar interpositus nucleus even after 5 min of ischemia. These results suggested that these areas were more vulnerable than others, although blood flow was markedly reduced in various regions of the hindbrain. In contrast, areas related to respiratory or cardiovascular control were rather resistant to ischemia. The present study suggests that selective vulnerability during hindbrain ischemia depends mainly on different metabolic characteristics inherent to various neurons in the hindbrain.