Improving neurovascular outcomes with bilateral forepaw stimulation in a rat photothrombotic ischemic stroke model

Optogenetic Functional Activation Is Detrimental During Acute Ischemic Stroke in Mice

BACKGROUND

Functional activation of the focal ischemic brain has been reported to improve outcomes by augmenting collateral blood flow. However, functional activation also increases metabolic demand and might thereby worsen outcomes. Indeed, preclinical and clinical reports have been conflicting. Here, we tested the effect of functional activation during acute ischemic stroke using distal middle cerebral artery occlusion in anesthetized mice.

METHODS

Using transgenic mice expressing channelrhodopsin-2 in neurons, we delivered functional activation using physiological levels of transcranial optogenetic stimulation of the moderately ischemic cortex (ie, penumbra), identified using real-time full-field laser speckle perfusion imaging during a 1-hour distal microvascular clip of the middle cerebral artery. Neuronal activation was confirmed using evoked field potentials, and infarct volumes were measured in tissue slices 48 hours later.

RESULTS

Optogenetic stimulation of the penumbra was associated with more than 2-fold larger infarcts than stimulation of the contralateral homotopic region and the sham stimulation group (n=10, 7, and 9; 11.0±5.6 versus 5.1±4.3 versus 4.1±3.7 mm3; P=0.008, 1-way ANOVA). Identical stimulation in wild-type mice that do not express channelrhodopsin-2 did not have an effect. Optogenetic stimulation was associated with a small increase in penumbral perfusion that did not explain enlarged infarcts.

CONCLUSIONS

Our data suggest that increased neuronal activity during acute focal arterial occlusions can be detrimental, presumably due to increased metabolic demand, and may have implications for the clinical management of hyperacute stroke patients.

Constructing a Transient Ischemia Attack Model Utilizing Flexible Spatial Targeting Photothrombosis with Real-Time Blood Flow Imaging Feedback

Transient ischemic attack (TIA) is an early warning sign of stroke and death, necessitating suitable animal models due to the associated clinical diagnostic challenges. In this study, we developed a TIA model using flexible spatially targeted photothrombosis combined with real-time blood flow imaging feedback. By modulating the excitation light using wavefront technology, we precisely created a square light spot (50 × 250 µm), targeted at the distal middle cerebral artery (dMCA). The use of laser speckle contrast imaging (LSCI) provided real-time feedback on the ischemia, while the excitation light was ceased upon reaching complete occlusion. Our results demonstrated that the photothrombus formed in the dMCA and spontaneously recanalized within 10 min (416.8 ± 96.4 s), with no sensorimotor deficits or infarction 24 h post-TIA. During the acute phase, ischemic spreading depression occurred in the ipsilateral dorsal cortex, leading to more severe ischemia and collateral circulation establishment synchronized with the onset of dMCA narrowing. Post-reperfusion, the thrombi were primarily in the sensorimotor and visual cortex, disappearing within 24 h. The blood flow changes in the dMCA were more indicative of cortical ischemic conditions than diameter changes. Our method successfully establishes a photochemical TIA model based on the dMCA, allowing for the dynamic observation and control of thrombus formation and recanalization and enabling real-time monitoring of the impacts on cerebral blood flow during the acute phase of TIA.

Topiramate suppresses peri-infarct spreading depolarization and improves outcomes in a rat model of photothrombotic stroke

Ischemic stroke can cause depolarized brain waves, termed peri-infarct depolarization (PID). Here, we evaluated whether topiramate, a neuroprotective drug used to treat epilepsy and alleviate migraine, has the potential to reduce PID. We employed a rat model of photothrombotic ischemia that can reliably and reproducibly induce PID and developed a combined electrocorticography-laser speckle contrast imaging (ECoG-LSCI) platform to monitor neuronal activity and cerebral blood flow (CBF) simultaneously. Topiramate administration after photothrombotic ischemia did not rescue CBF but significantly restored somatosensory evoked potentials in the forelimb area of the primary somatosensory cortex. Moreover, infarct volume was investigated by 2,3,5-triphenyltetrazolium chloride (TTC) staining, and neuronal survival was evaluated by Nissl staining. Mechanistically, the levels of inflammatory markers, such as ED1 (CD68), Iba-1, and GFAP, decreased significantly after topiramate administration, as did BDNF expression, while the expression of NeuN and Bcl-2/Bax increased, which is indicative of reduced inflammation and improved neuroprotection.

In vivo laser speckle contrast imaging of 4-aminopyridine- or pentylenetetrazole-induced seizures

Clinical and preclinical studies on epileptic seizures are closely linked to the study of neurovascular coupling. Obtaining reliable information about cerebral blood flow (CBF) in the area of epileptic activity through minimally invasive techniques is crucial for research in this field. In our studies, we used laser speckle contrast imaging (LSCI) to gather information about the local blood circulation in the area of epileptic activity. We used two models of epileptic seizures: one based on 4-aminopyridine (4-AP) and another based on pentylenetetrazole (PTZ). We verified the duration of an epileptic seizure using electrocorticography (ECoG). We applied the antiepileptic drug topiramate (TPM) to both models, but its effect was different in each case. However, in both models, TPM had an effect on neurovascular coupling in the area of epileptic activity, as shown by both LSCI and ECoG data. We demonstrated that TPM significantly reduced the amplitude of 4-AP-induced epileptic seizures (4-AP+TPM: 0.61 ± 0.13 mV vs 4-AP: 1.08 ± 0.19 mV; p < 0.05), and it also reduced gamma power in ECoG in PTZ-induced epileptic seizures (PTZ+TPM: 38.5% ± 11.9% of the peak value vs PTZ: 59.2% ± 3.0% of peak value; p < 0.05). We also captured the pattern of CBF changes during focal epileptic seizures induced by 4-AP. Our data confirm that the system of simultaneous cortical LSCI and registration of ECoG makes it possible to evaluate the effectiveness of pharmacological agents in various types of epileptic seizures in in vivo models and provides spatial and temporal information on the process of ictogenesis.

Visible CCD Camera-Guided Photoacoustic Imaging System for Precise Navigation during Functional Rat Brain Imaging

In photoacoustic (PA) imaging, tissue absorbs specific wavelengths of light. The absorbed energy results in thermal expansion that generates ultrasound waves that are reconstructed into images. Existing commercial PA imaging systems for preclinical brain imaging are limited by imprecise positioning capabilities and inflexible user interfaces. We introduce a new visible charge-coupled device (CCD) camera-guided photoacoustic imaging (ViCPAI) system that integrates an ultrasound (US) transducer and a data acquisition platform with a CCD camera for positioning. The CCD camera accurately positions the US probe at the measurement location. The programmable MATLAB-based platform has an intuitive user interface. In vitro carbon fiber and in vivo animal experiments were performed to investigate the precise positioning and imaging capabilities of the ViCPAI system. We demonstrated real-time capturing of bilateral cerebral hemodynamic changes during (1) forelimb electrical stimulation under normal conditions, (2) forelimb stimulation after right brain focal photothrombotic ischemia (PTI) stroke, and (3) progression of KCl-induced cortical spreading depression (CSD). The ViCPAI system accurately located target areas and achieved reproducible positioning, which is crucial in animal and clinical experiments. In animal experiments, the ViCPAI system was used to investigate bilateral cerebral cortex responses to left forelimb electrical stimulation before and after stroke, showing that the CBV and SO₂ in the right primary somatosensory cortex of the forelimb (S1FL) region were significantly changed by left forelimb electrical stimulation before stroke. No CBV or SO₂ changes were observed in the bilateral cortex in the S1FL area in response to left forelimb electrical stimulation after stroke. While monitoring CSD progression, the ViCPAI system accurately locates the S1FL area and returns to the same position after the probe moves, demonstrating reproducible positioning and reducing positioning errors. The ViCPAI system utilizes the real-time precise positioning capability of CCD cameras to overcome various challenges in preclinical and clinical studies.

Multimodal Magnetic Resonance and Photoacoustic Imaging of Tumor-Specific Enzyme-Responsive Hybrid Nanoparticles for Oxygen Modulation

Multimodal imaging contrast agents for cancer that can not only perform diagnostic functions but also serve as tumor microenvironment–responsive biomaterials are encouraging. In this study, we report the design and fabrication of a novel enzyme-responsive T₁ magnetic resonance imaging (MRI) contrast agent that can modulate oxygen in the tumor microenvironment via the catalytic conversion of H₂O₂ to O₂. The T₁ contrast agent is a core–shell nanoparticle that consists of manganese oxide and hyaluronic acid (HA)–conjugated mesoporous silica nanoparticle (HA-MnO@MSN). The salient features of the nanoparticle developed in this study are as follows: 1) HA serves as a targeting ligand for CD44-expressing cancer cells; 2) HA allows controlled access of water molecules to the MnO core via the digestion of enzyme hyaluronidase; 3) the generation of O₂ bubbles in the tumor by consuming H₂O₂; and 4) the capability to increase the oxygen tension in the tumor. The r₁ relaxivity of HA-MnO@MSN was measured to be 1.29 mM⁻¹s⁻¹ at a magnetic field strength of 9.4 T. In vitro results demonstrated the ability of continuous oxygen evolution by HA-MnO@MSN. After intratumoral administration of HA-MnO@MSN to an HCT116 xenograft mouse model, T₁ weighted MRI contrast was observed after 5 h postinjection and retained up to 48 h. In addition, in vivo photoacoustic imaging of HA-MnO@MSN demonstrated an increase in the tumor oxygen saturation over time after i. t. administration. Thus, the core–shell nanoparticles developed in this study could be helpful in tumor-targeted T₁ MR imaging and oxygen modulation.

Photoacoustic assessment of the fetal brain and placenta as a method of non-invasive antepartum and intrapartum monitoring

A noninvasive monitor for concurrent evaluation of placental and fetal sagittal sinus sO 2 for both antepartum surveillance at the late 2nd and 3rd trimesters and intrapartum monitoring would be a great advantage over current methods. A PA fetal brain and placental monitor has potential value to rapidly identify the fetus at risk for developing hypoxia and ischemia of a sufficient degree that brain injury or death may develop, which may be prevented by intervention with delivery and other follow-up treatments.

In Vivo Assessment of Hypoxia Levels in Pancreatic Tumors Using a Dual-Modality Ultrasound/Photoacoustic Imaging System

Noninvasive anatomical and functional imaging has become an essential tool to evaluate tissue oxygen saturation dynamics in preclinical or clinical studies of hypoxia. Our dual-wavelength technique for photoacoustic (PA) imaging based on the differential absorbance spectrum of oxyhemoglobin (oxy-Hb) and deoxyhemoglobin (deoxy-Hb) can quantify tissue oxygen saturation using the intrinsic contrast property. PA imaging of tissue oxygen saturation can be used to monitor tumor-related hypoxia, which is a particularly relevant functional parameter of the tumor microenvironment that has a strong influence on tumor aggressiveness. The simultaneous acquisition of anatomical and functional information using dual-modality ultrasound (US) and PA imaging technology enhances the preclinical applicability of the method. Here, the developed dual-modality US/PA system was used to measure relative tissue oxygenation using the dual-wavelength technique. Tissue oxygen saturation was quantified in a pancreatic tumor mouse model. The differences in tissue oxygenation were detected by comparing pancreatic samples from normal and tumor-bearing mice at various time points after implantation. The use of an in vivo pancreatic tumor model revealed changes in hypoxia at various stages of tumor growth. The US/PA imaging data positively correlated with the results of immunohistochemical staining for hypoxia. Thus, our dual-modality US/PA imaging system can be used to reliably assess and monitor hypoxia in pancreatic tumor mouse models. These findings enable the use of a combination of US and PA imaging to acquire anatomical and functional information on tumor growth and to evaluate treatment responses in longitudinal preclinical studies.

Rapid development of strong, persistent, spatiotemporally extensive cortical synchrony and underlying oscillations following acute MCA focal ischemia

Stroke is a leading cause of death and the leading cause of long-term disability, but its electrophysiological basis is poorly understood. Characterizing acute ischemic neuronal activity dynamics is important for understanding the temporal and spatial development of ischemic pathophysiology and determining neuronal activity signatures of ischemia. Using a 32-microelectrode array spanning the depth of cortex, electrophysiological recordings generated for the first time a continuous spatiotemporal profile of local field potentials (LFP) and multi-unit activity (MUA) before (baseline) and directly after (0-5 h) distal, permanent MCA occlusion (pMCAo) in a rat model. Although evoked activity persisted for hours after pMCAo with minor differences from baseline, spatiotemporal analyses of spontaneous activity revealed that LFP became spatially and temporally synchronized regardless of cortical depth within minutes after pMCAo and extended over large parts of cortex. Such enhanced post-ischemic synchrony was found to be driven by increased bursts of low multi-frequency oscillations and continued throughout the acute ischemic period whereas synchrony measures minimally changed over the same recording period in surgical sham controls. EEG recordings of a similar frequency range have been applied to successfully predict stroke damage and recovery, suggesting clear clinical relevance for our rat model.

Spatiotemporal dynamics of pial collateral blood flow following permanent middle cerebral artery occlusion in a rat model of sensory-based protection: a Doppler optical coherence tomography study

There is a growing recognition regarding the importance of pial collateral flow in the protection from impending ischemic stroke both in preclinical and clinical studies. Collateral flow is also a major player in sensory stimulation-based protection from impending ischemic stroke. Doppler optical coherence tomography has been employed to image spatiotemporal patterns of collateral flow within the dorsal branches of the middle cerebral artery (MCA) as it provides a powerful tool for quantitative in vivo flow parameters imaging (velocity, flux, direction of flow, and radius of imaged branches). It was employed prior to and following dorsal permanent MCA occlusion (pMCAo) in rat models of treatment by protective sensory stimulation, untreated controls, or sham surgery controls. Unexpectedly, following pMCAo in the majority of subjects, some MCA branches continued to show anterograde blood flow patterns over time despite severing of the MCA. Further, in the presence of protective sensory stimulation, the anterograde velocity and flux were stronger and lasted longer than in retrograde flow branches, even within different branches of single subjects, but stimulated retrograde branches showed stronger flow parameters at 24 h. Our study suggests that the spatiotemporal patterns of collateral-based dorsal MCA flow are dynamic and provide a detailed description on the differential effects of protective sensory stimulation.

Protecting the ischaemic penumbra as an adjunct to thrombectomy for acute stroke

After ischaemic stroke, brain damage can be curtailed by rescuing the 'ischaemic penumbra' - that is, the severely hypoperfused, at-risk but not yet infarcted tissue. Current evidence-based treatments involve restoration of blood flow so as to salvage the penumbra before it evolves into irreversibly damaged tissue, termed the 'core'. Intravenous thrombolysis (IVT) can salvage the penumbra if given within 4.5 h after stroke onset; however, the early recanalization rate is only ~30%. Direct removal of the occluding clot by mechanical thrombectomy considerably improves outcomes over IVT alone, but despite early recanalization in > 80% of cases, ~50% of patients who receive this treatment do not enjoy functional independence, usually because the core is already too large at the time of recanalization. Novel therapies aiming to 'freeze' the penumbra - that is, prevent core growth until recanalization is complete - hold potential as adjuncts to mechanical thrombectomy. This Review focuses on nonpharmacological approaches that aim to restore the physiological balance between oxygen delivery to and oxygen demand of the penumbra. Particular emphasis is placed on normobaric oxygen therapy, hypothermia and sensory stimulation. Preclinical evidence and early pilot clinical trials are critically reviewed, and future directions, including clinical translation and trial design issues, are discussed.

Real-Time Cerebral Hemodynamic Response to Tactile Somatosensory Stimulation

BACKGROUND AND PURPOSE

Recent studies in rodents suggest that somatosensory stimulation could provide neuroprotection during ischemic stroke by inducing plasticity in the cortex-vasculature relationship. While functional magnetic resonance imaging (fMRI) has shown that somatosensory stimulation increases cerebral blood flow (CBF) over several seconds, subsecond changes in CBF in the basal cerebral arteries have rarely been studied due to temporal resolution limitations. This study characterized hemodynamic changes in the middle cerebral arteries (MCAs) during somatosensory stimulation with high temporal resolution (100 samples/s) using functional transcranial Doppler ultrasound (fTCD).

METHODS

Pneumotactile somatosensory stimulation, consisting of punctate pressure pulses traversing the glabrous skin of the hand at 25 cm/s, was used to induce CBF velocity (CBFV) response curves. Changes in CBFV were measured in the bilateral MCAs using fTCD. All 12 subjects underwent three consecutive trials consisting of 20 seconds of stimulation followed by 5 minutes of rest.

RESULTS

Sharp, bilateral increases in CBFV of about 20% (left MCA = 20.5%, right MCA = 18.8%) and sharp decreases in pulsatility index of about 8% were observed during stimulation. Left lateralization of up to 3.9% was also observed. The magnitude of the initial increase in CBFV showed significant adaptation between subsequent trials.

CONCLUSIONS

Pneumotactile somatosensory stimulation is a potent stimulus that can evoke large, rapid hemodynamic changes, with adaptation between successive stimulus applications. Due to its high temporal resolution, fTCD is useful for identifying quickly evolving hemodynamic responses, and for correlating changes in hemodynamic parameters such as pulsatility index (PI) and CBFV.

Simultaneous functional photoacoustic microscopy and electrocorticography reveal the impact of rtPA on dynamic neurovascular functions after cerebral ischemia

The advance of thrombolytic therapy has been hampered by the lack of optimization of the therapy during the hyperacute phase of focal ischemia. Here, we investigate neurovascular dynamics using a custom-designed hybrid electrocorticography (ECoG)-functional photoacoustic microscopy (fPAM) imaging system during the hyperacute phase (first 6 h) of photothrombotic ischemia (PTI) in male Wistar rats following recombinant tissue plasminogen activator (rtPA)-mediated thrombolysis. We reported, for the first time, the changes in neural activity and cerebral hemodynamic responses following rtPA infusion at different time points post PTI. Interestingly, very early administration of rtPA (< 1 h post PTI) resulted in only partial recovery of neurovascular dynamics (specifically , neural activity recovered to 71 ± 3.5% of baseline and hemodynamics to only 52 ± 2.6% of baseline) and late administration of rtPA (> 4 h post PTI) resulted in the deterioration of neurovascular function. A therapeutic window between 1 and 3 h post PTI was found to improve recovery of neurovascular function (i.e. significant restoration of neural activity to 93 ± 4.2% of baseline and hemodynamics to 81 ± 2.1% of baseline, respectively). The novel combination of fPAM and ECoG enables direct mapping of neurovascular dynamics and serves as a platform to evaluate potential interventions for stroke.

Integrated treatment modality of cathodal-transcranial direct current stimulation with peripheral sensory stimulation affords neuroprotection in a rat stroke model

Cathodal-transcranial direct current stimulation induces therapeutic effects in animal ischemia models by preventing the expansion of ischemic injury during the hyperacute phase of ischemia. However, its efficacy is limited by an accompanying decrease in cerebral blood flow. On the other hand, peripheral sensory stimulation can increase blood flow to specific brain areas resulting in rescue of neurovascular functions from ischemic damage. Therefore, the two modalities appear to complement each other to form an integrated treatment modality. Our results showed that hemodynamics was improved in a photothrombotic ischemia model, as cerebral blood volume and hemoglobin oxygen saturation ([Formula: see text]) recovered to 71% and 76% of the baseline values, respectively. Furthermore, neural activities, including somatosensory-evoked potentials (110% increase), the alpha-to-delta ratio (27% increase), and the [Formula: see text] ratio (27% decrease), were also restored. Infarct volume was reduced by 50% with a 2-fold preservation in the number of neurons and a 6-fold reduction in the number of active microglia in the infarct region compared with the untreated group. Grip strength was also better preserved (28% higher) compared with the untreated group. Overall, this nonpharmacological, nonintrusive approach could be prospectively developed into a clinical treatment modality.

Neurovascular function recovery after focal ischemic stroke by enhancing cerebral collateral circulation via peripheral stimulation-mediated interarterial anastomosis

Current treatments for ischemic stroke have focused on the administration of a tissue plasminogen activator, although the associated side effects and subsequent reperfusion injury remain challenging. Peripheral electrical stimulation has shed light on therapeutic interventions for ischemia by increasing cerebral blood flow (CBF) to the target region through collateral circulation, although the mechanism remains elusive. Here, a focal photothrombotic ischemic (PTI) stroke was induced in the right hemispheric primary somatosensory forelimb cortex (S1FL) of rat brains, and the therapeutic effects of forelimb and hindlimb stimulation were characterized at the contralesional S1FL. We observed that PTI stroke rats that received forelimb stimulation exhibited significantly restored CBF of the ischemic penumbra ([Formula: see text] for the S1FL and [Formula: see text] for the primary somatosensory hindlimb cortex, respectively), electrocorticography (ECoG) delta band coherence of the intercortical S1FL ([Formula: see text]) at the 75th min poststroke and an ischemic infarct ([Formula: see text]) via collateral circulation recruitment. Importantly, anterior cerebral artery/middle cerebral artery (ACA-MCA) interarterial anastomotic regulation occurred upon forelimb stimulation and played roles in the recovery of neurovascular functions. These results indicated that receptive field-specific stimulation further restores CBF, neuronal activities, and tissue viability through the enhancement of ACA-MCA interarterial anastomosis-mediated collateral circulation and provides a feasible therapeutic intervention for stroke recovery.

Peripheral sensory stimulation is neuroprotective in a rat photothrombotic ischemic stroke model

Ischemic stroke is one of the leading causes of death and disability in the world. Thrombolytic therapy using recombinant tissue plasminogen activator (rtPA), the only FDA-approved drug for acute ischemia, is limited by a narrow therapeutic time window and risk of hemorrhage. There is a serious need for a neuroprotective therapy which is clinically viable. We earlier demonstrated that peripheral sensory stimulation (PSS) is a potential therapeutic intervention for hyperacute ischemia resulting in recovery of neurovascular functions when administered immediately following ischemia onset in a rat model. Here, we investigated the potential neuroprotective effect of PSS during the hyperacute phase of stroke in a rat photothrombotic ischemia (PTI) model. We employed electrocorticography (ECoG) to image cortical neural activity responses pre-and post-ischemia. Results showed that the neural activity including somatosensory evoked potentials (SSEPs) and alpha-to-delta ratio (ADR) were restored following administration of PSS. Further, immunohistochemistry and TTC staining also indicated the neuroprotective effect of PSS intervention, protecting more neurons and reduced infarct. Overall, the study demonstrated that PSS administered immediately following ischemia induction in a rat PTI model can significantly promote neuroprotection via inhibition of peri-infarct expansion and enhanced cortical neural activity functions, suggesting effective recovery. Future work utilizing multimodal imaging to probe changes in neurovascular functions, will explore application of PSS as an adjuvant intervention for improving rtPA thrombolysis therapy.

Biocompatible Red Fluorescent Organic Nanoparticles with Tunable Size and Aggregation-Induced Emission for Evaluation of Blood-Brain Barrier Damage

Detection of damage to the blood-brain barrier (BBB) is important for the diagnosis of brain diseases and therapeutic drug evaluation. The widely used probe, Evans blue, suffers from low specificity and high toxicity in vivo. It is shown that organic nanoparticles with tuneable size, good biocompatibility, and aggregation-induced emission characteristics offer high detection specificity to detect BBB damage via a photothrombotic ischemia rat model.

An integrated neuroprotective intervention for brain ischemia validated by ECoG-fPAM

Brain ischemia is a neurological deficit caused by a reduction in the blood supply to tissue, and one of the leading causes of disability in the world. Currently, the most well-known therapeutic agent for ischemia recovery is recombinant tissue plasminogen activator (rtPA), but it is viable for only a small portion (approximately 3.6%) of ischemic patients and may cause side effects such as tissue damage. Thus, introducing a new therapeutic concept for ischemia, we proposed an integrated intervention combining global and focal stimulations in this article. To investigate the potential therapeutic effect of cathodal-transcranial direct current stimulation (C-tDCS) with peripheral sensory stimulation (PSS) during the hyperacute phase of stroke, the present study evaluated neurovascular and neuroprotective responses of the rat cortex following ischemic insult. A hybrid, dual-modality system, including electrocorticography (ECoG) and functional photoacoustic microscopy (fPAM), termed ECoG-fPAM, was used to image cortical functional responses pre- and post-ischemia. Using ECoG-fPAM, results showed that cerebral blood volume (CBV) was able to be recovered during the intervention. In addition, neural activity including somatosensory evoked potentials (SSEPs) and alpha-to-delta ratio (ADR) were restored and greater than the baseline value when the integrated intervention was administered. The results of NeuN/ED-1 immunohistochemical staining and TTC staining also supported the neuroprotective effect of this intervention, protecting more neurons and decreasing the infarct size. Overall, the results acquired from the ECoG-fPAM system demonstrated that C-tDCS + PSS administered immediately following ischemia induction can significantly promote neuroprotection via inhibition of ischemia expansion and reversed cortical neurovascular functions, suggesting effective recovery.

Plastic Change along the Intact Crossed Pathway in Acute Phase of Cerebral Ischemia Revealed by Optical Intrinsic Signal Imaging

The intact crossed pathway via which the contralesional hemisphere responds to the ipsilesional somatosensory input has shown to be affected by unilateral stroke. The aim of this study was to investigate the plasticity of the intact crossed pathway in response to different intensities of stimulation in a rodent photothrombotic stroke model. Using optical intrinsic signal imaging, an overall increase of the contralesional cortical response was observed in the acute phase (≤48 hours) after stroke. In particular, the contralesional hyperactivation is more prominent under weak stimulations, while a strong stimulation would even elicit a depressed response. The results suggest a distinct stimulation-response pattern along the intact crossed pathway after stroke. We speculate that the contralesional hyperactivation under weak stimulations was due to the reorganization for compensatory response to the weak ipsilateral somatosensory input.