Improved selective, simple, and contrast staining of acidophilic neurons with vanadium acid fuchsin

A detection method for neuronal death indicates abnormalities in intracellular membranous components in neuronal cells that underwent delayed death

Acute neuronal degeneration is always preceded under the light and electron microscopes by a stage called microvacuolation, which is characterized by a finely vacuolar alteration in the cytoplasm of the neurons destined to death. In this study, we reported a method for detecting neuronal death using two membrane-bound dyes, rhodamine R6 and DiOC₆(3), which may be associated with the so-called microvacuolation. This new method produced a spatiotemporally similar staining pattern to Fluoro-Jade B in kainic acid-damaged brains in mice. Further experiments showed that increased staining of rhodamine R6 and DiOC₆(3) was observed only in degenerated neurons, but not in glia, erythrocytes, or meninges. Different from Fluoro-Jade-related dyes, rhodamine R6 and DiOC₆(3) staining is highly sensitive to solvent extraction and detergent exposure. Staining with Nile red for phospholipids and filipin III for non-esterified cholesterol supports that the increased staining of rhodamine R6 and DiOC₆(3) might be associated with increased levels of phospholipids and free cholesterol in the perinuclear cytoplasm of damaged neurons. In addition to kainic acid-injected neuronal death, rhodamine R6 and DiOC₆(3) were similarly useful for detecting neuronal death in ischemic models either in vivo or in vitro. As far as we know, the staining with rhodamine R6 or DiOC₆(3) is one of a few histochemical methods for detecting neuronal death whose target molecules have been well defined and therefore may be useful for explaining experimental results as well as exploring the mechanisms of neuronal death. (250 words).

Safety of focused ultrasound neuromodulation in humans with temporal lobe epilepsy

OBJECTIVE

Transcranial Focused Ultrasound (tFUS) is a promising new potential neuromodulation tool. However, the safety of tFUS neuromodulation has not yet been assessed adequately. Patients with refractory temporal lobe epilepsy electing to undergo an anterior temporal lobe resection present a unique opportunity to evaluate the safety and efficacy of tFUS neuromodulation. Histological changes in tissue after tFUS can be examined after surgical resection, while further potential safety concerns can be assessed using neuropsychological testing.

METHODS

Neuropsychological functions were assessed in eight patients before and after focused ultrasound sonication of the temporal lobe at intensities up to 5760 mW/cm². Using the BrainSonix Pulsar 1002, tFUS was delivered under MR guidance, using the Siemens Magnetom 3T Prisma scanner. Neuropsychological changes were assessed using various batteries. Histological changes were assessed using hematoxylin and eosin staining, among others.

RESULTS

With respect to safety, the histological analysis did not reveal any detectable damage to the tissue, except for one subject for whom the histology findings were inconclusive. In addition, neuropsychological testing did not show any statistically significant changes in any test, except for a slight decrease in performance on one of the tests after tFUS.

SIGNIFICANCE

This study supports the hypothesis that low-intensity Transcranial Focused Ultrasound (tFUS) used for neuromodulation of brain circuits at intensities up to 5760 mW/cm² may be safe for use in human research. However, due to methodological limitations in this study and inconclusive findings, more work is warranted to establish the safety. Future directions include greater number of sonications as well as longer exposure at higher intensity levels to further assess the safety of tFUS for modulation of neuronal circuits.

Rapid Intramitochondrial Zn2+ Accumulation in CA1 Hippocampal Pyramidal Neurons After Transient Global Ischemia: A Possible Contributor to Mitochondrial Disruption and Cell Death

Mitochondrial Zn2+ accumulation, particularly in CA1 neurons, occurs after ischemia and likely contributes to mitochondrial dysfunction and subsequent neurodegeneration. However, the relationship between mitochondrial Zn2+ accumulation and their disruption has not been examined at the ultrastructural level in vivo. We employed a cardiac arrest model of transient global ischemia (TGI), combined with Timm's sulfide silver labeling, which inserts electron dense metallic silver granules at sites of labile Zn2+ accumulation, and used transmission electron microscopy (TEM) to examine subcellular loci of the Zn2+ accumulation. In line with prior studies, TGI-induced damage to CA1 was far greater than to CA3 pyramidal neurons, and was substantially progressive in the hours after reperfusion (being significantly greater after 4- than 1-hour recovery). Intriguingly, TEM examination of Timm's-stained sections revealed substantial Zn2+ accumulation in many postischemic CA1 mitochondria, which was strongly correlated with their swelling and disruption. Furthermore, paralleling the evolution of neuronal injury, both the number of mitochondria containing Zn2+ and the degree of their disruption were far greater at 4- than 1-hour recovery. These data provide the first direct characterization of Zn2+ accumulation in CA1 mitochondria after in vivo TGI, and support the idea that targeting these events could yield therapeutic benefits.

Application of Focal Photoinduced Thrombosis for Modeling Spinal Cord Ischemia

Typical ischemic damage to neurons were detected in the focus of experimental photothrombosis and in the transition zone. They were associated with symptoms of impaired motor functions and dysfunction of pelvic organs. The applied method of focal photothrombosis can be used for simulation of spinal cord ischemia for the development of methods for pharmacological correction and restoration of impaired sensorimotor functions.

Safety of transcranial focused ultrasound stimulation: A systematic review of the state of knowledge from both human and animal studies

BACKGROUND

Low-intensity transcranial focused ultrasound stimulation (TFUS) holds great promise as a highly focal technique for transcranial stimulation even for deep brain areas. Yet, knowledge about the safety of this novel technique is still limited.

OBJECTIVE

To systematically review safety related aspects of TFUS. The review covers the mechanisms-of-action by which TFUS may cause adverse effects and the available data on the possible occurrence of such effects in animal and human studies.

METHODS

Initial screening used key term searches in PubMed and bioRxiv, and a review of the literature lists of relevant papers. We included only studies where safety assessment was performed, and this results in 33 studies, both in humans and animals.

RESULTS

Adverse effects of TFUS were very rare. At high stimulation intensity and/or rate, TFUS may cause haemorrhage, cell death or damage, and unintentional blood-brain barrier (BBB) opening. TFUS may also unintentionally affect long-term neural activity and behaviour. A variety of methods was used mainly in rodents to evaluate these adverse effects, including tissue staining, magnetic resonance imaging, temperature measurements and monitoring of neural activity and behaviour. In 30 studies, adverse effects were absent, even though at least one Food and Drug Administration (FDA) safety index was frequently exceeded. Two studies reported microhaemorrhages after long or relatively intense stimulation above safety limits. Another study reported BBB opening and neuronal damage in a control condition, which intentionally and substantially exceeded the safety limits.

CONCLUSION

Most studies point towards a favourable safety profile of TFUS. Further investigations are warranted to establish a solid safety framework for the therapeutic window of TFUS to reliably avoid adverse effects while ensuring neural effectiveness. The comparability across studies should be improved by a more standardized reporting of TFUS parameters.

Elevated Serum Melatonin under Constant Darkness Enhances Neural Repair in Spinal Cord Injury through Regulation of Circadian Clock Proteins Expression

We investigated the effects of environmental lighting conditions regulating endogenous melatonin production on neural repair, following experimental spinal cord injury (SCI). Rats were divided into three groups randomly: the SCI + L/D (12/12-h light/dark), SCI + LL (24-h constant light), and SCI + DD (24-h constant dark) groups. Controlled light/dark cycle was pre-applied 2 weeks before induction of spinal cord injury. There was a significant increase in motor recovery as well as body weight from postoperative day (POD) 7 under constant darkness. However, spontaneous elevation of endogenous melatonin in cerebrospinal fluid was seen at POD 3 in all of the SCI rats, which was enhanced in SCI + DD group. Augmented melatonin concentration under constant dark condition resulted in facilitation of neuronal differentiation as well as inhibition of primary cell death. In the rostrocaudal region, elevated endogenous melatonin concentration promoted neural remodeling in acute phase including oligodendrogenesis, excitatory synaptic formation, and axonal outgrowth. The changes were mediated via NAS-TrkB-AKT/ERK signal transduction co-regulated by the circadian clock mechanism, leading to rapid motor recovery. In contrast, exposure to constant light exacerbated the inflammatory responses and neuroglial loss. These results suggest that light/dark control in the acute phase might be a considerable environmental factor for a favorable prognosis after SCI.

Nanotechnology for CNS delivery of bio-therapeutic agents

The current therapeutic strategies are not efficient in treating disorders related to the central nervous system (CNS) and have only shown partial alleviation of symptoms, as opposed to, disease modifying effects. With change in population demographics, the incidence of CNS disorders, especially neurodegenerative diseases, is expected to rise dramatically. Current treatment regimens are associated with severe side-effects, especially given that most of these are chronic therapies and involve elderly population. In this review, we highlight the challenges and opportunities in delivering newer and more effective bio-therapeutic agents for the treatment of CNS disorders. Bio-therapeutics like proteins, peptides, monoclonal antibodies, growth factors, and nucleic acids are thought to have a profound effect on halting the progression of neurodegenerative disorders and also provide a unique function of restoring damaged cells. We provide a review of the nano-sized formulation-based drug delivery systems and alternate modes of delivery, like the intranasal route, to carry bio-therapeutics effectively to the brain.

Combination of the multipotent mesenchymal stromal cell transplantation with administration of temozolomide increases survival of rats with experimental glioblastoma

Glioblastoma multiforme (GM) is an aggressive malignant tumor of the brain. The standard treatment of GM is surgical resection with consequent radio- and chemotherapy with temozolomide. The prognosis is unfavorable, with a survival time of 12-14 months. The phenomenon of targeted migration to the tumor in the brain opens novel possibilities for the treatment of GM. Multipotent mesenchymal stromal cells (MMSCs) are a cell type with anti-carcinogenic properties and can be used to optimize GM therapy. The aim of the present study was to investigate the effects of MMSC transplantation in the chemotherapy of a rat model of C6 glioma. A total of 130 animals were divided into a control group, a temozolomide group, MMSCs group and temozolomide + MMSCs group. The experiment was performed over 70 days, and a combination of molecular biology, surgical and neuroimaging techniques, as well as histological and physiological examinations was used. Tumor size was smallest in the temozolomide (115.76 ± 16.25 mm(3)) and in temozolomide + MMSCs (114.74 ± 5.54 mm(3)) groups, which was significantly smaller than the neoplastic node size in the control group (202.09 ± 39.72 mm(3)) (P<0.05). The animals in the temozolomide + MMSCs group showed significantly higher survival rates in comparison with those in the control and temozolomide groups. The MMSCs migrated from the site of implantation to the neoplastic focus and interacted with glioma cells; however, the mechanism requires further research. In conclusion, MMSC transplantation combined with temozolomide treatment significantly extended the survival of experimental animals in comparison with those treated with temozolomide only.

Single-cell resolution mapping of neuronal damage in acute focal cerebral ischemia using thallium autometallography

Neuronal damage shortly after onset or after brief episodes of cerebral ischemia has remained difficult to assess with clinical and preclinical imaging techniques as well as with microscopical methods. We here show, in rodent models of middle cerebral artery occlusion (MCAO), that neuronal damage in acute focal cerebral ischemia can be mapped with single-cell resolution using thallium autometallography (TlAMG), a histochemical technique for the detection of the K(+)-probe thallium (Tl(+)) in the brain. We intravenously injected rats and mice with thallium diethyldithiocarbamate (TlDDC), a lipophilic chelate complex that releases Tl(+) after crossing the blood-brain barrier. We found, within the territories of the affected arteries, areas of markedly reduced neuronal Tl(+) uptake in all animals at all time points studied ranging from 15 minutes to 24 hours after MCAO. In large lesions at early time points, areas with neuronal and astrocytic Tl(+) uptake below thresholds of detection were surrounded by putative penumbral zones with preserved but diminished Tl(+) uptake. At 24 hours, the areas of reduced Tl(+)uptake matched with areas delineated by established markers of neuronal damage. The results suggest the use of (201)TlDDC for preclinical and clinical single-photon emission computed tomography (SPECT) imaging of hyperacute alterations in brain K(+) metabolism and prediction of tissue viability in cerebral ischemia.

Detection of intracerebral hemorrhage and transient blood-supply shortage in focused-ultrasound-induced blood-brain barrier disruption by ultrasound imaging

Focused ultrasound (FUS) in the presence of microbubbles can selectively open the blood-brain barrier (BBB). However, since overexcitation by FUS probably induces intracerebral hemorrhage, it is essential to develop an imaging approach for real-time detection of hemorrhage and blood-flow changes during FUS-induced BBB disruption. Here we investigated the feasibility of using ultrasound imaging to monitor the transient responses of FUS-induced BBB disruption. The BBB was disrupted with in-house-manufactured microbubbles in rats by 1-MHz FUS with a pressure of 1.1 MPa (pulse repetition frequency: 1 Hz, pulse duration: 10 ms, exposure time: 60 s) and imaged for the next 2 h. Ultrasound B-mode imaging was used to detect hyperechoic changes induced by hemorrhage and contrast-enhanced ultrasound (US) imaging was performed to analyze changes in blood flow. Hyperechoic spots appeared in B-mode images at 5 s after FUS sonication and contrast-enhanced US images simultaneously showed a region of transient blood-supply shortage in the sonicated area. Thus, the location of hyperechoic spots correlated with hemorrhagic patterns and the blood-supply-shortage region was consistent with the BBB-disrupted areas. Furthermore, we detected a transient hyperemic response in the unsonicated contralateral hemisphere brain. Our approach has potential as an immediate-feedback control tool for preventing the induction of intracerebral hemorrhage during FUS treatment.

An early decrease in cell proliferation after pentylenetetrazole-induced seizures

There are increasing data on the influence of seizures on neurogenesis in the adult brain. However, data on cell proliferation and differentiation during the early stages of kindling are scarce. We have used pentylenetetrazole (PTZ)-induced kindling to investigate the temporal profile of cytogenesis in the germinative zones of adult rat brain. For comparison, we also used a single PTZ-induced generalized tonic-clonic seizure. During kindling development, the density of 5-bromo-2'-deoxyuridine-positive cells demonstrated similar changes in all germinative zones: a dramatic decrease after the first subthreshold PTZ injection, and a gradual increase to the control level following repeated PTZ administration. On the contrary, a single PTZ-induced generalized tonic-clonic seizure was followed by an increase in the number of proliferating cells in both the dentate gyrus and the subventricular zone. These results may indicate the existence of global mechanisms affecting cellular proliferation in adult brain during seizures. Different temporal profiles of neuronal damage and proliferation changes suggest that neurodegeneration is unlikely to be a global proliferation-regulating factor. The data may contribute to better understanding of the initial phase of kindling development and epileptogenesis.

Focused ultrasound modulates region-specific brain activity

We demonstrated the in vivo feasibility of using focused ultrasound (FUS) to transiently modulate (through either stimulation or suppression) the function of regional brain tissue in rabbits. FUS was delivered in a train of pulses at low acoustic energy, far below the cavitation threshold, to the animal's somatomotor and visual areas, as guided by anatomical and functional information from magnetic resonance imaging (MRI). The temporary alterations in the brain function affected by the sonication were characterized by both electrophysiological recordings and functional brain mapping achieved through the use of functional MRI (fMRI). The modulatory effects were bimodal, whereby the brain activity could either be stimulated or selectively suppressed. Histological analysis of the excised brain tissue after the sonication demonstrated that the FUS did not elicit any tissue damages. Unlike transcranial magnetic stimulation, FUS can be applied to deep structures in the brain with greater spatial precision. Transient modulation of brain function using image-guided and anatomically-targeted FUS would enable the investigation of functional connectivity between brain regions and will eventually lead to a better understanding of localized brain functions. It is anticipated that the use of this technology will have an impact on brain research and may offer novel therapeutic interventions in various neurological conditions and psychiatric disorders.

Immunochemical analysis of glial fibrillary acidic protein as a tool to assess astroglial reaction in experimental C6 glioma

In experiments on Wistar rats with experimental C6 glioma, the immunohistochemical features of the astroglial reaction over 30 days after implantation were characterized. The formation of a glial border consisting of GFAP-positive reactive astrocytes at the periphery of C6 glioma was observed on postimplantation day 3 and until the death of the experimental animals. Reactive astrocytes encompassed not only the primary gliomal focus, but all tumor invasion foci. Quantitative assessment of astroglial reaction around glioma was carried out with immunofluorescent assay of glial fibrillary acidic protein (GFAP) on cerebral sections. The size of glioma and necrotic foci were analyzed morphometrically in parallel with enzyme immunoassay of serum GFAP. A correlation between morphometric indices of glioma and serum level of GFAP was found. It was concluded that serum concentration of GFAP correlated with the size of intracranial glioma, necrotic foci, and most strongly with the degree of reactive astrogliosis. Monitoring of the level of serum GFAP can serve as an additional diagnostic index reporting the state of intracranial glioma.

Morphofunctional changes in the rat spinal cord after focal photothrombosis

The aim of the present work was to study pathomorphological and functional changes after induced focal photothrombosis of blood vessels in the thoracic part of the spinal cord in rats. Neuron abnormalities characteristic of ischemia were seen at the focus of experimental photothrombosis and in the transitional zone, along with symptoms of impaired motor and pelvic organ function. The focal photothrombosis method can be used to model spinal cord ischemia for the development of pharmacological correction methods and the recovery of impaired sensorimotor functions.

Ultrasound for drug and gene delivery to the brain

Noninvasive, transient, and local image-guided blood-brain barrier disruption (BBBD) has been demonstrated with focused ultrasound exposure in animal models. Most studies have combined low pressure amplitude and low time average acoustic power burst sonications with intravascular injection of pre-formed micro-bubbles to produce BBBD without damage to the neurons. The BBB has been shown to be healed within a few hours after the exposure. The combination of focused ultrasound beams with MR image guidance allows precise anatomical targeting as demonstrated by the delivery of several marker molecules in different animal models. This method may in the future have a significant impact on the diagnosis and treatment of central nervous system (CNS) disorders. Most notably, the delivery of the chemotherapy agents (liposomal Doxorubicin and Herceptin) has been shown in a rat model.

Modeling and immunohistochemical analysis of C6 glioma in vivo

A reproducible in vivo model of C6 glioma was developed in Wistar rats. Analysis of histological preparations showed similar morphology of rat C6 glioma and human glioblastoma. The formation of a glial border at the periphery of the glioma, consisting of GFAP-positive reactive astrocytes, was shown by the immunohistochemical method. The border appeared on day 8 after implantation, astrogliosis was observed until animal death (day 28). Reactive astrocytes with branched processes surrounded not only the primary glioma focus, but also all sites of tumor invasion in the nervous tissue. Expression of EBA (blood-brain barrier marker) was disturbed and synthesis of AMVB1 (endothelial antigen) increased in neoplastic endotheliocytes, which suggested pronounced functional restructuring of the blood-tumor barrier in comparison with the blood-brain barrier. The phenomenon of predominant expression of GFAP and AMVB in the tumor tissue can be used for the development of systems for targeted drug transport into the tumor by means of appropriate antibodies.

Induction of apoptosis in vivo in the rabbit brain with focused ultrasound and Optison

Histologic effects of focused ultrasound (FUS) exposures combined with an ultrasound contrast agent (Optison) were investigated to examine whether the lesions were dominated by apoptosis or necrosis. The rabbit brains (n = 17) were sonicated (1.5 MHz, peak rarefactional pressure amplitude: 1.4 to 8.8 MPa) after Optison was injected intravenously (IV). MRI and light microscopy were used to examine tissue effects. To detect apoptosis, TUNEL staining based on labeling of DNA strand breaks was used. The average number of apoptotic and necrotic cells in 300 x 220 microm microscopic fields were counted in 18 representative lesions. Lesions in the rabbit brains were created at lowered acoustic power levels when FUS was combined with Optison. In histology, the lesions exhibited red blood cell extravasations and destruction of blood vessels. At 4 h after sonication, the lesions lost many cells, and the remaining cells exhibited both necrotic and apoptotic features. Overall, apoptosis dominated; there were, on average, 32.3 +/- 13.2 apoptotic cells per microscopic field compared with only 5.1 +/- 3.4 necrotic cells per field. In conclusion, FUS combined with Optison could produce lesions that are dominated by apoptosis, presumably induced primarily via ischemia after cavitation-produced damage to the brain vasculature.

Focal disruption of the blood-brain barrier due to 260-kHz ultrasound bursts: a method for molecular imaging and targeted drug delivery

OBJECT

The goal of this study was to explore the feasibility of using low-frequency magnetic resonance (MR) image-guided focused ultrasound as a noninvasive method for the temporary disruption of the blood-brain barrier (BBB) at targeted locations.

METHODS

Rabbits were placed inside a clinical 1.5-tesla MR imaging unit, and sites in their brains were targeted for 20-second burst sonications (frequency 260 kHz). The peak pressure amplitude during the burst varied between 0.1 and 0.9 MPa. Each sonication was performed after an intravenous injection of an ultrasound contrast agent (Optison). The disruption of the BBB was evaluated with the aid of an injection of an MR imaging contrast agent (MAG-NEVIST). Additional tests involving the use of MION-47, a 20-nm magnetic nanoparticle contrast agent, were also performed. The animals were killed at different time points between 3 minutes and 5 weeks postsonication, after which light or electron microscopic evaluation was performed. The threshold for BBB disruption was approximately 0.2 MPa. More than 80% of the brain sites sonicated showed BBB disruption when the pressure amplitude was 0.3 MPa; at 0.4 MPa, this percentage was greater than 90%. Tissue necrosis, ischemia, and apoptosis were not found in tissue in which the pressure amplitude was less than 0.4 MPa; however, in a few areas of brain tissue erythrocytes were identified outside blood vessels following exposures of 0.4 MPa or higher. Survival experiments did not show any long-term adverse events.

CONCLUSIONS

These results demonstrate that low-frequency ultrasound bursts can induce local, reversible disruption of the BBB without undesired long-term effects. This technique offers a potential noninvasive method for targeted drug delivery in the brain aided by a relatively simple low-frequency device.

Noninvasive localized delivery of Herceptin to the mouse brain by MRI-guided focused ultrasound-induced blood-brain barrier disruption

Antibody-based anticancer agents are promising chemotherapeutic agents. Among these agents, Herceptin (trastuzumab), a humanized anti-human epidermal growth factor receptor 2 (HER2/c-erbB2) monoclonal antibody, has been used successfully in patients with breast cancer. However, in patients with brain metastasis, the blood-brain barrier limits its use, and a different delivery method is needed to treat these patients. Here, we report that Herceptin can be delivered locally and noninvasively into the mouse central nervous system through the blood-brain barrier under image guidance by using an MRI-guided focused ultrasound blood-brain barrier disruption technique. The amount of Herceptin delivered to the target tissue was correlated with the extent of the MRI-monitored barrier opening, making it possible to estimate indirectly the amount of Herceptin delivered. Histological changes attributable to this procedure were minimal. This method may represent a powerful technique for the delivery of macromolecular agents such as antibodies to treat patients with diseases of the central nervous system.

Pentylenetetrazole kindling induces neuronal cyclin B1 expression in rat hippocampus

The purpose of the study was to explore the involvement of cell cycle events in the neuronal death induced by repeated seizures. Pentylenetetrazole (PTZ) kindling was used as a model of seizure-induced hippocampal neurodegeneration. Immunohistochemical approach was applied to detect cell cycle markers (cyclins and cycline-dependent kinases) in hippocampus. PTZ-kindling in rats induced moderate neuronal cell loss in hippocampal fields CA1, CA 3, CA 4, and dentate gyrus. The majority of damaged cells in hippocampi of PTZ-kindled rats were cycline B1 positive, while no expression of either other cell cycle markers or TUNEL-positive (apoptotic) nuclei could be revealed. Since cycline B1 expression has been described in hippocampal neurons of patients with temporal lobe epilepsy by [Z. Nagy, M.M. Esiri, Neuronal cyclin expression in the hippocampus in temporal lobe epilepsy, Exp. Neurol. 150 (1998) 240-247], it is suggested that PTZ-kindling may be a suitable model to study the mechanisms of seizure-induced neuronal death.

MRI-guided targeted blood-brain barrier disruption with focused ultrasound: histological findings in rabbits

Focused ultrasound offers a method to disrupt the blood-brain barrier (BBB) noninvasively and reversibly at targeted locations. The purpose of this study was to test the safety of this method by searching for ischemia and apoptosis in areas with BBB disruption induced by pulsed ultrasound in the presence of preformed gas bubbles and by looking for delayed effects up to one month after sonication. Pulsed ultrasound exposures (sonications) were performed in the brains of 24 rabbits under monitoring by magnetic resonance imaging (MRI) (ultrasound: frequency = 1.63 MHz, burst length = 100 ms, PRF = 1 Hz, duration = 20 s, pressure amplitude 0.7 to 1.0 MPa). Before sonication, an ultrasound contrast agent (Optison, GE Healthcare, Milwaukee, WI, USA) was injected IV. BBB disruption was confirmed with contrast-enhanced MR images. Whole brain histologic examination was performed using haematoxylin and eosin staining for general histology, vanadium acid fuchsin-toluidine blue staining for ischemic neurons and TUNEL staining for apoptosis. The main effects observed were tiny regions of extravasated red blood cells scattered around the sonicated locations, indicating affected capillaries. Despite these vasculature effects, only a few cells in some of the sonicated areas showed evidence for apoptosis or ischemia. No ischemic or apoptotic regions were detected that would indicate a compromised blood supply was induced by the sonications. No delayed effects were observed either by MRI or histology up to 4 wk after sonication. Ultrasound-induced BBB disruption is possible without inducing substantial vascular damage that would result in ischemic or apoptotic death to neurons. These findings indicate that this method is safe for targeted drug delivery, at least when compared with the currently available invasive methods.

Anxious and hyperactive phenotype following brief ischemic episodes in mice

BACKGROUND

Poststroke emotional and behavioral abnormalities have an impact on outcome but have scarcely been characterized in animal models. We tested whether brief ischemic episodes induce behavioral changes in mice.

METHODS

129/Sv mice were subjected to 30-min occlusion of left or right middle cerebral artery (MCAo) followed by reperfusion or sham operation (n = 9 or 10 per group). Eight to ten weeks later, mice were tested for spontaneous locomotor activity, anxiety in the elevated plus maze, and depressive behavior in the modified Porsolt forced swim test. Outcome was correlated to monoamine and amino acid levels and compared with histologic damage at 10 weeks.

RESULTS

Ischemia was associated with increased activity (right MCAo) and anxiety (left MCAo), but not poststroke depression. Noradrenaline increased by 30%-45% in the ischemic striatum and correlated with locomotor activity (r = .48); dopamine and homovanillinic acid were decreased compared with sham. The lesion was confined to the striatum, and scattered neuronal death was observed in a number of remote brain regions.

CONCLUSION

Brief ischemic episodes in the mouse induce an anxious, hyperactive but not depressive phenotype that may relate to left versus right hemispheric lesion location, alterations in brain monoamine levels, and selective neurodegeneration.

Lasting blood-brain barrier disruption induces epileptic focus in the rat somatosensory cortex

Perturbations in the integrity of the blood-brain barrier have been reported in both humans and animals under numerous pathological conditions. Although the blood-brain barrier prevents the penetration of many blood constituents into the brain extracellular space, the effect of such perturbations on the brain function and their roles in the pathogenesis of cortical diseases are unknown. In this study we established a model for focal disruption of the blood-brain barrier in the rat cortex by direct application of bile salts. Exposure of the cerebral cortex in vivo to bile salts resulted in long-lasting extravasation of serum albumin to the brain extracellular space and was associated with a prominent activation of astrocytes with no inflammatory response or marked cell loss. Using electrophysiological recordings in brain slices we found that a focus of epileptiform discharges developed within 4-7 d after treatment and could be recorded up to 49 d postoperatively in >60% of slices from treated animals but only rarely (10%) in sham-operated controls. Epileptiform activity involved both glutamatergic and GABAergic neurotransmission. Epileptiform activity was also induced by direct cortical application of native serum, denatured serum, or albumin-containing solution. In contrast, perfusion with serum-adapted electrolyte solution did not induce abnormal activity, thereby suggesting that the exposure of the serum-devoid brain environment to serum proteins underlies epileptogenesis in the blood-brain barrier-disrupted cortex. Although many neuropathologies entail a compromised blood-brain barrier, this is the first direct evidence that it may have a role in the pathogenesis of focal cortical epilepsy, a common neurological disease.

Local and reversible blood-brain barrier disruption by noninvasive focused ultrasound at frequencies suitable for trans-skull sonications

The purpose of this study was to test the hypothesis that burst ultrasound in the presence of an ultrasound contrast agent can disrupt the blood-brain barrier (BBB) with acoustic parameters suitable for completely noninvasive exposure through the skull. The 10-ms exposures were targeted in the brains of 22 rabbits with a frequency of 690 kHz, a repetition frequency of 1 Hz, and peak rarefactional pressure amplitudes up to 3.1 MPa. The total exposure (sonication) time was 20 s. Prior to each sonication, a bolus of ultrasound contrast agent was injected intravenously. Contrast-enhanced MR images were obtained after the sonications to detect localized BBB disruption via local enhancement in the brain. Brain sections were stained with H&E, TUNEL, and vanadium acid fuchsin (VAF)-toluidine blue staining. In addition, horseradish peroxidase (HRP) was injected into four rabbits prior to sonications and transmission electron microscopy was performed. The MRI contrast enhancement demonstrated BBB disruption at pressure amplitudes starting at 0.4 MPa with approximately 50%; at 0.8 MPa, 90%; and at 1.4 MPa, 100% of the sonicated locations showed enhancement. The histology findings following 4 h survival indicated that brain tissue necrosis was induced in approximately 70-80% of the sonicated locations at a pressure amplitude level of 2.3 MPa or higher. At lower pressure amplitudes, however, small areas of erythrocyte extravasation were seen. The electron microscopy findings demonstrated HRP passage through vessel walls via both transendothelial and paraendothelial routes. These results demonstrate that completely noninvasive focal disruption of the BBB is possible.

Histochemical study on neurodegeneration in the olfactory bulb after transient forebrain ischaemia in the Mongolian gerbil

In the present study, we investigated the ischaemia-related neurodegeneration in the main and accessory olfactory bulb (AOB) after 5 min transient forebrain ischaemia in the Mongolian gerbil using the acid fuchsin staining method. Between 5 and 15 days after ischaemia, acid fuchsin positive cells markedly increased in the external plexiform layer (EPL), mitral cell layer (ML) and glomerular layer (GL) of the main olfactory bulb (MOB), and in the mixed cell layer (MCL) and GL of the AOB. By 30 days after ischaemia reperfusion, acid fuchsin positive neurons were shrunken and showed low acidophilia in somata. Many necrotic vacuoles were found in the EPL and GL of the MOB 30 days after ischaemia. At this time, necrotic vacuoles were very few in the AOB. Therefore, our results suggest that the GL and EPL of the MOB are vulnerable to ischaemic damage at a later time after ischaemic insult, and that the AOB is more resistant to ischaemic damage as compared with the MOB.

In vivo neuroprotective adaptation of the glutamate/glutamine cycle to neuronal death

Synaptic increase of glutamate level, when not coupled to a heightened energy production, renders neurons susceptible to death. Astrocyte uptake and recycling of synaptic glutamate as glutamine is a major metabolic pathway dependent on energy metabolism, which inter-relationships are not fully understood and remain controversial. We examine how the glutamate-glutamine cycle and glucose metabolism are modified in two in vivo models of severe and mild brain injury. Graded reductions of glutaminase, the glutamate synthetic enzyme, were evidenced combined with increases in glutamine synthetase, the inactivating glutamate enzyme. Increased lactate dhydrogenase (LDH) activity was only present after a more severe injury. These results indicate an in vivo adaptation of the glutamate-glutamine cycle in order to increase the net glutamine output, reduce glutamate excitotoxicity, and avoid neuronal death. We conclude that the graded modification of the glutamate-glutamine correlation and neuronal lactate availability may be key factors in the apoptotic and necrotic neuronal demise, whose control may prove highly useful to potentiate neuronal survival.

MRI investigation of the threshold for thermally induced blood-brain barrier disruption and brain tissue damage in the rabbit brain

The ability of MRI-derived thermometry to predict thermally induced tissue changes in the brain was tested, and the thermal thresholds for blood-brain barrier (BBB) disruption and brain tissue damage were estimated. In addition, the ability of standard MRI to detect threshold-level effects was confirmed. These safety thresholds are being investigated to provide guidelines for clinical thermal ablation studies in the brain. MRI-monitored focused ultrasound heating was delivered to 63 locations in 26 rabbits. Tissue changes were detected in T(2)-weighted imaging and T(1)-weighted imaging (with and without contrast) and with light microscopy. The probability for tissue damage as a function of the accumulated thermal dose, the peak temperature achieved, the applied acoustic energy, and the peak acoustic power was estimated with probit regression. The discriminative abilities of these parameters were compared using the areas under the receiver operator characteristic (ROC) curves. In MRI, BBB disruption was observed in contrast-enhanced T(1)-weighted imaging shortly after the ultrasound exposures, sometimes accompanied by changes in T(2)-weighted imaging. Two days later, changes in T(2)-weighted imaging were observed, sometimes accompanied by changes in T(1)-weighted imaging. In histology, tissue damage was seen at every location where MRI changes were observed, ranging from small (diameter <1.0 mm) areas of tissue necrosis to severe vascular damage and associated hemorrhagic infarct. In one location, small (diameter: 0.8 mm) damage was not detected in MRI. The thermal dose and peak temperature thresholds were between 12.3-40.1 equivalent min at 43 degrees C and 48.0-50.8 degrees C, respectively, and values of 17.5 equivalent min at 43 degrees C and 48.4 degrees C were estimated to result in tissue damage with 50% probability. Thermal dose and peak temperature were significantly better predictors than the applied acoustic energy and peak acoustic power (P < 0.01). BBB disruption was always accompanied by tissue damage. The temperature information was better than the applied acoustic power or energy for predicting the damage than the ultrasound parameters. MRI was sensitive in detecting threshold-level damage.

Hypoxia-induced stroke tolerance in the mouse is mediated by erythropoietin

BACKGROUND AND PURPOSE

Cellular response to hypoxia is mainly controlled by hypoxia-inducible factor 1 (HIF-1). The HIF-1 target gene erythropoietin (EPO) has been described as neuroprotective. Thus, we hypothesize EPO to be an essential mediator of protection in hypoxic preconditioning.

METHODS

We randomized Sv129 mice into groups for different pretreatments, different hypoxia-ischemia intervals, or different durations of ischemia. For hypoxic preconditioning, the animals were exposed to a hypoxic gas mixture (8% O2 and 92% N2) for 30, 60, 180, 300, or 360 minutes. At 0, 24, 48, 72, or 144 hours later, we performed middle cerebral artery occlusion and allowed reperfusion after 30, 45, 60, or 120 minutes, or occlusion was left to be permanent. We studied EPO gene expression in brain tissue with a real-time reverse transcriptase-polymerase chain reaction and measured HIF-1 DNA-binding activity with an electrophoretic mobility shift assay. To block endogenously produced EPO, we instilled soluble EPO receptor into the cerebral ventricle.

RESULTS

Hypoxic preconditioning for 180 or 300 minutes induced relative tolerance to transient focal cerebral ischemia, as evidenced by a reduction of infarct volumes to 75% or 54% of the control, respectively. Hypoxic pretreatment was effective only when applied 48 or 72 hours before middle cerebral artery occlusion. Sixty minutes after hypoxia, we found a marked activation of HIF-1 DNA-binding activity and a 7-fold induction of EPO transcription. Infusion of soluble EPO receptor significantly reduced the protective effect of hypoxic pretreatment by 40%.

CONCLUSIONS

Endogenously produced EPO is an essential mediator of ischemic preconditioning.

The threshold for brain damage in rabbits induced by bursts of ultrasound in the presence of an ultrasound contrast agent (Optison)

The purpose of this study was to test the hypothesis that burst ultrasound (US) in the presence of a US contrast agent using parameters similar to those used in brain blood flow measurements causes tissue damage. The brains of 10 rabbits were sonicated in 3-8 locations with 1.5-MHz, 10- micro s bursts repeated at a frequency of 1 kHz at temporal peak acoustic pressure amplitudes ranging from 2 to 12.7 MPa. The total sonication time for each location was 20 s. Before each sonication, a bolus of US contrast agent was injected IV. Contrast-enhanced magnetic resonance (MR) images were obtained after the sonications to detect local enhancement in the brain. Whole brain histological evaluation was performed, and the sections were stained with hematoxylin and eosin (H and E), TUNEL, and vanadium acid fuchsin (VAF) staining to evaluate tissue effects, including apoptosis and ischemia. Both the magnetic resonance imaging (MRI) contrast enhancement and histology findings indicated that brain tissue damage was induced at a pressure amplitude level of 6.3 MPa. The damage included vascular wall damage, hemorrhage and, eventually, necrosis. Mild vascular damage was observed localized in a few microscopic tissue volumes in about half of the sonicated locations at all pressure values tested (down to 2 MPa). However, these sonications did not induce any detectable tissue effects, including ischemia or apoptosis. As a conclusion, the study showed that the US exposure levels currently used for blood flow measurements in brain are below the threshold of blood-brain barrier opening or brain tissue damage. However, one should be aware that brain damage can be induced if the exposure level is increased.

Tissue-saving infarct volumetry using histochemistry validated by MRI in rat focal ischemia

Lesion size is an important outcome parameter in experimental stroke research. However, most methods of measuring the infarct volume in rodents either require expensive equipment or render the brain tissue unusable for further analysis. We report on an inexpensive, tissue-saving method for quantifying the infarct volume in small rodents. After 3 h of middle cerebral artery occlusion (MCAO) and 24 h of reperfusion in male Wistar rats, the lesion was first identified using MRI with T2-weighted sequences. The infarct was then visualized in unfixed brain cryosections using microtubule associated protein 2 (MAP2)-immunohistochemistry and silver infarct staining. The lesion areas detected by all three different methods completely overlapped. The infarct volume was calculated for each method from the lesion area size on serial sections and the distance between them. Significant differences in lesion size were found between the individual animals (p = 0.000056), but not between different methods (p > 0.05). MAP2 immunohistochemistry is a convenient and valid method to measure stroke lesion volume; in addition 98% of the brain tissue is saved and available for use in further histological, immunohistochemical, and biochemical analysis.

Tolerance against ischemic neuronal injury can be induced by volatile anesthetics and is inducible NO synthase dependent

BACKGROUND AND PURPOSE

We tested whether volatile anesthetics induce neuroprotection that is maintained for a prolonged time.

METHODS

Rats were pretreated for 3 hours with 1 minimal anesthetic concentration of isoflurane or halothane in normal air (anesthetic preconditioning [AP]). The animals were subjected to permanent middle cerebral artery occlusion (MCAO) at 0, 12, 24, or 48 hours after AP. Halothane-pretreated animals were subjected to MCAO 24 hours after AP. Histological evaluation of infarct volumes was performed 4 days after MCAO. Cerebral glucose utilization was measured 24 hours after AP with isoflurane. Primary cortical neuronal cultures were exposed to 1.4% isoflurane for 3 hours. Oxygen-glucose deprivation (OGD) was performed 24 hours after AP. Injury was assessed 24 hours later by measuring the release of lactate dehydrogenase into the medium 24 hours after OGD.

RESULTS

Isoflurane anesthesia at 0, 12, and 24 hours before MCAO or halothane anesthesia 24 hours before MCAO significantly reduced infarct volumes (125+/-42 mm3, P=0.024; 118+/-51 mm3, P=0.008; 120+/-49 mm3, P=0.009; and 121+/-48 mm3, P=0.018, respectively) compared with control volumes (180+/-51 mm3). Three hours of isoflurane anesthesia in rats did not have any effect on local or mean cerebral glucose utilization measured 24 hours later. Western blot analysis from cortical extracts of AP-treated animals revealed an increase of the inducible NO synthase (iNOS) protein beginning 6 hours after AP. The iNOS inhibitor aminoguanidine (200 mg/kg IP) eliminated the infarct-sparing effect of AP. In cultured cortical neurons, isoflurane exposure 24 hours before OGD decreased the OGD-induced release of lactate dehydrogenase by 49% (P=0.002).

CONCLUSIONS

Pretreatment with volatile anesthetics induces prolonged neuroprotection in vitro and in vivo, a process in which iNOS seems to be critically involved.

Desferrioxamine induces delayed tolerance against cerebral ischemia in vivo and in vitro

The widely prescribed drug desferrioxamine is a known activator of the hypoxia-inducible transcription factor 1 (HIF-1) and the subsequent transcription of erythropoietin. In the brain, HIF-1 is a master switch of the transcriptional response to hypoxia, whereas erythropoietin is a potent neuroprotectant. The authors show that desferrioxamine dose-dependently and time-dependently induces tolerance against focal cerebral ischemia in rats and mice, and against oxygen-glucose deprivation in purified cortical neurons. Desferrioxamine induced HIF-1 DNA binding and transcription of erythropoietin in vivo, the temporal kinetics of which were congruent with tolerance induction. Desferrioxamine is a promising drug for the induction of tolerance in humans when ischemia can be anticipated.

A modified roller method for organotypic brain cultures: free-floating slices of postnatal rat hippocampus

We describe a novel procedure for organotypic cultivation of free-floating brain sections of postnatal rats with a modified roller technique. Three hundred to 350-microm-thick sections of hippocampus are cultured for 13-15 days at 35.5 degrees C in 10-15 ml of feeding medium in 50-100 ml bottles under constant rotation on a horizontal high-speed mini-roller (60 rpm). Histological analysis (paraffin sections, Nissl Cresyl Violet and Hematoxylin/Eosin staining) demonstrates good survival of neuronal and glial cells and complete preservation of the neuronal organization of cultivated hippocampus with minimal central necrosis. This novel protocol permits not only survival and development of long-term three-dimensional organotypic postnatal brain tissue but also allows simultaneous cultivation of any number of brain sections in one bottle (up to 50 and even more) and therefore is useful for high throughput study of neurocytotoxic and hypoxic/ischemic neuronal damage with subsequent histological, immunocytochemical, biochemical, and molecular analysis.