Singlet oxygen induced cerebral vasospasm: an experimental study in rats

A new experimental model is described which can be used as an alternative to study the effects of subarachnoid hemorrhage (SAH) in rats. Vasospasm of the basilar artery is induced photochemically after transpalatal illumination of intracisternally injected rose bengal in two different rat strains. Singlet oxygen, generated in the subarachnoid space, elicits vasospasm which has been demonstrated angiographically at 90 min and 24 h after photosensitisation. Sprague Dawley rats responded better than Wistar rats. Dilution of rose bengal in water was more vasospastic than dilution of rose bengal in artificial CSF. Since the action of singlet oxygen is similar to that of free radicals, this experiment gives an argument for the hypothesis that free radicals play a leading role in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage.     

The intra-arterial ultrasonography as an exclusive exploration method to determine atherosclerotic lesions of the arterial wall in a preclinical stage.

An intravascular ultrasonography of the peripheral arterial system was applied following on the coronarography to 56 patients suffering from one or several critical stenoses on the coronary arteries. Though the clinical vascular examination and the subsequent noninvasive examination of the peripheral arterial system of all these patients turned out to be completely normal, the intra-arterial ultrasonography was able to reveal important atherosclerotic alterations in the wall of the abdominal aorta and of the iliac arteries in the case of 51 of these patients. The intra-arterial ultrasonography appears to be a very sensitive method of exploration, permitting atherosclerotic changes of the arterial wall to be detected at a very early pre-clinical stage, even long before these anomalies could have caused a specific pattern of complaints.     

Are the various thrombolytic agents equally effective in the treatment of acute transmural myocardial infarction?

While it is no longer possible to imagine the treatment of an acute transmural myocardial infarction without the use of thrombolytic agents, some discussion still exists as to the choice of the thrombolytic agent. Our study concerns a group of 160 patients with an acute transmural myocardial infarction, 60 of whom were treated with anistreplase, 52 with streptokinase and 48 with alteplase. Statistically, the administration of anistreplase was associated with a significantly higher frequency of ventricular arrhythmias in comparison to the other thrombolytic agents, whereas after subsequent coronary angiography, the anistreplase group revealed a significantly lower number of completely occluded coronary arteries. The data from this study demonstrate that anistreplase is a very valuable thrombolytic agent. It may even be more effective than streptokinase and alteplase in the treatment of acute myocardial infarction when the patency of the coronary arteries 1 month after the acute coronary event is considered the primary endpoint.     

Dorsal-ventral gradient in vulnerability of CA1 hippocampus to ischemia: a combined histological and electrophysiological study

Transverse hippocampal slices were prepared after 7 days survival from rats subjected to 8 min of global incomplete ischemia by temporary occlusion of both carotid arteries and hypotension. The slices demonstrated a dorsal-ventral gradient in the amount of ischemic neuronal necrosis in the CA1 region. Histologically ischemic cell change decreased from 90% dorsoseptally to 10% ventrotemporally. Electrophysiological analysis of the number of slices with viable synaptic transmission in CA1 also revealed a septotemporal gradient in susceptibility to ischemia.     

Development of a novel fluorescent microsphere technique to combine serial cerebral blood flow measurements with histology in the rat

The aim of the study was to evaluate the microsphere technique for the quantitative assessment of regional cerebral blood flow (rCBF) at different time points in the same animal. Yellow-green and red fluorescent microspheres with a diameter of 15 microm were injected into the rat at two different time points via a cannula inserted into the left ventricle of the heart. The reproducibility of the rCBF measurements in normocapnic conditions (n=7) and the responsiveness of the flow to hypercapnia induced by 7% CO(2) (n=7) was examined. The fluorescent spheres were counted on 100 microm vibratome sections of perfusion-fixed brains and rCBF was calculated. The median total CBF in normocapnic rats was 224 ml/min/100 g for the first microsphere injection and 216 ml/min/100 g for the second one. In the hypercapnic group CBF amounted to 400 ml/min/100 g and after 30 min of normocapnia decreased to 178 ml/min/100 g. No differences between the left and right hemisphere were found and there was no indication that the first injection might have influenced the second one. The described approach allows combining the assessment of rCBF at different time points in physiological or pathological conditions with histological evaluation of related morphological alterations in the same brain region of the same animal.     

The course of vasospasm following subarachnoid haemorrhage in rats

Summary The course of vasospasm following subarachnoid haemorrhage in rats was studied using vertebrobasilar angiography. Wistar and Sprague Dawley rats were compared with respect to vasospastic response after bleeding. A more pronounced vasospasm was found in Sprague Dawley rats. In order to avoid a possible toxic effect on the contrast medium, only one angiogram per animal was initially performed. However, a comparison with the results obtained in a separate series of non-challenged animals demonstrated a difficulty due to high variability in basilar artery size in the latter group. Therefore, vasospasm can be more readily shown if multiple angiograms are used in the same animal so that the vasospasm can be expressed as a percentage of the initial diameter of the basilar artery. It was found that multiple angiograms are well tolerated when nonionic contrast media are used.     

Haemodynamic,intracranial pressure and electrocardiographic changes following subarachnoid haemorrhage in rats

Summary Experimental induction of subarachnoid haemorrhage in rats resulted in acute haemodynamic changes. Heart rate decreased concomitantly with a rise in arterial blood pressure. Intracranial pressure increased and consequently cerebral perfusion pressure dropped. These changes as well as the observed electrocardiographic (ECG) changes were comparable to those reported in patients. Apart from blood also saline, when introduced into the cisterna magna, was able to elicit such abnormalities. The haemodynamic and electrocardiographic changes, which result from subarachnoid haemorrhage, may even become aggravated, when repetitive injections of blood or saline are given into the cisterna magna and when cerebral angiography is performed prior to induction of the subarachnoid haemorrhage. Chronic intracranial pressure monitoring during the 48 hours following subarachnoid haemorrhage revealed no significant rise in pressure.A thorough control of the experimental conditions is thus of utmost importance in order to give a valid interpretation of the observed anomalies.     

Method for the determination of the levels of beta-amyloid peptide in the CSF sampled from freely moving rats

INTRODUCTION: In the present study, a model was developed to determine the effect of secretase inhibition on beta-amyloid peptide (Abeta) levels in the cerebrospinal fluid (CSF) of freely moving adult rats. METHODS: Rats were chronically implanted with a cannula into the cisterna magna and CSF samples were collected at different time points from the same animal without anaesthesia. The levels of CSF Abeta were measured by a sandwich ELISA assay. RESULTS: Administration of DAPT, a functional gamma-secretase inhibitor, resulted in a substantial reduction of Abeta40 and Abeta42, confirming the in vivo functionality of the CSF as a biomarker source for endogenous APP processing modulation by secretase inhibitors. DISCUSSION: Thus, the present work provides clear evidence for the usefulness of CSF sampling from the freely moving rat model for testing the effectiveness of small molecule inhibitors of Abeta production.     

Impaired autoregulation of cerebral blood flow in an experimental model of traumatic brain injury

In order to study the pathophysiology and the intracranial hemodynamics of traumatic brain injury, we have developed a modified closed-head injury model of impact-acceleration that expresses several features of severe head injury in humans, including acute and long-lasting intracranial hypertension, diffuse axonal injury, neuronal necrosis, bleeding, and edema. In view of the clinical relevance of impaired autoregulation of cerebral blood flow after traumatic brain injury, and aiming at further characterization of the model, we investigated the autoregulation efficiency 24 h after experimental closed-head injury. Cortical blood flow was continuously monitored with a laser-Doppler flowmeter, and the mean arterial blood pressure was progressively decreased by controlled hemorrhage. Relative laser-Doppler flow was plotted against the corresponding mean arterial blood pressure, and a two-line segmented model was applied to determine the break point and slopes of the autoregulation curves. The slope of the curve at the right hand of the break point was significantly increased in the closed head injury group (0.751 +/- 0.966%/mm Hg versus -0.104 +/- 0.425%/mm Hg,p = 0.028). The break point tended towards higher values in the closed head injury group (62.2 +/- 20.8 mm Hg versus 46.9 +/- 12.7 mm Hg; mean +/- SD, p = 0.198). It is concluded that cerebral autoregulation in this modified closed head injury model is impaired 24 h after traumatic brain injury. This finding, in addition to other characteristic features of severe head injury established earlier in this model, significantly contributes to its clinical relevance.