Brief electrical stimulation of cerebellar fastigial nucleus conditions long-lasting salvage from focal cerebral ischemia: conditioned central neurogenic neuroprotection

Cerebellar fastigial nucleus electrostimulation attenuates inflammation in a Post-Infarction rat model by activating cholinergic anti-inflammatory pathways

There are negative correlations between indices of heart rate variability (HRV) and markers of inflammation. The inflammation plays an important role in myocardial damages after myocardial infarction (MI). Our previous study found that fastigial nucleus electrostimulation (FNS) improved abnormal HRV in a rat model of MI. Whether and how it can reduce inflammation and improve cardiac function after MI and the underlying mechanisms remain unknown. 66 Sprague Dawley rats were randomly divided into 4 groups as follows: i) Sham operation group (Sham); ii) Myocardial infarction group (MI); iii) FNS+MI group (FNS plus MI): left fastigial nucleus electrostimulation; iv) FNL+FNS+MI group (left fastigial nucleus lesion plus FNS plus MI). The serum expressions of acetylcholine (ACh), pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and anti-inflammatory cytokines IL-10 after FNS were measured using ELISA. Subsequently, the infarct size, the infiltration of inflammatory cells, the fibrotic area, and cardiac function were also evaluated. Additionally, the effects of FNS on the cholinergic anti-inflammatory pathway (CAP)-related proteins expression were determined by Western blot. We found that FNS significantly upregulated ACh and IL-10 expressions in serum, and decreased TNF-α and IL-6 levels. FNS significantly attenuated inflammatory cell infiltration and infarct size, decreased fibrosis, increased left ventricular ejection fraction (LVEF), and reduced mortality. Besides, the levels of p-STAT3/STAT3 and p-NF-κB/NF-κB significantly elevated after MI. FNS down-regulated the expression of p-STAT3/STAT3 and p-NF-κB/NF-κB. The protective effects of FNS were partially reversed by the fastigial nucleus lesion. Our data suggested that FNS can alleviate the inflammation after MI, and its cardiac neuroprotective mechanism may be achieved by increasing vagus tone, releasing ACh, and further activating the CAP via α7nAChR. The precise mechanism remains to be elucidated.

Effects of fastigial nucleus electrostimulation on cardiac nerve regeneration, neurotransmitter release, and malignant arrhythmia inducibility in a post-infarction rat model

The reduced density of cardiac autonomic nerves plays an important role in malignant arrhythmia after myocardial infarction (MI). Previous studies have shown that there is an interaction between the brain and the heart, and fastigial nucleus electrostimulation (FNS) promotes central nerve regeneration. Whether and how it can promote cardiac nerve regeneration after MI and the underlying mechanisms remain unknown. This study investigated whether FNS promotes cardiac nerve regeneration and reduces malignant arrhythmia inducibility in a post-infarction rat model. Ninety-eight Wistar rats were randomly assigned to Sham control, MI (left anterior descending coronary artery ligation without FNS), FNS (MI plus FNS), and FNL (fastigial nucleus lesion plus FNS plus MI) groups. The frequency of malignant arrhythmia was significantly lower in the FNS group than in the MI and FNL groups. The density of cardiac autonomic nerves was less in the MI group than in the Sham group, which was promoted by FNS. The nerve growth factor (NGF) mRNA expression was downregulated in the MI group compared to the Sham group, which was significantly enhanced by FNS. The expression levels of norepinephrine (NE) and acetylcholine (ACh) were higher and lower respectively in the MI and FNL groups than in the Sham group. After FNS, NE concentration was reduced and Ach level was elevated compared to the MI group. These data suggested that FNS promoted the regeneration of cardiac autonomic nerves and reduced the incidence of malignant arrhythmias in MI rat model. The mechanisms might involve up-regulation of NGF mRNA expression, decrease of NE release and increase of ACh release.

PRIMED2 Preclinical Evidence Scoring Tool to Assess Readiness for Translation of Neuroprotection Therapies

Many neuroprotective and other therapies for treatment of acute ischemic stroke have failed in translation to human studies, indicating a need for more rigorous, multidimensional quality assessment of the totality of preclinical evidence supporting a therapy prior to conducting human trials. A consensus panel of stroke preclinical model and human clinical trial experts assessed candidate items for the translational readiness scale, compiled from prior instruments (STAIR, ARRIVE, CAMARADES, RoB 2) based on importance, reliability, and feasibility. Once constructed, the tool was applied by two independent raters to four current candidate acute stroke therapies, including two pharmacologic agents [nerinetide and trans-sodium crocetinate] and two device interventions [cathodal transcranial direct current stimulation and fastigial nucleus stimulation]. The Preclinical evidence of Readiness In stroke Models Evaluating Drugs and Devices (PRIMED²) assessment tool rates the totality of evidence available from all reported preclinical animal stroke model studies in 11 domains related to diversity of tested animals, time windows, feasibility of agent route of delivery, and robustness of effect magnitude. Within each content domain, clearly operationalized rules assign strength of evidence ratings of 0–2. When applied to the four assessed candidate agents, inter-rater reliability was high (kappa = 0.88), and each agent showed a unique profile of evidentiary strengths and weaknesses. The PRIMED² assessment tool provides a multidimensional assessment of the cumulative preclinical evidence for a candidate acute stroke therapy on factors judged important for successful basic-to-clinical translation. Further evaluation and refinement of this tool is desirable to improve successful translation of therapies for acute stroke.

Noninvasive Neuromodulation in Migraine

PURPOSE OF REVIEW

The past two decades has seen an influx of noninvasive neuromodulation devices aimed at treatment of various primary headache disorders, including cluster headache and migraine. This narrative review is to summarize the current options in noninvasive neuromodulation in migraine.

RECENT FINDINGS

A variety of noninvasive neuromodulation devices have been FDA cleared and marketed for use in migraine, including single-pulse transcranial magnetic stimulation (sTMS), noninvasive vagal nerve stimulators (nVNS), and external trigeminal nerve stimulators (eTNS). Newer devices include peripheral electrical stimulation devices (PES), caloric stimulation, and others. Each has varying levels of evidence supporting its use in migraine, tolerability profiles, and access issues. Noninvasive neuromodulation devices can be beneficial when used in patients with migraine, with minimal side effects. As more devices are developed, approved, and marketed in the future, rigorous research on efficacy and safety remain a top priority.

Percutaneous mastoid electrical stimulator improves Poststroke depression and cognitive function in patients with Ischaemic stroke: a prospective, randomized, double-blind, and sham-controlled study

Background

Poststroke depression can lead to functional dependence, cognitive impairment and reduced quality of life. The aim of this study was to evaluate the effects of a percutaneous mastoid electrical stimulator (PMES) plus antidepressants on poststroke depression and cognitive function.

Methods

This study was a prospective, randomized, double-blind, and sham-controlled study. A total of 258 clinically depressed ischaemic stroke patients within 14 days of index stroke were randomly assigned to the PMES plus antidepressant (PMES group, N = 125) and sham plus antidepressant (sham group, N = 133) groups. All patients underwent the Montreal Cognitive Assessment (MoCA) and Hamilton Rating Scale for Depression (HRSD) test at 2 weeks (baseline), and 6 months(M6) after ischaemic stroke. Primary outcomes were the percentage of patients showing a treatment response (≥50% reduction in HRSD score) and depression remission (HRSD score ≤ 9) at 6 months. The secondary outcome was the percentage of patients with a MoCA score < 26.

Results

The percentages of patients showing a treatment response and depression remission were significantly higher in the PMES group than in the sham group (57.60% vs 41.35%, P = 0.009; 44.00% vs 29.32%, P = 0.014 respectively). The mean value of the HRSD score change [M (month)6-baseline] was significantly higher in the PMES group than in the sham group at 6 months (− 11.93 ± 5.32 vs − 10.48 ± 6.10, P = 0.036, respectively). The percentage of patients with MoCA scores < 26 was lower in the PEMS group than in the sham group (12.0% vs 24.06%, P = 0.012,respectively), and the mean value of the MoCA score change (M6-baseline) was higher in the PMES group than in the sham group (3.50 ± 2.55 vs 2.72 ± 2.52, P = 0.005, respectively).

Conclusion

These findings demonstrate that PMES adjunctive to antidepressant therapy is effective in reducing depression, achieving remission in the short term, and improving cognition.

Trial registration

This trial was retrospectively registered (registration number: ChiCTR1800016463) on 03 June 2018.

Central Nervous System Electrical Stimulation for Neuroprotection in Acute Cerebral Ischemia: Meta-Analysis of Preclinical Studies

Background and Purpose- Brain electrical stimulation, widely studied to facilitate recovery from stroke, has also been reported to confer direct neuroprotection in preclinical models of acute cerebral ischemia. Systematic review of controlled preclinical acute cerebral ischemia studies would aid in planning for initial human clinical trials. Methods- A systematic Medline search identified controlled, preclinical studies of central nervous system electrical stimulation in acute cerebral ischemia. Studies were categorized among 6 stimulation strategies. Three strategies applied different stimulation types to tissues within the ischemic zone (cathodal hemispheric stimulation [CHS], anodal hemispheric stimulation, and pulsed hemispheric stimulation), and 3 strategies applied deep brain stimulation to different neuronal targets remote from the ischemic zone (fastigial nucleus stimulation, subthalamic vasodilator area stimulation, and dorsal periaqueductal gray stimulation). Random-effects meta-analysis assessed electrical stimulation modification of final infarct volume. Study-level risk of bias and intervention-level readiness-for-translation were assessed using formal rating scales. Results- Systematic search identified 28 experiments in 21 studies, including a total of 350 animals, of electrical stimulation in preclinical acute cerebral ischemia. Overall, in animals undergoing electrical stimulation, final infarct volumes were reduced by 37% (95% CI, 34%-40%; P<0.001), compared with control. There was evidence of heterogeneity of efficacy among stimulation strategies (I²=93.1%, P_{heterogeneity}<0.001). Among the within-ischemic zone stimulation strategies, only CHS significantly reduced the infarct volume (27 %; 95% CI, 22%-33%; P<0.001); among the remote-from ischemic zone approaches, all (fastigial nucleus stimulation, subthalamic vasodilator area stimulation, and dorsal periaqueductal gray stimulation) reduced infarct volumes by approximately half. On formal rating scales, CHS studies had the lowest risk of bias, and CHS had the highest overall quality of intervention-level evidence supporting readiness to proceed to clinical testing. Conclusions- Electrical stimulation reduces final infarct volume across preclinical studies. CHS shows the most robust evidence and is potentially appropriate for progression to early-stage human clinical trial testing as a promising neuroprotective intervention.

Cerebellar fastigial nucleus electrical stimulatin protects against cerebral ischemic damage by upregulating telomerase activity

BACKGROUND

Cerebellar fastigial nucleus electrical stimulation (FNS) in rats has been shown to protect against brain ischemia/reperfusion (I/R) damage. Activation of telomerase has been reported to provide neuroprotection in animal models of stroke.

OBJECTIVE

The aim of this study was to explore whether precondition FNS increases the expression of telomerase reverse transcriptase (TERT) and telomerase activity in rats after cerebral I/R injury.

METHODS

One day after continuous stimulation of the fastigial cerebellar nucleus for 1 h, adult male Sprague Dawley rats were subjected to middle cerebral artery occlusion (MCAO) for 2 h and reperfusion for 24 h, 48 h and 72 h, while the I/R control groups received the same treatment without FNS. Ischemic lesion volumes were measured following TTC staining. The number of apoptotic cells was measured by using TUNEL assays. Subsequently, telomerase activity was examined by using TRAP-silver staining. Additionally, the expression level of TERT mRNA was assessed by using real-time fluorescence quantitative PCR. Finally, the expression of TERT protein was measured by using Western blotting.

RESULTS

The results of our study demonstrated that FNS significantly decreased infarct volumes and improved neurological deficits when compared with the I/R control group. The telomerase activity in the I/R + FNS group was significantly increased compared with that in the I/R control group, particularly in the 24 h reperfusion subgroup (P < 0.05). FNS treatment significantly decreased the number of TUNEL-positive cells when compared with that in the I/R control group. Expression of TERT gradually increased, with the peak occurring after or before 48 h reperfusion and the 24 h and 72 h reperfusion subgroups demonstrating higher expression than each I/R control group (P < 0.05).

CONCLUSIONS

Our results show that pre-FNS exerts neuroprotective effects that may be achieved by upregulating the expression of TERT and then by increasing telomerase activity.

Integrity of Cerebellar Fastigial Nucleus Intrinsic Neurons Is Critical for the Global Ischemic Preconditioning

Excitation of intrinsic neurons of cerebellar fastigial nucleus (FN) renders brain tolerant to local and global ischemia. This effect reaches a maximum 72 h after the stimulation and lasts over 10 days. Comparable neuroprotection is observed following sublethal global brain ischemia, a phenomenon known as preconditioning. We hypothesized that FN may participate in the mechanisms of ischemic preconditioning as a part of the intrinsic neuroprotective mechanism. To explore potential significance of FN neurons in brain ischemic tolerance we lesioned intrinsic FN neurons with excitotoxin ibotenic acid five days before exposure to 20 min four-vessel occlusion (4-VO) global ischemia while analyzing neuronal damage in Cornu Ammoni area 1 (CA1) hippocampal area one week later. In FN-lesioned animals, loss of CA1 cells was higher by 22% compared to control (phosphate buffered saline (PBS)-injected) animals. Moreover, lesion of FN neurons increased morbidity following global ischemia by 50%. Ablation of FN neurons also reversed salvaging effects of five-minute ischemic preconditioning on CA1 neurons and morbidity, while ablation of cerebellar dentate nucleus neurons did not change effect of ischemic preconditioning. We conclude that FN is an important part of intrinsic neuroprotective system, which participates in ischemic preconditioning and may participate in naturally occurring neuroprotection, such as "diving response".

Migraine prevention with percutaneous mastoid electrical stimulator: A randomized double-blind controlled trial

Objective To evaluate the effectiveness and safety of episodic migraine prevention with the percutaneous mastoid electrical stimulator (PMES). Methods This was a randomized, double-blind, and sham-controlled trial that involved four medical centers. Episodic patients with at least two migraine attacks every month were randomly 1:1 to PMES or sham stimulation treatment. The treatments were performed daily for 45 minutes over 3 months. The primary outcomes were change in migraine days per month and the 50% response rate. Results The PMES group had a significantly greater reduction of migraine days in the third month than the sham group (-71.3% vs. -14.4%, p < 0.001). The 50% response rate of migraine days in the PMES group (≥50% reduction of migraine days compared with the baseline) was significantly higher than that in the sham group (82.5% vs. 17.5%, p < 0.001). In the PMES group, 60% of the patients had a ≥75% reduction of migraine days in the third month, and 35% of the patients had no migraine attack in the third month. No patients in the sham group had a ≥75% reduction of migraine days. There were no adverse events in either group. Conclusion Treatment of migraine using non-invasive PMES was safe and effective.

MicroRNA involvement in mechanism of endogenous protection induced by fastigial nucleus stimulation based on deep sequencing and bioinformatics

BACKGROUND

Neurogenic neuroprotection is a promising approach for treating patients with ischemic brain lesions. Fastigial nucleus stimulation (FNS) has been shown to reduce the tissue damage resulting from focal cerebral ischemia in the earlier studies. However, the mechanisms of neuroprotection induced by FNS remain unclear. MicroRNAs (miRNAs) are a newly discovered group of non-coding small RNA molecules that negatively regulate target gene expression and involved in the regulation of pathological process. To date, there is a lack of knowledge on the expression of miRNA in response to FNS. Thus, we study the regulation of miRNAs in the rat ischemic brain by the neuroprotection effect of FNS.

METHODS

In this study, we used an established focal cerebral ischemia/reperfusion (IR) model in rats. MiRNA expression profile of rat ischemic cortex after 1 h of FNS were investigated using deep sequencing. Microarray was performed to study the expression pattern of miRNAs. Functional annotation on the miRNA was carried out by bioinformatics analysis.

RESULTS

Two thousand four hundred ninety three miRNAs were detected and found to be miRNAs or miRNA candidates using deep sequencing technology. We found that the FNS-related miRNAs were differentially expressed according microarray data. Bioinformatics analysis indicated that several differentially expressed miRNAs might be a central node of neuroprotection-associated genetic networks and contribute to neuroprotection induced by FNS.

CONCLUSIONS

MiRNA acts as a novel regulator and contributes to FNS-induced neuroprotection. Our study provides a better understanding of neuroprotection induced by FNS.

Electrical stimulation of cerebellar fastigial nucleus: mechanism of neuroprotection and prospects for clinical application against cerebral ischemia

For around two decades, electrical fastigial nucleus stimulation (FNS) has been demonstrated to induce neuroprotection involving multiple mechanisms. In this review, we summarize the protective effects of FNS against cerebral ischemia through the inhibition of electrical activity around the lesion, excitotoxic damage on neurons, and brain inflammatory response, as well as apoptosis. Moreover, FNS has been reported to promote nerve tissue repair, reconstruction, and neurological rehabilitation and improve stroke-related complications including poststroke cognitive dysfunction, depression, and abnormal heart rate variability. We thus further discuss the potential of FNS for clinical applications. Given the absence of any risk of inducing sublethal damage, FNS may offer a new approach to preconditioned neuroprotection against cerebral ischemia.

Immune mechanisms in cerebral ischemic tolerance

Stressor-induced tolerance is a central mechanism in the response of bacteria, plants, and animals to potentially harmful environmental challenges. This response is characterized by immediate changes in cellular metabolism and by the delayed transcriptional activation or inhibition of genetic programs that are not generally stressor specific (cross-tolerance). These programs are aimed at countering the deleterious effects of the stressor. While induction of this response (preconditioning) can be established at the cellular level, activation of systemic networks is essential for the protection to occur throughout the organs of the body. This is best signified by the phenomenon of remote ischemic preconditioning, whereby application of ischemic stress to one tissue or organ induces ischemic tolerance (IT) in remote organs through humoral, cellular and neural signaling. The immune system is an essential component in cerebral IT acting simultaneously both as mediator and target. This dichotomy is based on the fact that activation of inflammatory pathways is necessary to establish IT and that IT can be, in part, attributed to a subdued immune activation after index ischemia. Here we describe the components of the immune system required for induction of IT and review the mechanisms by which a reprogrammed immune response contributes to the neuroprotection observed after preconditioning. Learning how local and systemic immune factors participate in endogenous neuroprotection could lead to the development of new stroke therapies.

Regional genome transcriptional response of adult mouse brain to hypoxia

BACKGROUND

Since normal brain function depends upon continuous oxygen delivery and short periods of hypoxia can precondition the brain against subsequent ischemia, this study examined the effects of brief hypoxia on the whole genome transcriptional response in adult mouse brain.

RESULT

Pronounced changes of gene expression occurred after 3 hours of hypoxia (8% O(2)) and after 1 hour of re-oxygenation in all brain regions. The hypoxia-responsive genes were predominantly up-regulated in hindbrain and predominantly down-regulated in forebrain - possibly to support hindbrain survival functions at the expense of forebrain cognitive functions. The up-regulated genes had a significant role in cell survival and involved both shared and unshared signaling pathways among different brain regions. Up-regulation of transcriptional signaling including hypoxia inducible factor, insulin growth factor (IGF), the vitamin D3 receptor/retinoid X nuclear receptor, and glucocorticoid signaling was common to many brain regions. However, many of the hypoxia-regulated target genes were specific for one or a few brain regions. Cerebellum, for example, had 1241 transcripts regulated by hypoxia only in cerebellum but not in hippocampus; and, 642 (54%) had at least one hepatic nuclear receptor 4A (HNF4A) binding site and 381 had at least two HNF4A binding sites in their promoters. The data point to HNF4A as a major hypoxia-responsive transcription factor in cerebellum in addition to its known role in regulating erythropoietin transcription. The genes unique to hindbrain may play critical roles in survival during hypoxia.

CONCLUSION

Differences of forebrain and hindbrain hypoxia-responsive genes may relate to suppression of forebrain cognitive functions and activation of hindbrain survival functions, which may coordinately mediate the neuroprotection afforded by hypoxia preconditioning.

Neurovascular protection by ischaemic tolerance: role of nitric oxide

Nitric oxide (NO) has emerged as a key mediator in the mechanisms of ischaemic tolerance induced by a wide variety of preconditioning stimuli. NO is involved in the brain protection that develops either early (minutes-hours) or late (days-weeks) after the preconditioning stimulus. However, the sources of NO and the mechanisms underlying the protective effects differ substantially. While in early preconditioning NO is produced by the endothelial and neuronal isoform of NO synthase, in delayed preconditioning NO is synthesized by the inducible or 'immunological' isoform of NO synthase. Furthermore, in early preconditioning, NO acts through the canonical cGMP pathway, possibly through protein kinase G and opening of mitochondrial K(ATP) channels. In late preconditioning, the protection is mediated by peroxynitrite formed by the reaction of NO with superoxide derived from the enzyme NADPH oxidase. The mechanisms by which peroxynitrite exerts its protective effect may include improvement of post-ischaemic cerebrovascular function, leading to enhancement of blood flow to the ischaemic territory, and expression of prosurvival genes resulting in cytoprotection. The evidence suggests that NO can engage highly effective and multifunctional prosurvival pathways, which could be exploited for the prevention and treatment of cerebrovascular pathologies.

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.

Pre- and post-conditioning treatment with an ultra-low dose of Δ9-tetrahydrocannabinol (THC) protects against pentylenetetrazole (PTZ)-induced cognitive damage

Preconditioning, a phenomenon where a minor noxious stimulus protects from a subsequent more severe insult, and post-conditioning, where the protective intervention is applied following the insult, offer new insight into the neuronal mechanism(s) of neuroprotection and may provide new strategies for the prevention and treatment of brain damage. We have previously reported that a single administration of an extremely low dose of Δ(9)-tetrahydrocannabinol (THC; the psychoactive ingredient of marijuana) to mice induced minor long-lasting cognitive deficits. In the present study we examined the possibility that such a low dose of THC will protect the mice from more severe cognitive deficits induced by the epileptogenic drug pentylenetetrazole (PTZ). THC (0.002 mg/kg, a dose that is 3-4 orders of magnitude lower than the doses that induce the conventional effects of THC) was administered 1-7 days before, or 1-3 days after the injection of PTZ (60 mg/kg). The consequences of this treatment were studied 3-7 weeks later by various behavioral tests that evaluated different aspects of memory and learning. We found that a single administration of THC either before or after PTZ abolished the PTZ-induced long-lasting cognitive deficits. Biochemical studies indicated a concomitant reduction in phosphorylated-ERK (extracellular signal-regulated kinase) in the cerebella of mice 7 weeks following the injection of THC. Our results suggest that a pre- or post-conditioning treatment with extremely low doses of THC, several days before or after brain injury, may provide safe and effective long-term neuroprotection.

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells.

Neuroprotective effect of transcorneal electrical stimulation on light-induced photoreceptor degeneration

Direct electrical stimulation of neural tissues is a strategic approach to treat injured axons by accelerating their outgrowth [Al-Majed, A.A., Neumann, C.M., Brushart, T.M., Gordon, T., 2000. Brief electrical stimulation promotes the speed and accuracy of motor axonal regeneration. J. Neurosci. 20, 2602-2608] and promoting their regeneration [Geremia, N.M., Gordon, T., Brushart, T.M., Al-Majed, A.A., Verge, V.M.K., 2007. Electrical stimulation promotes sensory neuron regeneration and growth-associated gene expression. Exp. Neurol. 205, 347-359]. Recently, transcorneal electrical stimulation (TCES), a novel less invasive method, has been shown to rescue axotomized and damaged retinal ganglion cells [Morimoto, T., Miyoshi, T., Matsuda, S., Tano, Y., Fujikado, T., Fukuda, Y., 2005. Transcorneal electrical stimulation rescues axotomized retinal ganglion cells by activating endogenous retinal IGF-1 system. Invest. Ophthalmol. Vis. Sci. 46(6), 2147-2155]. Here, we investigated the neuroprotection of TCES on light-induced photoreceptor degeneration and the underlying mechanism. Adult male Sprague-Dawley (SD) rats received TCES before (pre-TCES) or after (post-TCES) intense light exposure. After fourteen days of light exposure, retinal histology and electroretinography were performed to evaluate the neuroprotective effect of TCES. The mRNA and protein levels of apoptotic-associated genes including Bcl-2, Bax, Caspase-3 as well as ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) in the retinas were determined by real-time PCR and Western blot analysis. The localization of these gene products in the retinas was examined by immunohistochemistry. Both pre- and post-TCES ameliorated the progressive photoreceptor degeneration. The degree of rescue depended on the strength of the electric charge. Post-TCES showed a relatively better and longer-term protective effect than pre-TCES. Real-time PCR and Western blot analysis revealed an upregulation of Bcl-2, CNTF, and BDNF and a downregulation of Bax in the retinas after TCES. Immunohistochemical studies showed that Bcl-2 and CNTF were selectively upregulated in Müller cells. These findings provide a new therapeutic method to prevent or delay photoreceptor degeneration through activating the intrinsic survival system.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Electrical forepaw stimulation during reversible forebrain ischemia decreases infarct volume

BACKGROUND AND PURPOSE

Functional stimulation is accompanied by increases in regional cerebral blood flow which exceed metabolic demands under normal circumstances, but it is unknown whether functional stimulation is beneficial or detrimental in the setting of acute ischemia. The aim of this study was to determine the effect of forepaw stimulation during temporary focal ischemia on neurological and tissue outcome in a rat model of reversible focal forebrain ischemia.

METHODS

Sprague-Dawley rats were prepared for temporary occlusion of the right middle cerebral artery (MCA) using the filament model. Cerebral blood flow in the MCA territory was continuously monitored with a laser-Doppler flowmeter. Subdermal electrodes were inserted into the dorsal forepaw to stimulate either the forepaw ipsilateral or contralateral to the occlusion starting 1 minute into ischemia and continuing throughout the ischemic period. A neurological evaluation was undertaken after 24 hours of reperfusion, and animals were then euthanized and brain slices stained with 2,3,5-triphenyltetrazolium chloride. Cortical and striatal damage was measured separately.

RESULTS

The cortical and striatal infarct volumes were both significantly reduced in the contralateral stimulated group compared with the ipsilateral stimulated group (48% total reduction). There were no statistically significant differences in the neurobehavioral scores between the 2 groups, or in the laser-Doppler flow measurements from the MCA core.

CONCLUSIONS

Functional stimulation of ischemic tissue may decrease tissue damage and improve outcome from stroke. Although the precise mechanism of this effect remains to be determined, functional stimulation could readily be translated to clinical practice.

Mitochondria are involved in the neurogenic neuroprotection conferred by stimulation of cerebellar fastigial nucleus

Activation of neural pathways originating in the cerebellar fastigial nucleus (FN) protects the brain from the deleterious effects of cerebral ischemia and excitotoxicity, a phenomenon termed central neurogenic neuroprotection. The neuroprotection is, in part, mediated by suppression of apoptosis. We sought to determine whether FN stimulation exerts its anti-apoptotic effect through mitochondrial mechanisms. Mitochondria were isolated from the cerebral cortex of rats in which the FN was stimulated for 1 h (100 microA; 1 s on/1 s off), 72 h earlier. Stimulation of the dentate nucleus (DN), a brain region that does not confer neuroprotection, served as control. Mitochondria isolated from FN-stimulated rats exhibited a marked increase in their ability to sequester Ca2+ and an increased resistance to Ca2+-induced membrane depolarization and depression in respiration. FN stimulation also leads to reduction in the release in cytochrome c, induced either by Ca2+ or the mitochondrial toxin mastoparan. Furthermore, in brain slices, FN stimulation reduced the staurosporine-induced insertion of the pro-apoptotic protein Bax into the mitochondria, a critical step in the mitochondrial mechanisms of apoptosis. Collectively, these results provide evidence that FN stimulation protects the mitochondria from dysfunction induced by Ca2+ loading, and inhibits mitochondrial pathways initiating apoptosis. These mitochondrial mechanisms are likely to play a role in the neuroprotection exerted by FN stimulation.

Anatomical basis for the fastigial pressor response

Electrical stimulation of rostromedial portion of cerebellar fastigial nucleus elicits integrated cardiovascular effects, which are neurally and humorally mediated. In this study, we sought to demonstrate the anatomical substrates of the fastigial pressor response (FPR) in the rat. The response was electrophysiologically localized in anesthetized, paralyzed-ventilated rats. Anterograde transport techniques were used to study the efferent projections of the fastigial pressor area; the distribution of efferent projection cells were then mapped by injecting retrograde tracers into anterogradely labeled sites. Electrolytic lesions were then placed bilaterally in selected brainstem areas in the attempt to block the pressor response. Sites of cerebellar stimulation and of brainstem lesions were subsequently histologically identified. The following lesions abolished the FPR: in nine animals lesions involved portions of the nucleus gigantocellularis dorsalis (NGCd), paramedian reticular formation (PMN) and the nucleus tractus solitarii (NTS) (in two animals fairly selectively the caudal NTS); in two other animals lesions destroyed the rostral ventrolateral medulla (C1 area) and in one animal the area encompassing the dorsal convexity of the superior cerebellar peduncle bordering the locus coeruleus-lateral parabrachial complex; partially effective were unilateral lesions of NGCd and NTS (three), bilateral lesions confined to NGCd and PMN (two), to vestibular complex and uncinate fasciculus (UF) (three), to UF and locus coeruleus (three) and to nucleus reticularis ventralis (two). Ineffective lesions involved A1 area, the nucleus gigantocellularis ventralis (NGCv), the spinal trigeminal nucleus and nucleus reticularis parvocellularis, the A5 area of the ventrolateral pons, the central gray and lateral mesencephalic tegmentum. It seems therefore that the pressor response elicited by stimulation of the cerebellar fastigial nucleus utilizes central specific pathways, as lesions involving other brainstem regions also known to participate in cardiovascular control do not affect the response. Furthermore, the FPR persisted after midbrain decerebration, thus demonstrating that it is organized beneath the midbrain.

Electrical stimulation of the dorsal periaqueductal gray decreases volume of the brain infarction independently of accompanying hypertension and cerebrovasodilation

We investigated whether selective stimulation of neurons of the sympathoinhibitory ventral periaqueductal gray (VPAG), or sympathoexcitatory dorsal periaqueductal gray (DPAG), differentially modulates CBF and EEG and exerts neuroprotection. Electrical stimulation of either regions of PAG comparably elevated AP and CBF, whereas chemical stimulation with the D,L-homocysteine produced either sympathoinhibition accompanied by decrease in CBF from ventral region or sympathoexcitation accompanied by increase in CBF from dorsal region in nonspinalized rats. The CBF effects evoked from DPAG and VPAG by chemical stimulation were preserved in spinalized rats supporting that the evoked CBF responses result directly from stimulation and are not secondary to AP changes. Stimulation of either region, whether chemical or electrical, synchronized the EEG. To explore whether PAG stimulation might protect the brain against ischemic injury, in other rats the VPAG or DPAG were stimulated for 1 h (50 Hz, 1 s on/1 s off, 75-100 microA) and the middle cerebral artery occluded 72 h later. Stimulation of the DPAG, but not VPAG, significantly reduced infarction volumes relative to sham-stimulated controls as determined 24 h after occlusion. Elevations of AP and CBF did not differ between groups. We conclude: (a). intrinsic neurons of D- and VPAG differentially regulate CBF; (b). neurons of DPAG are neuroprotective independently of changes in CBF and/or AP. The DPAG effect on infarct volume may be related to the central neuroprotective pathway evoked by stimulation of the cerebellar FN.

The neurobiological consequences of early stress and childhood maltreatment

Early severe stress and maltreatment produces a cascade of neurobiological events that have the potential to cause enduring changes in brain development. These changes occur on multiple levels, from neurohumoral (especially the hypothalamic-pituitary-adrenal [HPA] axis) to structural and functional. The major structural consequences of early stress include reduced size of the mid-portions of the corpus callosum and attenuated development of the left neocortex, hippocampus, and amygdala. Major functional consequences include increased electrical irritability in limbic structures and reduced functional activity of the cerebellar vermis. There are also gender differences in vulnerability and functional consequences. The neurobiological sequelae of early stress and maltreatment may play a significant role in the emergence of psychiatric disorders during development.

Electrical stimulation of cerebellar fastigial nucleus protects rat brain, in vitro, from staurosporine-induced apoptosis

Electrical stimulation of the cerebellar fastigial nucleus (FN) elicits a prolonged ( approximately 10 days) and substantial (50-80%) protection against ischemic and excitotoxic injuries. The mechanism(s) of protection are unknown. We investigated whether FN stimulation directly protects brain cells against apoptotic cell death in an in vitro rat brain slice culture model. Rats were electrically stimulated in FN or, as control, the cerebellar dentate nucleus (DN). Coronal slices through the forebrain were explanted, exposed to staurosporine, harvested, and analyzed for caspase-3 activity by a fluorescence assay. FN, but not DN, stimulation significantly reduced staurosporine-induced caspase-3 activity by 39 +/- 7% at 3 h, 31 +/- 3% at 6 h and 26 +/- 4% at 10 h of incubation. Immunocytochemistry revealed FN-specific reductions in activated caspase-3 mainly in glial-like cells throughout the forebrain. FN stimulation also results in a 56.5% reduction in cytochrome c release upon staurosporine incubation. We conclude that neuroprotection elicited from FN stimulation can directly modify the sensitivity of brain cells to apoptotic stimuli and thereby suppress staurosporine induced apoptosis in adult rat brain slices. This model indicates that neuroprotection can be studied in vitro and provides new insight into the potential role of glial cells in ischemic protection of neurons induced by FN stimulation.

Stimulation of the subthalamic vasodilator area and fastigial nucleus independently protects the brain against focal ischemia

We investigated whether stimulation of the functionally discrete subthalamic region, subthalamic cerebrovasodilator area (SVA), which increases cerebral blood flow (CBF) when excited, would, like stimulation of cerebellar fastigial nucleus (FN), produce central neurogenic neuroprotection. A 1-h electrical stimulation of SVA or FN reduced infarctions triggered by permanent occlusion of middle cerebral artery (MCA) by 48-55% in Sprague-Dawley rats and by 59% in Fisher rats. The salvaging effect of SVA stimulation, similar to FN, was long lasting and reduced the volume of infarctions placed 72 h or 10 days later by 58 and 26%, respectively, in Fisher rats. Bilateral lesioning of FN neurons by the microinjection of ibotenic acid 5 days before SVA stimulation did not affect SVA-evoked neuroprotection. Bilateral lesions of SVA neurons administered 5 days before FN stimulation had no effect on FN-induced neuroprotection but reversed the stimulus-locked increase in CBF accompanying FN stimulation. This study demonstrates that (1) excitation of neurons and/or fibers projecting through the SVA reduces ischemic infarctions as substantially as excitation of FN neurons; (2) the effects are long-lasting and not attributable to increases in cerebral blood flow, changes in blood gases or brain temperature, or rat strain; (3) the neuroprotective effects of SVA and FN stimulation are mutually independent and (4) FN-evoked cerebrovasodilation is mediated by SVA neurons. The SVA and FN are part of a neuronal system in CNS, which is distributed and, when excited, acts to protect the brain from ischemic injury.

Role of potassium channels in the central neurogenic neuroprotection elicited by cerebellar stimulation in rat

Electrical stimulation of the cerebellar fastigial nucleus (FN) in spontaneously hypertensive (SHR), Wistar-Kyoto (WKY) and Fisher rats reduced, by approximately 50%, the infarctions produced by occlusion of the middle cerebral artery. Blockade of ATP-dependent potassium (K-ATP) channels with glibenclamide (i.c.v.) abolished salvage only in the SHR rat. While blockade of K-ATP channels failed to abolish salvage in WKY and Fisher rats, participation of potassium channels in neurogenic neuroprotection cannot be excluded.

Neuroprotective electrical stimulation of cerebellar fastigial nucleus attenuates expression of periinfarction depolarizing waves (PIDs) and inhibits cortical spreading depression

In rat, electrical stimulation of the cerebellar fastigial nucleus (FN) for 1 h reduces the volume of focal ischemic infarctions produced by occluding the middle cerebral artery (MCAO), even 10 days later. The mechanism by which this 'central neurogenic neuroprotection' salvages ischemic brain is not known but does not result from changes in cerebral perfusion. MCAO also triggers periodic periinfarction depolarizing waves (PIDs) in the ischemic penumbra, the territory of salvage. These may contribute to neuronal death and promote infarct expansion. Conceivably, FN stimulation, which can otherwise modify cortical excitability, may alter the development of PIDs. We investigated in anesthetized rats whether FN stimulation modifies PIDs expression and, if so, the threshold for evoking cortical spreading depression (CSD), a process sharing characteristics with PIDs and an index of cortical excitability. Stimulation of FN immediately or 72 h before MCAO decreased infarction volumes by approximately 45% (p<0.01), increased PID latency >10-fold, and decreased the number of PIDs by >50% (p<0.001). In normal rats, stimulation of FN increased the threshold current for eliciting CSD by 175% and slowed its propagation velocity by 35% (p<0.01 for each) immediately, but not 72 h, after FN stimulation. We conclude: FN stimulation elicits long-lasting suppression of PIDs in parallel with neuroprotection. However, PIDs suppression over time is unlikely to result from a major increase in cortical tolerance to depolarization and probably is not the principal mechanism of salvage.

Stimulation of cerebellar fastigial nucleus inhibits interleukin-1beta-induced cerebrovascular inflammation

Electrical stimulation of the cerebellar fastigial nucleus (FN) in rat protects the brain against ischemia. We studied whether FN could reduce the cerebrovascular inflammation as a mechanism of protection. FN or dentate nucleus (sham controls) was electrically stimulated for 1 h, and 72 h later rats were either injected with interleukin (IL)-1beta into the striata or processed to analyze inflammatory responses in isolated brain microvessels. In striata, IL-1beta induced a recruitment of leukocytes that was reduced by 50% by FN stimulation. In isolated microvessels, IL-1beta induced the transient and dose-dependent upregulation of the mRNAs encoding for the inducible nitric oxide synthase (NOS-2), intercellular adhesion molecule 1 (ICAM-1), and inhibitory kappaB-alpha (IkappaB-alpha), an inhibitor of nuclear factor-kappaB. FN stimulation decreased the upregulation of NOS-2 and ICAM-1 mRNAs, whereas it increased IkappaB-alpha mRNA expression. Dentate nucleus stimulation did not mimic the FN actions. These findings suggest that FN stimulation may render brain microvessels refractory to IL-1beta by overproduction of IkappaB-alpha and support the hypothesis that alteration of microvascular inflammation may contribute to the central neurogenic neuroprotection elicited from the FN.

Cerebellar stimulation reduces inducible nitric oxide synthase expression and protects brain from ischemia

A focal infarction produced by occlusion of the middle cerebral artery (MCAO) in spontaneously hypertensive rats induced expression of inducible nitric oxide synthase (iNOS) mRNA, measured by competitive reverse transcription-polymerase chain reaction. The mRNA appeared simultaneously in the ischemic core and penumbra at 8 h, peaked between 14 and 24 h, and disappeared by 48 h. At 24 h, inducible nitric oxide synthase (iNOS)-like immunoreactivity was present in the endothelium of cerebral microvessels and in scattered cells, probably representing leukocytes or activated microglia. Electrical stimulation of the cerebellar fastigial nucleus (FN) for 1 h, 48 h before MCAO, reduced infarct volumes by 45% by decreasing cellular death in the ischemic penumbra. It also reduced by >90% the expression of iNOS mRNA and protein in the penumbra, but not core, and decreased by 44% the iNOS enzyme activity. We conclude that excitation of neuronal networks represented in the cerebellum elicits a conditioned central neurogenic neuroprotection associated with the downregulation of iNOS mRNA and protein. This neuroimmune interaction may, by blocking the expression of iNOS, contribute to neuroprotection.