Effect of selective lesions in the hypothalamic-pituitary region on the development of cerebral vasospasm following an experimental subarachnoid hemorrhage in the rat

Pathophysiology of Delayed Cerebral Ischemia After Subarachnoid Hemorrhage: A Review

Delayed cerebral ischemia is a major predictor of poor outcomes in patients who suffer subarachnoid hemorrhage. Treatment options are limited and often ineffective despite many years of investigation and clinical trials. Modern advances in basic science have produced a much more complex, multifactorial framework in which delayed cerebral ischemia is better understood and novel treatments can be developed. Leveraging this knowledge to improve outcomes, however, depends on a holistic understanding of the disease process. We conducted a review of the literature to analyze the current state of investigation into delayed cerebral ischemia with emphasis on the major themes that have emerged over the past decades. Specifically, we discuss microcirculatory dysfunction, glymphatic impairment, inflammation, and neuroelectric disruption as pathological factors in addition to the canonical focus on cerebral vasospasm. This review intends to give clinicians and researchers a summary of the foundations of delayed cerebral ischemia pathophysiology while also underscoring the interactions and interdependencies between pathological factors. Through this overview, we also highlight the advances in translational studies and potential future therapeutic opportunities.

The influence of noradrenergic blockade on vasospasm and the quantity of cerebral dopamine ß-hydroxylase following subarachnoid haemorrhage in rabbits

BACKGROUND

The aim of this study of experimental subarachnoid haemorrhage (SAH) and exclusion of the sympathetic nervous system (SNS) in rabbits was to find out if changes in the central noradrenergic areas of the hypothalamus and brain stem could be ascertained, in parallel with measurement of the intensity of chronic cerebral vasospasm in the basilar arteries.

METHODS

Histologic specimens were prepared by perfusion fixation on day 8 after the SAH. The spastic effect of experimentally induced SAH in New Zealand rabbits was investigated: firstly, using our previously developed method for measuring the corrugation coefficient (CC) of the vessel intima on precisely defined locations of the basilar artery (BA) with the aid of computer image analysis; and secondly, by immunohistochemical assessment of the concentration and localization of dopamine beta-hydroxylase (DBH), using anti-DBH, at precisely defined sites of the hypothalamus and brain stem of the same rabbit.

RESULTS

The intima of the BA, assessed by CC, was significantly less corrugated and had significantly less DBH in group A (the control group without SAH and without additional interventions; mean CC = 1.192, P = 0.004; median DBH = 0.50, P = 0.044), in group C (SAH and alpha-blocker phenoxybenzamine; mean CC = 1.142, P = 0.000; median DBH = 0.75, P = 0.001), and in group D (SAH and cervical gangliectomy; mean CC = 1.210, P = 0.003; median DBH = 0.50, P = 0.002) compared with group B (rabbits with SAH and without medication). Group B showed a significantly more intensive accumulation of DBH (median DBH = 1.15) and, according to the CC (mean CC = 1.369), more intensive corrugation of the intima of BA than all other groups. The correlation between CC and DBH for all the rabbits (groups A, B, C and D together) was significantly positive (Spearman Rho = 0.470; p = 0.010).

CONCLUSIONS

The results of this study demonstrated: firstly, an intensive excitatory influence of SAH on the quantity of DBH in central noradrenergic areas in the hypothalamus and brain stem; secondly, a very effective influence of peripheral and systemic sympathetic exclusion on lowering the quantity of central sympathetic DBH; thirdly, that the changes in the BA of individual rabbits occur simultaneously with corresponding changes in DBH-containing neurons, thus suggesting the likelihood of SNS involvement in the pathogenesis of post-SAH vasospasm in rabbits.

Symptomatic vasospasm after resection of a suprasellar pilocytic astrocytoma: case report and possible pathogenesis

BACKGROUND

Cerebral vasospasm from pathology other than subarachnoid hemorrhage is uncommon. A case of severe vasospasm after resection of a suprasellar pilocytic astrocytoma is reported.

METHODS

A 45-year-old male presented with headache, left facial numbness, bilateral visual loss, and ataxia. Evaluation revealed a large suprasellar tumor, which was resected. Pathologic examination showed pilocytic astrocytoma. The patient developed hemiparesis and aphasia on the fifth postoperative day. Vascular spasm was documented on angiography and by transcranial Doppler.

RESULTS

Intraarterial papaverine resulted in moderate angiographic improvement. Attempts to open middle cerebral artery branches with angioplasty were unsuccessful. The patient subsequently developed a left middle cerebral artery infarct.

CONCLUSIONS

To our knowledge, this is the first description of vasospasm after resection of an astrocytoma. Possible mechanisms contributing to this unusual complication after resection of tumors are discussed.

Direct magnification technique for cerebral angiography in the rat

RATIONALE AND OBJECTIVES

The authors evaluated the performance of direct magnification radiography (DIMA) with digital image processing for cerebral angiography in the rat.

METHODS

A microfocal x-ray unit with a focal spot of 5 microns was used for cerebral angiography in 10 rats. The animals were examined form x 4 up to x 20 magnification after injection of 0.2 mL x-ray contrast medium into the common carotid artery.

RESULTS

Direct magnification radiography technology provides high resolution images and enables the visualization of very small vessels with high quality. It allows the peripheral branches of the middle cerebral artery or the ophthalmic artery to be visualized. Superimposition and noise effects can be excluded with digital subtraction and image processing.

CONCLUSIONS

The experiments show that DIMA radiography is a suitable technique for cerebral angiography in the rat.

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.

Cerebrovascular sensory innervation involved in the development of cerebral vasospasm following a subarachnoid hemorrhage

Cerebral vasospasm following subarachnoid hemorrhage was induced in the squirrel monkey in order to evaluate the involvement of cerebrovascular sensory nerves in the development of the vasospasm. A unilateral surgical section of the trigeminal nerve at post- but not at pre-Gasserian level caused constriction of the major ipsilateral cerebral arteries. A pre- or postganglionic trigeminal lesion induced an increased glucose uptake globally without influencing the cerebral blood flow. Following a subarachnoid hemorrhage, the decrease in cerebral blood flow was similar of that seen in control animals, while post-ganglionically lesioned animals had an additional increase in glucose uptake. Intrathecal injection of gamma-globulin against substance P prevented the occurrence of vasospasm and the decrease in cerebral blood flow, while calcitonin gene-related peptide (CGRP) anti-gamma-globulin injection significantly reduced the resting vessel diameter and did not influence spasm development. It is concluded that a nervous reflex mechanism could underlie cerebral vasospasm. The cerebrovascular sensory nerves have both a peripheral and a central function. A peripheral or axon reflex mechanism exerts a tonic effect on the cerebral arteries. Central neurotransmission seems to be involved in the regulation of cerebral metabolism and possibly in the coordination of cerebral blood flow and glucose metabolism. CGRP could be the transmitter involved in a peripheral axon reflex and substance P might be the neurotransmitter conveying information to the brainstem vascular centers.

Effect of spantide, a substance-P antagonist, on cerebral vasospasm in primates

Experimental SAH in the squirrel monkey induces an angiographically demonstrable late spasm of about 23% at six days post subarachnoid haemorrhage (SAH). The late spasm is associated with a generalized reduction in cerebral blood flow (CBF) of about 30%. Intracisternal administration of the substance P (SP) antagonist spantide two hours and three days post SAH significantly reduces the degree of late spasm and also decreases the degree of CBF reduction. The findings suggest that SP is involved in the development of both angiographical spasm and CBF changes post SAH.

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)

Cerebrovascular changes following administration of gammaglobulins against substance P or calcitonin gene related peptide in monkey with subarachnoid haemorrhage

Cerebrovascular changes after intrathecal (ith) administration of gammaglobulins against substance P (SP) or calcitonin gene-related peptide (CGRP) were investigated before and following a simulated subarachnoid haemorrhage (SAH) in the squirrel monkey. The SAH was produced by injection of homologous blood into the interpeduncular fossa and the cisterna magna. The gammaglobulins were given both prior to the blood injections and daily in 5 days post-SAH. The effect of the gammaglobulins was examined by angiography pre-SAH and at 10 min and at 6 days post-SAH, i.e. the time points for maximal acute and late spasm in the present model. Cerebral blood flow (CBF) was measured under general anesthesia at day 6 post-SAH with an autoradiographic technique. Five of nine animals treated with CGRP antigammaglobulin died from respiratory failure. Four animals received SP antigammaglobulin and two control animals received normal globulin. SP antigammaglobulin per se had no effect on baseline arterial diameter, while CGRP antigammaglobulin significantly reduced the diameter of the arteries. SP antigammaglobulin prevented the occurrence of acute spasm and significantly reduced the degree of late spasm. Moreover, the reduction in CBF noted in the control SAH animals was significantly reduced. In contrast, CGRP antigammaglobulin treatment had no effect on the degree of spasm and did not cause any change in CBF as compared to controls. The finding that CGRP but not SP antigammaglobulin significantly reduces the arterial diameter in conjunction with our previous demonstration that a post-, but not preganglionic trigeminal lesion reduces the baseline arterial diameter, indicates that CGRP could be the transmitter involved in a peripheral axon reflex. The function of SP might be as a neurotransmitter conveying information to the brainstem. The transmitter role is supported by the effect of SP antigammaglobulin impairing SP containing neurons and, in that way, mimicking a bilateral trigeminal rhizotomy.

BQ-123, a peptidic endothelin ETA receptor antagonist, prevents the early cerebral vasospasm following subarachnoid hemorrhage after intracisternal but not intravenous injection

The aim of this study was to evaluate the role of endothelin and endothelin ETA receptor in the early cerebral vasoconstriction following subarachnoid hemorrhage (SAH) in the rat. SAH induced by injection of autologous blood in the cisterna magna reduced by 22 to 38% cerebral blood flow (CBF) measured with radioactive microspheres at 30, 60 and 120 min after SAH. The cyclic pentapeptide BQ-123, a selective antagonist of the ETA receptor, injected intravenously (3 mg/kg) had no effect on this decrease in CBF. However, intracisternal BQ-123 (10 nmol) completely prevented the decrease in CBF at 60 and 120 min after SAH. These results suggest that BQ-123 does not cross the blood-brain barrier, but demonstrate that endothelin acting on ETA receptor plays a role in the pathogenesis of cerebral vasoconstriction in this rat model of SAH.

Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: a review

Delayed or secondary neuronal damage following traumatic injury to the central nervous system (CNS) may result from pathologic changes in the brain's endogenous neurochemical systems. Although the precise mechanisms mediating secondary damage are poorly understood, posttraumatic neurochemical changes may include overactivation of neurotransmitter release or re-uptake, changes in presynaptic or postsynaptic receptor binding, or the pathologic release or synthesis of endogenous "autodestructive" factors. The identification and characterization of these factors and the timing of the neurochemical cascade after CNS injury provides a window of opportunity for treatment with pharmacologic agents that modify synthesis, release, receptor binding, or physiologic activity with subsequent attenuation of neuronal damage and improvement in outcome. Over the past decade, a number of studies have suggested that modification of postinjury events through pharmacologic intervention can promote functional recovery in both a variety of animal models and clinical CNS injury. This article summarizes recent work suggesting that pharmacologic manipulation of endogenous systems by such diverse pharmacologic agents as anticholinergics, excitatory amino acid antagonists, endogenous opioid antagonists, catecholamines, serotonin antagonists, modulators of arachidonic acid, antioxidants and free radical scavengers, steroid and lipid peroxidation inhibitors, platelet activating factor antagonists, anion exchange inhibitors, magnesium, gangliosides, and calcium channel antagonists may improve functional outcome after brain injury.

Effect of lesioning of medullary catecholamine neurons or the median eminence on the development of cerebral vasospasm in the squirrel monkey

Injections of blood into the interpeduncular fossa and cisterna magna in the squirrel monkey produce an angiographically demonstrable, biphasic cerebral vasospasm with a maximal acute spasm at ten minutes and a maximal late spasm at six days after the subarachnoid haemorrhage (SAH). Selective lesioning of the A2 nucleus in the medulla oblongata or the median eminence in the hypothalamus prior to the SAH prevents the development of both the acute and late cerebral vasospasm. The present data indicate that the A2 nucleus and the median eminence participate in the development of vasospasm in the squirrel monkey.

A primate model for acute and late cerebral vasospasm: angiographic findings

A subarachnoid haemorrhage (SAH) in the squirrel monkey was produced by injection of blood via a permanently implanted catheter connected to the cisterna magna and a cannula stereotactically inserted into the interpeduncular cistern. Repeated angiographic examinations of the vertebro-basilar and right internal carotid arteries revealed a biphasic vasospasm with a maximal acute spasm at ten minutes and maximal late spasm at six days after blood injection. The present study has shown that a reproducible biphasic vasospasm can be produced in the squirrel monkey and evaluated by repeated angiographic examinations. The model is suitable in the study of basic mechanisms underlying vasospasm in a primate and, due to the size of the animal, autoradiographic evaluation of the cerebral blood flow and metabolism can be performed at an acceptable cost.

Central projections of the sensory innervation to the middle cerebral artery in the squirrel monkey

To analyze the brainstem projections of the innervation to the middle cerebral artery (MCA) in the squirrel monkey, transganglionic tracing of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) was used. After application of WGA-HRP to the middle cerebral artery (MCA), labelled cell bodies were identified in the ipsilateral trigeminal and superior cervical ganglia. In the brainstem, positive labelling indicative of preterminals and terminals occurred in a discontinuous pattern throughout the trigeminal brainstem nuclear complex. At the level of the obex, nerve terminations were identified in the nucleus tractus solitarius, nucleus motorius dorsalis nervi vagi and the nucleus nervi hypoglossi. Positive WGA-HRP profiles were also observed in the periaqueductal gray matter.

Effect of unilateral pre- and postganglionic lesioning of the trigeminal nerve on the development of cerebral vasospasm in the squirrel monkey: angiographic findings

Bilateral carotid angiography was performed in the squirrel monkey before and after unilateral pre- and postganglionic trigeminal lesioning. A unilateral postganglionic lesion caused a significant constriction of about 27% of the ipsilateral cerebral arteries, while a preganglionic lesion did not change the baseline arterial diameter. Following a subarachnoid haemorrhage (SAH) the degree of vasoconstriction in the animals with a preganglionic lesion did not differ significantly from that seen in controls. In the postganglionically lesioned animals, the vasoconstriction was more pronounced (12% at both 10 min and 6 days post SAH) on the lesioned as compared with the non-lesioned side. At day 6 post SAH the degree of vasoconstriction was 19% more pronounced on the lesioned side in post- as compared with the preganglionically lesioned animals. There was no difference in the degree of spasm on the non-lesioned side between the two groups. The findings indicate that the trigeminal system has both a peripheral and a central function. The peripheral, or axon reflex mechanism, exerts a tonic effect on the cerebral vessels. Following a SAH the axon reflex seems to attenuate cerebral vasospasm.

Involvement of perivascular sensory fibers in the pathophysiology of cerebral vasospasm following subarachnoid hemorrhage

The involvement of perivascular sensory fibers containing substance P (SP) and calcitonin gene-related peptide (CGRP) in the events occurring in conjunction with subarachnoid hemorrhage (SAH) has been studied in a rat model. Two days after blood injection, the time point at which maximum vasoconstriction is occurring in this model, immunocytochemistry and radioimmunoassay showed a reduction in SP- and CGRP-like immunoreactivity (LI). The quantitative measurements revealed a significant 50% reduction of CGRP-LI and a slight reduction of SP-LI in SAH as compared to controls. This partial reduction in neurotransmitter content (denervation) caused no change in the sensitivity of the rat basilar artery to SP or CGRP as studied using a sensitive in vitro method. However, the maximum relaxant response to CGRP was increased from 52 to 81% (p less than 0.05), while there was no change in the maximum SP-induced relaxations. It is suggested that not only a pre-, but also a postsynaptic modulation of perivascular sensory fibers may occur in experimental SAH.

Prevention of cerebral vasospasm in the rat by depletion or inhibition of substance P in conducting vessels

Cisternal blood injection in the rat induces a biphasic angiographic vasospasm, with a maximal acute spasm at 10 minutes and a maximal late spasm at 2 days after the subarachnoid hemorrhage (SAH). Depletion of substance P-containing sensory nerves to the cerebral arteries with capsaicin prior to SAH prevents the development of both acute and late spasm. Intrathecal administration of the substance P antagonist spantide 2 hours prior to SAH also prevents the development of vasospasm, while spantide administration 1 hour before SAH only hinders the occurrence of late vasospasm. Intracisternal administration of spantide 2 hours post-SAH prevents the development of late vasospasm. This antagonist per se can induce a short-lasting dose-dependent angiographic vasoconstriction. Substance P-containing nerve fibers on the cerebral arteries could constitute the sensory link in a reflex arc system involved in the development of vasospasm in which the presence of blood in the subarachnoid space stimulates sensory substance P-containing nerve fibers on the cerebral arteries inducing a centripetal impulse to the A2-nucleus tractus solitarius setting into motion the events in the brain stem leading to acute and late vasospasm.

Ultrastructural cerebrovascular changes in a model of subarachnoid hemorrhage in baboon based on triple cisternal blood injection

In a subarachnoid hemorrhage model in the baboon, achieved through three cisternal blood injections with 1-day intervals, the cerebral arteries were dissected out 7 days after the first blood injection for electron microscopy All the animals showed ultrastructural changes in the cerebral arteries: two with severe, one with moderate, and three with mild alterations in the vessel walls. The most constant findings were seen in the muscle cells of the media layer. Fragmentation of the nuclei was frequently observed together with cytoplasmic vacuoles. Scattered groups or single degenerated muscle cells were also noted. In the intima the changes included rounding of the nuclei along with the appearance of cytoplasmic vacuoles. Desquamation or flattening of the endothelium and loss of tight junctions were encountered in some vessel areas. Degenerating mitochondria were a common finding.

The role of vasopressin in acute cerebral vasospasm. Effect on spasm of a vasopressin antagonist or vasopressin antiserum

An experimental model of subarachnoid hemorrhage (SAH) in the Sprague-Dawley rat induces angiographically demonstrable, reproducible biphasic vasospasm of the vertebrobasilar system. The acute vasospasm is maximum at 10 minutes and the maximum late vasospasm occurs 2 days after the SAH. Brattleboro rats, which are deficient in arginine vasopressin (AVP), do not have acute vasospasm after SAH but exhibit a degree of late vasospasm that is not significantly different from that seen in Sprague-Dawley rats. Cisternal injection of AVP induced acute vasospasm in Sprague-Dawley rats with a duration similar to that seen after cisternal blood injection; however, at 2 days, the vessel diameter was normal. Intravenous AVP antagonist or intracisternal AVP antiserum administered prior to the SAH prevented the development of acute vasospasm without affecting the late phase. The data suggest that an increased release of AVP in the cerebrospinal fluid is involved in the development of acute cerebral vasospasm.

Perivascular innervation of the cerebral circulation: involvement in the pathophysiology of subarachnoid hemorrhage

The authors describe the perivascular innervation of cerebral circulation. The different nerve fiber systems can be classified as follows: 1. Sympathetic (noradrenaline, neuropeptide Y), 2. Parasympathetic (acetylcholine, vasoactive intestinal peptide/peptide histidine isoleucine (methionine), 3. Sensory (tachykinins, calcitonin gene-related peptide). Each of these systems is outlined by their basic anatomical and physiological facts. Then, the etiology of cerebral vasospasm after subarachnoid hemorrhage is discussed in relation to the cerebrovascular innervation.

Effect of neonatal 6-hydroxydopamine treatment on experimental vasospasm following a subarachnoid hemorrhage in the rat

Intracisternal injection of blood in the rat produces an angiographically demonstrable biphasic cerebral arterial vasospasm. Systemic 6-hydroxydopamine (6-OHDA) treatment in the neonatal stage, which causes a depletion of noradrenaline (NA) from both sympathetic and central NA-containing nerve fibers, prevents the development of the late spasm phase, while the acute spasm occurs to the same extent as in normal animals. The occurrence of acute spasm can be prevented by lesioning in the mesencephalon of the ascending catecholamine fibers originating in the lower brainstem and projecting to the hypothalamus. It is suggested that 6-OHDA treatment results in the altered spasm pattern via its effect on catecholamine fibers projecting between the medullary A1 and A2 nuclei and the hypothalamus. The occurrence of acute but not late spasm indicates that there is a different pathway underlying the two spasm phases.