The time course of intracranial pathophysiological changes following experimental subarachnoid haemorrhage in the rat

Diffusion MR imaging during acute subarachnoid hemorrhage in rats

BACKGROUND AND PURPOSE

We analyzed the temporal and spatial pattern of water diffusion changes during acute subarachnoid hemorrhage (SAH) in rat brain to identify factors contributing to the acute pathophysiology of SAH.

METHODS

Subarachnoid hemorrhage was remotely induced via perforation of the circle of Willis with an endovascular suture during MR imaging. A fast echo-planar imaging technique was used to acquire 60 maps of the apparent diffusion coefficient (ADC) beginning 1 min before and continuing for 11 min after induction of SAH. A high-resolution spin-echo diffusion sequence was used to follow diffusion changes over 6 h after SAH. Sham-operated control (n=3), nonheparinized (n=6), and heparinized (n=5) groups were studied.

RESULTS

Sham-operated control animals did not show ADC changes over time. In both SAH groups, however, a sharp decline of ADC within 2 min of SAH was consistently observed in the ipsilateral somatosensory cortex. These decreases in diffusion then spread within minutes over the ipsilateral hemisphere. Similar ADC decreases on the contralateral side started with a further time delay of 1 to 3 min. From 30 min onward, the extent of the diffusion abnormality decreased progressively in the nonheparinized animals. No recovery was observed in heparinized rats.

CONCLUSIONS

MR diffusion imaging allows new insight into the pathophysiology of acute SAH: The spatial and temporal pattern of diffusion changes suggests the initial occurrence of acute vasospasm and subsequently "spreading depolarization" of brain tissue. Persistent hemorrhage in heparinized animals was reflected by early decline of ADC values throughout the entire brain.

Antivasospastic and brain-protective effects of a hydroxyl radical scavenger (AVS) after experimental subarachnoid hemorrhage

OBJECT

The radical scavenger (+/-)-N,N'-propylenedinicotinamide (AVS) was shown recently to ameliorate delayed neurological deficits resulting from ischemia in patients who have had an aneurysmal subarachnoid hemorrhage (SAH). The aim of this study was to evaluate the effect of AVS administration after experimental SAH on 1) behavioral deficits; 2) angiographically confirmed basilar artery (BA) spasm; and 3) blood-brain barrier (BBB) permeability changes.

METHODS

These parameters were measured by 1) using a battery of well-characterized chronic assessment tasks over a 5-day observation period; 2) assessing in vivo the mean vessel diameter 2 days after SAH; and 3) evaluating the extravasation of protein-bound Evans Blue dye by using a spectrophotofluorimetric technique 2 days after SAH. Groups of eight to 10 rats received injections of 400 microl of autologous blood into the cisterna magna. Within 5 minutes after the surgical procedures were completed the rats were treated with an intravenously administered continuous infusion of saline (Group III) or AVS (1 mg/kg/minutes, Group IV). Results were compared with those in sham-operated animals treated with intravenously administered saline (Group I) or AVS (Group II). The AVS-treated rats had significantly improved balance beam scores on Days 1 to 2 (p < 0.05), shorter beam traverse times on Day 1 (p < 0.05), and better beam walking performance on Days 1 to 4 (p < 0.01), but no significant effect was seen in terms of SAH-related changes in body weight. Treatment with AVS also attenuated the SAH-induced BA spasm (p < 0.05) and decreased BBB permeability changes in frontal, temporal, parietal, occipital, and cerebellar cortices, and in the subcortical and cerebellar gray matter and brainstem (p < 0.01).

CONCLUSIONS

These results demonstrate useful antivasospastic and brain-protective actions of AVS after induction of experimental SAH and provide support for observations of beneficial effects of AVS made in the clinical setting.

Anticardiolipin antibody aggravates cerebral vasospasm after subarachnoid hemorrhage in rabbits

BACKGROUND AND PURPOSE

We previously reported that patients with antiphospholipid antibodies (aPLs) frequently demonstrate cerebral infarction due to cerebral vasospasm after subarachnoid hemorrhage (SAH). To examine the participation of aPLs in the pathogenesis of vasospasm after SAH, we studied the relationships of aPLs and SAH in an animal model.

METHODS

SAH was produced in 34 rabbits that received two subarachnoid injections of autologous arterial blood. The animals were divided into four experimental groups: SAH was induced in group A (n=9), intracutaneous injection of cardiolipin (CL) was performed before the induction of SAH in group B (n=5), intravenous injection of CL was performed before SAH in group C (n=12), and cyclosporin A was infused intravenously after the intravenous injection of CL and induction of SAH in group D (n=8). Enzyme-linked immunosorbent assay identifying the titer of IgG CL antibodies, neurological evaluation, cerebral angiography, and histological examination were performed in all four groups.

RESULTS

A significant elevation of anti-CL antibodies, aggravation of neurological deficit, and reduction of caliber of the basilar artery were observed in rabbits that received the intravenous immunization of CL (group C). The administration of cyclosporin A reduced the titer of anti-CL antibody, aggravation of neurological deficit, constriction of basilar artery, and the incidence of cerebral infarction (group D).

CONCLUSIONS

Anti-CL antibodies may therefore be involved in the deterioration of cerebral vasospasm after SAH.

Acute vasoconstriction after subarachnoid hemorrhage

OBJECTIVE

Decreased cerebral blood flow (CBF) and cerebral ischemia occurring immediately after subarachnoid hemorrhage (SAH) may be caused by acute microvascular constriction. However, CBF can also be influenced by changes in intracranial pressure (ICP) and cerebral perfusion pressure (CPP). The goal of these experiments was to assess the significance of acute vasoconstriction after SAH and its relationship to changes in CBF, ICP, CPP, and extracellular glutamate concentrations.

METHODS

Three experiments were performed using the endovascular filament technique to produce SAH. In the first experiment, CBF, ICP, and CPP were measured for 60 minutes after SAH (n = 21) and were correlated with the 24-hour mortality rate. In the second experiment, rats undergoing SAH (n = 23) or a sham procedure (n = 7) were perfused 60 minutes after SAH for measurement of the circumference and wall thickness of the internal carotid and anterior cerebral arteries and correlation with CBF, ICP, and CPP. In the third experiment (n = 11), extracellular glutamate concentrations determined by hippocampal and cortical microdialysis and high performance liquid chromatography were correlated with physiological changes.

RESULTS

CBF reductions to less than 40% of baseline for 60 minutes after SAH predicted 24-hour mortality with 100% accuracy and were used to define "lethal" SAH. In contrast, ICP and CPP 60 minutes after SAH were not correlated with the mortality rate. The vascular circumference was significantly smaller in lethal than in sublethal SAH or sham-operated rats (P < 0.001). Vessel measurements were correlated with both CBF and hemorrhage size (P < 0.01). Extracellular glutamate concentration increased to 600% of baseline after lethal SAH in both hippocampus and cortex and was inversely correlated with CBF (r = 0.9, P < 0.001) but did not increase after sublethal SAH.

CONCLUSION

Acute vasoconstriction after SAH occurs independently of changes in ICP and CPP and is associated with decreased CBF, larger hemorrhage size, persistent elevations of extracellular glutamate, and poor outcome. Acute vasoconstriction seems to contribute directly to ischemic brain injury after SAH. Further evaluations of pharmacological agents with the potential to reverse acute vasoconstriction may increase CBF and improve outcome.

An improved canine model of subarachnoid hemorrhage using intrathecal indwelling catheters

In the present study, the feasibility of intrathecal indwelling catheters in the preparation of a repeated subarachnoid hemorrhage (SAH) model in dogs, as well as chronic intrathecal administration of therapeutic agents against the ensuing cerebral vasospasm was examined. Briefly, through a small suboccipital incision, two catheters were introduced into the subarachnoid space so that their tips were positioned in the prepontine cistern. One was used to induce SAH by infusing autologous blood, and the other to administer pharmacological agents (saline and/or saline containing a dye in this study) by means of an osmotic pump. The occurrence of cerebral vasospasm was followed by angiography via the catheter placed in the vertebral artery. The obtained results show: i) the injected blood effectively formed a subarachnoid clot in the prepontine cistern, invariably leading to the occurrence of severe cerebral vasospasm of the basilar artery; ii) the fluid injected by the osmotic pump was evenly distributed in the cisterns around the brain stem; iii) on post mortem pathological examination, no injury of the brain or the major arteries ascribable to the placement of catheters was found. Therefore, the present model is considered to be useful for both the investigation of pathophysiology and therapy of cerebral vasospasm following SAH, to be more favorable from the standpoint of animal protection, and more convenient and reliable than those used until now.

Focal hyperexpression of hemeoxygenase-1 protein and messenger RNA in rat brain caused by cellular stress following subarachnoid injections of lysed blood

Induction of the hemeoxygenase-1 (ho-1) stress gene is of importance for rapid heme metabolism and protection against oxidative injury in vitro and in vivo. Although ho-1 expression is observed in glia following exposure to whole blood and oxyhemoglobin, expression is mild, and other stress genes are not induced simultaneously in this setting. Hemeoxygenase-1 can be induced by several other physiological stresses in addition to heme. In the brain, ho-1 induction has been observed in the penumbra following focal cerebral ischemia. Because lysed blood is a spasmogen, the authors studied focal hyperexpression of the ho-1 gene after injection of lysed blood, whole blood, or saline into the cisterna magna of adult rats. Immunocytochemical analysis of HO-1 was performed at 1, 2, 3, and 4 days after the injections. Because the 70-kD inducible heat shock protein (HSP70) is induced by cellular stress, alternate sections were immunostained for HSP70 to assess whether focal hyperexpression was a stress phenomenon. An oligonucleotide probe was also used for in situ hybridization to demonstrate that ho-1 messenger (m)RNA was present. Focal HO-1 immunostained areas were observed after lysed blood injection only and were located mainly in the basal cortex and cerebellar hemisphere, although focal hyperexpression was also found in many other regions. The intensity of staining and the number of regions were maximum at 1 day. Double-labeled immunofluorescence revealed that many HO-1-immunoreactive cells were microglia. The HSP70 immunostaining of adjacent sections from the same animals demonstrated focal regions of immunoreactivity whose topography corresponded exactly with the topography of the HO-1-immunostained areas. Conventional histology in regions of HO-1 hyperexpression was often normal. In situ hybridization using the same oligonucleotide demonstrated that ho-1 mRNA was induced in focal areas of forebrain and in large regions of cerebellum within 6 hours of injection. These results demonstrate that focal hyperexpression of the ho-1 stress gene occurs after lysed blood injection and appears to be an indicator of cellular stress and injury in regions in which infarction does not occur. These results also suggest that cellular injury that occurs after injection of lysed blood may go undetected using conventional histology. Although direct heme metabolism was not investigated, our results indicate that rapid metabolism of heme, both intracellular and extracellular, may prove to be beneficial after subarachnoid hemorrhage.

Systemic complement depletion inhibits experimental cerebral vasospasm

OBJECTIVE

Cerebral vasospasm is the leading cause of morbidity and mortality in patients who are hospitalized because of aneurysmal subarachnoid hemorrhage (SAH). Recent work has suggested that activation of the complement cascade contributes to the development of cerebral vasospasm. To further examine this hypothesis, a rabbit model of SAH was employed.

METHODS

Two milliliters of autologous arterial blood was injected into the region of the perimesencephalic cistern. Forty-eight hours after SAH was induced, intravital perfusion-fixation was performed. Morphometric analysis of the basilar artery was used to assess the extent of cerebral vasospasm after pretreatment with the complement depleting agent, cobra venom factor (CVF), or vehicle. Rabbits were randomized to one of four groups: 1) sham (n = 5); 2) sham + CVF (n = 4); 3) SAH (n = 10); or 4) SAH + CVF (n = 7). Twenty-four hours before induction of SAH, the animals received either 100 units/kg CVF or vehicle. The total hemolytic potential of the serum confirmed a significant (P < 0.05) reduction in serum complement activity 24 hours after the administration of CVF.

RESULTS

Pretreatment with CVF significantly (P < 0.0083) reduced the extent of vasospasm, as assessed by lumen diameter from 393.9 +/- 100.1 microns (mean +/- standard deviation) in the SAH group to 510.7 +/- 72.8 microns in the SAH + CVF group, when compared with the sham (594.5 +/- 27.9 microns) and sham + CVF (587.7 +/- 47.3 microns) groups.

CONCLUSION

The results suggest a role for complement activation in SAH.

Brain energy metabolism in the acute stage of experimental subarachnoid haemorrhage: local changes in cerebral glucose utilization

An experimental model was used to investigate acute alterations of cerebral metabolic activity in rats subjected to subarachnoid haemorrhage (SAH). Haemorrhages were produced in anaesthetized animals by injecting 0.3 ml of autologous, arterial nonheparinized blood into the cisterna magna. Control rats received subarachnoid injections of mock-cerebrospinal fluid to study the effect of sudden raised intracranial pressure, or underwent sham operation. Three hours after SAH rats were given an intravenous injection of [14C]-2-deoxyglucose. Experiments were terminated by decapitation, and the brains were removed and frozen. Regional brain metabolic activity was studied by quantitative autoradiography. In comparison with sham-operated controls, cerebral metabolic activity was diffusely decreased after SAH. Statistically significant decreases in metabolic rate were observed in 23 of 27 brain regions studied. Subarachnoid injections of mock-cerebrospinal fluid also produced depression of cerebral metabolic activity, but quantitatively these changes were not as pronounced and diffuse as in SAH rats. The present study shows that a widespread depression of brain metabolism occurs in the acute stage after experimental SAH and is probably secondary to the subarachnoid presence of blood itself and/or blood products.

Acute Cerebral Artery Constriction in the Spontaneously Hypertensive Rat following Blood and Plasma Administration into the Subarachnoid Space

The purpose of the present study was to demonstrate, using a vascular casting technique, acute vasoconstrictive changes in the cerebral vasculature 1 h following whole-blood or plasma infusion into the subarachnoid space of conscious spontaneously hypertensive rats. Vascular casts from animals infused (over 20 min) with 0.45 ml of heparinized autologous arterial blood or plasma exhibited incomplete filling, while casts from saline-infused controls exhibited virtually no filling defects. Significant elevations in intracranial pressure were noted in blood, but not in plasma- or saline-infused rats. Two characteristic forms of constriction occurred, depending upon the vessel lumen diameter. Vessels with lumen diameters >100 &mgr;m were flattened longitudinally with deep endothelial nuclear imprints, while smaller vessels had focal circular constrictions resembling beads. Arterial cast filling terminated in vessels with lumen diameters from 70 to 120 &mgr;m with focal signs of constriction at or near the point of cast termination. The results indicate that the presence of both blood and plasma in the subarachnoid space produces acute small-artery constriction. This phenomenon is due to a noncellular blood component and does not correlate with increases in intracranial pressure. Copyright 1996 S. Karger AG, Basel

Characterization of an anterior circulation rat subarachnoid hemorrhage model

BACKGROUND AND PURPOSE

Our aim was to demonstrate the feasibility of an angiographically controlled rat model for the study of macrocirculatory and microcirculatory changes of the anterior intracranial circulation after subarachnoid hemorrhage.

METHODS

Subarachnoid hemorrhage was induced by transorbital injection of 0.3 mL of nonheparinized autologous arterial blood into the chiasmatic cistern. Changes in regional cerebral blood flow were continuously recorded with the use of laser-Doppler flowmetry over the parietal cortex. Angiographic verification of middle cerebral artery diameter was performed by carotid catheterization at baseline and 2 days after injection of blood or artificial cerebrospinal fluid. We monitored intracranial and systemic blood pressure during and after injections.

RESULTS

Injection of artificial cerebrospinal fluid in the control group did not change the diameter of the middle cerebral artery. Injection of blood caused a significant arterial narrowing of 17.5%, from 0.37 +/- 0.04 mm to 0.31 +/- 0.04 mm after 2 days (P = .0001). In the control group regional cerebral blood flow decreased to 75.9 +/- 16.8% of preinjection control but quickly recovered to 99.7 +/- 19.4%. Intracranial pressure increased for 5 minutes after the injection to a maximum of 27.3 +/- 8.9 mm Hg, accompanied by a 10% decrease in mean arterial pressure. A fall in cerebral blood flow to 53.1 +/- 26.3% in blood-injected animals that recovered to only 80.7 +/- 16.9% of baseline values during the observation period of 30 minutes was noted. A peak intracranial pressure of 45.7 +/- 11.5 mm Hg occurred 2 minutes after injection with a decrease in mean arterial pressure of 13%, resulting in a markedly lower cerebral perfusion pressure than in the control group.

CONCLUSIONS

An angiographically controlled model of subarachnoid hemorrhage primarily involving the anterior circulation is feasible in the rat. The resulting narrowing of the middle cerebral artery reflects moderate vasospasm and will allow further microcirculatory studies with cranial windows.

Comparative evaluation of acute cerebral vasospasm by the microsphere and the angiography techniques

Experimental subarachnoid haemorrhage (SAH) induces an acute transient cerebral vasospasm. The goal of this study was to compare angiography with iterative measurements of regional cerebral blood flow (rCBF) by the microsphere technique for tracking acute cerebral vasospasm after SAH. Cerebral vasospasm was induced in anaesthetised rabbits by injecting 1 ml of fresh blood in the cisterna magna. In a first experiment, the diameter of the basilar artery was measured by repeated angiograms over 60 min. In a second experiment, rCBF was measured over 60 min by the radioactive microspheres method without and with bilateral ligation of the carotid artery. Without carotid ligation, despite a profound transient vasospasm of the basilar artery, rCBF was unchanged in the cerebellum and cerebrum and was not statistically decreased in the brain stem. However, with bilateral carotid ligation, rCBF dramatically decreased at 5 and 15 min after haemorrhage. At 30 min, despite a persistent 50% decrease in the basilar cross-sectional area, rCBF was no longer different from the control group. Thus in a model of acute vasospasm of the basilar artery, rCBF evaluation by the microsphere technique parallels the cerebral vasospasm evaluated by angiography only when both carotid arteries are ligated.

The Sheffield model of subarachnoid hemorrhage in rats

BACKGROUND AND PURPOSE

There is no comprehensive and reliable model available in small animals that is suitable for the study of subarachnoid hemorrhage (SAH). Most of the existing models either require extensive surgery to achieve SAH or neglect the importance of an injury to the vessel and the impact of suddenly raised intracranial pressure (ICP). The presented model is designed to overcome these shortcomings.

METHODS

Forty-three male Wistar rats were anesthetized. Regional cerebral blood flow was measured using the H2 clearance method bilaterally in the middle cerebral artery territory. ICP and blood pressure were continuously monitored. Blood gases were kept within physiological limits. SAH was produced by passing a nylon thread up through the right internal carotid artery and piercing a hole in the right anterior cerebral artery. The animals were divided into three experimental groups treated with varied operative techniques. After 3 hours the surviving animals were killed, and SAH was confirmed by postmortem examination.

RESULTS

The described method proved to be a reliable way of producing SAH in rats. The onset of SAH was characterized by a sudden increase in ICP. There were some differences in the reduction of regional cerebral blood flow and the survival rate in the experimental groups. This may represent differing degrees of severity of the produced SAH.

CONCLUSIONS

We present an inexpensive and reliable model of SAH in the rat that allows the early course of biochemical, physiological, and pathological changes to be studied.

Cortical blood flow and cerebral perfusion pressure in a new noncraniotomy model of subarachnoid hemorrhage in the rat

BACKGROUND AND PURPOSE

Acute cerebral ischemia after subarachnoid hemorrhage (SAH) is a major cause of morbidity whose precise etiology is unclear. The purpose of this study was to examine the relationships between cerebral perfusion pressure (CPP) and cortical blood flow during SAH using a new experimental model in the rat.

METHODS

CPP (mean arterial pressure minus intracranial pressure), cortical laser-Doppler flowmetry (LDF), and electroencephalogram were continuously recorded during and after SAH in 16 ventilated rats. SAH was produced by advancing an intraluminal suture from the external carotid artery through the internal carotid artery to perforate the vessel near its intracranial bifurcation.

RESULTS

Eight rats (50%) died within 24 hours of SAH. In all rats, blood was widely distributed throughout the basal, convexity, and interhemispheric subarachnoid spaces and throughout the ventricular system. CPP decreased after SAH at an initial rate of 1.1 +/- 0.2 mm Hg/s, reaching its nadir 59 +/- 9 seconds after the onset of SAH. During the same period, LDF fell at a rate of 1.4 +/- 0.3%/s (P = NS vs CPP). After reaching its nadir, CPP rose at a rate of 0.4 +/- 0.01 mm Hg/s, but LDF continued to fall at 0.2 +/- 0.03%/s (P < .05 vs CPP) reaching a nadir of 21.7 +/- 2.5% significantly later than CPP (189.5 +/- 39 s after SAH, P < .05). No correlation was found between peak changes in CPP and LDF. Electroencephalogram activity followed the changes in LDF, reaching nadir values 289 +/- 55 seconds after SAH.

CONCLUSIONS

These findings demonstrate that although reduced CPP causes the initial decrease in cortical blood flow after SAH, secondary reductions occurring after CPP has reached its nadir are caused by other factors such as acute vasoconstriction. This noncraniotomy model of SAH in the rat has several advantages over existing models.

Erythrocyte counts in the cerebrospinal fluid associated with continuous spinal anaesthesia

Continuous spinal anaesthesia technique can be associated with peridural haemorrhage due to blood vessel damage caused by the needle or the catheter. We studied whether thrombosis prophylaxis or anticoagulation medications increase the risk of subarachnoid haemorrhage when continuous spinal anaesthesia is used. Twenty arthroplasty patients received low-molecular-weight heparin preoperatively and twenty-two vascular surgery patients received heparin (100 IU kg-1) peroperatively; eight of the latter patients were on regular preoperative antiplatelet medication. Twenty-four prostate surgery patients, not exposed to heparin or other drugs affecting coagulation, served as controls. A 22-gauge spinal catheter was used and bupivacaine was injected through the catheter. Within the following 24 hours, 4-5 cerebrospinal fluid samples were collected for erythrocyte counts. In the arthroplasty and the vascular group there were five patients each and in the control group seven patients with more than 100 x 10(6) l-1 erythrocytes in at least one of the samples. The highest erythrocyte count was 23900 x 10(6) l-1 in a control patient. The 24-hour sample was blood-tinged (erythrocytes > 1000 x 10(6) l-1) in two patients in the arthroplasty group, in one patient in the vascular group and in four patients in the control group. In spite of the haemorrhages detected in this study, no related neurological symptoms or other serious consequences were observed. The risk of subarachnoid haemorrhage was not increased by drugs affecting coagulation.

Acute subdural hematoma: is the blood itself toxic?

Recently developed rodent models of acute subdural hematoma have shown an associated large area of infarction underlying the clot. Excitotoxic processes have been postulated to play an important role in the extensive cell death seen with these models. However, whether increased pressure, vasoactive effects, or toxicity of the blood itself is responsible for initiating or sustaining these processes remains unclear. To study the effect of blood itself, an opaque layer of autologous clot was placed on the widely exposed parietal cortex of 15 Long-Evans rats and left in place for 72 h. In control animals the cortical surface was exposed but no blood was placed and contact with blood products was carefully limited. These animals were compared to a group in whom blood was injected into the closed subdural space. Histologic analysis showed that the majority of the cortex in both control and experimental animals in the open cranial model group appeared normal. Scattered small, discrete hemorrhagic lesions on the cortical surface of both control and experimental animals were seen, which had the appearance of focal mechanical trauma or vessel avulsion. There was no significant difference in average volume of lesions between experimental and control animals (9.1 versus 9.7 mm3, p = 0.85). No areas of infarction or selective neuronal loss were seen. In comparison, animals in which blood was injected into the subdural space had significantly larger lesions underlying clot, averaging 133.6 mm3 in volume (p < 0.0003). Blood in prolonged contact with the cortical surface in the absence of increased pressure, ischemia, or other insult is insufficient to cause underlying infarction like that seen when a similar volume of blood is injected into the closed subdural space.

Behavioral deficits following experimental subarachnoid hemorrhage in the rat

To characterize some of the short-term and long-term functional consequences of subarachnoid hemorrhage (SAH) in rats, we employed a battery of well-characterized tests for assessment of acute and chronic behavioral and neurologic performances. Three groups of 10 rats (blood injected, mock CSF injected and sham-operated controls) were studied. During the acute stage, simple nonpostural somatomotor reflexes (pinna and corneal reflexes), simple postural responses (paw flexion, tail flexion, and head support), startle response, and postural functions (righting reflex) did not differ significantly between the experimental groups. Assessments of body weight, beam walking ability, and beam balancing revealed significant disturbances in blood-injected rats. This work demonstrates that this single-hemorrhage rodent model of SAH is associated with the induction of enduring neurologic and behavioral deficits. Because of the significant interspecies difference, a direct extrapolation of our results to humans may not be appropriate. However, we suggest that the observed behavioral and neurologic changes may parallel those seen in humans after SAH. Results reported here further confirm the rat model of SAH as a viable laboratory instrument for the study of the pathophysiology of SAH and provide normative values for the evaluation of new treatment modalities.

Effect of subarachnoid haemorrhage on trigeminovascular calcitonin-gene-related peptide and substance P of the rat dura mater versus cerebral vasculature

While the presence of a robust perivascular neural network accompanying cerebral and dural blood vessels that contain various neuropeptides is well documented, the functional significance of this innervation is unclear. Following experimentally induced subarachnoid haemorrhage (SAH) in animal models, immunocytochemical studies have revealed that changes occur in the staining intensity of some of these neuropeptides. This study compared the immunostaining intensity of calcitonin-gene-related peptide (CGRP) and substance P (SP) in cerebral and dural perivascular nerve fibers after SAH in the rat. Subarachnoid haemorrhage was produced by injecting 0.3 ml of autologous blood into the cisterna magna of male Sprague Dawley rats. Sham operated animals received an equal volume of buffered lactated Ringer's solution (pH 7.4). Changes in the immunostaining intensity of cerebral and dural vessels were evaluated by independent observers at 6, 24, and 48 hours after SAH. Immunostaining of CGRP was reduced in cerebral vessels at 6 hours and returned to normal by 48 hours. In contrast, CGRP immunostaining of dural perivascular nerve fibers was unchanged at all time periods examined. A marked decrease in SP immunostaining was documented at 6 hours in both the cerebral and dural vessels in all animals; at 48 hours, the staining intensity had returned to control levels. These results support the idea that several subpopulations of trigeminovascular neurons containing CGRP, SP, or both project to cerebral and dural vessels. Since these subpopulations may be differentially activated in pathologic conditions, such as SAH or vascular headache, the potential exists for pharmacologic intervention of specific neuropeptides with the resultant abatement of a pathologic process.

The kinetics of lymphocyte subsets and macrophages in subarachnoid space after subarachnoid hemorrhage in rats

BACKGROUND AND PURPOSE

Although it has been suggested that humoral immunity plays a role in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage, there has been no quantitative assay for cellular immunity. We studied the kinetics of immune cells in the subarachnoid space after subarachnoid hemorrhage in the rat.

METHODS

One hundred fourteen Sprague-Dawley rats were used in this study. The animals were divided into two groups and injected with either autologous blood (0.3 mL) or saline into the major cistern. They were killed at the specified time: 10 minutes or 1, 2, 3, 5, or 7 days after subarachnoid hemorrhage. For immunohistochemical analysis, the rats' whole brains were frozen, and cryostat sections were prepared. For flow cytometric analysis of immune cell presence, their whole brains underwent enzymatic digestion.

RESULTS

Histopathologic study revealed pathological change of the arterial wall, and immunohistochemical study revealed the existence of macrophages and T cells in the subarachnoid space in animals with a survival time of 2 to 5 days after subarachnoid hemorrhage. A flow cytometric study revealed the peak of appearance of T cells and macrophages 2 days after subarachnoid hemorrhage. The helper-suppressor T cell ratio also reached a peak 2 days after subarachnoid hemorrhage.

CONCLUSIONS

A serial response of immunoreactive cells, which resembles that of the chronic allergic reaction observed in autoimmune diseases or delayed-type hypersensitivity, exists in the subarachnoid space after subarachnoid hemorrhage. The present results suggest that the initial response in cellular immunity, which is followed by humoral immunity and eicosanoid reactions, plays a role in eliciting the development of cerebral vasospasm.

Dural neuropeptide changes after subarachnoid hemorrhage in rats

The effect of subarachnoid hemorrhage (SAH) on the neuropeptides and mast cells of the rat dura mater has not been reported. We examined the outcome of SAH on the rat supratentorial dura mater to determine whether dural nerves undergo effects similar to those of nerves accompanying cerebral blood vessels after SAH. Following the injection of fresh autologous arterial blood into the cisterna magna, animals were sacrificed at 6, 24, and 48 h, and 6 days post-SAH. Dural whole mounts were immunohistochemically reacted with antibodies to calcitonin gene-related peptide (CGRP), substance P (SP), neuropeptide Y (NPY), and serotonin (5-HT). SP-like immunostaining was substantially reduced after SAH and subsequently returned to control levels at 6 days. NPY-like fiber innervation of the dura was markedly reduced after SAH; although immunostaining intensity increased, it had not returned to control levels at 6 days. The 5-HT content of dural mast cells identified by immunostaining markedly decreased at 6 and 24 h and returned to control levels at 48 h. In contrast, CGRP immunostaining was unchanged in all experimental groups. One possible explanation for this differential response is that subpopulations of trigeminovascular neurons containing SP, CGRP, or CGRP and SP respond differently to various stimuli, including SAH. Another possibility is a differential release of SP or CGRP from the same fiber. To the best of our knowledge this is the first documentation that the dura is also a target for intracranial pathological processes, such as SAH.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of c-fos-like immunoreactivity in brainstem after meningeal irritation by blood in the subarachnoid space

The expression of c-fos protein was examined by immunohistochemistry in serial sections of brainstem following the instillation of either autologous arterial blood (0.3 ml) or mock cerebrospinal fluid (0.3 ml) through a catheter placed in the cisterna magna, or following catheter placement alone in pentobarbital-anesthetized Sprague-Dawley rats. After injection, blood was distributed within the subarachnoid space surrounding the brainstem and in the region of the circle of Willis. c-fos protein-like immunoreactivity was present at 1 h, peaked at 2 h and decreased by 8 h. At 2 h, immunoreactivity was strongly expressed within trigeminal nucleus caudalis (lamina I, IIo), as well as within nucleus of the solitary tract, area postrema, ependyma, pia mater and arachnoid in every animal. Moderate labeling was found in parabrachial nucleus, medullary lateral reticular nucleus and central gray. Sparse labeling was present in trigeminal nucleus caudalis (lamina III-V) and trigeminal nucleus interpolaris; few or no labeled cells were detected in other parts of the trigeminal nuclear complex, thalamus, cerebral cortex, cerebellar cortex or trigeminal ganglion. The number of positive cells was not related to the volume of injectate but was related to the amount of injected blood. The density of cell labeling evoked by injecting mock cerebrospinal fluid or after catheter placement was markedly lower than after blood in all brainstem areas. The number of labeled cells was greatly reduced within trigeminal nuclear complex, parabrachial nucleus and medullary lateral reticular nucleus, but not within the nucleus of the solitary tract, area postrema or ependyma when blood was injected into adult animals in which unmyelinated C-fibers were destroyed by neonatal capsaicin treatment. Similar results were obtained after blood was instilled into the cisterna magna of rats in which meningeal afferents were chronically sectioned at the ethmoidal foramen bilaterally. We conclude that blood in the subarachnoid space is an effective stimulus for activating c-fos expression within subpopulations of brainstem neurons. Activation within trigeminal nucleus caudalis is mediated in large part by excitation of small-caliber meningeal afferents (trigeminovascular fibers), whereas c-fos expression within nucleus of the solitary tract and area postrema may reflect direct stimulation of blood or blood products, or possibly the response to autonomic activation from noxious stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood-brain barrier permeability changes after experimental subarachnoid hemorrhage

Basic mechanisms underlying cerebrovascular permeability responses to subarachnoid hemorrhage (SAH) are still to be defined in detail. Previous investigations examining the occurrence of blood-brain barrier (BBB) breakdown after SAH in the experimental setting have yielded conflicting results. In a rat model of SAH, we assessed BBB changes by means of the quantitative [14C]-alpha-aminoisobutyric acid technique. Experiments were carried out on the second day post-SAH. In blood-injected rats [14C]-alpha-aminoisobutyric acid transport across the BBB increased significantly in cerebral cortices and cerebellar gray matter, averaging 1.3 to 1.5 times control values. The present data indicate that SAH induces well-defined changes in BBB function, possibly involved in the pathogenesis of post-SAH cerebral dysfunction in humans. Results reported here have also potential clinical implications for the management of aneurysm patients.

CP-93,129, sumatriptan, dihydroergotamine block c-fos expression within rat trigeminal nucleus caudalis caused by chemical stimulation of the meninges

1. The effects of intravenously administered 5-HT1B receptor agonists were examined on c-fos like immunoreactivity, an indicator of neuronal activation, within the brain stem. C-fos was induced by injecting an algesic, vasoconstrictor substance (0.3 ml of autologous blood) or a pro-inflammatory molecule, carrageenin (1 mg in 0.1 ml saline) into the cisterna magna of pentobarbitone-anaesthetized Sprague-Dawley rats and was visualized in serial sections (50 micrometers) by use of a polyclonal antiserum. 2. As previously reported, the injection of blood caused significant labelling within laminae I, IIo of the trigeminal nucleus caudalis, a major nociceptive brain stem nucleus, as well as within nucleus of the solitary tract and area postrema. A similar pattern of expression with fewer cells per section was detected after carrageenin instillation. The number of expressing cells was reduced by 54% in trigeminal nucleus caudalis but not within the nucleus of the solitary tract or area postrema when blood was injected in adult rats neonatal capsaicin treatment. 3. Pretreatment with 5-HT1 agonists with some selectivity for the 5-HT1B receptor, CP-93,129 (460 nmol kg-1 x 2, i.v.), sumatriptan (720 nmol kg-1 x 2, i.v.) or dihydroergotamine (86 nmol kg-1 x 2, i.v.) reduced positive cells by 39%, 31%, and 33% respectively in trigeminal nucleus caudalis but not in nucleus of the solitary tract or area postrema after blood instillation. Pretreatment with the analgesic morphine (15 mumol kg-1, s.c.) also decreased the number of positive cells by 63% in trigeminal nucleus caudalis. 4. CP-93,129 (460 nmol kg-1 x 2, i.v.) reduced the number of c-fos labelled cells by 47% within lamina I, IIo after carrageenin instillation. 5. Drug-induced blockade appeared to be tissue-dependent. Pretreatment with sumatriptan (720 nmol kg-1 x 2, i.v.) did not block c-fos expression in trigeminal nucleus caudalis following formalin application to the nasal mucosa.6. Drug-induced blockade may be mediated by an action on primary afferent (trigeminovascular) fibres in as much as CP-93,129 (460 nmol kg-' x 2, i.v.) did not reduce the number of expressing cells within the trigeminal nucleus caudalis following blood instillation in rats treated as neonates with capsaicin.7. We infer from these results that the analgesic actions of agonists at 5-HTB receptors (the receptor subtype analogous to 5-HTID in man) need not depend upon the presence of vasodilatation and, that 5-HTID receptor-mediated blockade of neurotransmission contributes significantly to the analgesic effects of these drugs in headache.8. Based on the demonstrated effects of 5-HTB/D agonists against the actions of two chemicallyunrelated meningeal stimulants, we suggest that treatment with 5-HTID agonists may be useful for the alleviation of pain in other headache conditions associated with meningeal irritation. Bacterial, viral(including AIDS meningovascular inflammation) and other forms of chemical meningitis merit further investigation.