Spreading Depolarization Waves in Neurological Diseases: A Short Review about its Pathophysiology and Clinical Relevance

Nimodipine prophylaxis in aneurysmal subarachnoid hemorrhage, a question of tradition or evidence: A scoping review

BACKGROUND

The prophylactic use of nimodipine following subarachnoid hemorrhage is a practice established four decades ago when clinical management differed from current and the concept of Delayed Cerebral Ischemia (DCI) was not established. The applicability of the original studies is limited by the fact of not reflecting current practice; by utilising a dichotomised outcome measure such as good neurological outcome versus death and vegetative state; by applying variable dosing regimens and including all causes of poor neurological outcome different than DCI. This study aims to review the available evidence to discuss the ongoing role of nimodipine in contemporaneous clinical practice.

METHODS

PRISMA guidelines based review, evaluated the evidence on the prophylactic use of nimodipine. The following search engines: Medline, Embase, Cochrane, Web of Science and PubMed, identified Randomized Control Trials (RCTs) with neurological benefit as outcome measure and the impact of fixed versus weight-based nimodipine dosing regimens.

RESULTS

Eight RCT were selected. Three of those trials with a total of 349 patients, showed a reduction on death and vegetative state (pooled RR: 0.62; 95 % confidence interval-CI: 0.45, 0.86) related to DCI. Amongst all studies, all cause death (pooled RR = 0.73, [95 % CI: 0.56, 0.97]) favoured a fixed-dose regimen (pooled RR: 0.60; [95 % CI: 0.43, 0.85]).

CONCLUSION

Available evidence demonstrates that nimodipine only reduces the risk for DCI-related death or vegetative state and that fixed-dose regimens favour all cause infarct and death independent of DCI. Contemporaneous studies assessing the benefit of nimodipine beyond death or vegetative states and applying individualized dosing are warranted.

Temporal Changes in Cerebral Blood Flow during Migraine with Aura of Alternating Left and Right Homonymous Hemianopsia

A 16-year-old boy presented with sudden left homonymous hemianopsia followed by right ocular and occipital pain. Arterial spin labeling (ASL), a non-contrast magnetic resonance imaging technique used to evaluate perfusion, showed a decrease in cerebral blood flow in the right occipital lobe. Three hours after admission, the patient experienced right homonymous hemianopsia and ocular-to-occipital pain on the contralateral side. ASL revealed a decreased cerebral blood flow in the left occipital lobe. We ultimately diagnosed the patient with first-time migraine with aura, in which cortical spreading depression was visualized as decreased cerebral blood flow using ASL.

Spatial and Temporal Comparisons of Calcium Channel and Intrinsic Signal Imaging During in Vivo Cortical Spreading Depolarizations in Healthy and Hypoxic Brains

BACKGROUND

Spreading depolarizations (SDs) can be viewed at a cellular level using calcium imaging (CI), but this approach is limited to laboratory applications and animal experiments. Optical intrinsic signal imaging (OISI), on the other hand, is amenable to clinical use and allows viewing of large cortical areas without contrast agents. A better understanding of the behavior of OISI-observed SDs under different brain conditions is needed.

METHODS

We performed simultaneous calcium and OISI of SDs in GCaMP6f mice. SDs propagate through the cortex as a pathological wave and trigger a neurovascular response that can be imaged with both techniques. We imaged both mechanically stimulated SDs (sSDs) in healthy brains and terminal SDs (tSDs) induced by system hypoxia and cardiopulmonary failure.

RESULTS

We observed a lag in the detection of SDs in the OISI channels compared with CI. sSDs had a faster velocity than tSDs, and tSDs had a greater initial velocity for the first 400 µm when observed with CI compared with OISI. However, both imaging methods revealed similar characteristics, including a decrease in the sSD (but not tSD) velocities as the wave moved away from the site of initial detection. CI and OISI also showed similar spatial propagation of the SD throughout the image field. Importantly, only OISI allowed regional ischemia to be detected before tSDs occurred.

CONCLUSIONS

Altogether, data indicate that monitoring either neural activity or intrinsic signals with high-resolution optical imaging can be useful to assess SDs, but OISI may be a clinically applicable way to predict, and therefore possibly mitigate, hypoxic-ischemic tSDs.

The effect of neuroinflammation on the cerebral metabolism at baseline and after neural stimulation in neurodegenerative diseases

Neuroinflammation is a reaction of nervous tissue to an attack caused by an infection, a toxin, or a neurodegenerative disease. It involves brain metabolism adaptation in order to meet the increased energy needs of glial cell activation, but the nature of these adaptations is still unknown. Increasing interest concerning neuroinflammation leads to the identification of its role in neurodegenerative diseases. Few reports studied the effect of metabolic alteration on neuroinflammation. Metabolic damage initiates a pro-inflammatory response by microglial activation. Moreover, the exact neuroinflammation effect on cerebral cell metabolism remains unknown. In this study, we reviewed systematically the neuroinflammation effect in animal models' brains. All articles showing the relationship of neuroinflammation with brain metabolism, or with neuronal stimulation in neurodegenerative diseases were considered. Moreover, this review examines also the mitochondrial damage effect in neurodegeneration diseases. Then, different biosensors are classified regarding their importance in the determination of metabolite change. Finally, some therapeutic drugs inhibiting neuroinflammation are cited. Neuroinflammation increases lymphocyte infiltration and cytokines' overproduction, altering cellular energy homeostasis. This review demonstrates the importance of neuroinflammation as a mediator of disease progression. Further, the spread of depolarization effects pro-inflammatory genes expression and microglial activation, which contribute to the degeneration of neurons, paving the road to better management and treatment of neurodegenerative diseases.

Galvanic vestibular stimulation down-regulated NMDA receptors in vestibular nucleus of PD model

Parkinsonian symptoms relief by electrical stimulation is constructed by modulating neural network activity, and Galvanic vestibular stimulation (GVS) is known to affect the neural activity for motor control by activating the vestibular afferents. However, its underlying mechanism is still elusive. Due to the tight link from the peripheral vestibular organ to vestibular nucleus (VN), the effect by GVS was investigated to understand the neural mechanism. Using Sprague Dawley (SD) rats, behavioral response, extracellular neural recording, and immunohistochemistry in VN were conducted before and after the construction of Parkinson's disease (PD) model. Animals' locomotion was tested using rota-rod, and single extracellular neuronal activity was recorded in VN. The immunohistochemistry detected AMPA and NMDA receptors in VN to assess the effects by different amounts of electrical charge (0.018, 0.09, and 0.18 coulombs) as well as normal and PD with no GVS. All PD models showed the motor impairment, and the loss of TH⁺ neurons in medial forebrain bundle (mfb) and striatum was observed. Sixty-five neuronal extracellular activities (32 canal & 33 otolith) were recorded, but no significant difference in the resting firing rates and the kinetic responding gain were found in the PD models. On the other hand, the numbers of AMPA and NMDA receptors increased after the construction of PD model, and the effect by GVS was significantly evident in the change of NMDA receptors (p < 0.018). In conclusion, the increased glutamate receptors in PD models were down-regulated by GVS, and the plastic modulation mainly occurred through NMDA receptor in VN.

Vascular Response to Spreading Depolarization Predicts Stroke Outcome

BACKGROUND

Cortical spreading depolarization (CSD) is a massive neuro-glial depolarization wave, which propagates across the cerebral cortex. In stroke, CSD is a necessary and ubiquitous mechanism for the development of neuronal lesions that initiates in the ischemic core and propagates through the penumbra extending the tissue injury. Although CSD propagation induces dramatic changes in cerebral blood flow, the vascular responses in different ischemic regions and their consequences on reperfusion and recovery remain to be defined.

METHODS

Ischemia was performed using the thrombin model of stroke and reperfusion was induced by r-tPA (recombinant tissue-type plasminogen activator) administration in mice. We used in vivo electrophysiology and laser speckle contrast imaging simultaneously to assess both electrophysiological and hemodynamic characteristics of CSD after ischemia onset. Neurological deficits were assessed on day 1, 3, and 7. Furthermore, infarct sizes were quantified using 2,3,5-triphenyltetrazolium chloride on day 7.

RESULTS

After ischemia, CSDs were evidenced by the characteristic propagating DC shift extending far beyond the ischemic area. On the vascular level, we observed 2 types of responses: some mice showed spreading hyperemia confined to the penumbra area (penumbral spreading hyperemia) while other showed spreading hyperemia propagating in the full hemisphere (full hemisphere spreading hyperemia). Penumbral spreading hyperemia was associated with severe stroke-induced damage, while full hemisphere spreading hyperemia indicated beneficial infarct outcome and potential viability of the infarct core. In all animals, thrombolysis with r-tPA modified the shape of the vascular response to CSD and reduced lesion volume.

CONCLUSIONS

Our results show that different types of spreading hyperemia occur spontaneously after the onset of ischemia. Depending on their shape and distribution, they predict severity of injury and outcome. Furthermore, our data show that modulating the hemodynamic response to CSD may be a promising therapeutic strategy to attenuate stroke outcome.

Loss of Kir6.1 facilitates peri-infarct depolarizations in focal cerebral ischemia

OBJECTIVE

Peri-infarct depolarizations (PIDs) are spontaneous waves that propagate slowly across the penumbra region following stroke, contributing to secondary infarct growth and negatively affecting stroke outcomes. K_ATP channels are generally spread in the brain. Under conditions of ischemia and/or hypoxia, K_ATP channels play a cytoprotective role in neurons. However, it is still unknown whether K_ATP channels are involved in the initiation and propagation of PIDs.

METHODS

The Kir6.1 knockout (Kir6.1^-/-) mice, Kir6.2 knockout (Kir6.2^-/-) mice, and wild-type C57Bl6 mice (n = 8) were used. The middle cerebral artery occlusion (MCAO) stroke model was made and PIDs were detected by an optical intrinsic signal (OIS) imaging system.

RESULTS

Much more PIDs appeared in Kir6.1^-/-mice than that in Kir6.2^-/- and WT mice in both the first hour and 4 hours following MCAO (3.9 ± 0.7 vs. 1.5 ± 0.3, p < 0,05; 3.9 ± 0.7 vs. 1.9 ± 0.3, p < 0.05; 20.0 ± 2.5 vs. 10.4 ± 2.4, p < 0.05; 20.0 ± 2.5 vs. 11.3 ± 1.4, p < 0.05). Furthermore, the first PID occurred much earlier in Kir6.1^-/- mice than that in Kir6.2^-/- mice and WT mice (21.3 ± 2.1 min vs. 34.1 ± 4.8 min, p < 0.05; 21.3 ± 2.1 min vs. 38.8 ± 3.4 min, p < 0.01). No significant differences in other characteristics of PIDs including originating sites, duration time, propagation patterns, and velocity were detected. Additionally, the migration of originating sites was observed.

CONCLUSION

This study shows that loss of Kir6.1, not Kir6.2 facilitates the induction of PIDs in focal cerebral ischemia, indicating that Kir6.1-forming channels in the brain may provide protection against PIDs.

Transcutaneous vagus nerve stimulation (tVNS) in stroke: the evidence, challenges and future directions

Stroke is one of the leading causes of death and disability globally. A significant proportion of stroke survivors are left with long term neurological deficits that have a detrimental effect on personal wellbeing and wider socioeconomic impacts. As such, there is an unmet need for novel therapies that improve neurological recovery after stroke. Invasive vagus nerve stimulation (VNS) paired with rehabilitation has been shown to improve upper limb motor function in chronic stroke. However, invasive VNS requires a surgical procedure and therefore may not be suitable for all stroke patients. Non-invasive, transcutaneous VNS (tVNS) via auricular vagus nerve stimulation in the ear (taVNS) and cervical vagus nerve stimulation in the neck (tcVNS) have been shown to activate similar vagal nerve projections in the central nervous system to invasive VNS. A number of pre-clinical studies indicate that tVNS delivered in acute middle cerebral artery occlusion reduces infarct size through anti-inflammatory effects, reduced excitotoxicity and increased blood-brain barrier integrity. Longer term effects of tVNS in stroke that may mediate neuroplasticity include microglial polarisation, angiogenesis and neurogenesis. Pilot clinical trials of taVNS indicate that taVNS paired with rehabilitation may improve upper limb motor and sensory function in patients with chronic stroke. In this review, we summarise and critically appraise the current pre-clinical and clinical evidence, outline the major ongoing clinical trials and detail the challenges and future directions regarding tVNS in acute and chronic stroke.

Frequency selective neuronal modulation triggers spreading depolarizations in the rat endothelin-1 model of stroke

Ischemia is one of the most common causes of acquired brain injury. Central to its noxious sequelae are spreading depolarizations (SDs), waves of persistent depolarizations which start at the location of the flow obstruction and expand outwards leading to excitotoxic damage. The majority of acute stage of stroke studies to date have focused on the phenomenology of SDs and their association with brain damage. In the current work, we investigated the role of peri-injection zone pyramidal neurons in triggering SDs by optogenetic stimulation in an endothelin-1 rat model of focal ischemia. Our concurrent two photon fluorescence microscopy data and local field potential recordings indicated that a ≥ 60% drop in cortical arteriolar red blood cell velocity was associated with SDs at the ET-1 injection site. SDs were also observed in the peri-injection zone, which subsequently exhibited elevated neuronal activity in the low-frequency bands. Critically, SDs were triggered by low- but not high-frequency optogenetic stimulation of peri-injection zone pyramidal neurons. Our findings depict a complex etiology of SDs post focal ischemia and reveal that effects of neuronal modulation exhibit spectral and spatial selectivity.

Neuroinflammation and Neuronal Loss in the Hippocampus Are Associated with Immediate Posttraumatic Seizures and Corticosterone Elevation in Rats

Hippocampal damage after traumatic brain injury (TBI) is associated with late posttraumatic conditions, such as depression, cognitive decline and epilepsy. Mechanisms of selective hippocampal damage after TBI are not well understood. In this study, using rat TBI model (lateral fluid percussion cortical injury), we assessed potential association of immediate posttraumatic seizures and changes in corticosterone (CS) levels with neuroinflammation and neuronal cell loss in the hippocampus. Indices of distant hippocampal damage (neurodegeneration and neuroinflammation) were assessed using histological analysis (Nissl staining, Iba-1 immunohistochemical staining) and ELISA (IL-1β and CS) 1, 3, 7 and 14 days after TBI or sham operation in male Wistar rats (n = 146). IL-1β was elevated only in the ipsilateral hippocampus on day 1 after trauma. CS peak was detected on day 3 in blood, the ipsilateral and contralateral hippocampus. Neuronal cell loss in the hippocampus was demonstrated bilaterally; in the ipsilateral hippocampus it started earlier than in the contralateral. Microglial activation was evident in the hippocampus bilaterally on day 7 after TBI. The duration of immediate seizures correlated with CS elevation, levels of IL-1β and neuronal loss in the hippocampus. The data suggest potential association of immediate post-traumatic seizures with CS-dependent neuroinflammation-mediated distant hippocampal damage.

Cortical Spreading Depolarization in Chronic Subdural Hematoma: Bridging the Gap

Cortical spreading depolarization (CSD) is recognized as a cause of transient neurological symptoms (TNS) in various clinical entities. Although scientific literature has been flourishing in the field of CSD, it remains an underrecognized pathophysiology in clinical practice. The literature evoking CSD in relation to subdural hematoma (SDH) is particularly scarce. Patients with SDH frequently suffer from TNS, most being attributed to seizures despite an atypical semiology, evolution, and therapeutic response. Recent literature has suggested that a significant proportion of those patients' TNS represent the clinical manifestations of underlying CSD. Recently, the term Non-Epileptical Stereoytpical Intermittent Symptoms (NESIS) has been proposed to describe a subgroup of patients presenting with TNS in the context of SDH. Indirect evidence and recent research suggest that the pathophysiology of NESIS could represent the clinical manifestation of CSD. This review should provide a concise yet thorough review of the current state of literature behind the pathophysiology of CSD with a particular focus on recent research and knowledge regarding the presence of CSD in the context of subdural hematoma. Although many questions remain in the evolution of knowledge in this field would likely have significant diagnostic, therapeutic, and prognostic implications.