In vitro testing of a funnel-tip catheter with different clot types to decrease clot migration in mechanical thrombectomy

BACKGROUND

Mechanical thrombectomy is the standard treatment for acute ischemic stroke in patients with large vessel occlusion and can be performed up to 24h after symptom onset. Despite high recanalization rates, embolism in new territories has been reported in 8.6% of the cases. Causes for this could be clot abruption during stent retrieval into the smaller opening of a standard distal access catheter, and antegrade blood flow via collaterals despite proximal balloon protection. A funnel-shaped tip with a larger internal diameter was developed to increase the rate of first-pass recanalization and to improve the safety and efficacy of mechanical thrombectomy.

METHODS

This in vitro study compared the efficacy of a funnel-shaped tip with a standard tip in combination with different clot compositions. Mechanical thrombectomy was performed 80 times for each tip, using two stent retrievers (Trevo XP ProVue 3/20 mm, 4/20 mm) and four different clot types (hard vs. soft clots, 0-24h vs. 72h aged clots).

RESULTS

Significantly higher first-pass recanalization rates (mTICI 3) were observed for the funnel-shaped tip, 70.0% versus 30.0% for the standard tip (absolute difference, 32; relative difference 57.1%; P < .001), regardless of the clot type and stent retriever. Recanalization could be increased using harder Chandler loop clots versus softer statically generated clots, as well as 0-24h versus 72h aged clots, respectively.

CONCLUSION

The funnel-shaped tip achieved higher first-pass recanalization rates than the smaller standard tip and lower rates of clot abruption at the tip. Clot compositions and aging times impacted recanalization rates.

An experimental study on long term outcomes after magnetic esophageal compression anastomosis in piglets

BACKGROUND/PURPOSE

Previous studies have shown that a patent, watertight esophageal anastomosis can be accomplished safely using specially-shaped magnets in piglets. However, it is unclear whether such a magnetic esophageal compression anastomosis (MECA) remains patent in the long-term. The purpose of this study was to evaluate the long-term outcome of MECA in an experimental pig model over an observation period of 2 months.

METHODS

Ten piglets underwent creation of an MECA with custom-made 8 mm magnets and a U-shaped esophageal bypass loop to allow peroral nutrition at eight weeks of life. Two weeks later, the bypass loop was closed surgically, requiring the pigs to swallow via the newly created magnetic compression anastomosis. The pigs were fed soft chow for 2 months. They were monitored for weight gain and signs of dysphagia. At the endpoint of two months, esophagoscopy and contrast esophagography was performed. After removal of the esophagus, the tissues were macroscopiocally and histologically assessed.

RESULTS

Six piglets survived until the endpoint. In two pigs, closure of the bypass loop failed, these demonstrated mean weight gain of 792 gs/day [95% Confidence interval 575 to 1009 gs/day]. Weight gain in four pigs that exclusively fed via the magnetic anastomosis averaged 577 gs/day [95% confidence interval 434 to 719 gs/day (p = 0.18)]. There were no signs of dysphagia. All magnets passed with the stool within 16 days. After 2 months, a well-formed magnetic compression anastomosis was visible and easily negotiated with a 6.5 mm endoscope. Esophogram and macroscopic findings confirmed patentency of the esophageal anastomoses. Histopathology showed a circular anastomosis lined with contiguous epithelium.

CONCLUSION

MECA creates a long-term functional and patent anastomosis in pigs. This concept may facilitate minimally-invasive esophageal atresia repair by obviating a technically challenging and time-consuming hand-sewn anastomosis.

Does granulocyte-colony stimulating factor stimulate peripheral nerve regeneration? An experimental study on traumatic lesion of the sciatic nerve in rats

AIM OF THE STUDY

To analyse the therapeutic potential of granulocyte-colony stimulating factor (G-CSF) treatment using a rat model of traumatic sciatic nerve lesion.

CLINICAL RATIONALE FOR THE STUDY

G-CSF has proven strong neurotrophic properties in various models of ischaemic and traumatic brain injury. Fewer studies exist regarding the influence of G-CSF on posttraumatic peripheral nerve regeneration. Currently, the possibilities of pharmacological prevention or treatment of mechanical nerve injury are limited, and there is an urgent need to find new treatment strategies applicable in clinical situations.

MATERIAL AND METHODS

A controlled traumatic right sciatic nerve lesion was set using a waterjet device. Three treatment groups were created. In the first group, G-CSF was administered after sciatic nerve injury. The second group received G-CSF before and after trauma, while the third group was treated with glucose 5%-solution. Sciatic nerve function was assessed clinically and electrophysiologically at day 1, and after weeks 1, 2, 4 and 6. Additionally, α-motoneurons of the spinal cord and sciatic nerve fibres were counted at week 6.

RESULTS

Clinically, rats in both G-CSF groups improved faster compared to the control group. Additionally, animals treated with G-CSF had a significantly better improvement of motor potential amplitude and motor nerve conduction velocity at week 6 (p < 0.05). Histologically, G-CSF treatment resulted in a significantly higher number of α-motoneurons and small myelinated nerve fibres compared to placebo treatment (p < 0.05).

CONCLUSIONS AND CLINICAL IMPLICATIONS

Under G-CSF treatment, the recovery of motor nerve conduction velocity and amplitude was enhanced. Further, signs of nerve regeneration and preservation of α-motoneurons were observed. These results indicate that G-CSF might accelerate and intensify the recovery of injured nerves. Thus, treatment with G-CSF may be beneficial for patients with peripheral nerve damage, and should be explored in further clinical studies.

Implantable Sensors Based on Gold Nanoparticles for Continuous Long-Term Concentration Monitoring in the Body

Implantable sensors continuously transmit information on vital values or biomarker concentrations in bodily fluids, enabling physicians to survey disease progression and monitor therapeutic success. However, currently available technologies still face difficulties with long-term operation and transferability to different analytes. We show the potential of a generalizable platform based on gold nanoparticles embedded in a hydrogel for long-term implanted biosensing. Using optical imaging and an intelligent sensor/reference-design, we assess the tissue concentration of kanamycin in anesthetized rats by interrogating our implanted sensor noninvasively through the skin. Combining a tissue-integrating matrix, robust aptamer receptors, and photostable gold nanoparticles, our technology has strong potential to extend the lifetime of implanted sensors. Because of the easy adaptability of gold nanoparticles toward different analytes, our concept will find versatile applications in personalized medicine or pharmaceutical development.

A Continuous Suture Anastomosis Outperforms a Simple Interrupted Suture Anastomosis in Esophageal Elongation

INTRODUCTION

 Long-gap esophageal atresia represents a distinct entity among the esophageal atresia spectrum. In many patients, achieving a reasonable anastomosis depends on some millimeters of tissue. We aimed to determine what effect the suturing technique would have on esophageal ex vivo elongation as it may determine the strength of a primary anastomosis.

MATERIALS AND METHODS

 In an analysis of porcine esophagi from animals for slaughter (100-120 days old with a weight of 100-120 kg), we determined esophageal length gain of simple continuous and simple interrupted suture anastomoses subjected to linear traction until linear breaking strength was reached. Statistical power of 80% was ensured based on an a priori power analysis using five specimens per group in a separate exploratory experiment.

RESULTS

 The simple continuous suture anastomosis in 15 porcine esophagi (  = 4.47 cm, 95% confidence interval: 4.08-4.74 cm) outperformed the simple interrupted suture anastomosis in another 15 esophagi (  = 3.03 cm, 95% confidence interval: 2.59-3.43 cm) in length gain (Δ = 1.44 cm, 95% confidence interval: 0.87-2.01 cm, p < 0.0001).

CONCLUSION

 Simple continuous anastomoses achieved higher length gain compared with simple interrupted suture anastomoses. This effect warrants an experimental assessment in vivo to assess its potential merits for clinical applicability.

Comparing Aachen Minipigs and Pietrain Piglets as Models of Experimental Pediatric Urology to Human Reference Data

INTRODUCTION

Swine had special roles in the development of minimally invasive procedures to treat vesicoureteral reflux, and minipigs have been gaining ground in recent years in experimental pediatric urology as they combine small size with less vulnerable adult physiology, but their suitability as a model has never been assessed. We therefore compared a landrace piglet with a juvenile minipig to elucidate comparability.

METHODS

We evaluated five 3-week old Pietrain piglets and five 3-month old Aachen Minipigs as representatives of landrace and minipig models based on their expected bodyweight being similar to a newborn human. We compared renal weight, volume - via the ellipsoid formula - and ureteral length. In addition, we calculated porcine renal function via Gasthuys' formula. In order to compare the groups with previously published values for infants, we used resampling techniques to allow comparison to humans.

RESULTS

Renal weight was higher in humans than in Pietrain piglets (ΔL = 7.6 g; ΔR = 5.4 g) and Aachen Minipigs (ΔL = 11 g; ΔR = 9.4 g). Renal volumes in humans were higher than in both Pietrain piglets (ΔL = 5.6 mL, p < 0.001; ΔR = 3.7 mL, p = 0.004) and Aachen Minipigs (ΔL = 8.1 mL; ΔR = 6.6 mL; both p < 0.001). Ureteral lengths in humans and both pig breeds were comparable as were estimated renal functions between both pig breeds.

DISCUSSION AND CONCLUSION

Both landrace piglets and juvenile minipigs are suitable models for experimental pediatric urology as parameters did not differ between them. In addition, the anatomic parameters are comparable or smaller than in infants. This might facilitate translational research as technical failure is less likely in larger organs. Additional research is necessary to cover higher age ranges than those included in the present pilot study.

Using simple interrupted suture anastomoses may impair translatability of experimental rodent oesophageal surgery

Background/purpose: Irreproducibility and missing translatability are major drawbacks in experimental animal studies. Hand-sewn anastomoses in oesophageal surgery are usually continuous, whereas those in experimental oesophageal surgery are widely performed using the simple interrupted technique. It has been implicated to be inferior in tolerating anastomotic tension, which we aimed to test in rats due to their importance as an animal model in oesophageal surgery.Methods: We determined linear breaking strengths for the native oesophagus (n = 10), the simple interrupted suture anastomosis (n = 11), and the simple stitch (n = 9) in 8-week old Sprague-Dawley rats. Experiments were powered to a margin of error of 10% around the results of exploratory investigations. The comparison of anastomotic resilience between native organ and simple interrupted suture anastomosis was a priori powered to 99%.Results: Native oesophagi sustained traction forces of 4.25 N (95% CI: 4.03-4.58 N), but the simple interrupted suture anastomosis had only 38.6% (Δ= -2.78 N, 95% CI: -2.46 to -3.11 N, p < .0001) of the resilience of native oesophagi.Conclusions: Oesophageal division and re-anastomosis markedly decreases resilience to traction forces compared to the native organ. This effect is even more pronounced in rats compared to other species and might impair transferability of results.

5-Aminolevulinic Acid Multispectral Imaging for the Fluorescence-Guided Resection of Brain Tumors: A Prospective Observational Study

Fluorescence-guided surgery with five-aminolevulinic acid (5-ALA) is the state-of-the-art treatment of high-grade gliomas. However, intraoperative visualization of 5-ALA under blue light remains challenging, especially when blood covers the surgical field and thereby fluorescence. To overcome this problem and combine the brightness of visible light with the information delivered with fluorescence, we implemented multispectral fluorescence (MFL) in a surgical microscope, a technique that is able to project both information in real-time. We prospectively examined 25 patients with brain tumors. One patient was operated on two different lesions in the same setting. The tumors comprised: six glioblastomas, four anaplastic astrocytomas, one anaplastic oligodendroglioma, two meningiomas, 11 metastatic tumors, one acoustic neuroma, and one ependymoma. The MFL technique with a real-time overlay of fluorescence and white light was compared intraoperatively to the classic blue filter. All lesions were clearly visible and highlighted from the surrounding tissue. The pseudocolor we chose was green, representing fluorescence, with the surrounding brain tissue remaining in its original color. When blood was covering the surgical field, orientation was easy to maintain. The MFL technique opens the way for precise and clear visualization of fluorescence in real-time under white light. It can be easily used for the resection of all tumors accumulating 5-ALA. Drawbacks of classic PpIX fluorescence such as hidden fluorescence, intraoperative changes could be overcome with the presence of additional white light in MFL technique.

Real-Time Overlapping of Indocyanine Green—Video Angiography With White Light Imaging for Vascular Neurosurgery: Technique, Implementation, and Clinical Experience

BACKGROUND

Fluorescent-guided techniques in vascular neurosurgery can be demonstrated via black and white indocyanine green videoangiography (ICG-VA). Multispectral imaging (MFL) is a new method, which overlaps fluorescence with the white light and provides a fluorescent white light augmented reality image to the surgeon.

OBJECTIVE

To investigate (a) whether MFL can enhance the visualization of the blood-flow with simultaneous visualization of the anatomic structures and (b) if MFL can ergonomically improve the microvascular surgical treatment compared to ICG-VA.

METHODS

A digital imaging of the blood flow after intravenous injection of ICG on 7 pigs was performed in real time under white light, standard fluorescence, and MFL. The blood flow was interrupted with a surgical clip, demonstrating the blockage of the blood flow. We prospectively included 30 patients with vascular deformities. The vasculature was visualized on the microscope's monitor and through the microscope's eyepiece.

RESULTS

In the animal experiment, the visualization of the anatomy and the blood flow under MFL produced high resolution images. The occlusion of blood vessels demonstrated sufficiently the blockage of tissue perfusion and its reperfusion after clip removal. During all 30 surgical cases, the MFL technique and the direct delivery of the pseudo-colored image through the eyepiece allowed for enhanced anatomic and dynamic data.

CONCLUSION

MFL was shown to be superior to the classic ICG-VA, delivering enhanced data and notably improving the workflow due to the simultaneous and precise white light visualization of the blood flow and the surrounding anatomic structures.

An experimental study on magnetic esophageal compression anastomosis in piglets

INTRODUCTION

Fashioning a patent, watertight anastomosis in patients with esophageal atresia is a challenging task in pediatric surgery, particularly when performed under tension. A reproducible suture-less alternative would decrease operative time. We evaluated magnetic esophageal compression anastomoses in a novel bypass-loop swine model.

METHODS

Eight-week-old piglets underwent thoracotomy to mobilize the esophagus at the carina to create a U-shaped loop. Custom-made 8 mm diameter Neodymium Magnets were inserted into the esophagus proximal and distal to the loop, then mated side-to-side at the future anastomosis site. Pigs were observed for 8 (n = 4), 10 (n = 6), and 12 (n = 2) days and then sacrificed. The magnetic compression anastomosis was evaluated macroscopically, by radiography, burst pressure testing, and histology.

RESULTS

All 12 pigs survived until the endpoint. Separation of the magnets occurred at a median of 9 days. Contrast esophagrams showed patency and no leak. All anastomoses withstood pressures well over 13 kPa without leak. Histopathology showed epithelialized circular scar tissue.

CONCLUSION

Magnetic compression anastomoses of the esophagus using our specially-designed magnets are formed between the 8th and 10th postoperative day, are patent and mechanically resistant to supraphysiologic intraluminal pressures. These data lay the basis for a potential clinical application in patients born with esophageal atresia.

LEVEL OF EVIDENCE

Not applicable (experimental animal study).

Using multidimensional scaling in model choice for congenital oesophageal atresia: similarity analysis of human autopsy organ weights with those from a comparative assessment of Aachen Minipig and Pietrain piglets

Swine models had been popular in paediatric oesophageal surgery in the past. Although being largely replaced by rodent models, swine experienced a revival with the establishment of minipig models. However, none of them has ever been investigated for similarity to humans. We conducted a pilot study to determine whether three-week old Pietrain piglets and three-month old Aachen Minipigs are suitable for experimental paediatric oesophageal atresia surgery. We tested the operation's feasibility, performed a necropsy, weighed organs, measured organ length and calculated relative weights and lengths, and measured laboratory parameters. We used multidimensional scaling to assess the similarity of the swine breeds with previously published human data. Pietrain piglets had a higher a priori bodyweight than Aachen Minipigs (Δ = 1.31 kg, 95% confidence interval (CI): 0.37-2.23, p = 0.015), while snout-to-tail length was similar. Pietrain piglets had higher absolute and relative oesophageal lengths (Δ = 5.43 cm, 95% CI: 2.2-8.6; p = 0.0062, q1* = 0.0083 and Δ = 11.4%, 95% CI: 5.1-17.6; p = 0.0025, q3* = 0.0053). Likewise, absolute and relative small intestinal lengths were higher in Pietrains, but all other parameters did not differ, with the exception of minor differences in laboratory parameters. Multidimensional scaling revealed three-week old Pietrain piglets to be similar to two-month old humans based on their thoracoabdominal organ weights. This result indicates three-week old Pietrain piglets are a suitable model of paediatric oesophageal atresia surgery, because clinically many procedures are performed at around eight weeks age. Three-month old Aachen Minipigs were more dissimilar to eight-week old humans than three-week old Pietrain piglets.

Esophageal Blood Flow May Not Be Directly Influenced by Anastomotic Tension: An Exploratory Laser Doppler Study in Swine

BACKGROUND

 Anastomotic tension has been linked to leakage and stenosis in esophageal surgery in both adults and children. We aimed to determine the effects of esophageal topography, operative technique, and anastomotic tension on esophageal blood flow.

MATERIALS AND METHODS

 We divided and reanastomosed the esophagi at the carinal level with increasing levels of anastomotic tension in piglets (n = 10) and sham controls (n = 4). We examined esophageal blood flow pre- and postoperatively using laser Doppler flowmetry at the anastomosis and two predetermined proximal and distal points. Blood flow in relation to distance from the anastomosis was examined by multivariate linear regression.

RESULTS

 Thoracotomy alone did not influence perfusion at the carinal level in shams (Δ = 3.13 laser Doppler units, 95% confidence interval: -3.4 to 9.7, p = 0.2686). We constructed a (F[5,134] = 6.34, p < 0.0001) multinomial regression model based on distance to the anastomotic site and pre-/postoperative measurements (adjusted R ² = 0.1624). Tissue blood flow was higher distant to the carina, but lower postoperatively and not influenced by the tension resulting from the extent of resection (F[1, 8] = 1.134, p = 0.318).

CONCLUSION

 Esophageal blood flow is higher at greater distances to the carinal level and hampered by esophageal division and reanastomosis. The extent of resection has less influence than previously assumed. Therefore, leakage and stenosis after esophageal anastomosis may not solely be caused by insufficient anastomotic blood flow.

Crucial role for Nox2 and sleep deprivation in aircraft noise-induced vascular and cerebral oxidative stress, inflammation, and gene regulation

Aims

Aircraft noise causes endothelial dysfunction, oxidative stress, and inflammation. Transportation noise increases the incidence of coronary artery disease, hypertension, and stroke. The underlying mechanisms are not well understood. Herein, we investigated effects of phagocyte-type NADPH oxidase (Nox2) knockout and different noise protocols (around-the-clock, sleep/awake phase noise) on vascular and cerebral complications in mice.

Methods and results

C57BL/6j and Nox2^−/− (gp91phox^−/−) mice were exposed to aircraft noise (maximum sound level of 85 dB(A), average sound pressure level of 72 dB(A)) around-the-clock or during sleep/awake phases for 1, 2, and 4 days. Adverse effects of around-the-clock noise on the vasculature and brain were mostly prevented by Nox2 deficiency. Around-the-clock aircraft noise of the mice caused the most pronounced vascular effects and dysregulation of Foxo3/circadian clock as revealed by next generation sequencing (NGS), suggesting impaired sleep quality in exposed mice. Accordingly, sleep but not awake phase noise caused increased blood pressure, endothelial dysfunction, increased markers of vascular/systemic oxidative stress, and inflammation. Noise also caused cerebral oxidative stress and inflammation, endothelial and neuronal nitric oxide synthase (e/nNOS) uncoupling, nNOS mRNA and protein down-regulation, and Nox2 activation. NGS revealed similarities in adverse gene regulation between around-the-clock and sleep phase noise. In patients with established coronary artery disease, night-time aircraft noise increased oxidative stress, and inflammation biomarkers in serum.

Conclusion

Aircraft noise increases vascular and cerebral oxidative stress via Nox2. Sleep deprivation and/or fragmentation caused by noise triggers vascular dysfunction. Thus, preventive measures that reduce night-time aircraft noise are warranted.

Evaluation of a New Multiparameter Brain Probe for Simultaneous Measurement of Brain Tissue Oxygenation, Cerebral Blood Flow, Intracranial Pressure, and Brain Temperature in a Porcine Model

BACKGROUND

A novel multiparameter brain sensor (MPBS) allows the simultaneous measurement of brain tissue oxygenation (ptiO₂), cerebral blood flow (CBF), intracranial pressure (ICP), and brain temperature with a single catheter. This laboratory investigation evaluates the MPBS in an animal model in relation to established reference probes.

METHODS

The study group consisted of 17 juvenile male pigs. Four MPBS and four reference probes were implanted per pig and compared simultaneously. The measured parameters were challenged by standardized provocations such as hyperoxia, dobutamine, and norepinephrine application, hypercapnia and hypoxia in combination with and without a controlled cortical impact (CCI) injury. Mean values over 2 min were collected for predefined time points and were analyzed using Bland-Altman plots.

RESULTS

The protocol was successfully conducted in 15 pigs of which seven received CCI. ICP and ptiO₂ were significantly influenced by the provocations. Subtraction of MPBS from reference values revealed a mean difference (limits of agreement) of 3.7 (- 20.5 to 27.9) mm Hg, - 2.9 (- 7.9 to 2.1) mm Hg, and 5.1 (- 134.7 to 145.0) % for ptiO₂, ICP, and relative CBF, respectively.

CONCLUSIONS

The MPBS is a promising measurement tool for multiparameter neuromonitoring. The conducted study demonstrates the in vivo functionality of the probe. Comparison with standard probes revealed a deviation which is mostly analogous to other multiparameter devices. However, further evaluation of the device is necessary before it can reliably be used for clinical decision making.

Technical Aspects in Esophageal Lengthening: An Investigation of Traction Procedures and Suturing Techniques in Swine

INTRODUCTION

 Traction procedures are useful to preserve the child's own esophagus in long-gap forms of esophageal atresia. To date, it remains unclear what suture size or position of the traction sutures is optimal to account for differences in anatomy and to reduce the risk of traction sutures being torn out of the esophageal tissue.

MATERIALS AND METHODS

 Explanted porcine esophagi (from swine aged 100-120 days and weighing 100-120 kg) were divided at the carinal level. Traction sutures were either placed circumferentially or only in the dorsal wall and the breaking strength-circumferential disruption of the muscular layer-was measured. Suture size (USP 4-0 vs. 5-0) was also evaluated in a similar way.

RESULTS

 Neither traction suture position did not influence breaking strengths between circumferentially placed traction sutures or those exclusively placed in the dorsal esophageal wall (Δ = 0.47 N, 95% confidence interval: -2.83 to 3.76 N, p = 0.771, n = 11 per group) nor differing suture sizes of USP 4-0 and USP 5-0 (Δ = 1.46 N, 95% confidence interval: -3.2 to 0.28 N, p = 0.0946, n = 9 per group) affected breaking strengths.

CONCLUSION

 Suture size and suture positioning do not affect mechanical stability in Foker's procedure and therefore can be adapted as needed according to patient's anatomy and size.

Confocal-Assisted Multispectral Fluorescent Microscopy for Brain Tumor Surgery

Optimal surgical therapy for brain tumors is the combination of complete resection with minimal invasion and damage to the adjacent normal tissue. To achieve this goal, we need advanced imaging techniques on a scale from macro- to microscopic resolution. In the last decade, the development of fluorescence-guided surgery has been the most influential breakthrough, marginally improving outcomes in brain tumor surgery. Multispectral fluorescence microscopy (MFL) is a novel imaging technique that allows the overlapping of a fluorescent image and a white light image in real-time, with delivery of the merged image to the surgeon through the eyepieces of a surgical microscope. MFL permits the detection and characterization of brain tumors using fluorescent molecular markers such as 5-aminolevulinic acid (5-ALA) or indocyanine green (ICG), while simultaneously obtaining high definition white light images to create a pseudo-colored composite image in real-time. Limitations associated with the use of MFL include decreased light imaging intensity and decreased levels of magnification that may compromise maximal tumor resection on a cellular scale. Confocal laser endomicroscopy (CLE) is another novel advanced imaging technique that is based on miniaturization of the microscope imaging head in order to provide the possibility of in vivo microscopy at the cellular level. Clear visualization of the cellular cytoarchitecture can be achieved with 400-fold-1,000-fold magnification. CLE allows on the one hand the intra-operative detection and differentiation of single tumor cells (without the need for intra-operative histologic analysis of biopsy specimens) as well as the definition of borders between tumor and normal tissue at a cellular level, dramatically improving the accuracy of surgical resection. The application and implementation of CLE-assisted surgery in surgical oncology increases not only the number of options for real-time diagnostic imaging, but also the therapeutic options by extending the resection borders of cancer at a cellular level and, more importantly, by protecting the functionality of normal tissue in the adjacent areas of the human brain. In this article, we describe our experience using these new techniques of confocal-assisted fluorescent surgery including analysis on the technology, usability, indications, limitations, and further developments.

Five-fold Gastrointestinal Electrical Stimulation With Electromyography-based Activity Analysis: Towards Multilocular Theranostic Intestinal Implants

Background/Aims

Motility disorders are common and may affect the entire gastrointestinal (GI) tract but current treatment is limited. Multilocular sensing of GI electrical activity and variable electrical stimulation (ES) is a promising option. The aim of our study is to investigate the effects of adjustable ES on poststimulatory spike activities in 5 GI segments.

Methods

Six acute porcine experiments were performed with direct ES by 4 ES parameter sets (30 seconds, 25 mA, 500 microseconds or 1000 microseconds, 30 Hz or 130 Hz) applied through subserosal electrodes in the stomach, duodenum, ileum, jejunum, and colon. Multi-channel electromyography of baseline and post-stimulatory GI electrical activity were recorded for 3 minutes with hook needle and hook-wire electrodes. Spike activities were algorithmically calculated, visualized in a heat map, and tested for significance by Poisson analysis.

Results

Post-stimulatory spike activities were markedly increased in the stomach (7 of 24 test results), duodenum (8 of 24), jejunum (23 of 24), ileum (18 of 24), and colon (5 of 24). ES parameter analysis revealed that 80.0% of the GI parts (all but duodenum) required a pulse width of 1000 microseconds, and 60.0% (all but jejunum and colon) required 130 Hz frequency for maximum spike activity. Five reaction patterns were distinguished, with 30.0% earlier responses (type I), 42.5% later or mixed type responses (type II, III, and X), and 27.5% non-significant responses (type 0).

Conclusions

Multilocular ES with variable ES parameters is feasible and may significantly modulate GI electrical activity. Automated electromyography analysis revealed complex reaction patterns in the 5 examined GI segments.

Beyond Magnamosis: A Method to Test Sutureless Esophageal Anastomotic Devices in Living Swine by Creating an Esophageal Bypass Loop for Natural Oral Nutrition

Introduction: Thoracoscopic esophageal atresia repair has become increasingly popular, but is still limited to a few expert centers and has some challenges and shortcomings. One of them has a longer operation time compared with conventional thoracotomy. Magnetic compression anastomosis may contribute toward shorter operation times by avoiding the time-consuming anastomotic suturing. We aimed to establish a method of testing sutureless anastomoses in parallel to having swine eating the natural way. Materials and Methods: We used four juvenile Pietrain swine-aged 8 weeks, weighing 15 kg-to establish a living animal model after preceding cadaver tests. Esophagi were fully mobilized through right-sided thoracotomy to gain sufficient length to create an esophageal loop that served as a bypass for food after magnet deployment. Six hours later, patency of the bypass esophageal loop was assessed by passing an orogastric tube and by allowing swine to drink methylene blue-stained water. We also tested the device stability using the classical burst pressure test. Results: The esophageal lumen was patent for feeding tube. Swine were able to drink and methylene blue colored fluid reached the stomach. Clinical signs of obstruction such as regurgitation or coughing were absent. Magnets sustained burst pressures up to 200,000 Pascal until they became disrupted. At 6 hours after magnet placing, we already saw subtle esophageal mucosa erosions indicating the beginning of anastomotic formation. Conclusion: This animal model is useful to test different magnet designs for sutureless esophageal anastomosis or even future devices for in vivo tissue engineering.

Bodyweight, not age, determines oesophageal length and breaking strength in rats

BACKGROUND/PURPOSE

Delayed primary repair is still the method of choice in the management of long-gap oesophageal atresia in many centres, but the timing of anastomoses varies. Some assume the infant's bodyweight to be an important factor, whereas others prefer age. We therefore aimed to clarify whether age or bodyweight determined oesophageal length in a rodent model.

METHODS

We explanted the oesophagi of 20 Sprague-Dawley rats, aged 15 to 444 days (n = two per time point), measured bodyweight, oesophageal length, weight, and linear breaking strength to measure tissue resilience. Univariate and multivariate regression analyses were conducted to determine the influence of age and bodyweight on oesophageal length and linear breaking strength.

RESULTS

All parameters were highly correlated (R > 0.8), except for age and linear breaking strength (R = 0.65). Both age and bodyweight were univariate significant predictors of oesophageal length, weight, and linear breaking strength (p < 0.0001). Multivariate analyses showed bodyweight to be a significant predictor of oesophageal length (p < 0.0001), whereas age was not (p = 0.18) [adjusted R² = 0.9031]. This was also true for linear breaking strength (p = 0.0007 and p = 0.97, respectively) [adjusted R² = 0.71]. Moreover, the influence of age was negligible, as the adjusted R² and the regression coefficient of bodyweight and its 95% confidence interval were almost identical between univariate und multinomial regressions.

CONCLUSIONS

Only weight determines oesophageal length and tissue resilience in rodents, whereas age is irrelevant. If a similar relationship exists in humans, it may facilitate choosing the optimum time point for delayed primary anastomosis.

LEVEL OF EVIDENCE

IV - Experimental Paper.

Esophageal Biomechanics Revisited: A Tale of Tenacity, Anastomoses, and Suture Bite Lengths in Swine

BACKGROUND

Anastomotic tension has repeatedly been associated with anastomotic leakages after esophagectomy for cancer or esophageal atresia repair. We therefore aimed to determine which anastomotic technique would come as close as possible to the native esophagus in sustaining traction forces. Constant traction for several minutes at esophageal remnants and large suture bites are also considered relevant in long-gap esophageal atresia repair.

METHODS

Porcine esophagi were subjected to linear traction using a motorized horizontal test stand. We compared breaking strengths of native esophagi to simple continuous, simple interrupted, stapled, and barbed suture anastomoses. We also investigated the effects of suture bite length and phases of constant traction on breaking strengths and powered all experiments to at least 80% using exploratory investigations (n = 5 per group).

RESULTS

Continuous suture anastomoses had a breaking strength comparable to native esophagi (Δ = -5.25 Newton, 95% confidence interval: -10.69 to 0.19 Newton, p = 0.058) and outperformed all other investigated anastomoses (Δ ≥14.01 Newton, p ≤ 0.02). Breaking strength correlated with suture bite length (R = 0.905) and predicted breaking strength for the simple stitch (adjusted R² = 0.812, p < 0.0001), but not for anastomoses. Phases of incrementally increasing constant traction resulted in higher breaking strengths (Δ = 13.36 Newton, 95% confidence interval: 9.93 to 16.79 Newton, p < 0.0001) and higher length gain (Δ = 1.06 cm, 95% confidence interval: 0.65 to 1.48 cm, p < 0.0001) compared with controls.

CONCLUSIONS

Only simple continuous anastomoses achieved the linear breaking strength of native tissue. Our study provides important insights in tolerance to traction forces, but its results have to be corroborated in living animals as anastomotic leakages are multifactorial processes.

Accelerometer-Based Assessment of Intestinal Peristalsis: Toward Miniaturized Low-Power Solutions for Intestinal Implants

Intestinal electrical stimulation via implants is already used to treat several disorders like constipation or incontinence. Stimulation parameters are most often empiric and not based on systematic studies. One prerequisite to evaluate effects of intestinal electrical stimulation is a direct assessment of intestinal motility. Some common methods are strain gauge transducers or manometry. With both the methods, it is not possible to record the exact 3-D movement. Therefore, we established a new method to record gastrointestinal motility with ultraminiaturized accelerometers, directly glued to the outer surface of the stomach, small intestine, and colon. With this technique, we were able to record precise local motility changes after electrical stimulation. Due to the low energy demand and the small size of the system, it is potentially useful for chronic measurements at multiple sites of the intestinal tract. We will present our first results regarding stimulation-dependent motility changes using up to eight implanted accelerometers in an acute pig model.

Motility analysis by means of video tracked markers

The motility of the gastrointestinal tract is crucial for digestive activity and dysfunction can lead to severe disease pattern. A method for analysing the motility is needed when treatment approaches shall be evaluated. Therefore markers attached to different locations on the stomach and the bowel of pigs are video tracked in this research study. The markers are designed to provide a high contrast and have an adhesive side for fixation. Above the operation field a video camera has been placed to film the markers during the procedure. To analyse the video data a special algorithm has been implemented. The algorithm requires a registration process at the beginning of each recording which allows the parallel tracking of multiple markers. After the registration the algorithm tracks the position of the marker frame by frame. Each frame is converted into a greyscale picture by adding specified colour values of each pixel. This allows emphasizing certain colours. The centre of the marker is determined by computing the horizontal and vertical centre of the marker starting at the corresponding marker position of the previous frame. After completion the data is stored as coordinates and a video with the marker position displayed for further processing. For advanced analysis the data can be synchronized with electromyography signals, for example. The marked videos show a promising tracking of the markers. However, if the algorithm loses track of a marker during a recording, it is unlikely to relocate it due to the successive processing of the frames. Nevertheless this method provides a simple and easy to use solution for movement detection of the gastrointestinal tract.

Electrical stimulation with motility analysis of five parts of the gastrointestinal tract

Gastrointestinal (GI) motility disorders are frequent and clinically significant conditions with impairment of patient’s quality of life. Examples range from upper GI symptoms such as dysphagia and gastroparesis to lower GI manifestations, namely chronic-intestinal pseudo obstruction, diarrhea and constipation. Furthermore, postoperative motility disorders are common. Currently, available pharmacological or dietetic treatment options are limited. Since GI motility is based on myoelectric activity, electrical stimulation (ES) is a promising alternative. Numerous studies have demonstrated suitable pacing strategies and parameters in different GI segments. However, results of multilocular ES are rare. We report the first experimental study to evaluate ES of five GI parts in a porcine model. Multi-channel electromyography (EMG) recordings of gastrointestinal baseline and poststimulatory electrical activity were realized together with video-based marker tracking (VBMT). ES provoked visible GI contractions and appeared to modulate frequencies of slow waves and spikes. Further investigations are needed for analysis of locoregional and cross-organ effects of ES on the GI tract.

Cecal Resection with Bipolar Sealing Devices in a Rat Model

Background: Bipolar sealing devices are routinely used to seal blood vessels. The aim of the study is to evaluate the feasibility and safety of colonic sealing with the use of the bipolar energy devices in rats as model for experimental appendectomy. Methods: Seventy-five male Wistar rats underwent a cecal resection with four different bipolar sealing devices or a linear stapler. The harvesting procedure was performed immediately or at postoperative day (POD) 7. The sealing front bursting pressure (BP) was measured in both groups. At POD7, the resection line was clinically examined and the hydroxyproline (HDP) levels were determined. Hematoxylin and Eosin (H&E) staining was used for histopathological evaluation of the sealing front as well. Results: There was no mortality and no insufficiency. The BPs between the bipolar sealing devices showed no statistical differences. The early phase of the seal (POD 0) provides a low BP with an 30.8% increase until POD 7. The BPs in the stapler group showed significant better values. The hydroxyproline levels did not differ statistically between the groups. Histopathologically, there were more signs of ischemic necrosis in the stapler group than in the sealing devices groups. Conclusion: The resection and sealing of the cecum as an experimental appendectomy model with the use of bipolar energy devices proved feasible and safe in rats. The different energy devices in this study produce comparable results. To justify clinical practice in humans, several studies on the underlying mechanisms of early stage wound healing are needed.

Pringle maneuver increases the risk of anastomotic leakage after colonic resection in rats

BACKGROUND

Many centers use the Pringle's maneuver during liver resections. Since this maneuver might impair healing of bowel anastomoses, we evaluated its influence on the healing of colonic anastomosis in rats.

METHODS

Male Wistar rats underwent median laparotomy and sigmoid resection with end-to-end anastomosis under inhalation anesthesia. Thereafter, rats received a 25 minutes Pringle's maneuver (PM, group 1) or were kept under anesthesia for the same period of time (group 2). The anastomotic bursting pressure (BP) was measured on postoperative days (POD) 3, 6 and 9. Hematoxylin and Eosin (H&E) staining was used for histopathological evaluation of the anastomosis. The Mann-Whitney U and χ² -tests were used, p<0.05 values were considered significant.

RESULTS

All animals (n=48) lost body weight (BW) until POD3 (95.2% vs. 85.7%, p=0.003), and BW remained lower after PM (106.2% vs. 92.8%, p=0.001). The anastomotic BP was lower in group 1 compared to group 2 on POD 3 (116mmHg vs. 176.28mmHg, p=0.001), POD 6 (182.8mmHg vs. 213mmHg, p=0.029) and POD 9 (197.2mmHg vs. 251.7mmHg, p=0.009), and mortality was higher in group 1 (1 vs. 7, p=0.022).

CONCLUSIONS

Pringle's maneuver increases anastomotic complications in rats. Therefore, a Pringle's maneuver should be avoided during simultaneous liver and colorectal surgery.

Transcutaneous sacral nerve stimulation for intraoperative verification of internal anal sphincter innervation

BACKGROUND

The current standard for pelvic intraoperative neuromonitoring (pIONM) is based on intermittent direct nerve stimulation. This study investigated the potential use of transcutaneous sacral nerve stimulation for non-invasive verification of pelvic autonomic nerves.

METHODS

A consecutive series of six pigs underwent low anterior rectal resection. For transcutaneous sacral nerve stimulation, an array of ten electrodes (cathodes) was placed over the sacral foramina (S2 to S4). Anodes were applied on the back, right and left thigh, lower abdomen, and intra-anally. Stimulation using the novel method and current standard were performed at different phases of the experiments under electromyography of the autonomic innervated internal anal sphincter (IAS).

KEY RESULTS

Transcutaneous stimulation induced increase of IAS activity could be observed in each animal under specific cathode-anode configurations. Out of 300 tested configurations, 18 exhibited a change in the IAS activity correlated with intentional autonomic nerve damage. The damage resulted in a significant decrease of the relative area under the curve of the IAS frequency spectrum (P<.001). Comparison of the IAS spectra under transcutaneous and direct stimulation revealed no significant difference (after rectal resection: median 5.99 μV•Hz vs 7.78 μV•Hz, P=.12; after intentional nerve damage: median -0.27 μV•Hz vs 3.35 μV•Hz, P=.29).

CONCLUSIONS AND INFERENCES

Non-invasive selective transcutaneous sacral nerve stimulation could be used for verification of IAS innervation.

Potent low dose platelet inhibitory effects of clopidogrel and aspirin on coronary thrombus formation in an animal model of acute unstable angina

Application of clopidogrel before percutaneous coronary intervention in patients with acute coronary syndrome reduces the risk of cardiac events. Clopidogrel administration before surgery increases bleeding complications after CABG. Therefore, the antithrombotic effect of the low-dose combination of clopidogrel and aspirin was investigated in an in vivo pig model of coronary artery thrombus formation with cyclic flow reductions. The platelet inhibitory effect was determined by platelet aggregation and CFR, according to the methodology described by Folts. CFR were initiated by endothelial damage and placement of a constrictor around the LAD. 30 min after CFR were established, clopidogrel (0.1 mg/kg or5 mg/kg), aspirin (1 mg/kg or 7 mg/kg) or LDC (0.1 mg/kg clopidogrel and 1 mg/kg aspirin) were administered orally. CFR-frequency was determined for further 240 min. CFR-frequency (CFR/30 min) was significantly reduced at 60 min in response to aspirin (7 mg/kg, −48%, p<0.05), and at 120 min in response to clopidogrel (5 mg/kg, −65%, p<0.05) but not at low doses of either compound. In contrast, LDC of clopidogrel (0.1 mg/kg) plus aspirin (1 mg/kg) resulted in a complete and rapid abrogation of CFR at 90 min (−70%, p<0.05). Furthermore, LDC led to reduction of platelet aggregation when CFR-frequency was already significantly decreased. In contrast, high dose groups presented a significant reduction of platelet aggregation prior to CFR-frequency decrease. Low dose combination of clopidogrel plus aspirin demonstrates a potent over additive anti-thrombotic effect in vivo with a significant reduction in thrombus formation early after drug application. The effect occurs before inhibition of platelet aggregation is detectable.

Spreading depression and focal venous cerebral ischemia enhance cortical neurogenesis

Endogenous neurogenesis can arise from a variety of physiological stimuli including exercise, learning, or "enriched environment" as well as pathological conditions such as ischemia, epilepsy or cortical spreading depression. Whether all these conditions use a common trigger to set off endogenous neurogenesis is yet unclear. We hypothesized that cortical spreading depression (CSD) induces neurogenesis in the cerebral cortex and dentate gyrus after cerebral venous ischemia. Forty-two Wistar rats alternatively underwent sham operation (Sham), induction of ten CSDs or venous ischemia provoked via occlusion of two adjacent superficial cortical vein followed by ten induced CSDs (CSD + 2-VO). As an additional control, 15 naïve rats received no intervention except 5-bromo-2'-deoxyuridine (BrdU) treatment for 7 days. Sagittal brain slices (40 μm thick) were co-stained for BrdU and doublecortin (DCX; new immature neuronal cells) on day 9 or NeuN (new mature neuronal cells) on day 28. On day 9 after sham operation, cell proliferation and neurogenesis occurred in the cortex in rats. The sole induction of CSD had no effect. But on days 9 and 28, more proliferating cells and newly formed neurons in the ipsilateral cortex were observed in rats subjected to CSD + 2VO than in rats subjected to sham operation. On days 9 and 28, cell proliferation and neurogenesis in the ipsilateral dentate gyrus was increased in sham-operated rats than in naïve rats. Our data supports the hypothesis that induced cortical neurogenesis after CSD + 2-VO is a direct effect of ischemia, rather than of CSD alone.

Surface Electromyography Reliably Records Electrophysiologically Evoked Internal Anal Sphincter Activity: A More Minimally Invasive Approach for Monitoring Extrinsic Innervation

BACKGROUND

Even in the case of minimally invasive pelvic surgery, sparing of the autonomic nerve supply is a prerequisite for maintaining anal sphincter function. Internal anal sphincter (IAS) innervation could be electrophysiologically identified based on processed electromyographic (EMG) recordings with conventional bipolar needle electrodes (NE). This experimental study aimed for the development of a minimally invasive approach via intra-anal surface EMG for recordings of evoked IAS activity.

METHODS

Six male pigs underwent nerve-sparing low anterior rectal resection. Electric autonomic nerve stimulations were performed under online-processed EMG of the IAS. EMG recordings were simultaneously carried out with conventional bipolar NE as the reference method and newly developed intra-anal surface electrodes (SE) in different designs.

RESULTS

In all experiments, the IAS activity could be continuously visualized via EMG recordings based on NE and SE. The median number of bipolar electric stimulations per animal was 27 (range 5-52). The neurostimulations resulted in significant EMG amplitude increases for both recording types [NE: median 3.0 µV (interquartile range, IQR 2.8-3.5) before stimulation vs. 7.1 µV (IQR 3.9-13.8) during stimulation, p < 0.001; SE: median 3.6 µV (IQR 3.1-4.3) before stimulation vs. 6.8 µV (IQR 4.8-10.3) during stimulation, p < 0.001].

CONCLUSIONS

Intra-anal SE enabled reliable EMG of electrophysiologically evoked IAS activity similar to the conventional recording via NE. The transfer of the method to access platforms for transanal total mesorectal excision or robotics may offer a practical more minimally invasive approach for monitoring extrinsic innervation.

Description of the response of a new multi-parametric brain sensor to physiological and pathophysiological challenges in the cortex of juvenile pigs

AIM

Monitoring of intracranial pressure (ICP), local cerebral blood flow (CBF) and oxygen is part of modern intensive critical care medicine. Preclinical evaluation of newly developed catheters that should monitor several parameters simultaneously is reported poorly in the literature. The goal of our study was (1) to evaluate a new multi-parametric sensor in brain tissue and (2) to establish a testing protocol using pathophysiological challenges that target measured parameters of the sensor and autoregulatory boundaries and could be used as preclinical standard protocol in future studies.

MATERIAL AND METHODS

We describe data from 12 new multi-parametric brain sensors (MPBS) that were implanted into 3 porcine brains and combined measurement of brain tissue oxygenation (ptiO2), ICP, CBF and brain temperature for the first time. Pigs were treated with a period of hyperoxygenation, hypercapnia, hypoxia, dobutamine, and norepinephrine.

RESULTS

None of the 12 MPBS failed. Our testing protocol induced standardized pathophysiological changes that were picked up by the new MPBS as significant alterations in brain ptiO2, ICP and CBF. The magnitude of changes was >20% in most tested MPBS.

CONCLUSION

An experimental protocol with pre-defined end-points for O2, CO2, blood pressure and cardiac output should be standardized and reported if new sensors for multi-parametric brain monitoring are evaluated. The use of several sensors per brain of only a few animals is sufficient to determine functionality of new sensors in vivo as basis for a larger study with reference sensors and brain injury.

Endothelial LRP1 transports amyloid-β(1-42) across the blood-brain barrier

According to the neurovascular hypothesis, impairment of low-density lipoprotein receptor-related protein-1 (LRP1) in brain capillaries of the blood-brain barrier (BBB) contributes to neurotoxic amyloid-β (Aβ) brain accumulation and drives Alzheimer's disease (AD) pathology. However, due to conflicting reports on the involvement of LRP1 in Aβ transport and the expression of LRP1 in brain endothelium, the role of LRP1 at the BBB is uncertain. As global Lrp1 deletion in mice is lethal, appropriate models to study the function of LRP1 are lacking. Moreover, the relevance of systemic Aβ clearance to AD pathology remains unclear, as no BBB-specific knockout models have been available. Here, we developed transgenic mouse strains that allow for tamoxifen-inducible deletion of Lrp1 specifically within brain endothelial cells (Slco1c1-CreER(T2) Lrp1(fl/fl) mice) and used these mice to accurately evaluate LRP1-mediated Aβ BBB clearance in vivo. Selective deletion of Lrp1 in the brain endothelium of C57BL/6 mice strongly reduced brain efflux of injected [125I] Aβ(1-42). Additionally, in the 5xFAD mouse model of AD, brain endothelial-specific Lrp1 deletion reduced plasma Aβ levels and elevated soluble brain Aβ, leading to aggravated spatial learning and memory deficits, thus emphasizing the importance of systemic Aβ elimination via the BBB. Together, our results suggest that receptor-mediated Aβ BBB clearance may be a potential target for treatment and prevention of Aβ brain accumulation in AD.

Comparative analysis of in situ versus ex situ perfusion on micro circulation in liver procurement--an experimental trial in a porcine model

INTRODUCTION

The Achilles heel of liver transplantation remains the biliary system. The crucial step for liver preservation is effective rinsing and perfusion of the peribiliary plexus (PBP). Due to the physiology of the vascular tree, it seems almost impossible to achieve the necessary physiologic ranges of pressure and flow by the in situ perfusion technique. We investigated the role of additional ex situ perfusion via the hepatic artery in this animal model.

MATERIALS AND METHODS

Fifteen German Landrace pigs underwent standardized multiorgan procurement. In situ perfusion and additional ex situ perfusion were performed consecutively. Meanwhile the external pressure applied to the perfusion system was increased stepwise. To visualize the effects on the liver parenchyma and PBP, we administered colored microparticles (MPs; 10 μm). Frozen sections of the explanted liver were studied histologically by quantitative evaluation of the MPs.

RESULTS

Ex situ perfusion was able to build up significantly higher values of pressure (P < .001) and flow (P < .001) than in situ perfusion. Those of ex situ perfusion reached physiological levels under application of an external pressure of 200 mm Hg. Considering the liver parenchyma, significantly higher amounts of MPs originating from ex situ perfusion were evident (P < .001) and PBP (P < .001).

CONCLUSION

MPs provide an appropriate tool to determine organ perfusion quantitatively in experimental models. Considering flow, pressure, and microcirculation, we consider that additional ex situ perfusion of the liver is more effective than in situ perfusion.

Neuroprotective effect of ceftriaxone on the penumbra in a rat venous ischemia model

OBJECTIVE

Glutamate transporter-1 (GLT-1) maintains low concentrations of extracellular glutamate by removing glutamate from the extracellular space. It is controversial, however, whether upregulation of GLT-1 is neuroprotective under all ischemic/hypoxic conditions. Recently, a neuroprotective effect of preconditioning with a β-lactam antibiotic ceftriaxone (CTX) that increases expression of GLT-1 has been reported in animal models of focal ischemia. On the other hand, it is said that CTX does not play a neuroprotective role in an in vitro study. Thus, we examined the effect of CTX on ischemic injury in a rat model of two-vein occlusion (2VO). This model mimics venous ischemia during, e.g. tumor surgery, a clinical situation that is best suitable for pretreatment with CTX.

METHODS

CTX (100mg/kg, 200mg/kg per day) or vehicle (0.9% NaCl) was intraperitoneally injected into Wistar rats for 5days before venous ischemia (n=57). Then, animals were prepared for occlusion of two adjacent cortical veins (2VO) by photothrombosis with rose bengal that was followed by KCl-induced cortical spreading depression (CSD). Infarct volume was evaluated with hematoxylin and eosin (H&E) staining 2days after venous occlusion. [(3)H]MK-801, [(3)H]AMPA and [(3)H]Muscimol ligand binding were examined autoradiographically in additional two groups without 2VO (n=5/group). Animals were injected either with NaCl (vehicle) or CTX 200mg/kg for 5days in order to evaluate whether NMDA, AMPA and GABAA ligand binding densities were affected.

RESULTS

CTX pretreatment reduced infarct volume compared to vehicle pretreatment (p<0.05). The effect of CTX pretreatment was attenuated by administration of the GLT-1 inhibitor, dihydrokainate (DHK) 30min before 2VO. CTX had no effect on the number of spontaneous spreading depressions after 2VO. Analysis of quantitative receptor autoradiography showed no statistically significant difference between rats after administration with CTX compared to control rats.

CONCLUSIONS

Pretreatment with CTX has neuroprotective potential without effect on NMDA, AMPA and GABAA receptor density and spontaneous spreading depression. This effect can be abolished by GLT-1 inhibition, indicating that upregulation of GLT-1 is an important mechanism for neuroprotective action in penumbra-like conditions, e.g. if neurosurgeons plan to occlude cerebral veins during tumor surgery.

Impedance spectroscopy--an outstanding method for label-free and real-time discrimination between brain and tumor tissue in vivo

Until today, brain tumors especially glioblastoma are difficult to treat and therefore, results in a poor survival rate of 0-14% over five years. To overcome this problem, the development of novel therapeutics as well as optimization of neurosurgical procedures to remove the tumor tissue are subject of intensive research. The main problem of the tumor excision, as the primary clinical intervention is the diffuse infiltration of the tumor cells in unaltered brain tissue that complicates the complete removal of residual tumor cells. In this context, we are developing novel approaches for the label-free discrimination between tumor tissue and unaltered brain tissue in real-time during the surgical process. Using our impedance spectroscopy-based measurement system in combination with flexible microelectrode arrays we could successfully demonstrate the discrimination between a C6-glioma and unaltered brain tissue in an in vivo rat model. The analysis of the impedance spectra revealed specific impedance spectrum shape characteristics of physiologic neuronal tissue in the frequency range of 10-500 kHz that were significantly different from the tumor tissue. Moreover, we used an adapted equivalent circuit model to get a deeper understanding for the nature of the observed effects. The impedimetric label-free and real-time discrimination of tumor from unaltered brain tissue offers the possibility for the implementation in surgical instruments to support surgeons to decide, which tissue areas should be removed and which should be remained.

The neuroprotective effect of lactate is not due to improved glutamate uptake after controlled cortical impact in rats

For many years lactate was considered to be a waste product of glycolysis. Data are accumulating that suggest that lactate is an important energy substrate for neurons during activation. In severe traumatic brain injury (TBI) glutamate release and ischemic cerebral blood flow (CBF) are major factors for a mismatch between energy demand and supply and for neuronal cell death. Although ATP and behavior could be improved by lactate treatment after TBI, no histological correlate nor any linkage to better astrocytic glutamate uptake or CBF as possible mechanisms have been described. We subjected male rats to a controlled cortical impact (CCI; 5 m/sec, 2.5 mm). To study the effects of lactate treatment on lesion volume, glutamate release, and CBF, animals were infused with either NaCl or 100 mM lactate for up to 3 h. The role of endogenous lactate was investigated by inhibiting transport with α-cyano-4-hydroxy-cinnamic acid (4-CIN; 90 mg/kg). Lactate treatment 15 min post-CCI reduced lesion volume from 21.1±2.8 mm³ to 12.1±1.9 mm³ at day 2 after CCI. Contusion produced a significant three- to fourfold increase of glutamate in microdialysates, but there was no significant difference between treatments that began 30 min before CCI. In this experiment lesion volume was significantly reduced by lactate at day 7 post-CCI (23.7±4 to 9.3±1-2 mm³). CBF increased immediately after CCI and dropped thereafter below baseline in all animals. Lactate infusion 15 min post-CCI elevated CBF for 20 min in 7 of 10 animals, whereas 7 of 8 NaCl-treated animals showed a further CBF decline. Neuroprotection was achieved by lactate treatment following contusion injury, whereas blocking of endogenous lactate transport exerted no adverse effects. Neuroprotection was not achieved by improved glutamate uptake into astrocytes, but was supported by augmented CBF following CCI. Due to its neuroprotective property, lactate might be a beneficial pharmacological treatment for TBI patients.

Sub-cellular tumor identification and markerless differentiation in the rat brain in vivo by multiphoton microscopy

OBJECTIVE/BACKGROUND

Aim of the current study was to localize and differentiate between tumor (glioma) and healthy tissue in rat brains on a cellular level. Near-infrared multiphoton microscopy takes advantage of the simultaneous absorption of two or more photons to analyze various materials such as cell and tissue components via the observation of endogenous fluorophores such as NAD(P)H, FAD, porphyrins, melanin, elastin, and collagen, with a very high resolution, without inducing the problems of photo-bleaching on out-of-focus areas.

METHODS

In vitro and in vivo studies on healthy rat brains as well as C6 glioma cell line allografts have been performed. Near-infrared laser pulses (λ = 690-1060 nm, τ ~140 fs) generated by an ultrafast Ti:Sapphire tunable laser system (Chameleon, Coherent GmbH, Santa Clara, CA) were coupled into a laser scanning microscope (LSM 510 META, Carl Zeiss, Germany) to observe high quality images.

RESULTS

Several image acquisitions have been performed by varying the zoom scale of the multiphoton microscope, image acquisition time and the wavelength (765, 840 nm) to detect various tissue components. With a penetration depth of ~200 µm in vitro and about 30-60 µm in vivo into the brain tissue it was possible to differentiate between tumor and healthy brain tissue even through thin layers of blood.

CONCLUSION

Near-infrared multiphoton microscopy allows the observation and possibly differentiation between tumor (glioma) and healthy tissue in rat brains on a cellular level. Our findings suggest that a further miniaturization of this technology might be very useful for scientific and clinical applications in neurosurgery.

Cluster analysis of mRNA expression levels identifies multiple sequential patterns following focal cerebral ischemia

AIM

The purpose of this study is to detect gene expression patterns following focal cerebral ischemia.

MATERIAL AND METHODS

25 male Wistar rats were divided into control (n = 8) and ischemic (n = 17) groups. In the ischemic group, slowly progressing focal ischemia was simulated by two-vein occlusion with spreading depression (SD) a cortical microinjection of KCl induced. Ischemic tissue was removed at 2, 8, 24, or 72 h postischemia. Using semiquantitative reverse transcription polymerase chain reaction, we investigated mRNA expression levels of 13 representative genes related to cerebral ischemia. Cluster analysis of the gene expression levels was done.

RESULTS

In the ischemic group, the expression levels of c-fos, cyclin D1, and COX-2 were significantly higher at 2 h postischemia, and those of bcl-2, bcl-xL, and HO-1 at 72 h. Based on the cluster analysis, we statistically divided examined genes into three groups: group A, early expression (COX-2, c-fos, and bcl-2); group B, s expression (c-jun, SOD-1, bad, p53, SOD-2, bcl-xL, and bax); and group C, late expression (cyclin D1, c-myc, and HO-1).

CONCLUSION

We statistically classified the genes into three groups after focal ischemia. The genes of the early- and late-expression groups can be possible therapeutic targets for the treatment of cerebral ischemia.

Spontaneous cortical spreading depression and intracranial pressure following acute subdural hematoma in a rat

Acute subdural hemorrhage (ASDH) is a frequent and devastating consequence of traumatic brain injury. Tissue damage develops rapidly and makes treatment even more difficult. Management of increased intracranial pressure (ICP) due to extravasated blood volume and brain swelling is often insufficient to control all adverse effects of ASDH. In addition to sheer volume, spontaneously triggered cortical spreading depression (CSD) that leads to cell death following ischemia or trauma may contribute to injury development after ASDH. Therefore, we explored the occurrence of CSD by tissue impedance (IMP) measurement in a rat model subjected to ASDH. IMP and intraventricular and mean arterial pressure were monitored before (baseline), during (blood infusion), and after ASDH for 3 h.Tissue impedance increased by around 203% of baseline during subdural infusion of 300 μl of autologous, venous blood and dropped back to baseline within 22 min. Fifty-six minutes after the start of ASDH a cluster of four short-lasting (3-3.5 min; 140-160% of baseline) IMP increases started that reflected spontaneous CSDs. This pattern presumes that CSD occurs early after ASDH and therefore may contribute to the rapid lesion development in this disease.

Online signal processing of internal anal sphincter activity during pelvic autonomic nerve stimulation: a new method to improve the reliability of intra-operative neuromonitoring signals

AIM

Intra-operative neuromonitoring is increasingly applied in several surgical disciplines and has been introduced to facilitate pelvic autonomic nerve preservation. Nevertheless, it has been considered a questionable tool for the minimization of risk, as the results are variable and might be misleading. The aim of the present experimental study was to develop an intra-operative neuromonitoring system with improved reliability for monitoring pelvic autonomic nerve function.

METHOD

Fifteen pigs underwent low anterior rectal resection with pelvic autonomic nerve preservation. Intra-operative neuromonitoring was performed under autonomic nerve stimulation with observation of electromyographic signals of the internal anal sphincter and bladder manometry. As the internal anal sphincter frequency spectrum during stimulation was found to be mainly in the range of 5-20 Hz, intra-operative neuromonitoring signals were postoperatively processed by implementation of matching band pass filters.

RESULTS

In 10 preliminary experiments, signal processing was performed offline in the postoperative analysis. Of 163 stimulations intra-operatively assessed by the surgeon as positive responses, 135 (83%) were confirmed after signal processing. In the following five consecutive experiments intra-operative online signal processing was realized and demonstrated reliable intra-operative neuromonitoring signals of internal anal sphincter activity with significant increase during pelvic autonomic nerve stimulation [0.5 μV (interquartile range = 0.3-0.7) vs 4.8 μV (interquartile range = 2.5-7.5); P < 0.001].

CONCLUSION

Online signal processing of internal anal sphincter activity aids reliable identification of pelvic autonomic nerves with potential for improvement of intra-operative neuromonitoring in pelvic surgery.

Effects of a small acute subdural hematoma following traumatic brain injury on neuromonitoring, brain swelling and histology in pigs

An acute subdural hematoma (ASDH) induces pathomechanisms which worsen outcome after traumatic brain injury, even after a small hemorrhage. Synergistic effects of a small ASDH on brain damage are poorly understood, and were studied here using neuromonitoring for 10 h in an injury model of controlled cortical impact (CCI) and ASDH. Pigs (n = 32) were assigned to 4 groups: sham, CCI (2.5 m/s), ASDH (2 ml) and CCI + ASDH. Intracranial pressure was significantly increased above sham levels by all injuries with no difference between groups. CCI and ASDH reduced ptiO(2) by a maximum of 36 ± 9 and 26 ± 11%, respectively. The combination caused a 31 ± 11% drop. ASDH alone and in combination with CCI caused a significant elevation in extracellular glutamate, which remained increased longer for CCI + ASDH. The same two groups had significantly higher peak lactate levels compared to sham. Somatosensory evoked potential (SSEP) amplitude was persistently reduced by combined injury. These effects translated into significantly elevated brain water content and histological damage in all injury groups. Thus, combined injury had stronger effects on glutamate and SSEP when compared to CCI and ASDH, but no clear-cut synergistic effects of 2 ml ASDH on trauma were observed. We speculate that this was partially due to the CCI injury severity.

The effect of a gap-junction blocker, carbenoxolone, on ischemic brain injury and cortical spreading depression

Cortical spreading depression (CSD) has been shown to cause secondary cell loss in experimental models of brain injury and in patients, and blocking of CSD is a potential neuroprotective strategy. Here we tested the hypothesis that gap junctions affect CSD under physiological conditions as well as infarct development in a rat two-vein occlusion model suited to study pathophysiology of the penumbra (n = 71). We applied the gap junction blocker carbenoxolone (CBX) or saline intra-ventricularly. Interestingly, CBX temporarily increased systemic blood pressure and cortical blood flow (41% and 53%, 15 min after 250 μg CBX). We induced CSD with cortical microinjection of potassium chloride (KCl), counted how many spontaneous CSDs after CSD induction were elicited and measured the propagation velocity. After 250 μg CBX administration, significant 37.5 ± 6.5 additional CSDs were seen. CSD velocity increased significantly after 50 μg and 250 μg CBX. Occlusion of two adjacent cortical veins using Rose Bengal dye and fiberoptic illumination followed by 250 μg CBX or saline showed a significant more than doubling of infarct volumes 7 days after CBX. The current experiments provide evidence that CBX can accelerate the initiation and propagation of CSD suggesting opening of gap junctions is not required for CSD propagation. Blocking gap junctions worsens outcome from focal cerebral ischemia. Hence, measures intended to improve spatial buffering via astroglial gap junctions could have therapeutic potential in disease processes involving CSD.