A simple and reliable technique to monitor intracranial pressure in the rat: technical note

A novel method for repeated cerebrospinal fluid sampling and long-term monitoring of intracranial pressure in rats

Cannulation implantation into the cisterna magna is an important procedure in cerebrospinal fluid (CSF) sampling and intracranial pressure (ICP) monitoring. The disadvantages of existing techniques include the risk of brain damage, compromised muscle mobility, and the complexity of the procedures. In the present study, the authors describe a modified, simple, and reliable procedure for long-term cannulation implantation into the cisterna magna in rats. The device consists of four parts: the puncture segment, the connection segment, the fixing segment, and the external segment. Intraoperative ICP monitoring and post-operative computed tomography (CT) scans were performed, which confirmed the accuracy and safety of this method. There were no limitations on the daily activities of the rats when long-term drainage was carried out for 1 week. This new technique offers an improved method of cannulation and will be a potentially useful method for CSF sampling and ICP monitoring in neuroscience research.

Diabetes exacerbates brain pathology following a focal blast brain injury: New role of a multimodal drug cerebrolysin and nanomedicine

Blast brain injury (bBI) is a combination of several forces of pressure, rotation, penetration of sharp objects and chemical exposure causing laceration, perforation and tissue losses in the brain. The bBI is quite prevalent in military personnel during combat operations. However, no suitable therapeutic strategies are available so far to minimize bBI pathology. Combat stress induces profound cardiovascular and endocrine dysfunction leading to psychosomatic disorders including diabetes mellitus (DM). This is still unclear whether brain pathology in bBI could exacerbate in DM. In present review influence of DM on pathophysiology of bBI is discussed based on our own investigations. In addition, treatment with cerebrolysin (a multimodal drug comprising neurotrophic factors and active peptide fragments) or H-290/51 (a chain-breaking antioxidant) using nanowired delivery of for superior neuroprotection on brain pathology in bBI in DM is explored. Our observations are the first to show that pathophysiology of bBI is exacerbated in DM and TiO₂-nanowired delivery of cerebrolysin induces profound neuroprotection in bBI in DM, not reported earlier. The clinical significance of our findings with regard to military medicine is discussed.

Preclinical update on regulation of intracranial pressure in relation to idiopathic intracranial hypertension

BACKGROUND

Elevated intracranial pressure (ICP) is observed in association with a range of brain disorders. One of these challenging disorders is idiopathic intracranial hypertension (IIH), characterized by raised ICP of unknown cause with significant morbidity and limited therapeutic options. In this review, special focus is put on the preclinical research performed in order to understand the pathophysiology behind ICP regulation and IIH. This includes cerebrospinal fluid dynamics, molecular mechanisms underlying disturbances in brain fluids leading to elevated ICP, role of obesity in IIH, development of an IIH model and ICP measurements in rodents. The review also discusses existing and new drug targets for IIH that have been evaluated in vivo.

CONCLUSIONS

ICP monitoring in rodents is challenging and different methods have been applied. Some of these methods are invasive, depend on use of anesthesia and only allow short-term monitoring. Long-term ICP recordings are needed to study IIH but existing methods are hampered by several limitations. As obesity is one of the most common risk factors for IIH, a rodent obese model has been developed that mimics some key aspects of IIH. The most commonly used drugs for IIH have been evaluated in vivo for their efficacy at lowering ICP in the existing animal models. These studies suggest these drugs, including acetazolamide, might have limited or no reducing effect on ICP. Two drug targets that can impact ICP in healthy rodents are topiramate and a glucagon-like peptide-1 receptor (GLP-1R) agonist. However, it remains to evaluate their effect in an IIH model with more precise and valid ICP monitoring system. Therefore, continued evaluation in the preclinical research with refined tools is of great importance to further understand the pathophysiology behind disorders with raised ICP and to explore new drug targets.

Bioresorbable Electrode Array for Electrophysiological and Pressure Signal Recording in the Brain

Medical implantation of an electrocorticography (ECoG) recording system for brain monitoring is an effective clinical tool for seizure focus location and brain disease diagnosis. Planar and flexible ECoG electrodes can minimize the risks of infection and serious inflammatory response, and their good shape adaptability allows the device to fit complex cortex shape and structure to record brain signals with high spatial and temporal resolution. However, these ECoG electrodes require an additional surgery to remove the implant, which imposes potential medical risks. Here, a novel flexible and bioresorbable ECoG device integrated with an intracortical pressure sensor for monitoring swelling of the cortex during operation is reported. The ECoG device is fabricated with poly(l-lactide) and polycaprolactone composite and transient metal molybdenum. In vivo tests on rats show that the ECoG system can record the dynamic changes in brain signals for the different epilepsy stages with high resolution, while the malleable pressure sensor shows a linear relationship between the pressure and resistance in in vitro tests. In vitro degradation experiments show that the ECoG system can work stably for about five days before loss of efficacy, and the whole ECoG system degrades completely in a phosphate buffer solution in about 100 days.

Characterization of Retinal Ganglion Cell and Optic Nerve Phenotypes Caused by Sustained Intracranial Pressure Elevation in Mice

Elevated intracranial pressure (ICP) can result in multiple neurologic sequelae including vision loss. Inducible models of ICP elevation are lacking in model organisms, which limits our understanding of the mechanism by which increased ICP impacts the visual system. We adapted a mouse model for the sustained elevation of ICP and tested the hypothesis that elevated ICP impacts the optic nerve and retinal ganglion cells (RGCs). ICP was elevated and maintained for 2 weeks, and resulted in multiple anatomic changes that are consistent with human disease including papilledema, loss of physiologic cupping, and engorgement of the optic nerve head. Elevated ICP caused a loss of RGC somas in the retina and RGC axons within the optic nerve, as well as a reduction in both RGC electrical function and contrast sensitivity. Elevated ICP also caused increased hypoxia-inducible factor (HIF)-1 alpha expression in the ganglion cell layer. These experiments confirm that sustained ICP elevation can be achieved in mice and causes phenotypes that preferentially impact RGCs and are similar to those seen in human disease. With this model, it is possible to model human diseases of elevated ICP such as Idiopathic Intracranial Hypertension and Spaceflight Associated Neuro-ocular Syndrome.

Curcumin mitigates cerebral vasospasm and early brain injury following subarachnoid hemorrhage via inhibiting cerebral inflammation

BACKGROUND AND PURPOSE

Subarachnoid hemorrhage (SAH)-induced cerebral vasospasm and early brain injury is a fatal clinical syndrome. Cerebral vasospasm and early brain injury are associated with inflammatory response and oxidative stress. Whether curcumin, which plays important roles to regulate inflammatory cytokines and inhibit oxidative stress, inhibits SAH-induced inflammation and oxidative stress are largely unknown.

METHODS

Adult male rats underwent autologous blood injection into prechiasmatic cistern to induce SAH. Curcumin (150 mg/kg) was administered at 0.5, 24 and 48 hr post-SAH. Mortality calculation and neurological outcomes as well as morphological vasospasm of anterior cerebral artery were studied. Superoxide dismutase, lipid peroxidation, and inflammatory cytokines (MCP-1 and TNF-α) expression in prefrontal region were quantified. Furthermore, p65 and phosphor-p65 were quantitatively analyzed.

RESULTS

Curcumin remarkedly reduced mortality and ameliorated neurological deficits after SAH induction (p < .05); morphological results showed that cerebral vasospasm in curcumin-treated group was mitigated (p < .05). SAH-induced MCP-1 and TNF-α overexpression were inhibited in curcumin-treated group (p < .05). Importantly, phosphor-p65 was significantly inhibited after curcumin treatment (p < .05).

CONCLUSIONS

Curcumin can inhibit SAH-induced inflammatory response via restricting NF-κB activation to alleviate cerebral vasospasm and early brain injury.

Recording of intracranial pressure in conscious rats via telemetry

Although cerebral perfusion pressure (CPP) is known to be fundamental in the control of normal brain function, there have been no previous long-term measurements in animal models. The aim of this study was to explore the stability and viability of long-term recordings of intracranial pressure (ICP) in freely moving rats via a telemetry device. We also developed a repeatable surgical approach with a solid-state pressure sensor at the tip of the catheter placed under the dura and in combination with arterial pressure (AP) measurement to enable the calculation of CPP. Telemeters with dual pressure catheters were implanted in Wistar rats to measure ICP and AP. We found that the signals were stable throughout the 28-day recording period with an average ICP value of 6 ± 0.8 mmHg. Significant light-dark differences were found in AP (3.1 ± 2.7 mmHg, P = 0.02) and HR (58 ± 12 beats/min, P = 0.003), but not ICP (0.3 ± 0.2 mmHg, P >0.05) or CPP (2.6 ± 2.8 mmHg, P > 0.05). Use of kaolin to induce hydrocephalus in several rats demonstrates the ability to measure changes in ICP throughout disease progression, validating this new solution for chronic measurement of ICP, CPP, and AP in conscious rats.

Elevated intracranial pressure causes optic nerve and retinal ganglion cell degeneration in mice

The purpose of this study was to develop a novel experimental system for the modulation and measurement of intracranial pressure (ICP), and to use this system to assess the impact of elevated ICP on the optic nerve and retinal ganglion cells (RGCs) in CD1 mice. This system involved surgical implantation of an infusion cannula and a radiowave based pressure monitoring probe through the skull and into the subarachnoid space. The infusion cannula was used to increase ICP, which was measured by the probe and transmitted to a nearby receiver. The system provided robust and consistent ICP waveforms, was well tolerated, and was stable over time. ICP was elevated to approximately 30 mmHg for one week, after which we assessed changes in optic nerve structure with transmission electron microscopy in cross section and RGC numbers with antibody staining in retinal flat mounts. ICP elevation resulted in optic nerve axonal loss and disorganization, as well as RGC soma loss. We conclude that the controlled manipulation of ICP in active, awake mice is possible, despite their small size. Furthermore, ICP elevation results in visual system phenotypes of optic nerve and RGC degeneration, suggesting that this model can be used to study the impact of ICP on the visual system. Potentially, this model can also be used to study the relationship between ICP and IOP, as well diseases impacted by ICP variation such as glaucoma, idiopathic intracranial hypertension, and the spaceflight-related visual impairment intracranial pressure syndrome.

The Touch and Zap method for in vivo whole-cell patch recording of intrinsic and visual responses of cortical neurons and glial cells

Whole-cell patch recording is an essential tool for quantitatively establishing the biophysics of brain function, particularly in vivo. This method is of particular interest for studying the functional roles of cortical glial cells in the intact brain, which cannot be assessed with extracellular recordings. Nevertheless, a reasonable success rate remains a challenge because of stability, recording duration and electrical quality constraints, particularly for voltage clamp, dynamic clamp or conductance measurements. To address this, we describe "Touch and Zap", an alternative method for whole-cell patch clamp recordings, with the goal of being simpler, quicker and more gentle to brain tissue than previous approaches. Under current clamp mode with a continuous train of hyperpolarizing current pulses, seal formation is initiated immediately upon cell contact, thus the "Touch". By maintaining the current injection, whole-cell access is spontaneously achieved within seconds from the cell-attached configuration by a self-limited membrane electroporation, or "Zap", as seal resistance increases. We present examples of intrinsic and visual responses of neurons and putative glial cells obtained with the revised method from cat and rat cortices in vivo. Recording parameters and biophysical properties obtained with the Touch and Zap method compare favourably with those obtained with the traditional blind patch approach, demonstrating that the revised approach does not compromise the recorded cell. We find that the method is particularly well-suited for whole-cell patch recordings of cortical glial cells in vivo, targeting a wider population of this cell type than the standard method, with better access resistance. Overall, the gentler Touch and Zap method is promising for studying quantitative functional properties in the intact brain with minimal perturbation of the cell's intrinsic properties and local network. Because the Touch and Zap method is performed semi-automatically, this approach is more reproducible and less dependent on experimenter technique.

A novel method for long-term monitoring of intracranial pressure in rats

BACKGROUND

In preclinical neurological studies, monitoring intracranial pressure (ICP) in animal models especially in rodents is challenging. Further, the lack of methods for long-term ICP monitoring has limited the possibilities to conduct prolonged studies on ICP fluctuations in parallel to disease progression or therapeutic interventions. For these reasons we aimed to set up a simple and valid method for long-term ICP recordings in rats.

NEW METHOD

A novel ICP method employing epidural probes was developed and validated by simultaneously ICP recordings in the lateral ventricle and in the epidural space. The two pressures were recorded twice a week for 59 days and the correlation was studied.

RESULTS

The two pressure recordings correlated exceptionally well and the R(2) values on each recording day ranged between 0.99 and 1.00. However, the ventricular probes caused a number of complications including loss of patency and tissue damage probably due to cerebral infection, whereas the epidural probes were safe and reliable throughout the entire study.

COMPARISON WITH EXISTING METHODS

Epidural probes are much easier to implant than ventricular probes. In addition, these new probes are far less invasive and induce no apparent mechanical tissue damage and highly decrease the infection risk associated with ICP recordings.

CONCLUSION

Epidural ICP recorded with this new method is identical to the ventricular ICP for at least 59 days but is far less complicated and safer for the animals. The long-term method described is reliable, valid, inexpensive, and may be used in multiple disease models to study ICP.

Chronic hydrocephalus after experimental subarachnoid hemorrhage

Chronic communicating hydrocephalus is a significant health problem affecting up to 20% of survivors of spontaneous subarachnoid hemorrhage (SAH). The development of new treatment strategies is hampered by the lack of well characterized disease models. This study investigated the incidence of chronic hydrocephalus by evaluating the temporal profile of intracranial pressure (ICP) elevation after SAH, induced by endovascular perforation in rats. Twenty-five adult male Sprague-Dawley rats (260-320 g) were subjected to either endovascular perforation or sham surgery. Five animals died after SAH induction. At 7, 14 and 21 days after surgery ICP was measured by stereotaxic puncture of the cisterna magna in SAH (n=10) and SHAM (n=10) animals. On day 21 T-maze test was performed and the number of alterations and latency to decision was recorded. On day 23, samples were processed for histological analyses. The relative ventricle area was evaluated in coronal Nissl stained sections. On day 7 after surgery all animals showed normal ICP. The absolute ICP values were significantly higher in SAH compared to SHAM animals on day 21 (8.26±4.53 mmHg versus 4.38±0.95 mmHg) but not on day 14. Observing an ICP of 10 mmHg as cut-off, 3 animals showed elevated ICP on day 14 and another animal on day 21. The overall incidence of ICP elevation was 40% in SAH animals. On day 21, results of T-maze testing were significantly correlated with ICP values, i.e. animals with elevated ICP showed a lower number of alterations and a delayed decision. Histology yielded a significantly higher (3.59 fold increased) relative ventricle area in SAH animals with ICP elevation compared to SAH animals without ICP elevation. In conclusion, the current study shows that experimental SAH leads to chronic hydrocephalus, which is associated with ICP elevation, behavioral alterations and ventricular dilation in about 40% of SAH animals.

Rat model of spinal cord injury preserving dura mater integrity and allowing measurements of cerebrospinal fluid pressure and spinal cord blood flow

PURPOSES

Cerebrospinal fluid (CSF) pressure elevation may worsen spinal cord ischaemia after spinal cord injury (SCI). We developed a rat model to investigate relationships between CSF pressure and spinal cord blood flow (SCBF).

METHODS

Male Wistar rats had SCI induced at Th10 (n = 7) or a sham operation (n = 10). SCBF was measured using laser-Doppler and CSF pressure via a sacral catheter. Dural integrity was assessed using subdural methylene-blue injection (n = 5) and myelography (n = 5).

RESULTS

The SCI group had significantly lower SCBF (p < 0.0001) and higher CSF pressure (p < 0.0001) values compared to the sham-operated group. Sixty minutes after SCI or sham operation, CSF pressure was 8.6 ± 0.4 mmHg in the SCI group versus 5.5 ± 0.5 mmHg in the sham-operated group. No dural tears were found after SCI.

CONCLUSION

Our rat model allows SCBF and CSF pressure measurements after induced SCI. After SCI, CSF pressure significantly increases.

Blood-brain barrier permeability is positively correlated with cerebral microvascular perfusion in the early fluid percussion-injured brain of the rat

The blood-brain barrier (BBB) opening following traumatic brain injury (TBI) provides a chance for therapeutic agents to cross the barrier, yet the reduction of the cerebral microvascular perfusion after TBI may limit the intervention. Meanwhile, optimizing the cerebral capillary perfusion by the strategies such as fluid administration may cause brain edema due to the BBB opening post trauma. To guide the TBI therapy, we characterized the relationship between the changes in the cerebral capillary perfusion and BBB permeability after TBI. First, we observed the changes of the cerebral capillary perfusion by the intracardiac perfusion of Evans Blue and the BBB disruption with magnetic resonance imaging (MRI) in the rat subjected to lateral fluid percussion (FP) brain injury. The correlation between two variables was next evaluated with the correlation analysis. Since related to BBB breakdown, matrix metalloproteinase-9 (MMP-9) activity was finally detected by gelatin zymography. We found that the ratios of the perfused microvessel numbers in the lesioned cortices were significantly reduced at 0 and 1 h post trauma compared with that in the normal cortex, which then dramatically recovered at 4 and 24 h after injury, and that the BBB permeability was greatly augmented in the ipsilateral parts at 4, 12, and 24 h, and in the contralateral area at 24 h after injury compared with that in the uninjured brain. The correlation analysis showed that the BBB permeability increase was related to the restoration of the cerebral capillary perfusion over a 24-h period post trauma. Moreover, the gelatin zymography analysis indicated that the MMP-9 activity in the injured brain increased at 4 h and significantly elevated at 12 and 24 h as compared to that at 0 or 1 h after TBI. Our findings demonstrate that the 4 h post trauma is a critical turning point during the development of TBI, and, importantly, the correlation analysis may guide us how to treat TBI.

Development of a large-animal model to measure dynamic cerebrospinal fluid pressure during spinal cord injury

Object

Spinal cord injury (SCI) often results in considerable permanent neurological impairment, and unfortunately, the successful translation of effective treatments from laboratory models to human patients is lacking. This may be partially attributed to differences in anatomy, physiology, and scale between humans and rodent models. One potentially important difference between the rodent and human spinal cord is the presence of a significant CSF volume within the intrathecal space around the human cord. While the CSF may “cushion” the spinal cord, pressure waves within the CSF at the time of injury may contribute to the extent and severity of the primary injury. The objective of this study was to develop a model of contusion SCI in a miniature pig and establish the feasibility of measuring spinal CSF pressure during injury.

Methods

A custom weight-drop device was used to apply thoracic contusion SCI to 17 Yucatan miniature pigs. Impact load and velocity were measured. Using fiber optic pressure transducers implanted in the thecal sac, CSF pressures resulting from 2 injury severities (caused by 50-g and 100-g weights released from a 50-cm height) were measured.

Results

The median peak impact loads were 54 N and 132 N for the 50-g and 100-g injuries, respectively. At a nominal 100 mm from the injury epicenter, the authors observed a small negative pressure peak (median −4.6 mm Hg [cranial] and −5.8 mm Hg [caudal] for 50 g; −27.6 mm Hg [cranial] and −27.2 mm Hg [caudal] for 100 g) followed by a larger positive pressure peak (median 110.5 mm Hg [cranial] and 77.1 mm Hg [caudal] for 50 g; 88.4 mm Hg [cranial] and 67.2 mm Hg [caudal] for 100 g) relative to the preinjury pressure. There were no significant differences in peak pressure between the 2 injury severities or the caudal and cranial transducer locations.

Conclusions

A new model of contusion SCI was developed to measure spinal CSF pressures during the SCI event. The results suggest that the Yucatan miniature pig is an appropriate model for studying CSF, spinal cord, and dura interactions during injury. With further development and characterization it may be an appropriate in vivo largeanimal model of SCI to answer questions regarding pathological changes, therapeutic safety, or treatment efficacy, particularly where humanlike dimensions and physiology are important.

A novel intravital method to evaluate cerebral vasospasm in rat models of subarachnoid hemorrhage: a study with synchrotron radiation angiography

Precise in vivo evaluation of cerebral vasospasm caused by subarachnoid hemorrhage has remained a critical but unsolved issue in experimental small animal models. In this study, we used synchrotron radiation angiography to study the vasospasm of anterior circulation arteries in two subarachnoid hemorrhage models in rats. Synchrotron radiation angiography, laser Doppler flowmetry-cerebral blood flow measurement, [¹²⁵I]N-isopropyl-p-iodoamphetamine cerebral blood flow measurement and terminal examinations were applied to evaluate the changes of anterior circulation arteries in two subarachnoid hemorrhage models made by blood injection into cisterna magna and prechiasmatic cistern. Using synchrotron radiation angiography technique, we detected cerebral vasospasm in subarachnoid hemorrhage rats compared to the controls (p<0.05). We also identified two interesting findings: 1) both middle cerebral artery and anterior cerebral artery shrunk the most at day 3 after subarachnoid hemorrhage; 2) the diameter of anterior cerebral artery in the prechiasmatic cistern injection group was smaller than that in the cisterna magna injection group (p<0.05), but not for middle cerebral artery. We concluded that synchrotron radiation angiography provided a novel technique, which could directly evaluate cerebral vasospasm in small animal experimental subarachnoid hemorrhage models. The courses of vasospasm in these two injection models are similar; however, the model produced by prechiasmatic cistern injection is more suitable for study of anterior circulation vasospasm.

Long-term subarachnoid catheter placement in the middle cranial fossa of the rat

Research using rats sometimes requires long-term placement of catheters in the subarachnoid space, the cavity between the arachnoid mater and the pia mater in the brain. These catheters can be used to experimentally induce subarachnoid bleeding by injecting blood or to locally administer drugs or other substances. To date, published techniques for penetrating the subarachnoid space of small experimental animals require the use of inflexible or relatively inflexible catheters. These catheters typically consist of metal or stiff plastic and are used to access the occipital or frontal cranial cavity or to directly access the cisterna magna via the atlantooccipital membrane. However, inflexible catheters are not ideal for long-term placement in the subarachnoid space. In this paper, the authors describe a reliable procedure for long-term catheterization of the subarachnoid cavity of the rat. For this method, personnel insert the catheter and keep it in place in the rat's middle cranial cavity, in the vicinity of the cerebral arterial circle. This new approach allows personnel to repeatedly use the catheter for a period of at least 2 weeks. The catheter, which is well-tolerated by rats, can be used for administering saline solutions and for injecting blood that has not been treated with heparin into the subarachnoid space.

Acute intracranial hypertension increases gastric tonus in anesthetized rats

We studied the acute effect of intracranial hypertension (ICH) on gastric tonus of anesthetized rats. Brain ventricles were cannulated bilaterally for intracerebro-ventricular pressure (ICP) monitoring and ICH induction. Next, a balloon catheter was inserted at the proximal stomach and coupled to a barostat for gastric volume (GV) monitoring by plethysmography. Arterial pressure (AP) and heart rate (HR) were monitored continuously during 80-min. After a 20-min basal period, they were submitted to control or ICH protocols. In controls, the ICP varied spontaneously up to the end. Other rats were subjected to ICP rising to 10, 20, 40 or 60 mmHg and kept at these levels for 30-min. Another group was subjected after basal period to stepwise ICH (ICP rising to 20, 40 and 60 mmHg at every 10-min interval). Next, the ICH rats were monitored for further 30-min. Other rats, previously submitted to a subdiaphragmatic vagotomy, splanchnicectomy plus ganglionectomy or their respective sham surgery, were also studied under ICH. Each subset consisted of 5-6 rats. Data were compared to respective basal values after ANOVA and Bonferroni's test. In controls, the GV, AP, HR values remained within stable levels. Besides inducing bradycardia and arterial hypertension, ICH10 mmHg decreased GV by 14.8% at the 50-min interval. In ICH20, 40 and 60 mmHg subsets, GV decreased 14.0, 24.5 and 30.6% at the 40-min interval, respectively. In stepwise ICH rats, GV decreased 10.2% and 12.7%, respectively under ICP of 40 and 60 mmHg. The GV values remained significantly lower than basal levels during the last 30-min of monitoring. Thus, ICH decreases the GV in an ICP-dependent pattern besides inducing Cushing's reflex.

Biochemical effects of experimental epidural hematoma on brain parenchyma of rats

INTRODUCTION

The management of epidural hematoma is classified into surgical or conservative treatment according to clinical and radiologic parameters. In the recent years, the number of paper suggesting conservative management has been increasing. The experimental works that have been performed are based on especially the effects of epidural hematomas. Basic pathophysiologic factors on ischemia result of brain trauma are based on biochemical mediators. Nitric oxide (NO) and malondialdehyde (MDA) are the substances that play important roles in brain damage after trauma.

MATERIAL AND METHOD

In this study, 36 rats are divided into three groups (n = 12/group). Epidural hematoma was achieved by 0.1 ml autolog blood in rat epidural space with balloon model. Early and late phase biochemical effects on parenchyma of epidural hematoma operated in a volume which neither alters intracranial pressure (ICP) nor creates shift effect were observed. Biochemical changes of NO and MDA levels were examined in each of three experimental groups.

RESULTS

NO values increased significantly in the early group (6 hours) compared with those in the control group. Difference of NO values between the control and late groups was not significant. An increase has been found in MDA values in the control group compared with those in the early group. MDA values of the late group (30 days) were closer to that of the control group.

CONCLUSION

In this study, considering biochemical results, we have found that conservative volumes which neither increase ICP nor cause brain shift do not lead to permanent changes on brain.

Cerebrospinal Fluid Pressure in the Anesthetized Rat

OBJECTIVE

The primary aims of this study were to determine the major frequencies and powers of oscillations in cerebrospinal fluid (CSF) pressure in the anesthetized rat, and determine whether the CSF pressure oscillations correlated with the major oscillation frequencies in the cardiovascular and respiratory systems as proposed by some chiropractic theories.

METHODS

The cardiac and ventilatory cycles, and CSF pressure were simultaneously recorded during spontaneous and positive-pressure mechanical ventilation in the anesthetized rat. Power spectra were generated from the raw data to identify the major oscillation frequencies in cardiorespiratory and CSF data sets. Entrainment of CSF pressure with ventilation was tested by mechanically pacing the ventilation over a range of frequencies.

RESULTS

The most powerful oscillation in CSF pressure was coincident with ventilatory chest movement during both spontaneous and mechanically paced ventilation. In 22 of 26 trials, there was also a very weak oscillation in CSF pressure that was entrained to heart rate. In addition, in 21 of 26 trials, it was possible to identify a low-frequency oscillation (<0.25 Hz) in CSF pressure that was coincident with a low-frequency oscillation in the power spectrum of the cardiac cycle.

CONCLUSIONS

This study suggests oscillations in CSF pressure in the anesthetized rat are entrained to and driven by ventilation. The arterial pulse pressure makes little contribution to oscillations in CSF pressure in the immobile, anesthetized rat. This study provides normative, quantitative data on which to develop studies concerning the effects of vertebral movements and spinal posture on CSF dynamics.

Acute microvascular platelet aggregation after subarachnoid hemorrhage

OBJECT

The mechanisms underlying acute cerebral ischemia after subarachnoid hemorrhage (SAH) are not well established. Platelets aggregate within major cerebral vessels hours after SAH, but this has not been studied in the microvasculature. Platelet aggregates within the microvasculature could mechanically obstruct the lumen and initiate events that injure vessel structure. In the present study the authors examined the hypothesis that platelets aggregate within the cerebral microvasculature acutely after SAH.

METHODS

Subarachnoid hemorrhage was induced in the rat by using the endovascular perforation model. The animals were killed between 10 minutes and 48 hours after SAH. Immunostaining for the platelet surface receptor glycoprotein (GP)IIb/IIIa, which mediates platelet aggregation, was used to detect platelet aggregation. Sham-operated animals were used as controls. The GPIIb/IIIa immunoreactive platelet aggregates were abundant in the microvasculature of the basal and frontal cortex, striatum, and hippocampus 10 minutes after SAH. These aggregates decreased in number from 1 to 6 hours post-SAH and then increased to a peak at 24 hours. No immunoreactive aggregates were observed 48 hours after SAH.

CONCLUSIONS

The data indicate that widespread platelet aggregation occurs very rapidly in response to SAH followed by a decrease within 6 hours and a subsequent increase 24 hours after SAH. Microvascular platelet aggregates may contribute to decreased cerebral blood flow and ischemic injury after SAH via a number of mechanisms.

Acute alterations in microvascular basal lamina after subarachnoid hemorrhage

Object. Aneurysmal subarachnoid hemorrhage (SAH) causes acute and delayed ischemic brain injuries. The mechanisms of acute ischemic injury following SAH are poorly understood, although an acute increase in microvascular permeability has been noted. The integrity of cerebral microvessels is maintained in part by components of basal lamina: collagen IV, elastin, lamina, and so forth. Destruction of basal lamina components by collagenases and matrix metalloproteinases (MMPs), especially MMP-9, has been known to occur in other ischemic models. The authors assessed the integrity of cerebral microvasculature after acute SAH by examining collagen IV and MMP-9 levels and collagenase activity in the microvessels.

Methods. Subarachnoid hemorrhage was induced in rats through endovascular perforation of the intracranial bifurcation of the internal carotid artery. Animals were killed 10 minutes to 48 hours after SAH or sham operation (time-matched controls). Levels of collagen IV and MMP-9 were studied in the microvasculature by performing immunoperoxidase and immunofluorescence staining, and collagenase activity was assessed by in situ zymography.

Little change occurred in collagen IV and MMP-9 immunostaining or collagenase activity at 10 minutes or 1 hour after SAH. Starting 3 hours after SAH, collagen IV immunostaining was reduced or eliminated along segments of microvessels whereas MMP-9 staining was segmentally increased. These effects reached a maximum at 6 hours and returned toward those values in sham-operated controls at 48 hours.

Conclusions. Results of this study demonstrated an acute loss of collagen IV from the cerebral microvasculature after SAH and indicated that MMP-9 contributes to this event. The loss of collagen IV might contribute to the known failure of the blood—brain barrier after SAH.

Nitric Oxide Synthase in Acute Alteration of Nitric Oxide Levels after Subarachnoid Hemorrhage

OBJECTIVE

Subarachnoid hemorrhage (SAH) is associated with acute decreases and subsequent recovery of cerebral nitric oxide (NO) levels, but the mechanisms of these alterations are not known. In this study, we measured NO synthase (NOS) protein and kinetics to determine its involvement in the alterations of cerebral NO levels after SAH.

METHODS

The endovascular rat model of SAH was used. The number of NOS-1 (neuronal) and NOS-2 (inducible)-positive cells (0-96 h) was determined by counting immunoreactive cells in 8-microm cryostat sections. The tissue content of active NOS and its kinetic parameters were studied with an enzymatic l-citrulline assay.

RESULTS

The number of NOS-1-positive cells increased between 1 and 3 hours after SAH, decreased to and below control values at 6 and 72 hours after SAH, and increased to control values 96 hours after SAH. The number of NOS-2-positive cells increased 1 hour after SAH, decreased to control values at 24 hours, and increased above control values 96 hours after SAH. The Michaelis-Menten kinetic parameters (V(max), K(m), slope) of NOS remained unchanged at 10 and 90 minutes after SAH.

CONCLUSION

NOS-1 and -2 proteins undergo a triphasic alteration after SAH, whereas the amount of active NOS and its kinetic parameters remain unchanged during the first 90 minutes after SAH. Depletion of NOS is not involved in the acute alterations of cerebral NO levels after SAH.

Signaling pathways for early brain injury after subarachnoid hemorrhage

Few studies have examined the signaling pathways that contribute to early brain injury after subarachnoid hemorrhage (SAH). Using a rat SAH model, the authors explored the role of vascular endothelial growth factor (VEGF) and mitogen-activation protein kinase (MAPK) in early brain injury. Male Sprague-Dawley rats (n = 172) weighing 300 to 350 g were used for the experimental SAH model, which was induced by puncturing the bifurcation of the left anterior cerebral and middle cerebral arteries. The blood-brain barrier (BBB), brain edema, intracranial pressure, and mortality were evaluated at 24 hours after SAH. The phosphorylation of VEGF and different MAPK subgroups (ERK1/2, p38, and JNK) were examined in both the cortex and the major cerebral arteries. Experimental SAH increased intracranial pressure, BBB permeability, and brain edema and produced high mortality. SAH induced phosphorylation of VEGF and MAPKs in the cerebral arteries and, to a lesser degree, in the cortex. PP1, an Src-family kinase inhibitor, reduced BBB permeability, brain edema, and mortality and decreased the phosphorylation of VEGF and MAPKs. The authors conclude that VEGF contributes to early brain injury after SAH by enhancing the activation of the MAPK pathways, and that the inhibition of these pathways might offer new treatment strategies for SAH.

New lumbar method for monitoring cerebrospinal fluid pressure in rats

OBJECTIVE

Monitoring cerebrospinal fluid pressure or intracranial pressure (ICP) is crucial in the study of neurosurgical disorders. In the present study, we report a new lumbar method for monitoring ICP in rats.

METHODS

A PE10 catheter connected to a pressure transducer was placed into the subarachnoid space of L5 through the duramater after laminectomy to record lumbar cerebrospinal fluid pressure (lumbar-ICP). ICP at the cisterna magna (cisterna-ICP) was recorded simultaneously via a catheter in the subarachnoid space at the cisterna magna. Eighteen anesthetized adult male S-D rats were subjected to baseline recording followed by either experimental subarachnoid hemorrhage (SAH) induced by intravascular puncture method or experimental intracerebral hemorrhage (ICH) induced by blood injection with a stereotaxic system.

RESULTS

Baseline lumbar-ICP and cisterna-ICP varied between 6 and 8 mmHg, and respiratory variation could be detected. A similar acute response to SAH was recorded in both the lumbar-ICP and cisterna-ICP in all rats. In rats subjected to SAH, the lumbar catheter continuously and accurately monitored lumbar-ICP, and reliable pressure tracings were obtained for up to 24 h after SAH. However, continued cisterna-ICP monitoring was abandoned in two rats in the cisterna magna method due to obstruction of the catheter by blood clots (hematoma).

CONCLUSION

This new lumbar-ICP method is simple, safe, easy, and reliable in rats. Continued lumbar-ICP measurements provided monitoring for up to 24 h after experimental manipulation.

Effect of hypertension on the integrity of blood brain and blood CSF barriers, cerebral blood flow and CSF secretion in the rat

Hypertension has been related to the development of brain damage, dementia and other CNS dysfunctions. Disruption of the blood-brain barrier (BBB) is thought to contribute to these disorders. In this study, the integrity of both blood-brain and blood-CSF barriers during chronic hypertension was investigated. For this, the entry of [14C]sucrose and of lanthanum into brain tissue, choroid plexus, and CSF was studied. Also brain regional blood flow and brain [14C]sucrose volume of distribution were measured using indicator fractionation and ventriculo-cisternal perfusion methods, respectively. The above measurements were performed in normotensive (WKY) rats and in the spontaneously hypertensive rats (SHR). Choroid plexus and CSF uptakes of [14C]sucrose were found to be significantly greater in SHR compared to WKY rats (P<0.05). Intercellular entry of lanthanum was observed in choroidal tissue of SHR but not in that of WKY rats and at the BBB. Choroid plexus blood flow was significantly greater in SHR, 2.82+/-0.21 ml g(-1) min(-1), compared to 2.4+/-0.08 ml g(-1) min(-1) in WKY (P<0.05). There were no significant differences (P>0.05) in brain % water content and extracellular fluid [14C]sucrose volume of distribution between SHR and WKY rats. However, choroid plexus showed greater % water content in SHR (85.7+/-1.9%) compared to the WKY rats (81.5+/-1.7%). These results suggest that chronic hypertension in SHR may cause more pronounced defects in the integrity of the blood-CSF barrier than in the BBB.

Experimental subarachnoid haemorrhage models in rats

There is no comprehensive and reliable model available in small animals that are suitable for the study of subarachnoid haemorrhage (SAH). In the study we reviewed the advantages and disadvantages of available SAH models in rats and presented our model. Experimental SAH was induced in a group of 350-450 g Sprague-Dawley rats. A 2 mm-diameter burr hole was drilled and, working under a microscope, haemorrhage was produced by transclival puncture of the basilar artery with a 20 microns thick piece of glass. The rats were assigned to either the experimental group (n: 7) or the control group (n: 7). Local cerebral blood flow (LCBF), intracranial pressure (ICP), and cerebral perfusion pressure (CPP) were measured for 60 min after SAH, after which the rats were decapitated. Microscopic examinations were done on three different segments of the basilar artery. There was a significant and sharp drop in LCBF just after SAH was induced (56.17 +/- 12.80 mlLD/min/100 g and 13.57 +/- 5.85 mlLD/min/100 g for baseline and post-SAH, respectively; p < 0.001), the flow slowly increased by the end of the experiment but never recovered to pre-SAH values (43.63 +/- 7.6 mlLD/min/100 g, p < 0.05). ICP (baseline 7.33 +/- 0.8 mmHg) increased acutely to 70.6 +/- 9.2 mmHg, and also returned to normal levels by 60 min after SAH. CPP (baseline 75.1 +/- 4.9 mmHg) dropped accordingly (to 21.0 +/- 6.3 mmHg) and then increased, reaching 70.1 +/- 4.9 mmHg at 60 min after SAH. Examinations of the arteries revealed decreased inner luminal diameter and distortion of the elastica layer. We present an inexpensive and reliable model of SAH in the rat that allows single and multiple haemorrhages and to study the early and late course of pathological changes.

Acute and delayed vasoconstriction after subarachnoid hemorrhage: local cerebral blood flow, histopathology, and morphology in the rat basilar artery

The decreased local cerebral blood flow (LCBF) and cerebral ischemia that occur after subarachnoid hemorrhage (SAH) may be caused by acute and/or delayed vasospasm. In 36 Sprague-Dawley (350-450 g) rats SAH was induced by transclival puncture of the basilar artery. Mean arterial blood pressure (MABP), LCBF, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) were measured in all rats for 30 min before and 60 min after SAH was induced. One set of control (n : 7) and experimental animals (n : 7) was sacrificed after the 60 min of initial post-hemorrhage measurements were recorded. Four days after SAH induction, LCBF and MABP were measured again for 60 min in subgroups of surviving experimental rats (n : 7) and control rats (n : 7). Histopathologic and morphologic examinations of the basilar artery were performed in each subgroup. There was a sharp drop in LCBF just after SAH was induced (55.50 +/- 11.46 mlLD/min/100 g and 16.1 +/- 3.6 mlLD/min/100 g for baseline and post-SAH, respectively; p < 0.001). The flow then gradually increased but had not returned to pre-SAH values by 60 min (p < 0.05). At 4 days after SAH induction, although LCBF was lower than that observed in the control group and pre-SAH values, it was not significantly different from either of these flow rates (p > 0.05). ICP (baseline 7.05 +/- 0.4 mmHg) increased acutely to 75.2 +/- 7.1 mmHg, but returned to normal levels by 60 min after SAH. CPP (baseline 84.5 +/- 6.3 mmHg) dropped accordingly (to 18.6 +/- 3.1 mmHg), and then increased, reaching 72.2 +/- 4.9 mmHg at 60 min after SAH (p > 0.05). Examinations of the arteries revealed decreased inner luminal diameter and distortion of the elastica layer in the early stage. LCBF in nonsurviver rats (n : 8) was lower than that in the animals that survived (p < 0.01). At 4 days post-hemorrhage, the rats' basilar arteries showed marked vasculopathy. The findings showed that acute SAH alters LCBF, ICP, and CPP, and that decreased LCBF affects mortality rate. Subsequent vasculopathy occurs in delayed fashion, and this was observed at 4 days after the hemorrhage event.

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.

Intracerebral clysis in a rat glioma model

OBJECTIVE

Intracerebral clysis (ICC) is a new term we use to describe convection-enhanced microinfusion into the brain. This study establishes baseline parameters for preclinical, in vivo, drug investigations using ICC in a rat glioma model.

METHODS

Intracranial pressure was measured, with an intraparenchymal fiber-optic catheter, in male Fischer rats 10, 15, 20, and 25 days after implantation of C6 glioma cells in the right frontal lobe (n = 80) and in control rats without tumor (n = 20), before and during ICC. A 25% albumin solution (100 microl) was infused through an intratumoral catheter at 0.5, 1.0, 2.0, 3.0, and 4.0 microl/min. Infusate distribution was assessed by infusion of fluorescein isothiocyanate-dextran (Mr 20,000), using the aforementioned parameters (n = 36). Brains were sectioned and photographed under ultraviolet light, and distribution was calculated by computer analysis (NIH Image for Macintosh). Safe effective drug distribution was demonstrated by measuring tumor sizes and apoptosis in animals treated with N,N'-bis(2-chloroethyl)-N-nitrosourea via ICC, compared with untreated controls. Magnetic resonance imaging noninvasively confirmed tumor growth before treatment.

RESULTS

Intracranial pressure increased with tumor progression, from 5.5 mm Hg at baseline to 12.95 mm Hg on Day 25 after tumor cell implantation. Intracranial pressure during ICC ranged from 5 to 21 mm Hg and was correlated with increasing infusion volumes and increasing rates of infusion. No toxicity was observed, except at the higher ends of the tumor size and volume ranges. Fluorescein isothiocyanate-dextran distribution was greater with larger infusion volumes (30 microl versus 10 microl, n = 8, P < 0.05). No significant differences in distribution were observed when different infusion rates were compared while the volume was kept constant. At tolerated flow rates, the volumes of distribution were sufficient to promote adequate drug delivery to tumors. N,N'-Bis(2-chloroethyl)-N-nitrosourea treatment resulted in significant decreases in tumor size, compared with untreated controls.

CONCLUSION

The C6 glioma model can be easily modified to study aspects of interstitial delivery via ICC and the application of ICC to the screening of potential antitumor agents for safety and efficacy.

Acute decrease in cerebral nitric oxide levels after subarachnoid hemorrhage

Disturbances in the nitric oxide (NO) vasodilatory pathway have been implicated in acute vasoconstriction and ischemia after subarachnoid hemorrhage (SAH). The authors hypothesize that blood released during SAH leads to vasoconstriction by scavenging NO and limiting its availability. This was tested by measuring the major NO metabolites nitrite and nitrate in five different brain regions before and after experimental SAH. The basal NO metabolites levels were as follows (mean +/- SD, micromol/mg wet weight): brain stem, 0.14 +/- 0.07; cerebellum, 0.12 +/- 0.08; ventral convexity cortex, 0.22 +/- 0.15; dorsal convexity cortex, 0.16 +/- 0.11; and hippocampus, 0.26 +/- 0.17. In sham-operated animals, no effect of the nitric oxide synthase (NOS) inhibitor L(G)-nitro-L-arginine-methyl-ester (30 mg/kg) was found on NO metabolites 40 minutes after administration, but a significant decrease was seen after 120 minutes. The NO metabolites decreased significantly 10 minutes after SAH in all brain regions except for hippocampus, and recovered to control levels in cerebellum at 60 minutes and in brain stem and dorsal cerebral cortex 180 minutes after SAH, while remaining low in ventral convexity cortex. Nitrite recovered completely in all brain regions at 180 minutes after SAH, whereas nitrate remained decreased in brain stem and ventral convexity cortex. Our results indicate that SAH causes acute decreases in cerebral NO levels by a mechanism other than NOS inhibition and provide further support for the hypothesis that alterations in the NO vasodilatory pathway contribute directly to the ischemic insult after SAH.

ICP monitoring in the rat: comparison of monitoring in the ventricle, brain parenchyma, and cisterna magna

Various methods of continuous intracranial pressure (ICP) monitoring during experimental procedures in the rat have been described. However, no systematic comparison of ICP monitoring in the ventricle, brain parenchyma, and cisterna magna has been reported. Since accurate and reliable ICP measurements are important in experimental models of traumatic brain injury, the present study was conducted to compare simultaneous ICP measurements from ventricular, cisterna magna, and intraparenchymal monitors during ICP changes. Subdural hematoma was produced by infusion of 0.3 ml of autologous blood into the subdural space over 6 min. The ventricular and the intraparenchymal fiberoptic catheter produced reliable and comparable pressure recordings, that did not statistically differ (p = 0.4), throughout the one hour monitoring time. In contrast, the cisterna magna catheter was less reliable and produced significantly lower readings throughout the monitoring time (p<0.001). The intraparenchymal device produced greater cortical damage than the ventricular catheter. In conclusion, ventricular ICP monitoring is the preferred method under these circumstances, since it is accurate and induces least brain damage.

Effects of S-nitrosoglutathione on acute vasoconstriction and glutamate release after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Subarachnoid hemorrhage (SAH) causes acute vasoconstriction that contributes to ischemic brain injury shortly after the initial bleed. It has been theorized that decreased availability of nitric oxide (NO) may contribute to acute vasoconstriction. Therefore we examined the effect of the NO donor N-nitroso glutathione (GSNO) on acute vasoconstriction and early ischemic glutamate release after experimental SAH.

METHODS

SAH was induced by the endovascular suture method in anesthetized rats. GSNO (1 micromol/L/kg, n=31) or saline (n=21) was injected 5 minutes after SAH. Sham-operated rats received GSNO (1 micromol/L/kg, n=5) 5 minutes after sham surgery. Arterial and intracranial pressures, cerebral blood flow (CBF), and extracellular glutamate release were measured serially for 60 minutes after SAH. SAH size was determined, and vascular measurements were made histologically.

RESULTS

GSNO had no effect on resting blood pressure, intracranial pressure, cerebral perfusion pressure, or CBF in sham-operated animals. However, administration of GSNO after SAH was associated with significantly increased CBF (161.6+/-26.6% versus saline 37.1+/-5.5%, 60 minutes after SAH, P<0.05), increased blood vessel diameter (internal carotid artery [ICA] 285.0+/-16.5 microm versus saline 149.2+/-14.1 microm, P<0.01), decreased vessel wall thickness (ICA12.9+/-0.7 microm versus saline 25.1+/-1.6 microm, P<0.01), and decreased extracellular glutamate levels (3315.6+/-1048.3% versus saline469. 7+/-134.3%, P<0.05). Blood pressure decreased transiently, whereas intracranial pressure, cerebral perfusion pressure, and SAH size were not affected.

CONCLUSIONS

These results suggest that GSNO can reverse acute vasoconstriction and prevent ischemic brain injury after SAH. This further implies that acute vasoconstriction contributes significantly to ischemic brain injury after SAH and is mediated in part by decreased availability of NO.

Acute intracranial hypertension-induced inhibition of gastric emptying: evaluation in conscious rats

To study the effect of raised intracranial pressure (ICP)-induced alterations in gastric emptying, and their modulation by pharmacological interventions, an experimental model was standardized in rats. A test meal of methylcellulose and phenol red was administered intragastrically. ICP was raised to 40, 60 and 80 mmHg by connecting a buffered saline pressure head to an intracerebroventricular (i.c.v.) cannula. Gastric emptying was estimated after killing the animals, from the residual stomach phenol red content. Inhibition of gastric emptying was observed when ICP was raised, the maximum being at 80 mmHg ICP (percent gastric emptying 26.5%+/-2.8 vs. 83.4+/-4.7 in sham-ICP). Pretreatment with clonidine, prazosin or ondansetron did not modify the raised ICP-induced inhibition of gastric emptying. Cisapride was ineffective at 1 mg/kg but caused a partial reversal at the 5- and 10-mg/kg doses (46.9+/-3.1% and 42.6+/-4.0%, respectively). Carbachol at a lower dose of 0.1 mg/kg i.p., produced a greater reversal (78.3+/-6.0%) than did the high dose (52.8+/-4.1). Bretylium partially reversed the inhibition of gastric emptying (45.7+/-4.3%). The protective effect of carbachol and cisapride suggests that suppression of vagal activity due to increased ICP may play an important role in the inhibition of gastric emptying due to intracranial hyper-tension.

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.

A chronic model to simultaneously measure intracranial pressure, cerebral blood flow, and study the pial microvasculature

In an effort to study changes in cerebral blood flow (CBF), intracranial pressure (ICP) and intracranial compliance (ICC) simultaneously, we have developed a chronic model in rats using a pial window crown with two ports. This model can also be used to study vasoreactivity of pial vessels. Female Sprague-Dawley rats weighing between 225-250 g underwent placement of cranial chamber with dual ports under pentobarbital anesthesia. To test the utility of this technique 45 groups of rats were studied. Group 1 consisted of control animals. Group 2 consisted of rats undergoing 15 min of global cerebral ischemia. Rats in group 3 were evaluated for changes in vessel diameter and ICP after adenosine injection. In group 4 leukocyte/endothelial interactions were evaluated. These groups demonstrate the ability of this model to monitor CBF, ICP, ICC and pial vessel architecture in chronic rat experiments.

A new approach for multiple sampling of cisternal cerebrospinal fluid in rodents with minimal trauma and inflammation

A new approach was developed to minimize inevitable damage to nervous and meningeal tissue due to implantation of a sampling tube allowing multiple withdrawal of cerebrospinal fluid (CSF) from the cisterna magna in adult rats. A tube was secured on the atlanto-occipital membrane. Thereafter, a hole was cut through the membrane, allowing flow of CSF from the cisterna magna to the tube. CSF could be sampled repeatedly for at least 1 week. There was no blood-brain barrier damage. The pressure in the cisterna magna remained normal as did the estimated rate of CSF formation. Very few blood cells contaminated the CSF. There was very little evidence of inflammation. The nervous tissue was undamaged as shown by exclusion of a dye-protein complex. The CSF concentrations of the cytosolic neuronal protein neuron-specific enolase (NSE), and of the astrocyte protein S-100 were very low. The pattern of amino acids remained within normal limits. Scanning electron microscopy revealed that clot and reactive changes were restricted to the vicinity of the connecting hole. We conclude that our approach to positioning a tube on the atlanto-occipital membrane and then connecting it to the cisterna magna reproducibly and reliably enables 'atraumatic' multiple sampling of CSF.

Method of recording cerebrospinal fluid pressure at three anatomic places in conscious and unrestrained adult wistar rats

There does not appear to be a consensus on the normal values of cerebrospinal fluid pressure (Pcsf) in rats because of the different conditions in which each experiment has been done. Anaesthesia, restraint or recordings from different anatomical places and the use of simultaneous infusions could produce a great variability in the obtained results and because of that the average Pcsf in rats has been reported to be between 2 and about 18.5 cm H2O. The aim of this study is to provide new information about the normal values of Pcsf in adult, conscious rats by carrying out long-term measurements, for 3 consecutive days, from different anatomical places. Thirty male Wistar rats divided in three experimental groups of ten animals each were used. A catheter of silicone was implanted into the lateral ventricles in group I, the cisterna magna in group II, and the lumbar subarachnoid space in group III to record the Pcsf values. This catheter was attached to a swivel system to allow unrestrained and free behaviour in the rats. Mean values of normal Pcsf values were 13.03 +/- 0.73 cm H2O from the lateral ventricles, 15.9 +/- 0.73 cm H2O from the cisterna magna, and 16.73 +/- 1.14 cm H2O from the lumbar subarachnoid space.

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.

Acute brain swelling in cerebral embolization model of rats. I: Epidural pressure monitoring

The authors measured epidural pressure of rats using a microballoon to monitor brain swelling after cerebral embolism. Rats with embolization of the major cerebral artery frequently demonstrated acute brain swelling. Within 5 hours of embolization, the increase in epidural pressure was 29.7 +/- 20.3 mm Hg (mean +/- SD), ranging from 3 to 68 mm Hg. The increase in epidural pressure tended to reach a near-maximal value within 30 minutes of embolization and thereafter stayed at that point until the end of the experiment. These results suggest that measuring epidural pressure can quantitatively assess acute brain swelling in rats.