The effect of a simulated subarachnoid hemorrhage on cerebral blood flow in the monkey

Endoscopic technique: a new model of subarachnoid hemorrhage in rats

It has become increasingly evident that the pathophysiology of cerebral vasospasm following subarachnoid hemorrhage (SAH) which described the ischemic consequences of cerebral arterial constriction is complex and multifactorial. In an attempt to study cerebral vasospasm, numerous investigators have used experimental animal models that resemble cerebral vasospasm in humans. No ideal model for SAH has been found as yet, and hence the quest for such a model continues. We developed an endoscopic technique that permits a direct vision of internal carotid artery and puncturing the artery to provoke SAH. This model will closely reflect the clinical setting of an aneurysm rupture. The onset of SAH was characterized by a sudden decrease of cerebral blood flow (CBF) and cerebral blood volume (CBV) by at least 40% in the first 20 min. Following this initial drop, there was an increase in the CBF and the CBV, however, they remained significantly below the base line values, at the end of 1 h. This study describes a new model of SAH in rat that simulates the clinical phenomenon of ruptured intracranial aneurysm that also produces cerebral vasospasm.

Induction of heat shock protein 70 in the rat brain following intracisternal infusion of autologous blood: evaluation of acute neuronal damage

OBJECT

Investigation into a potential treatment for the acute period following onset of spontaneous subarachnoid hemorrhage (SAH) is hampered by the lack of a standardized experimental model. For that purpose the authors elaborated on a small-animal model in which computer-controlled intracisternal blood infusion is used and investigated whether this model can reliably reproduce acute neuronal injury after SAH.

METHODS

Whole autologous blood (blood-infused group) or isotonic saline (control group) was infused into the cisterna magna or olfactory cistern of rats. The infusions decreased exponentially during a 5-minute period. Throughout the infusion period, intracranial pressure (ICP) was monitored. Neuronal injury was quantified by observing tissue immunoreactivity to a 70-kD heat shock protein (HSP70) and comparing this with the tissue's reaction to hematoxylin and eosin staining. On Days 1, 3, and 5, the CA1, CA3, and dentate gyrus regions of the hippocampus were analyzed, respectively. During saline infusion ICP increased within seconds beyond 80 mm Hg and afterward decreased in accordance with the infusion rate. During the infusion of blood, the same initial pressure peak was found, but the ICP remained increased beyond this pressure level throughout the 5-minute infusion period. The HSP70 immunoreactivity in the saline-infused group was found only on Day 1 in the CA1 region and the dentate gyrus, but not in the CA3. After injection of whole blood, there was HSP70-positive staining in the CA1, CA3, and dentate gyrus regions throughout the observation period.

CONCLUSIONS

The controlled cisternal infusion of blood caused neuronal injury that resembled that of previous experimental models that produce SAH by rupture of intracranial vessels with endovascular techniques. Unlike those experiments, the intracisternal infusion technique presented by the authors provides more standardized bleeding with regard to ICP, the volume of subarachnoid blood, and the extent of acute cellular injury.

Cerebral blood flow and intracranial pressure during experimental subarachnoid haemorrhage

The relationships of intracranial pressure (ICP), systemic blood pressure (SBP) and cerebral blood flow (CBF) during experimental subarachnoid haemorrhage were investigated in cats. Continuous monitoring of regional cerebral blood flow (rCBF) was done by a thermal diffusion method using a Peltier stack. During haemorrhage ICP rose within 5.4 +/- 0.97 minutes from 10.5 +/- 4.9 to 176.1 +/- 27.8 mmHg. This strong increase of ICP resulted in a temporary arrest of cerebral circulation. The Cushing response during the haemorrhage could not improve the cerebral circulation, but in contrast caused a further increase of ICP. After the haemorrhage the cerebral blood flow normalised within minutes. It is concluded, that the Cushing response during a subarachnoid haemorrhage should be regarded as a deleterious rather than a beneficial mechanism.

Experimental vasospasm: experiences with a canine model and failure of naloxone therapy

Experimental vasospasm was studied in a canine model utilizing subarachnoid injection of autologous blood. Alterations in the size of the basilar artery were noted angiographically. Naloxone, an opioid receptor antagonist, has been reported to have a beneficial effect on neurological dysfunction secondary to cerebral ischemia. No significant change in the diameter of the basilar artery was noted in dogs either with or without spasm when treated with naloxone. We have concluded that naloxone has no detectable vasodilatory effect on the cerebral arteries of dogs.

An experimental study of acute subarachnoid haemorrhage in baboons: changes in cerebral blood volume, blood flow, electrical activity and water content

Subarachnoid haemorrhage following transection of the posterior artery was produced in 10 baboons. Cerebral blood volume (CBV) decreased transiently after subarachnoid haemorrhage. Two basic patterns of intracranial pressure (ICP) were observed; in one ICP returned to normal but in the other it remained elevated. In this latter group four out of five animals showed an increase in CBV above the original level. There were delays in sensory conduction (measured using somatosensory evoked potentials) bilaterally; those on the contralateral side to the bleed were correlated with ICP whereas other factors are implicated on the ipsilateral side. Initial flow reduction and restoration of cerebral blood flow were both correlated with water content.

The blood-brain barrier following experimental subarachnoid hemorrhage. Part 1: Response to insult caused by arterial hypertension

In three groups of cats, the authors studied the effect of subarachnoid hemorrhage (SAH) on the permeability of the blood-brain barrier (BBB) to the penetration of Evans blue-protein complex. One group received arterial hypertension alone, one group SAH alone, and one group SAH followed by arterial hypertension. Animals subjected to arterial hypertension alone showed areas of BBB breakdown. However, when cats were rendered hypertensive after SAH, there were no demonstrable BBB lesions. The SAH was produced by intracisternal injection of whole blood and hypertension by the intravenous injection of metaraminol. The preservation of the BBB after SAH is discussed. Vasospasm is considered as a possible hemodynamic variable responsible for the protection of the BBB from hypertensive damage. The need for a new model is proposed to further investigate the state of the BBB after SAH.

Regional cerebral blood flow in the acute stage of experimentally induced subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) was induced in 13 adult mongrel cats by a slow injection of fresh autogenous blood into the cisterna magna. Serial determinations of regional cerebral blood flow (rCBF) in the cortex and deep-seated areas (internal capsule, thalamus, and caudate nucleus) were made during the following 2 hours, while intracranial pressure (ICP) was maintained at normal values. A decrease in rCBF was observed in all the areas examined. This reduction followed a characteristic triphasic pattern with an initial steep decline immediately after the SAH. The clinical implications of these findings are discussed.

Cerebrovascular responses to subarachnoid blood and serotonin in the monkey

Preliminary in vitro experiments were performed to determine the serum concentration of serotonin in the monkey, and the ability of cyproheptadine to block serotonin and serum-induced contractions in monkey cerebral arteries. Thirty-four cynomolgus monkeys were subsequently used to study changes in regional cerebral blood flow (CBF) obtained by the intracartoid 133Xe technique, and in the angiographic cerebral arterial caliber resulting from subarachnoid injection of artificial cerebrospinal fluid (CSF), blood, and serotonin. Five animals in each injection group were given 1.0 mg/kg intravenous cyproheptadine (a serotonin-blocking agent) during the post-injection period. Subarachnoid injection of artificial CSF produced no change in CBF or arterial caliber. Post-injection administration of cyproheptadine also had no effect on these parameters. A subarachnoid injection of fresh autogenous blood produced a significant but transient (less than 1 hour) decrease in CBF and moderate vasospasm, which lasted at least 3 hours. This vasospasm was essentially unaffected by intravenous cyproheptadine. The CBF and arterial caliber were unchanged following a subarachnoid injection of serotonin at concentrations (5 x 10(-6)M) present in normal monkey serum. In contrast, 5 x 10(-6) M serotonin invariably produced near maximal contractions in the in vitro cerebral artery preparations. Higher (x10) serotonin concentrations caused a transient CBF response similar to that obtained with blood. However, the cerebral vasospasm induced was of shorter duration than that obtained with blood. These results do not support a major role for serotonin in the production of post-subarachnoid hemorrhage vasospasm. Moreover, our data indicate that in vitro experiments do not reflect the ability of serotonin to constrict cerebral arteries in the intact animal.

Cerebral arterial responses to induced hypertension following subarachnoid hemorrhage in the monkey

Regional cerebral blood flow (rCBF), angiographic cerebral arterial caliber, and cerebrospinal fluid (CSF) pressure were measured in rhesus monkeys to determine the effect of experimentally induced subarachnoid hemorrhage (SAH) on cerebral arterial responses to graded increases in blood pressure. These measurements were also performed in a control group of monkeys subjected to a mock SAH by injection of artificial CSF into the cerebral space. Before subarachnoid injection of blood or artificial CSF, graded increases in mean arterial blood pressure (MABP) to a level 40% to 50% above baseline values had no effect on rCBF. The major cerebral arteries constricted and CSF pressure remained unchanged. Similar responses were observed after injections of artificial CSF. When MABP was increased in animals that had been subjected to subarachnoid injection of blood, rCBF increased and was associated with dilatation of the major cerebral arteries and moderate increases in CSF pressure. These results demonstrate that cerebral arterial responses to increases in blood pressure may be abnormal in the presence of subarachnoid blood. The manner in which abnormal cerebral arterial reactivity, changes in blood pressure, and vasospasm combine to determine the level of cerebral perfusion following SAH is postulated.