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

A new non-craniotomy model of subarachnoid hemorrhage in the pig: a pilot study

Subarachnoid hemorrhage (SAH) from rupture of an intracranial arterial aneurysm is a devastating disease affecting young people, with serious lifelong disability or death as a frequent outcome. Large animal models that exhibit all the cardinal clinical features of human SAH are highly warranted. In this pilot study we aimed to develop a non-craniotomy model of SAH in pigs suitable for acute intervention studies. Six Norwegian Landrace pigs received advanced invasive hemodynamic and intracranial pressure (ICP) monitoring. The subarachnoid space, confirmed by a clear cerebrospinal fluid (CSF) tap, was reached by advancing a needle below the ocular bulb through the superior orbital fissure and into the interpeduncular cistern. SAH was induced by injecting 15 mL of autologous arterial blood into the subarachnoid space. Macro- and microanatomical investigations of the pig brain showed a typical blood distribution consistent with human aneurysmal SAH (aSAH) autopsy data. Immediately after SAH induction ICP sharply increased with a concomitant reduction in cerebral perfusion pressure (CPP). ICP returned to near normal values after 30 min, but increased subsequently during the experimental period. Signs of brain edema were confirmed by light microscopy post-mortem. None of the animals died during the experimental period. This new transorbital injection model of SAH in the pig mimics human aSAH and may be suitable for acute intervention studies. However, the model is technically challenging and needs further validation.

Mechanisms of acute brain injury after subarachnoid hemorrhage

Brain injury after subarachnoid hemorrhage (SAH) is a biphasic event with an acute ischemic insult at the time of the initial bleed and secondary events such as cerebral vasospasm 3 to 7 days later. Although much has been learned about the delayed effects of SAH, less is known about the mechanisms of acute SAH-induced injury. Distribution of blood in the subarachnoid space, elevation of intracranial pressure, reduced cerebral perfusion and cerebral blood flow (CBF) initiates the acute injury cascade. Together they lead to direct microvascular injury, plugging of vessels and release of vasoactive substances by platelet aggregates, alterations in the nitric oxide (NO)/nitric oxide synthase (NOS) pathways and lipid peroxidation. This review will summarize some of these mechanisms that contribute to acute cerebral injury after SAH.

Progesterone administration modulates cortical TLR4/NF-κB signaling pathway after subarachnoid hemorrhage in male rats

Our previous study concerning brain trauma has shown that progesterone could regulate toll-like receptor 4 (TLR4) and nuclear factor-kappa B (NF-κB) signaling pathway in the brain, which also has been proved to play important roles in early brain injury (EBI) after subarachnoid hemorrhage (SAH). The aim of the current study was to investigate whether progesterone administration modulated TLR4/NF-κB pathway signaling pathway in the brain at the early stage of SAH. All SAH animals were subjected to injection of 0.3  ml fresh arterial, non-heparinized blood into prechiasmatic cistern in 20 seconds. Male rats were given 0 or 16  mg/kg injections of progesterone at post-SAH hours 1, 6, and 24. Brain samples were extracted at 48  h after SAH. As a result, SAH could induce a strong up-regulation of TLR4, NF-κB, pro-inflammatory cytokines, MCP-1, and ICAM-1 in the cortex. Administration of progesterone following SAH could down-regulate the cortical levels of these agents related to TLR4/NF-κB signaling pathway. Post-SAH progesterone treatment significantly ameliorated the EBI, such as the clinical behavior scale, brain edema, and blood-brain barrier (BBB) impairment. It was concluded that post-SAH progesterone administration may attenuate TLR4/NF-κB signaling pathway in the rat brain following SAH.

Delayed cell death related to acute cerebral blood flow changes following subarachnoid hemorrhage in the rat brain

Object. The authors tested the hypotheses that subarachnoid hemorrhage (SAH) leads to delayed cell death with the participation of apoptotic-like mechanisms and is influenced by the degree of acute decrease in the cerebral blood flow (CBF) following hemorrhage.

Methods. Subarachnoid hemorrhage was induced in rats by endovascular perforation of the internal carotid artery or injection of blood into the prechiasmatic cistern. Cerebral blood flow was measured using laser Doppler flowmetry for 60 minutes. Brain sections stained with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) showed DNA fragmentation at 2 and 7 days after both methods of inducing SAH in one third to two thirds of the surviving animals in the different experimental groups. More than 80% of the TUNEL-positive cells were neuron-specific nuclear protein—positive (neurons), but immunoreactivity to glial fibrillary acidic protein (astrocytes) and transferrin (oligodendrocytes) were markedly decreased in TUNEL-positive areas. Most of the TUNEL-positive cells displayed chromatin condensation and/or blebs and immunostained for increased Bax; approximately 50% of them were immunoreactive to cleaved caspase-3 and a few to Bcl-2. The duration of the acute CBF decrease below 30% of the baseline level was related to the degree of TUNEL staining.

Conclusions. Subarachnoid hemorrhage resulted in delayed cell death in a large proportion, but not all, of the surviving animals. The acute CBF decrease was related to the degree of subsequent cell death. These findings indicated the relevance of apoptotic-like pathways. There appears to be a temporal therapeutic window during which adequate treatment might reduce the final damage following SAH.

Experimental subarachnoid hemorrhage induces changes in the levels of hippocampal NMDA receptor subunit mRNA

NMDA receptors may play a crucial role in nerve cell death following subarachnoid hemorrhage (SAH). Changes in NMDA receptor-mediated transmission appear before neuronal death in rodent models of transient ischemia, and NMDA receptor function is known to be dependent on subunit composition. Here, we have investigated whether mRNA expression of the NMDA receptor subunits is altered in the hippocampal formation 3-5 h following experimental SAH, and correlated these early alterations to subsequent delayed cell death. SAH was induced by intraluminal perforation of the internal carotid artery intracranially, and cerebral blood flow (CBF) was bilaterally monitored by laser-Doppler flowmetry. Early changes in NMDA receptor subunit mRNA and early nerve cell death were analyzed at 3-5 h after SAH, and delayed nerve cell death was analyzed at 2-7 days after SAH. Duration of ipsilateral CBF reduction below 30% of baseline (CBF30) was predictive of ipsilateral delayed nerve cell death in the CA1 2-7 days after SAH. At CBF30 > 9 min, we found downregulation of mRNA for NR2A, NR2B, and NR3B at 3-5 h after SAH, whereas the levels of NR1 mRNA were unaffected. The downregulation of NR2A and NR2B mRNA may result in a reduced NMDA receptor function. Such reduction may be sufficient to provide neuroprotection in the dentate gyrus, where no cell death appears, but insufficient to rescue neurons in the hippocampus proper following SAH.

Experimental subarachnoid hemorrhage: subarachnoid blood volume, mortality rate, neuronal death, cerebral blood flow, and perfusion pressure in three different rat models

OBJECTIVE

To investigate which of three subarachnoid hemorrhage (SAH) models is the most suitable for studies of pathological and pathophysiological processes after SAH.

METHODS

SAH was induced in rats via intracranial endovascular perforation (perforation model), blood injection into the cisterna magna (300 microl), or blood injection into the prechiasmatic cistern (200 microl). The subarachnoid blood volume was quantitatively measured. Cerebral blood flow (CBF) (as assessed with laser Doppler flowmetry), intracranial pressure, and mean arterial blood pressure were recorded for 90 minutes after SAH. Mortality was recorded, and neuronal death was assessed in animals that survived 7 days after SAH.

RESULTS

The subarachnoid blood volume was close to the injected amount after prechiasmatic SAH. In the other models, the volume varied between 40 and 480 microl. The mortality rates were 44% in the perforation SAH group, 25% in the prechiasmatic SAH group, and 0% in the cisterna magna SAH group; the corresponding values for neuronal death were 11, 44, and 28%. Cerebral perfusion pressure approached baseline values within 5 minutes after SAH in all three models. CBF decreased to approximately 35% of baseline values immediately after SAH in all groups; it gradually increased to normal values 15 minutes after SAH in the cisterna magna SAH group and to 60 and 89% of baseline values 90 minutes post-SAH in the perforation and prechiasmatic SAH groups. CBF was significantly correlated with the subarachnoid blood volume.

CONCLUSION

The prechiasmatic SAH model seems to be the most suitable for study of the sequelae after SAH; it produces a significant decrease in CBF, an acceptable mortality rate, and substantial pathological lesions, with high reproducibility. The CBF reduction is predominantly dependent on the amount of subarachnoid blood.

A new experimental model in rats for study of the pathophysiology of subarachnoid hemorrhage

A new experimental model of subarachnoid hemorrhage (SAH) in rats is described. A needle was stereotaxically placed in the prechiasmatic cistern and 300, 250 or 200 microl of blood was injected manually, keeping the intracranial pressure (ICP) at the mean arterial blood pressure (MABP) level. An acceptable mortality was observed only after injection of 200 microl of blood. In this group, MABP and ICP increased immediately after SAH, but soon approached baseline levels. The subarachnoid blood was mainly distributed in the basal cisternal system and its estimated volume was about 95% of the amount injected. This new model resembles clinical SAH, is very reproducible, easy to use and seems to be a suitable model for studies of the pathophysiology of SAH.

Heat shock protein expression in cerebral vessels after subarachnoid hemorrhage

OBJECTIVE

The mechanisms of cerebral vasospasm after subarachnoid hemorrhage (SAH) remain controversial. Recent data have implicated two small heat shock proteins (HSPs), namely HSP20 and HSP27, in the regulation of vascular tone. Increases in the phosphorylation of HSP20 are associated with vasorelaxation, and increases in the phosphorylation of HSP27 are associated with impaired vasorelaxation. Therefore, we hypothesized that alterations in the expression and/or phosphorylation of these two small HSPs might play a role in cerebral vasospasm after SAH.

METHODS

A rat model of endovascular perforation was used to induce SAH. Middle cerebral arteries were harvested from control animals, sham-treated animals, and animals with SAH, 48 hours after SAH induction. Dose-response curves for endothelium-independent (sodium nitroprusside, 10(-8) to 10(-4) mol/L) and endothelium-dependent (bradykinin, 10(-10) to 10(-5) mol/L) relaxing agents were recorded ex vivo. Physiological responses were correlated with the expression and phosphorylation of HSP20 and HSP27 by using one- and two-dimensional immunoblots.

RESULTS

There was impaired endothelium-independent and endothelium-dependent relaxation in cerebral vessels after SAH. These changes were associated with decreased expression of both total and phosphorylated HSP20 and increases in the amount of phosphorylated HSP27.

CONCLUSION

In this model, impaired relaxation of cerebral vessels after SAH was associated with increases in the amount of phosphorylated HSP27 and decreases in the expression and phosphorylation of HSP20. These data are consistent with alterations in the expression and phosphorylation of these small HSPs in other models of vasospasm.

Influence of the type and rate of subarachnoid fluid infusion on lethal neurogenic pulmonary edema in rats

In patients who experience sudden death from spontaneous subarachnoid hemorrhage, more than 90% present with acute pulmonary edema. The underlying pathogenesis of this complication is poorly understood. In addition, the specific role of the extravasated blood products and the associated elevation in intracranial pressure leading to the systemic and pulmonary effects during subarachnoid hemorrhage are not well established. The authors tested a new model of acute and severe subarachnoid hemorrhage comparing fresh whole autologous blood (n = 20) with 5% albumin (n = 19) injected at two different rates (35 seconds versus 24 minutes) into the cisterna magna of anesthetized, mechanically ventilated rats. Cerebral and systemic hemodynamics and the corresponding pulmonary function were evaluated. The type of fluid injected had no influence on survival or hemodynamic and respiratory parameters. Rapid infusion of either blood or albumin (n = 14) produced an acute and transient rise in intracranial pressure (37.9 +/- 3.5 mm Hg) associated with systemic hypertension and increased cerebral perfusion pressure that was sustained in survivors but not in nonsurvivors. Slow infusion (n = 23) produced a more progressive increase in intracranial pressure to 31.2 +/- 7.1 mm Hg with a parallel and sustained increase of systemic blood pressure and preserved cerebral perfusion pressure in survivors, but produced a pattern of more severe hypertension followed by hypotension in nonsurvivors. Sixty-four percent of animals (rapid infusion) and 48% of animals (slow infusion) survived the challenge and presented no pulmonary alterations. In contrast, nonsurviving rats developed reduced lung compliance and gas exchange, an increased alveolar-arterial protein concentration ratio (0.36 +/- 0.02 versus 0.17 +/- 0.03 in survivors; P <.0001), and increased lung weight (5.7 +/- 0.3 g versus 2.0 +/- 0.1 g; P <.0001), demonstrating a fulminant increased permeability pulmonary edema, leading to death within one hour. These results indicate that the chosen rapid- and slow-injection rates resulted in a similar death rate of 50%. Mortality was similar for blood and albumin administration, pulmonary edema occurred in nonsurvivors in both the rapid- and slow-injection groups, and pulmonary edema is associated with more severe hypertension in the slow-injection group. Furthermore, these results suggest that the development of neurogenic pulmonary edema that is characterized by an acutely increased capillary permeability to proteins is independent of the degree of intracranial pressure increase or the type of fluid administrated.

Subarachnoid hemorrhage induces dynamic changes in regional cerebral metabolism in rats

Following a subarachnoid hemorrhage (SAH), adult rats exhibit dynamic regional changes in cerebral glucose metabolism characterized by an increase in metabolic rates and a subsequent upregulation of cytochrome oxidase (CO). We evaluated both local cerebral metabolic rates for glucose (ICMRglc: (mol/100 g/min) and CO in 23 brain regions of interest (ROI). Sham animals underwent anesthesia and superficial surgery; saline-controls received an injection of 0.9% saline into the cisterna magna; and SAH rats received an injection of autologous blood into the cisterna magna. This blood, measured by albumin labeled with radioactive carbon 14, distributed throughout the brain but predominated ventrally. After experimental animals were sacrificed at day 0 (3 h), 1, 3, and 7 days postinjection, ROI were analyzed using [14C]2-deoxy-D-glucose autoradiography and CO histochemistry. ICMRglc in SAH rats increased in many regions (ranging from 0.7% to 32.2% above sham levels). Cytochrome oxidase also increased from 1% to 9% above sham levels, peaking on day 3. Conversely, saline-controls exhibited prolonged depression of ICMRglc (ranging from 11% to 35% below sham levels) and CO (ranging from 4% to 11% below sham levels) from day 0 through day 7. All saline-control ROI for all time points showed this metabolic depression, and between 91% and 95% of saline-control ROI presented lower CO levels as compared to sham. Overall, ICMRglc and CO levels were greater in SAH than in saline-control ROI. However, when considering the influence of subarachnoid blood on metabolic changes in SAH animals, both CO and 2DG levels did not correlate well with the amount of 14C-albumin binding. While previous studies have measured both metabolic rates of glucose and CO soon after SAH, this is the first to simultaneously conduct these measurements in the same SAH rat model.

Decreased nitric oxide availability contributes to acute cerebral ischemia after subarachnoid hemorrhage

OBJECTIVE

Disturbances of the L-arginine-nitric oxide (NO) vasodilatory pathway have been implicated as a cause of acute vasoconstriction and ischemia after subarachnoid hemorrhage (SAH). Because NO-dependent vasodilatory mechanisms are still intact in this setting, acute vasoconstriction may be the result of limited NO availability after SAH. The present study examines this hypothesis by administration of the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME).

METHODS

SAH was induced by the endovascular suture method in anesthetized rats. L-NAME (30 mg/kg intravenously) was injected 20 minutes before or 15, 30, or 60 minutes after SAH. Control rats received normal saline. Arterial and intracranial pressure and cerebral blood flow (CBF) were measured continuously for 60 minutes after SAH.

RESULTS

L-NAME administration 20 minutes before SAH produced a significant decrease in resting CBF (29.4 +/- 3.4%; P < 0.05), but it had no effect on the acute decrease in CBF after SAH or on its early recovery up to 30 minutes after SAH. However, a significant decrease in CBF recovery was found in animals receiving L-NAME injections (28.7 +/- 9.4%; P < 0.05 versus controls) 60 minutes after SAH. Administration of L-NAME 15 or 30 minutes after SAH had no effect on CBF recovery, as compared with controls. However, when administered 60 minutes after SAH, L-NAME decreased CBF significantly (45.4 +/- 8.8%; P < 0.05 versus controls).

CONCLUSION

These results indicate a biphasic pattern of NO availability after SAH. NO-mediated vasodilation is limited during the first 30 minutes of SAH and is restored 60 minutes after SAH.