Reversal of cerebral vasospasm by sphenopalatine ganglion stimulation in a dog model of subarachnoid hemorrhage

Promising Cerebral Blood Flow Enhancers in Acute Ischemic Stroke

Ischemic stroke presents a major global economic and public health burden. Although recent advances in available endovascular therapies show improved functional outcome, a good number of stroke patients are either ineligible or do not have access to these treatments. Also, robust collateral flow during acute ischemic stroke independently predicts the success of endovascular therapies and the outcome of stroke. Hence, adjunctive therapies for cerebral blood flow (CBF) enhancement are urgently needed. A very clear overview of the pial collaterals and the role of genetics are presented in this review. We review available evidence and advancement for potential therapies aimed at improving CBF during acute ischemic stroke. We identified heme-free soluble guanylate cyclase activators; Sanguinate, remote ischemic perconditioning; Fasudil, S1P agonists; and stimulation of the sphenopalatine ganglion as promising potential CBF-enhancing therapeutics requiring further investigation. Additionally, we outline and discuss the critical steps required to advance research strategies for clinically translatable CBF-enhancing agents in the context of acute ischemic stroke models.

Cervical spinal cord stimulation for prevention and treatment of cerebral vasospasm after aneurysmal subarachnoid hemorrhage: clinical and radiographic outcomes of a prospective single-center clinical pilot study

BACKGROUND

Cerebral vasospasm induced by aneurysmal subarachnoid hemorrhage (aSAH) is a major cause of high morbidity and mortality, for which there is no consistently effective treatment. Cervical spinal cord stimulation (cSCS) has been shown to induce vasodilatation and improve peripheral and cerebral blood flow in both animal and human studies. This pilot study was performed to assess the clinical effect and long-term results of cSCS treatment in aSAH patients.

METHODS

This was the first IRB- and US FDA-approved prospective non-randomized non-controlled study comprising of 12 aSAH patients (8 women, 4 men, age range 34-62 years) treated between May and November 2008. All patients underwent up to 2 weeks of cSCS with a single percutaneously implanted 8-contact electrode. Neurological outcomes at discharge and follow-up of up to 13 years and mortality/complications rates were analyzed.

RESULTS

All 12 aSAH patients underwent cSCS electrode implantation immediately after securing the aneurysm. Patients were stimulated for 10-14 consecutive days starting within 3 days of aneurysm rupture. Angiographic vasospasm occurred in six patients; two patients developed new vasospasm-related neurological symptoms; both recovered completely by discharge time. One patient died from unrelated multi-system failure; the rest were followed up clinically (average, 7.5 years; range, 12-151 months) and angiographically (average, 6.5 years; range, 36-125 months). No delayed ischemic neurological deficits/strokes and no cSCS-related adverse effects were observed.

CONCLUSIONS

Our short- and long-term data suggest that cSCS is feasible and safe for patients in the acute aSAH settings. Small size of the patient cohort and lack of control do not allow us to conclude whether cSCS is able to prevent cerebral vasospasm, decrease its severity, and improve clinical outcomes in aSAH patients. However, our findings support further clinical trials and development of cSCS as a new concept to prevent and treat cerebral vasospasm.

TRIAL REGISTRATION

CLINICALTRIALS

gov NCT00766844, posted on 10/06/2008.

The Potential Role of Neuromodulation in Subarachnoid Hemorrhage

OBJECTIVES

Aneurysmal subarachnoid hemorrhage (SAH) continues to be a difficult cerebrovascular disease with limited pharmacologic treatment options. Cerebral vasospasm (CV) and delayed cerebral ischemia (DCI) are leading causes of morbidity and mortality after SAH. Despite the advances in the understanding of its pathophysiology and tremendous efforts to date, nimodipine is currently the sole Food and Drug Administration-approved treatment for patients with SAH, with benefits that are marginal at best. The neuromodulation therapies are promising, especially those that target CV and DCI to improve functional outcomes. The aim of this review is therefore to summarize the available evidence for each type of neuromodulation for CV and DCI, with a special focus on its pathophysiological mechanisms, in addition to their clinical utility and drawbacks, which we hope will lead to future translational therapy options after SAH.

MATERIALS AND METHODS

We conducted a comprehensive review of preclinical and clinical studies demonstrating the use of neuromodulation for SAH. The literature search was performed using PubMed, Embase, and ClinicalTrials.gov. A total of 21 articles published from 1992 to 2021 and eight clinical trials were chosen.

RESULTS

The studies reviewed provide a compelling demonstration that neuromodulation is a potentially useful strategy to target multiple mechanisms of DCI and thus to potentially improve functional outcomes from SAH. There are several types of neuromodulation that have been tested to treat CV and DCI, including the trigeminal/vagus/facial nerve stimulation, sphenopalatine ganglion and spinal cord stimulation, transcranial direct electrical stimulation, transcutaneous electrical neurostimulation, and electroacupuncture. Most of them are in the preclinical or early phases of clinical application; however, they show promising results.

CONCLUSIONS

DCI has a complex pathogenesis, making the unique anatomical distribution and pleiotropic capabilities of various types of neuromodulation a promising field of study. We may be at the cusp of a breakthrough in the use of these techniques for the treatment of this stubbornly difficult disease.

α7-Acetylcholine Receptor Signaling Reduces Neuroinflammation After Subarachnoid Hemorrhage in Mice

Aneurysmal subarachnoid hemorrhage (aSAH) causes a robust inflammatory response which leads worse brain injury and poor outcomes. We investigated if stimulation of nicotinic acetylcholine α7 receptors (α7-AChR) (receptors shown to have anti-inflammatory effects) would reduce inflammation and improve outcomes. To investigate the level of peripheral inflammation after aSAH, inflammatory markers were measured in plasma samples collected in a cohort of aSAH patients. To study the effect of α7-AChR stimulation, SAH was induced in adult mice which were then treated with a α7-AChR agonist, galantamine, or vehicle. A battery of motor and cognitive tests were performed 24 h after subarachnoid hemorrhage. Mice were euthanized and tissue collected for analysis of markers of inflammation or activation of α7-AChR-mediated transduction cascades. A separate cohort of mice was allowed to survive for 28 days to assess long-term neurological deficits and histological outcome. Microglia cell culture subjected to hemoglobin toxicity was used to assess the effects of α7-AChR agonism. Analysis of eighty-two patient plasma samples confirmed enhanced systemic inflammation after aSAH. α7-AChR agonism reduced neuroinflammation at 24 h after SAH in male and female mice, which was associated with improved outcomes. This coincided with JAK2/STAT3 and IRAK-M activity modulations and a robust improvement in neurological/cognitive status that was effectively reversed by interfering with various components of these signaling pathways. Pharmacologic inhibition partially reversed the α7-AChR agonist's benefits, supporting α7-AChR as a target of the agonist's therapeutic effect. The cell culture experiment showed that α7-AChR agonism is directly beneficial to microglia. Our results demonstrate that activation of α7-AChR represents an attractive target for treatment of SAH. Our findings suggest that α7-AChR agonists, and specifically galantamine, might provide therapeutic benefit to aSAH patients.

Topical intranasal lidocaine is not a sphenopalatine ganglion block

There is renewed interest in the central role of the sphenopalatine ganglion (SPG) in cerebrovascular autonomic physiology and the pathophysiology of different primary and secondary headache disorders. There are diverse neural structures (parasympathetic, sympathetic and trigeminal sensory) that convene into the SPG which is located within the pterygopalatine fossa (PPF). This makes the PPF an attractive target to neuromodulatory interventions of these different neural structures. Some experts advocate for the nasal application of local anesthetics as an effective route for SPG block with the belief that the local anesthetic can freely access the PPF. It is time to challenge this historical concept from the early 1900s. In this daring discourse, I will review anatomical studies, CT and MRI reports to debunk this old myth. Will provide anatomical evidence to explain that all these assumptions are untrue and the local anesthetic has to magically 'travel' a distance of 4-12 mm of adipose and connective tissue to reach the SPG in sufficient concentration and volume to effectively induce SPG blockade. Future research should focus on assessing a clinical biomarker to confirm SPG blockade. It could be regional cerebral blood flow or lacrimal gland secretion.

Sphenopalatine Ganglion Stimulation Upregulates Transport of Temozolomide across the Blood-Brain Barrier

Sphenopalatine ganglion (SPG) stimulation has been shown to reversibly alter blood-brain barrier (BBB) permeability. It is widely used for the treatment of cluster headaches in Europe and is well tolerated in humans. The therapeutic potential for SPG stimulation in other central nervous system (CNS) diseases has yet to be explored. Glioblastoma Multiforme (GBM) remains one of the most difficult primary CNS neoplasms to treat, with an average survival of approximately 18 months at the time of diagnosis. Since 2004, the gold standard of treatment for GBM in the United States includes surgery followed by treatment with temozolomide (TMZ) and radiation. We sought to determine if SPG stimulation could increase chemotherapy concentrations in rodent brains with an intact BBB. Here, we show a statistically significant (p = 0.0006), five-fold upregulation of TMZ crossing the BBB and reaching brain parenchyma in rats receiving low-frequency (LF, 10 Hz) SPG stimulation. All the measurements were performed using a highly sensitive liquid chromatography mass spectrometry (LCMS) method that was developed for quantitation of TMZ in plasma and brain tissue. Our treatment paradigm shows novel delivery route by which we could more effectively and safely deliver TMZ in a targeted manner, to minimize systemic toxicity and maximize action at the target tissue.

Low frequency activation of the sphenopalatine ganglion does not induce migraine-like attacks in migraine patients

Introduction

Cephalic autonomic symptoms occur in 27‒73% of migraine patients during attacks. The role of parasympathetic activation in migraine attack initiation remains elusive. Low frequency stimulation of the sphenopalatine ganglion increases parasympathetic outflow. In this study, we hypothesized that low frequency stimulation of the sphenopalatine ganglion would provoke migraine-like attacks in migraine patients.

Methods

In a double-blind randomized sham-controlled crossover study, 12 migraine patients with a sphenopalatine ganglion neurostimulator received low frequency or sham stimulation for 30 min on two separate days. We recorded headache characteristics, cephalic autonomic symptoms, ipsilateral mechanical perception and pain thresholds, mean blood flow velocity in the middle cerebral artery (VMCA) and diameter of the superficial temporal artery during and after stimulation.

Results

Five patients (42%) reported a migraine-like attack after low frequency stimulation compared to six patients (50%) after sham ( p = 1.000). We found a significant increase in mechanical detection thresholds during low frequency stimulation compared to baseline ( p = 0.007). Occurrence of cephalic autonomic symptoms and changes in mechanical perception thresholds, VMCA and diameter of the superficial temporal artery showed no difference between low frequency stimulation compared to sham ( p = 0.533).

Conclusion

Low frequency stimulation of the sphenopalatine ganglion did not induce migraine-like attacks or autonomic symptoms in migraine patients. These data suggest that increased parasympathetic outflow by the sphenopalatine ganglion neurostimulator does not initiate migraine-like attacks. Study protocol: ClinicalTrials.gov registration number NCT02510742

Mechanisms of action of acute and subacute sphenopalatine ganglion stimulation for ischemic stroke

BACKGROUND

Sphenopalatine ganglion stimulation (SPG-Stim) for ischemic stroke, starting 8-24 h after onset and continuing through five days in a pooled analysis of two recent, randomized, sham-controlled trials, improved outcome of acute ischemic stroke patients with confirmed cortical involvement. As a neuromodulatory therapy, SPG-Stim differs substantially from existing pharmacologic (lytic and antiplatelets) and device (endovascular thrombectomy) acute ischemic stroke treatments.

AIM

Focused review of SPG anatomy, physiology, and neurovascular and neurobiologic mechanisms of action mediating benefit of SPG-Stim in acute ischemic stroke.

SUMMARY OF REVIEW

Located posterior to the maxillary sinus, the SPG is the main source of parasympathetic innervation to the anterior circulation. Preclinical and human studies delineate four distinct mechanisms of action by which the SPG-Stim may confer benefit in acute ischemic stroke: (1) collateral vasodilation and enhanced cerebral blood flow, mediated by release of neurotransmitters with vasodilatory effects, nitric oxide, and acetylcholine, (2) stimulation frequency- and intensity-dependent stabilization of the blood-brain barrier, reducing edema (3) direct acute neuroprotection from activation of the central cholinergic system with resulting anti-inflammatory, anti-apoptotic, and anti-excitatory effects; and (4) neuroplasticity enhancement from enhanced central cholinergic and adrenergic neuromodulation of cortical networks and nitrous oxide release stimulating neurogenesis.

CONCLUSION

The benefit of SPG-Stim in acute ischemic stroke is likely conferred not only by potent collateral augmentation, but also blood-barrier stabilization, direct neuroprotection, and neuroplasticity enhancement. Further studies clarifying the relative contribution of these mechanisms and the stimulation protocols that maximize each may help optimize SPG-Stim as a therapy for acute ischemic stroke.

A Pilot Study of Facial Nerve Stimulation on Cerebral Artery Vasospasm in Subarachnoid Hemorrhage Patients

Background: The objective of this pilot study was to assess the safety and efficacy of VitalFlow stimulation in aneurysmal subarachnoid hemorrhage (aSAH) patients with vasospasm for the purpose of guiding the design of larger, controlled studies in vasospasm patients, a largely untreated condition [1]. Methods: Six patients with angiographic vasospasm developing post-aSAH were treated with VitalFlow stimulation. Digital subtraction angiograms were obtained at the time of diagnosis (baseline) and then 30 minutes post-stimulation. A single 2-minute period of stimulation was delivered to the patients using parameters previously shown to be safe, tolerable, and effective at increasing cerebral blood flow (CBF) in healthy volunteers. Results: VitalFlow stimulation improved tissue perfusion as assessed by parenchymography and reversed the constriction of vasospastic arteries. Two patients had only partial improvement and so were treated with intraarterial nimodipine after VitalFlow stimulation, whereas four patients had complete resolution of the vasospasm after VitalFlow stimulation per the treating neuroendovascular surgeon’s evaluation. Clinical examination showed improvement in Hunt and Hess Scale scores assessed post-stimulation. Conclusions: Non-invasive magnetic stimulation of the facial nerve with the VitalFlow stimulator appears to be a safe and effective means to reverse angiographic vasospasm in aSAH patients. Clinical Impact: This study provides Class IV evidence that non-invasive magnetic stimulation of the facial nerves reduce angiographic vasospasm in aSAH patients.

An injectable implant to stimulate the sphenopalatine ganglion for treatment of acute ischaemic stroke up to 24 h from onset (ImpACT-24B): an international, randomised, double-blind, sham-controlled, pivotal trial

BACKGROUND

Sphenopalatine ganglion stimulation increased cerebral collateral blood flow, stabilised the blood-brain barrier, and reduced infarct size, in preclinical models of acute ischaemic stroke, and showed potential benefit in a pilot randomised trial in humans. The pivotal ImpACT-24B trial aimed to determine whether sphenopalatine ganglion stimulation 8-24 h after acute ischaemic stroke improved functional outcome.

METHODS

ImpACT-24B is a randomised, double-blind, sham-controlled, pivotal trial done at 73 centres in 18 countries. It included patients (men aged 40-80 years and women aged 40-85 years) with anterior-circulation acute ischaemic stroke, not undergoing reperfusion therapy. Enrolled patients were randomly assigned via web-based randomisation to receive active sphenopalatine ganglion stimulation (intervention group) or sham stimulation (sham-control group) 8-24 h after stroke onset. Patients, clinical care providers, and all outcome assessors were masked to treatment allocation. The primary efficacy endpoint was the difference between active and sham groups in the proportion of patients whose 3-month level of disability improved above expectations. This endpoint was evaluated in the modified intention-to-treat (mITT) population (defined as all patients who received one active or sham treatment session) and the population with confirmed cortical involvement (CCI) and was analysed using the Hochberg multi-step procedure (significance in both populations if p<0·05 in both, and in one population if p<0·025 in that one). Safety endpoints at 3 months were all serious adverse events (SAEs), SAEs related to implant placement or removal, SAEs related to stimulation, neurological deterioration, and mortality. All patients who underwent an attempted sphenopalatine ganglion stimulator or sham stimulator placement procedure were included in the safety analysis. This trial is registered with ClinicalTrials.gov, number NCT00826059.

FINDINGS

Between June 10, 2011, and March 7, 2018, 1078 patients were enrolled and randomly assigned to either the intervention or the sham-control group. 1000 patients received at least one session of sphenopalatine ganglion stimulation or sham stimulation and entered the mITT population (481 [48%] received sphenopalatine ganglion stimulation, 519 [52%] were sham controls), among whom 520 (52%) patients had CCI on imaging. The proportion of patients in the mITT population whose 3-month disability level was better than expected was 49% (234/481) in the intervention group versus 45% (236/519) in the sham-control group (odds ratio 1·14, 95% CI 0·89-1·46; p=0·31). In the CCI population, the proportion was 50% (121/244) in the intervention group versus 40% (110/276) in the sham-control group (1·48, 1·05-2·10; p=0·0258). There was an inverse U-shaped dose-response relationship between attained sphenopalatine ganglion stimulation intensity and the primary outcome in the CCI population: the proportion with favourable outcome increased from 40% to 70% at low-midrange intensity and decreased back to 40% at high intensity stimulation (p=0·0034). There were no differences in mortality or SAEs between the intervention group (n=536) and the sham-control group (n=519) in the safety population.

INTERPRETATION

Sphenopalatine ganglion stimulation is safe for patients with acute ischaemic stroke 8-24 h after onset, who are ineligible for thrombolytic therapy. Although not reaching significance, the trial's results support that, among patients with imaging evidence of cortical involvement at presentation, sphenopalatine ganglion stimulation is likely to improve functional outcome.

FUNDING

BrainsGate Ltd.

Cranial parasympathetic activation induces autonomic symptoms but no cluster headache attacks

Background

Low frequency (LF) stimulation of the sphenopalatine ganglion (SPG) may increase parasympathetic outflow and provoke cluster headache (CH) attacks in CH patients implanted with an SPG neurostimulator.

Methods

In a double-blind randomized sham-controlled crossover study, 20 CH patients received LF or sham stimulation for 30 min on two separate days. We recorded headache characteristics, cephalic autonomic symptoms (CAS), plasma levels of parasympathetic markers such as pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) and vasoactive intestinal peptide (VIP), and mechanical detection and pain thresholds as a marker of sensory modulation.

Results

In the immediate phase (0–60 min), 16 (80%) patients experienced CAS after LF stimulation, while nine patients (45%) reported CAS after sham ( p = 0.046). We found no difference in induction of cluster-like attacks between LF stimulation (n = 7) and sham stimulation (n = 5) ( p = 0.724). There was no difference in mechanical detection and pain thresholds, and in PACAP and VIP plasma concentrations between LF and sham stimulation ( p ≥ 0.162).

Conclusion

LF stimulation of the SPG induced autonomic symptoms, but no CH attacks. These data suggest that increased parasympathetic outflow is not sufficient to induce CH attacks in patients.

Study protocol

ClinicalTrials.gov registration number NCT02510729

Aging-related alterations in eNOS and nNOS responsiveness and smooth muscle reactivity of murine basilar arteries are modulated by apocynin and phosphorylation of myosin phosphatase targeting subunit-1

Aging causes major alterations of all components of the neurovascular unit and compromises brain blood supply. Here, we tested how aging affects vascular reactivity in basilar arteries from young (<10 weeks; y-BA), old (>22 months; o-BA) and old (>22 months) heterozygous MYPT1-T-696A/+ knock-in mice. In isometrically mounted o-BA, media thickness was increased by ∼10% while the passive length tension relations were not altered. Endothelial denudation or pan-NOS inhibition (100 µmol/L L-NAME) increased the basal tone by 11% in y-BA and 23% in o-BA, while inhibition of nNOS (1 µmol/L L-NPA) induced ∼10% increase in both ages. eNOS expression was ∼2-fold higher in o-BA. In o-BA, U46619-induced force was augmented (pEC50 ∼6.9 vs. pEC50 ∼6.5) while responsiveness to DEA-NONOate, electrical field stimulation or nicotine was decreased. Basal phosphorylation of MLC20-S19 and MYPT1-T-853 was higher in o-BA and was reversed by apocynin. Furthermore, permeabilized o-BA showed enhanced Ca2+-sensitivity. Old T-696A/+ BA displayed a reduced phosphorylation of MYPT1-T696 and MLC20, a lower basal tone in response to L-NAME and a reduced eNOS expression. The results indicate that the vascular hypercontractility found in o-BA is mediated by inhibition of MLCP and is partially compensated by an upregulation of endothelial NO release.

Magnetic facial nerve stimulation in animal models of active seizure

PURPOSE

As part of our efforts to develop a non-invasive facial nerve stimulator as an emergency treatment for ischemic stroke, we considered possible safety consequences if the technology was misapplied to stroke mimics, e.g., seizure. We hypothesized that magnetic facial nerve stimulation would worsen epileptiform activity in two animal models of active seizures. The rat intraperitoneal kainate model and pig intracortical penicillin model were employed. Magnetic facial nerve stimulation was delivered unilaterally at a variety of stimulation parameters, and the effect on ictal epileptiform activity measured by electroencephalography was determined according to an established categorical scale.

PRINCIPAL RESULTS

In 6 rats and 3 pigs evaluated with 83 stimulation trials, only a single stimulation trial was associated with worsening epileptiform activity according to a standard categorization scheme. Surprisingly, a reduction in the severity of the epileptiform activity was observed in 20 of 50 stimulation trials using patterned stimulation (3 pulses at 30Hz repeated at 0.5-10Hz) versus 2 of 33 stimulation trials using simple monotonic patterns (P<0.005, chi-squared test). The reduction of epileptiform activity after stimulation lasted a few minutes and was reproducible. Major Conclusions Epileptiform activity measured by electroencephalography was not reliably worsened by repetitive facial nerve stimulation with pulsed magnetic energy, even when significant brain exposure to the magnetic field occurred as in the rat model. To the contrary, a temporary reduction in epileptiform activity was often, but not invariably, observed with certain stimulation parameters.

Facial nerve stimulation as a future treatment for ischemic stroke

Stimulation of the autonomic parasympathetic fibers of the facial nerve system (hereafter simply “facial nerve”) rapidly dilates the cerebral arteries and increases cerebral blood flow whether that stimulation is delivered at the facial nerve trunk or at distal points such as the sphenopalatine ganglion. Facial nerve stimulation thus could be used as an emergency treatment of conditions of brain ischemia such as ischemic stroke. A rich history of scientific research has examined this property of the facial nerve, and various means of activating the facial nerve can be employed including noninvasive means. Herein, we review the anatomical and physiological research behind facial nerve stimulation and the facial nerve stimulation devices that are in development for the treatment of ischemic stroke.

Parasympathetic innervation of vertebrobasilar arteries: is this a potential clinical target?

This review aims to summarise the contemporary evidence for the presence and function of the parasympathetic innervation of the cerebral circulation with emphasis on the vertebral and basilar arteries (the posterior cerebral circulation). We consider whether the parasympathetic innervation of blood vessels could be used as a means to increase cerebral blood flow. This may have clinical implications for pathologies associated with cerebral hypoperfusion such as stroke, dementia and hypertension. Relative to the anterior cerebral circulation little is known of the origins and neurochemical phenotypes of the parasympathetic innervation of the vertebrobasilar arteries. These vessels normally provide blood flow to the brainstem and cerebellum but can, via the Circle of Willis upon stenosis of the internal carotid arteries, supply blood to the anterior cerebral circulation too. We review the multiple types of parasympathetic fibres and their distinct transmitter mechanisms and how these vary with age, disease and species. We highlight the importance of parasympathetic fibres for mediating the vasodilatory response to sympathetic activation. Current trials are investigating the possibility of electrically stimulating the postganglionic parasympathetic ganglia to improve cerebal blood flow to reduce the penumbra following stroke. We conclude that although there are substantial gaps in our understanding of the origins of parasympathetic innervation of the vertebrobasilar arteries, activation of this system under some conditions might bring therapeutic benefits.

Advances in the understanding of cluster headache

INTRODUCTION

Cluster headache is the worst primary headache form; it occurs in paroxysmal excruciatingly severe unilateral head pain attacks usually grouped in cluster periods. The familial occurrence of the disease indicates a genetic component but a gene abnormality is yet to be disclosed. Activation of trigeminal afferents and cranial parasympathetic efferents, the so-called trigemino-parasympathetic reflex, can explain pain and accompanying oculo-facial autonomic phenomena. In particular, pain in cluster headache is attributed, at least in part, to the increased CGRP plasma levels released by activated trigeminal system. Posterior hypothalamus was hypothesized to be the cluster generator activating the trigemino-parasympathetic reflex. Efficacy of monoclonal antibodies against CRGP is under investigation in randomized clinical trials. Areas covered: This paper will focus on main findings contributing to consider cluster headache as a neurovascular disorder with an origin from within the brain. Expert commentary: Accumulated evidence with hypothalamic stimulation in cluster headache patients indicate that posterior hypothalamus terminates rather than triggers the attacks. More extensive studies on the genetics of cluster headache are necessary to disclose anomalies behind the increased familial risk of the disease. Results from ongoing clinical trials in cluster headache sufferers using monoclonal antibodies against CGRP will open soon a new era.

Sphenopalatine ganglion stimulation in cluster headache and other types of headache

Objectives The cluster headache is the most excruciatingly painful primary headache. In some patients, neither preventive treatment nor acute treatment is effective or treatment is poorly tolerated. The sphenopalatine ganglion (SPG) has an important role in the pathophysiology of cluster headache and, for this reason, SPG stimulation has been used to treat cluster headache. Methods We have reviewed the published literature on the role of the SPG in cluster headache and the use of different treatments targeting the SPG. Results Multiple procedures have been used over the SPG to treat pain and trigemino-autonomic symptoms in patients with refractory cluster headache. After obtaining good results in a small number of patients, a miniaturized stimulator was developed. Stimulation of the SPG with this device proved to be efficacious in acute and preventive treatment in a clinical trial involving patients with chronic refractory cluster headache. Implantation of the device is minimally invasive and the most frequent side-effects are mild, such as paraesthesia and pain over the maxillary area. In patients who have used the SPG device for longer than one year, the therapeutic effect remains effective and the side-effects decrease. Conclusions The reported studies have demonstrated that SPG stimulation is a safe and effective treatment for chronic cluster headache. Long-term studies have shown that the effect remains over time and this treatment could be a good choice in patients with chronic refractory headache. We need more data about its potential use in other forms of headache, such as other trigemino-autonomic headaches or migraine.

A Site-Specific, Sustained-Release Drug Delivery System for Aneurysmal Subarachnoid Hemorrhage

Nimodipine is the only drug approved for use by the Food and Drug Administration for improving outcome after aneurysmal subarachnoid hemorrhage (SAH). It has less than optimal efficacy, causes dose-limiting hypotension in a substantial proportion of patients, and is administered enterally 6 times daily. We describe development of site-specific, sustained-release nimodipine microparticles that can be delivered once directly into the subarachnoid space or cerebral ventricles for potential improvement in outcome of patients with aneurysmal SAH. Eight injectable microparticle formulations of nimodipine in poly(DL-lactide-co-glycolide) (PLGA) polymers of varying composition were tested in vitro, and 1 was advanced into preclinical studies and clinical application. Intracisternal or intraventricular injection of nimodipine-PLGA microparticles in rats and beagles demonstrated dose-dependent, sustained concentrations of nimodipine in plasma and cerebrospinal fluid for up to 29 days with minimal toxicity in the brain or systemic tissues at doses <2 mg in rats and 51 mg in beagles, which would be equivalent of up to 612-1200 mg in humans, based on scaling relative to cerebrospinal fluid volumes. Efficacy was tested in the double-hemorrhage dog model of SAH. Nimodipine-PLGA microparticles significantly attenuated angiographic vasospasm. This therapeutic approach shows promise for improving outcome after SAH and may have broader applicability for similar diseases that are confined to body cavities or spaces, are self-limited, and lack effective treatments.

Collaterals: Implications in cerebral ischemic diseases and therapeutic interventions

Despite the tremendous progress made in the treatment of cerebrovascular occlusive diseases, many patients suffering from ischemic brain injury still experience dismal outcomes. Although rehabilitation contributes to post-stroke functional recovery, there is no doubt that interventions that promote the restoration of blood supply are proven to minimize ischemic injury and improve recovery. In response to the acutely decreased blood perfusion during arterial occlusion, arteriogenesis, the compensation of blood flow through the collateral circulation during arterial obstructive diseases can act not only in a timely fashion but also much more efficiently compared to angiogenesis, the sprouting of new capillaries, and a mechanism occurring in a delayed fashion while increases the total resistance of the vascular bed of the affected territory. Interestingly, despite the vast differences between the two vascular remodeling mechanisms, some crucial growth factors and cytokines involved in angiogenesis are also required for arteriogenesis. Understanding the mechanisms underlying vascular remodeling after ischemic brain injury is a critical step towards the development of effective therapies for ischemic stroke. The present article will discuss our current views in vascular remodeling acutely after brain ischemia, namely arteriogenesis, and some relevant clinical therapies available on the horizon in augmenting collateral flow that hold promise in treating ischemic brain injury. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Current options for the management of aneurysmal subarachnoid hemorrhage-induced cerebral vasospasm: a comprehensive review of the literature

OBJECTIVES

Cerebral vasospasm is one of the leading causes of morbi-mortality following aneurysmal subarachnoid hemorrhage. The aim of this article is to discuss the current status of vasospasm therapy with emphasis on endovascular treatment.

METHODS

A comprehensive review of the literature obtained by a PubMed search. The most relevant articles related to medical, endovascular and alternative therapies were selected for discussion.

RESULTS

Current accepted medical options include the oral nimodipine and 'triple-H' therapy (hypertension, hypervolemia and hemodilution). Nimodipine remains the only modality proven to reduce the incidence of infarction. Although widely used, 'triple-H' therapy has not been demonstrated to significantly change overall outcome after cerebral vasospasm. Indeed, both induced hypervolemia and hemodilution may have deleterious effects, and more recent physiologic data favor normovolemia with induced hypertension or optimization of cardiac output. Endovascular options include percutaneous transluminal balloon angioplasty (PTA) and intra-arterial (IA) infusion of vasodilators. Multiple case reports and case series have been encountered in the literature using different drug regimens with diverse mechanisms of action. Compared with PTA, IA drug infusion has the advantages of distal penetration and a better safety profile. Its main disadvantages are the more frequent need for repeat treatments and its systemic hemodynamic repercussions. Alternative options using intraventricular/cisternal drug therapy and flow augmentation strategies have also shown possible benefits; however, their use is not yet as well established.

CONCLUSION

Blood pressure or cardiac output optimization should be the mainstay of hyperdynamic therapy. Endovascular treatment appears to have a positive impact on neurological outcome compared with the natural history of the disease. The role of intraventricular therapy and flow augmentation strategies in association with medical and endovascular treatment may, in the future, play a growing role in the management of patients with severe refractory vasospasm.

Dynamic expression of the suppressor of cytokine signaling-3 and cytokines in the cerebral basilar artery of rats with subarachnoid hemorrhage, and the effect of acetylcholine

BACKGROUND

There are complex interactions between acetylcholine (ACh), the suppressor of cytokine signaling-3 (SOCS-3), and cytokines, however, little is known about their dynamic expression or their effects on cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH). Therefore, we aimed to describe and clarify the dynamic expression of SOCS-3 and cytokines after SAH, as well as the relationships between the levels of SOCS-3, cytokines, and ACh.

METHODS

The rat model of single cisterna magna injection was used to mimic acute SAH. The degree of CVS was indicated by lumen diameter and artery wall thickness under H&E staining. A semi-quantitative immunohistochemical analysis method was used to clarify the role of SOCS-3 in the CVS after SAH. We also measured the content of IL-6 and IL-10 in cerebrospinal fluid.

RESULTS

We found that SOCS-3 expression levels increased rapidly within 12 h after SAH, more slowly after 12 h, and did not reach a peak within 48 h. Interleukin 6 (IL-6) levels rapidly increased within 24 h after SAH, reached a peak 24 h after SAH, and decreased slightly at 48 h. IL-10 levels increased during the first 6 h after SAH, after which this increase tapered off. ACh treatment reduced IL-6 levels and resulted in elevated levels of SOCS-3, but had no effect on IL-10 expression. Furthermore, ACh treatment relieved basilar arterial vasospasm, whereas mecamylamine pretreatment counteracted the activity of ACh.

CONCLUSIONS

Taken together, these data indicate that SOCS-3 was involved in vasospasm via an IL-6- and IL-10-related mechanism, and that CVS following SAH could be reversed by the intraventricular injection of ACh.

Stimulation of the sphenopalatine ganglion in intractable cluster headache: expert consensus on patient selection and standards of care

CONTEXT AND OVERVIEW

Chronic cluster headache (CCH) is a debilitating headache disorder with a significant impairment of the patients' lives. Within the past decade, various invasive neuromodulatory approaches have been proposed for the treatment of CCH refractory to standard preventive drug, but only very few randomized controlled studies exist in the field of neuromodulation for the treatment of drug-refractory headaches. Based on the prominent role of the cranial parasympathetic system in acute cluster headache attacks, high-frequency sphenopalatine ganglion (SPG) stimulation has been shown to abort ongoing attacks in some patients in a first small study. As preventive effects of SPG-stimulation have been suggested and the rate of long-term side effects was moderate, SPG stimulation appears to be a promising new treatment strategy.

AIMS AND CONCLUSION

As SPG stimulation is effective in some patients and the first commercially available CE-marked SPG neurostimulator system has been introduced for cluster headache, patient selection and care should be standardized to ensure maximal efficacy and safety. As only limited data have been published on SPG stimulation, standards of care based on expert consensus are proposed to ensure homogeneous patient selection and treatment across international headache centres. Given that SPG stimulation is still a novel approach, all expert-based consensus on patient selection and standards of care should be re-reviewed when more long-term data are available.

The role of the microcirculation in delayed cerebral ischemia and chronic degenerative changes after subarachnoid hemorrhage

The mortality after aneurysmal subarachnoid hemorrhage (SAH) is 50%, and most survivors suffer severe functional and cognitive deficits. Half of SAH patients deteriorate 5 to 14 days after the initial bleeding, so-called delayed cerebral ischemia (DCI). Although often attributed to vasospasms, DCI may develop in the absence of angiographic vasospasms, and therapeutic reversal of angiographic vasospasms fails to improve patient outcome. The etiology of chronic neurodegenerative changes after SAH remains poorly understood. Brain oxygenation depends on both cerebral blood flow (CBF) and its microscopic distribution, the so-called capillary transit time heterogeneity (CTH). In theory, increased CTH can therefore lead to tissue hypoxia in the absence of severe CBF reductions, whereas reductions in CBF, paradoxically, improve brain oxygenation if CTH is critically elevated. We review potential sources of elevated CTH after SAH. Pericyte constrictions in relation to the initial ischemic episode and subsequent oxidative stress, nitric oxide depletion during the pericapillary clearance of oxyhemoglobin, vasogenic edema, leukocytosis, and astrocytic endfeet swelling are identified as potential sources of elevated CTH, and hence of metabolic derangement, after SAH. Irreversible changes in capillary morphology and function are predicted to contribute to long-term relative tissue hypoxia, inflammation, and neurodegeneration. We discuss diagnostic and therapeutic implications of these predictions.

Sphenopalatine ganglion neuromodulation in migraine: what is the rationale?

OBJECTIVE

The objective of this article is to review the prospect of treating migraine with sphenopalatine ganglion (SPG) neurostimulation.

BACKGROUND

Fuelled by preliminary studies showing a beneficial effect in cluster headache patients, the potential of treating migraine with neurostimulation has gained increasing interest within recent years, as current treatment strategies often fail to provide adequate relief from this debilitating headache. Common migraine symptoms include lacrimation, nasal congestion, and conjunctival injection, all parasympathetic manifestations. In addition, studies have suggested that parasympathetic activity may also contribute to the pain of migraineurs. The SPG is the largest extracranial parasympathetic ganglion of the head, innervating the meninges, lacrimal gland, nasal mucosa, and conjunctiva, all structures involved in migraine with cephalic autonomic symptoms.

CONCLUSION

We propose two possible mechanisms of action: 1) interrupting the post-ganglionic parasympathetic outflow to inhibit the pain and cephalic autonomic symptoms, and 2) modulating the sensory processing in the trigeminal nucleus caudalis. To further explore SPG stimulation in migraineurs as regards therapeutic potential and mode of action, randomized clinical trials are warranted.

Vascular remodeling after ischemic stroke: mechanisms and therapeutic potentials

The brain vasculature has been increasingly recognized as a key player that directs brain development, regulates homeostasis, and contributes to pathological processes. Following ischemic stroke, the reduction of blood flow elicits a cascade of changes and leads to vascular remodeling. However, the temporal profile of vascular changes after stroke is not well understood. Growing evidence suggests that the early phase of cerebral blood volume (CBV) increase is likely due to the improvement in collateral flow, also known as arteriogenesis, whereas the late phase of CBV increase is attributed to the surge of angiogenesis. Arteriogenesis is triggered by shear fluid stress followed by activation of endothelium and inflammatory processes, while angiogenesis induces a number of pro-angiogenic factors and circulating endothelial progenitor cells (EPCs). The status of collaterals in acute stroke has been shown to have several prognostic implications, while the causal relationship between angiogenesis and improved functional recovery has yet to be established in patients. A number of interventions aimed at enhancing cerebral blood flow including increasing collateral recruitment are under clinical investigation. Transplantation of EPCs to improve angiogenesis is also underway. Knowledge in the underlying physiological mechanisms for improved arteriogenesis and angiogenesis shall lead to more effective therapies for ischemic stroke.

Stimulation of the sphenopalatine ganglion induces reperfusion and blood-brain barrier protection in the photothrombotic stroke model

Purpose

The treatment of stroke remains a challenge. Animal studies showing that electrical stimulation of the sphenopalatine ganglion (SPG) exerts beneficial effects in the treatment of stroke have led to the initiation of clinical studies. However, the detailed effects of SPG stimulation on the injured brain are not known.

Methods

The effect of acute SPG stimulation was studied by direct vascular imaging, fluorescent angiography and laser Doppler flowmetry in the sensory motor cortex of the anaesthetized rat. Focal cerebral ischemia was induced by the rose bengal (RB) photothrombosis method. In chronic experiments, SPG stimulation, starting 15 min or 24 h after photothrombosis, was given for 3 h per day on four consecutive days. Structural damage was assessed using histological and immunohistochemical methods. Cortical functions were assessed by quantitative analysis of epidural electro-corticographic (ECoG) activity continuously recorded in behaving animals.

Results

Stimulation induced intensity- and duration-dependent vasodilation and increased cerebral blood flow in both healthy and photothrombotic brains. In SPG-stimulated rats both blood brain-barrier (BBB) opening, pathological brain activity and lesion volume were attenuated compared to untreated stroke animals, with no apparent difference in the glial response surrounding the necrotic lesion.

Conclusion

SPG-stimulation in rats induces vasodilation of cortical arterioles, partial reperfusion of the ischemic lesion, and normalization of brain functions with reduced BBB dysfunction and stroke volume. These findings support the potential therapeutic effect of SPG stimulation in focal cerebral ischemia even when applied 24 h after stroke onset and thus may extend the therapeutic window of currently administered stroke medications.

Sphenopalatine ganglion stimulation for vasospasm after experimental subarachnoid hemorrhage

Object

Sphenopalatine ganglion stimulation activates perivascular vasodilatory nerves in the ipsilateral anterior circle of Willis. This experiment tested whether stimulation of the ganglion could reverse vasospasm and improve cerebral perfusion after subarachnoid hemorrhage (SAH) in monkeys.

Methods

Thirteen cynomolgus monkeys underwent baseline angiography followed by creation of SAH by placement of autologous blood against the right intradural internal carotid artery, the middle cerebral artery (MCA), and the anterior cerebral artery. Seven days later, angiography was repeated, and the right sphenopalatine ganglion was exposed microsurgically. Angiography was repeated 15 minutes after exposure of the ganglion. The ganglion was stimulated electrically 3 times, and angiography was repeated during and 15 and 30 minutes after stimulation. Cerebral blood flow (CBF) was monitored using laser Doppler flowmetry, and intracranial pressure (ICP) was measured throughout. The protocol was repeated again. Evans blue was injected and the animals were killed. The brains were removed for analysis of water and Evans blue content and histology.

Results

Subarachnoid hemorrhage was associated with significant vasospasm of the ipsilateral major cerebral arteries (23% ± 10% to 39% ± 4%; p < 0.05, paired t-tests). Exposure of the ganglion and sham stimulation had no significant effects on arterial diameters, ICP, or CBF (4 monkeys, ANOVA and paired t-tests). Sphenopalatine ganglion stimulation dilated the ipsilateral extracranial and intracranial internal carotid artery, MCA, and anterior cerebral artery compared with the contralateral arteries (9 monkeys, 7% ± 9% to 15% ± 19%; p < 0.05, ANOVA). There was a significant increase in ipsilateral CBF. Stimulation had no effect on ICP or brain histology. Brain water content did not increase but Evans blue content was significantly elevated in the MCA territory of the stimulated hemisphere.

Conclusions

Sphenopalatine ganglion stimulation decreased vasospasm and increased CBF after SAH in monkeys. This was associated with opening of the blood-brain barrier.

Late stimulation of the sphenopalatine-ganglion in ischemic rats: improvement in N-acetyl-aspartate levels and diffusion weighted imaging characteristics as seen by MR

PURPOSE

To assess, by MR spectroscopy (MRS) and diffusion weighted imaging (DWI), the ability of electrical stimulation of the sphenopalatine ganglion (SPG) to augment stroke recovery in transient middle cerebral artery occluded (t-MCAO) rats, when treatment is started 18 +/- 2 h post-occlusion.

MATERIALS AND METHODS

(1)H-MRS imaging ((1)H-MRSI) and DWI were used to evaluate ischemic brain tissue after SPG stimulation in rats subjected to 2 h of t-MCAO. Rats were examined by (1)H-MRSI, DWI, and behavioral tests at 16 +/- 2 h, 8 days, and 28 days post-MCAO.

RESULTS

N-Acetyl-aspartate (NAA) levels of the stimulated and control rats were the same 16 +/- 2 h post-MCAO (0.52 +/- 0.03, 0.54 +/- 0.03). At 28 days post-occlusion, NAA levels were significantly higher in the treated group (0.60 +/- 0.04) compared with those of the untreated animals (0.50 +/- 0.04; P < 0.05). This effect was more pronounced for regions with low NAA values (0.16 +/- 0.03) that changed to 0.32 +/- 0.03 (P = 0.04) for the treated group and to 0.10 +/- 0.03 (P = 0.20) for the controls. DWI data showed better ischemic tissue condition for the treated rats, but the measured parameters showed only a trend of improvement. The MR results were corroborated by behavioral examinations.

CONCLUSION

Our findings suggest that SPG stimulation may ameliorate MR tissue characteristics following t-MCAO even if treatment is started 18 h post-occlusion.

Prediction of early secondary complications in patients with spontaneous subarachnoid hemorrhage based on accelerated sympathovagal ratios

PURPOSE

The development of secondary complications following spontaneous subarachnoid hemorrhage (SAH) largely depends on sympathetic overexcitation. The roles of vagal activities, however, are poorly defined. Because both components of the autonomic nervous system can be explored in the frequency domain of heart rate variability (HRV), the present study aimed to determine the dynamic evolution of autonomic activities and to identify patients at high risk for complications following hemorrhage.

METHODS

Thirty patients with SAH were enrolled in our study. Those who suffered from symptomatic vasospasm, cerebral infarction, neurogenic pulmonary edema, or early mortality within 1 week of ictus were categorized into the complication group. Spectral analysis of HRV explored three important indices of sympathetic and vagal modulations: low-frequency (LF), high-frequency (HF), and LF/HF ratios. Patterns of HRV dynamics within the first 3 days were compared between complication and non-complication groups. The group trends, estimated by the slopes of HRV changes, were determined for further univariate and multivariate analysis.

RESULTS

Our study showed that daily HRV in the complication group exhibited an approximately 2.7-fold increase of sympathovagal ratio (denoted by LF/HF). This resulted from reciprocal changes of sympathoexcitation (LF) and vagal withdrawal (HF). Multivariate analysis revealed that LF/HF slope, an indicator of the trend of sympathovagal change, was an independent variable significantly associated with the development of complications.

CONCLUSIONS

This study confirmed that during early SAH period, patients with and without complications presented different patterns of sympathovagal changes. LF/HF slope during the first 3 days was a significant predictor of secondary complications after SAH.

Implant for Augmentation of Cerebral Blood Flow Trial 1: A Pilot Study Evaluating the Safety and Effectiveness of the Ischaemic Stroke System for Treatment of Acute Ischaemic Stroke

Introduction

In rat stroke models, sphenopalatine ganglion stimulation up to 24 h after stroke onset augments cerebral blood flow, reduces infarct volume and improves neurological deficits. The ischaemic stroke system 500 has been designed to stimulate the sphenopalatine ganglion in humans.

Objectives

( 1 ) To determine the safety and tolerability of the ischaemic stroke system 500 in acute ischaemic stroke within 24 h of stroke onset. ( 2 ) To determine the effectiveness of ischaemic stroke system 500 in acute ischaemic stroke treatment.

Design/Methods

Implant for augmentation of cerebral blood flow trial-1 is a multi-national open-label study in patients of acute ischaemic stroke in the anterior circulation with National Institutes of Health Stroke Scales 7–20. The treatment initiation will be within 24 h of stroke onset. The ischaemic stroke system is implanted adjacent to the sphenopalatine ganglion via the greater palatine canal using local anaesthesia and a minimally invasive approach. The treatment protocol is constituted as 3–4 h of daily stimulation over 5–7 days. Conclusions The implant for augmentation of cerebral blood flow trial-1 will determine the safety and tolerability of the ischaemic stroke system 500 in acute ischaemic stroke as reflected by the incidence of adverse events.

Neurological and neurobehavioral assessment of experimental subarachnoid hemorrhage

About 50% of humans with aneurysmal subarachnoid hemorrhage (SAH) die and many survivors have neurological and neurobehavioral dysfunction. Animal studies usually focused on cerebral vasospasm and sometimes neuronal injury. The difference in endpoints may contribute to lack of translation of treatments effective in animals to humans. We reviewed prior animal studies of SAH to determine what neurological and neurobehavioral endpoints had been used, whether they differentiated between appropriate controls and animals with SAH, whether treatment effects were reported and whether they correlated with vasospasm. Only a few studies in rats examined learning and memory. It is concluded that more studies are needed to fully characterize neurobehavioral performance in animals with SAH and assess effects of treatment.

Brainstem control of cerebral blood flow and application to acute vasospasm following experimental subarachnoid hemorrhage

Symptomatic ischemia following aneurysmal subarachnoid hemorrhage (SAH) is common but poorly understood and inadequately treated. Severe constriction of the major arteries at the base of the brain, termed vasospasm, traditionally has been thought to be a proximal event underlying these ischemias, although microvascular changes also have been described. The vast majority of studies aimed at understanding the pathogenesis of ischemic deficits, and vasospasm have focused on the interaction of the "spasmogen" of the extravasated blood with the smooth muscle and endothelium of the arteries. This has led to a comparative neglect of the contribution of the CNS to the maintenance of cerebral perfusion. In the present study, we focused on the role of the rostral ventromedial medulla (RVM) in modulating cerebral perfusion at rest and following an experimental SAH in the rat. Changes in cerebral blood flow (CBF) were measured using laser-Doppler flowmetry and three-dimensional optical microangiography. Focal application of a GABA(A) receptor agonist and antagonist was used to respectively inactivate and activate the RVM. We show here that the RVM modulates cerebral blood flow under resting conditions, and further, contributes to restoration of cerebral perfusion following a high-grade SAH. Failure of this brainstem compensatory mechanism could be significant for acute perfusion deficits seen in patients following subarachnoid hemorrhage.

Cholinergic signal transduction in the mouse sphenopalatine ganglion

The sphenopalatine ganglia (SPG) receive their preganglionic innervation from the ventro-lateral reticular formation and nuclei of the caudal pons, and are involved in parasympathetic control of cranial glandular and vascular components including the blood supply to specific brain areas. In 53% of all SPG neurons, a particular member (MOL2.3) of the odorant receptor superfamily is co-expressed with green fluorescent protein (GFP) in MOL2.3 transgenic mouse pups. Choline acetyltransferase and vesicular acetylcholine transporter (VAChT) could be demonstrated in 90% of the GFP-positive, and 60% of the GFP-negative cells, these cells thus representing cholinergic neurons. Some 50% of all SPG neurons were nitrergic at a high rate of VAChT co-expression, the majority of them being GFP-positive. Most SPG neurons received cholinergic innervation as demonstrated by perineuronal VAChT immunoreactive nerve terminals. To characterize cholinergic signal transduction in SPG neurons, calcium imaging experiments were performed in a SPG primary culture system containing GFP-positive and -negative neurons. Ganglionic neurons could repeatedly be activated by cholinergic stimulation in a dose-dependent manner, with calcium entering all cells from the extracellular compartment. Stimulation with specific agonists supported prevalence of nicotinic cholinergic receptors (nAChRs). Inhibition of cholinergically induced intracellular calcium signalling by various omega-conotoxins indicated functional expression of alpha 3 beta 4 and alpha 7 nAChR subtypes in murine SPG cells, which could be supported by RT-PCR analysis of the neonatal mouse SPG. With regard to secondary cholinergic activation, L- but not N-subtype voltage-gated calcium channels might represent a prime target. Nicotinic signal transduction did not prove to be different in GFP-positive as compared to-negative murine SPG neurons.

Neuronal and astrocytic apoptosis after subarachnoid hemorrhage: a possible cause for poor prognosis

Clinical evidence suggests that factors other than cerebral vasospasm, such as delayed neuronal and astrocytic cell death, may play a role in the poor prognosis of patients with subarachnoid hemorrhage (SAH). Here we examined this using immunohistochemistry and confocal microscopy in 3 different brain areas in a dog model of SAH. Using antibodies against neuronal marker neuronal nuclear protein (NeuN) and astrocyte marker glial fibrillary acidic protein (GFAP) in conjunction with apoptosis marker (cleaved caspase-3), we quantified neurons and astrocytes to monitor the degree of apoptosis in both groups. Experimental SAH group showed 44 +/- 1% caspase-3 positive neurons in comparison to the 2.0 +/- 0.1% in the control group (P < 0.001, 6 animals each group). For astrocytes, a total 25 +/- 1% were caspase-3 positive in day 7 SAH group, as compared to 0.40 +/- 0.01% for controls (P < 0.001). Regional analysis revealed that neuronal caspase-3 immunoreactivity in all 3 regions were significantly higher (P < 0.001) in SAH animals than that in the control animals. However, the analysis of total area, size and signal co-localization of GFAP with caspase-3 indicated that astrocytic reactivity and proliferation are seen primarily in the hippocampal area, with the least changes detectable in the brainstem. We conclude that in the dog model, there was a significant increase of neuronal and astrocytic cleaved caspase-3, possibly reflecting apoptosis, following SAH induction. These changes coupled with neurological deterioration seen in patients may present a possible reason for the poor outcome in SAH patients.

Stimulating Circle of Willis Nerve Fibers Preserves the Diffusion-Perfusion Mismatch in Experimental Stroke

Background and Purpose— Stimulation of the nerves traversing the ethmoidal foramen (including postsynaptic, parasympathetic projections from the sphenopalatine ganglion [SPG], henceforth referred to as “SPG-stimulation”) has been shown to elevate cerebral blood flow (CBF) and to be neuroprotective after permanent, middle cerebral artery occlusion (pMCAO).

Methods— Employing diffusion (DWI)- and perfusion (PWI) weighted MRI, the effect of SPG-stimulation (started at 60 minutes post-MCAO) on the spatiotemporal evolution of ischemia during and after pMCAO was investigated. In an additional experiment, regional CBF changes were investigated in the nonischemic brain.

Results— In the nonischemic brain, SPG stimulation significantly elevated CBF predominantly within areas supplied by the anterior cerebral artery (by 0.64 mL/g/min relative to baseline). In the ischemic brain, CBF only marginally increased within the penumbra and core (by up to 0.08 and 0.15 mL/g/min relative to prestimulation, respectively). However, the threshold-derived CBF lesion volume did not change significantly. Penumbral apparent diffusion coefficient (ADC)-values improved to almost baseline values and the threshold derived ADC/CBF-mismatch was preserved up to 180 minutes after MCAO. TTC-derived lesion volumes were significantly smaller in stimulated versus nonstimulated animals (120.4±74.1 mm 3 versus 239.3±68.5 mm 3 , respectively).

Conclusion— This study demonstrates that unilateral SPG-stimulation increases CBF bilaterally within the normal brain, acutely preserves the CBF/ADC mismatch largely independent of altering cerebral blood flow, and reduces infarct size in the rat permanent suture model.