A chronic model to simultaneously measure intracranial pressure, cerebral blood flow, and study the pial microvasculature

Toolkit for integrating millimeter-sized microfluidic biomedical devices with multiple membranes and electrodes

In recent years, microfluidic systems have evolved to incorporate increasingly complex multi-layer and multi-material structures. While conventional 2-dimensional microfluidic systems are typically fabricated with lithographic techniques, the increase in system complexity necessitates a more versatile set of fabrication techniques. Similarly, although 3D printing can easily produce intricate microfluidic geometries, integrating multiple membranes and electrode components remains challenging. This study proposes a toolkit for fabricating free-standing 3-dimensional microfluidic systems for biomedical devices, incorporating flow channels, electrodes, and membranes. The fabrication techniques include molding separation using 3D printed molds, laser-based processing, and component assembly, each achieving micron resolution. Here, we introduce a novel approach to integrate membranes into microfluidics by directly curing elastomer-based microfluidics with the membrane through replica molding, while preserving membrane functionality by effectively removing elastomer residues through reactive ion etching. The resulting membrane-elastomer microfluidic component significantly simplifies the assembly of intricate microfluidic systems, reducing the device size to millimeter dimensions, suitable for implantable applications. The toolkit's versatility is demonstrated by a redox flow iontophoretic drug delivery prototype at the millimeter scale, featuring two electrodes, four membranes, and four microfluidic channels.

Preclinical update on regulation of intracranial pressure in relation to idiopathic intracranial hypertension

BACKGROUND

Elevated intracranial pressure (ICP) is observed in association with a range of brain disorders. One of these challenging disorders is idiopathic intracranial hypertension (IIH), characterized by raised ICP of unknown cause with significant morbidity and limited therapeutic options. In this review, special focus is put on the preclinical research performed in order to understand the pathophysiology behind ICP regulation and IIH. This includes cerebrospinal fluid dynamics, molecular mechanisms underlying disturbances in brain fluids leading to elevated ICP, role of obesity in IIH, development of an IIH model and ICP measurements in rodents. The review also discusses existing and new drug targets for IIH that have been evaluated in vivo.

CONCLUSIONS

ICP monitoring in rodents is challenging and different methods have been applied. Some of these methods are invasive, depend on use of anesthesia and only allow short-term monitoring. Long-term ICP recordings are needed to study IIH but existing methods are hampered by several limitations. As obesity is one of the most common risk factors for IIH, a rodent obese model has been developed that mimics some key aspects of IIH. The most commonly used drugs for IIH have been evaluated in vivo for their efficacy at lowering ICP in the existing animal models. These studies suggest these drugs, including acetazolamide, might have limited or no reducing effect on ICP. Two drug targets that can impact ICP in healthy rodents are topiramate and a glucagon-like peptide-1 receptor (GLP-1R) agonist. However, it remains to evaluate their effect in an IIH model with more precise and valid ICP monitoring system. Therefore, continued evaluation in the preclinical research with refined tools is of great importance to further understand the pathophysiology behind disorders with raised ICP and to explore new drug targets.

Intracranial pressure monitoring in normal dogs using subdural and intraparenchymal miniature strain-gauge transducers

Background

Monitoring of intracranial pressure (ICP) is a critical component in the management of intracranial hypertension. Safety, efficacy, and optimal location of microsensor devices have not been defined in dogs.

Hypothesis/Objective

Assessment of ICP using a microsensor transducer is feasible in anesthetized and conscious animals and is independent of transducer location. Intraparenchymal transducer placement is associated with more adverse effects.

Animals

Seven adult, bred‐for‐research dogs.

Methods

In a prospective investigational study, microsensor ICP transducers were inserted into subdural and intraparenchymal locations at defined rostral or caudal locations within the rostrotentorial compartment under general anesthesia. Mean arterial pressure and ICP were measured continuously during physiological maneuvers, and for 20 hours after anesthesia.

Results

Baseline mean ± SD values for ICP and cerebral perfusion pressure were 7.2 ± 2.3 and 78.9 ± 7.6 mm Hg, respectively. Catheter position did not have a significant effect on ICP measurements. There was significant variation from baseline ICP accompanying physiological maneuvers (P < .001) and with normal activities, especially with changes in head position (P < .001). Pathological sequelae were more evident after intraparenchymal versus subdural placement.

Conclusions and Clinical Importance

Use of a microsensor ICP transducer was technically straightforward and provided ICP measurements within previously reported reference ranges. Results support the use of an accessible dorsal location and subdural positioning. Transient fluctuations in ICP are normal events in conscious dogs and large variations associated with head position should be accounted for when evaluating animals with intracranial hypertension.

Win 55212-2, a cannabinoid receptor agonist, attenuates leukocyte/endothelial interactions in an experimental autoimmune encephalomyelitis model

Multiple sclerosis (MS) is the most common of the immune demyelinating disorders of the central nervous system (C NS). Leukocyte/endothelial interactions are important steps in the progression of the disease and substances that interfere with these activities have been evaluated as potential therapeutic agents. C annabinoid receptor agonists have been shown to downregulate immune responses and there is preliminary evidence that they may slow the progress of MS. The purpo se of this investigation was to determine how cannabinoid recepto r agonists interfere with leukocyte rolling and adhesion. This was investigated in an experimental autoimmune encephalo myelitis (EAE) model using six to eight week old C 57BL/6 mice. Mouse myelin oligodendrocyte protein and pertussis toxin were used to induce EAE. WIN 55212-2, C B1 and C B2 antagonist were given. By use of in vivo intravital microscopy, leukocyte/endothelial interactio ns were evaluated via a cranial window implanted two days before. The results demonstrated that EAE increases leukocyte rolling and firm adhesion in the brain, and that this increased leukocyte/endothelial interactio n can be attenuated by administration of WIN 55212-2. Furthermore, use of the selective antagonists for the C B1 recepto r (SR 141716A) and the C B2 receptor (SR144528) in this study demonstrated that the cannabinoid’s inhibitory effects on leukocyte/endothelial interactions can be mediated by activating C B2 receptor.

Lab-on-a-brain: implantable micro-optical fluidic devices for neural cell analysis in vivo

The high-resolution imaging of neural cells in vivo has brought about great progress in neuroscience research. Here, we report a novel experimental platform, where the intact brain of a living mouse can be studied with the aid of a surgically implanted micro-optical fluidic device; acting as an interface between neurons and the outer world. The newly developed device provides the functions required for the long-term and high-resolution observation of the fine structures of neurons by two-photon laser scanning microscopy and the microfluidic delivery of chemicals or drugs directly into the brain. A proof-of-concept experiment of single-synapse stimulation by two-photon uncaging of caged glutamate and observation of dendritic spine shrinkage over subsequent days demonstrated a promising use for the present technology.

A novel method for long-term monitoring of intracranial pressure in rats

BACKGROUND

In preclinical neurological studies, monitoring intracranial pressure (ICP) in animal models especially in rodents is challenging. Further, the lack of methods for long-term ICP monitoring has limited the possibilities to conduct prolonged studies on ICP fluctuations in parallel to disease progression or therapeutic interventions. For these reasons we aimed to set up a simple and valid method for long-term ICP recordings in rats.

NEW METHOD

A novel ICP method employing epidural probes was developed and validated by simultaneously ICP recordings in the lateral ventricle and in the epidural space. The two pressures were recorded twice a week for 59 days and the correlation was studied.

RESULTS

The two pressure recordings correlated exceptionally well and the R(2) values on each recording day ranged between 0.99 and 1.00. However, the ventricular probes caused a number of complications including loss of patency and tissue damage probably due to cerebral infection, whereas the epidural probes were safe and reliable throughout the entire study.

COMPARISON WITH EXISTING METHODS

Epidural probes are much easier to implant than ventricular probes. In addition, these new probes are far less invasive and induce no apparent mechanical tissue damage and highly decrease the infection risk associated with ICP recordings.

CONCLUSION

Epidural ICP recorded with this new method is identical to the ventricular ICP for at least 59 days but is far less complicated and safer for the animals. The long-term method described is reliable, valid, inexpensive, and may be used in multiple disease models to study ICP.

Increased intracranial pressure in mini-pigs exposed to simulated solar particle event radiation

Changes in intracranial pressure (ICP) during space flight have stimulated an area of research in space medicine. It is widely speculated that elevations in ICP contribute to structural and functional ocular changes, including deterioration in vision, which is also observed during space flight. The aim of this study was to investigate changes in OP occurring as a result of ionizing radiation exposure (at doses and dose-rates relevant to solar particle event radiation). We used a large animal model, the Yucatan mini-pig, and were able to obtain measurements over a 90 day period. This is the first investigation to show long term recordings of ICP in a large animal model without an invasive craniotomy procedure. Further, this is the first investigation reporting increased ICP after radiation exposure.

The history of neurosurgery at Temple University

TEMPLE UNIVERSITY'S NEUROSURGERY program has had a colorful and distinguished history since its creation in 1929. It has always functioned under challenging circumstances with limited resources but with a strong sense of mission. It was one of the 20 neurosurgical training programs in existence when the American Board of Neurosurgery was founded in 1940. Over the past 64 years, the program has trained approximately the same number of neurosurgeons, many of whom have contributed significantly to our specialty. Some of the advances pioneered in part at Temple include clinical hypothermia (Fay), the biplanar stereoscopic angiographic unit (Chamberlain), human stereotactic surgery (Spiegel and Wycis), lumboperitoneal shunts (Scott), posterior lumbar interbody fusion (Lin), microsurgery for acoustic tumors (Buchheit), and new pharmacological approaches to neuroprotectors (Strauss and Narayan). The Temple neurosurgery program has survived many challenges in the past and will no doubt weather the current financial and medicolegal challenges that confront the neurosurgical community in Philadelphia. It remains a strong clinical program that serves an otherwise underserved community and attracts patients beyond its geographic area because of its strong clinical reputation and the excellence of its clinical faculty and residents.

New lumbar method for monitoring cerebrospinal fluid pressure in rats

OBJECTIVE

Monitoring cerebrospinal fluid pressure or intracranial pressure (ICP) is crucial in the study of neurosurgical disorders. In the present study, we report a new lumbar method for monitoring ICP in rats.

METHODS

A PE10 catheter connected to a pressure transducer was placed into the subarachnoid space of L5 through the duramater after laminectomy to record lumbar cerebrospinal fluid pressure (lumbar-ICP). ICP at the cisterna magna (cisterna-ICP) was recorded simultaneously via a catheter in the subarachnoid space at the cisterna magna. Eighteen anesthetized adult male S-D rats were subjected to baseline recording followed by either experimental subarachnoid hemorrhage (SAH) induced by intravascular puncture method or experimental intracerebral hemorrhage (ICH) induced by blood injection with a stereotaxic system.

RESULTS

Baseline lumbar-ICP and cisterna-ICP varied between 6 and 8 mmHg, and respiratory variation could be detected. A similar acute response to SAH was recorded in both the lumbar-ICP and cisterna-ICP in all rats. In rats subjected to SAH, the lumbar catheter continuously and accurately monitored lumbar-ICP, and reliable pressure tracings were obtained for up to 24 h after SAH. However, continued cisterna-ICP monitoring was abandoned in two rats in the cisterna magna method due to obstruction of the catheter by blood clots (hematoma).

CONCLUSION

This new lumbar-ICP method is simple, safe, easy, and reliable in rats. Continued lumbar-ICP measurements provided monitoring for up to 24 h after experimental manipulation.