Intraparenchymal Infusion Research Articles

Molecular Neurosurgery: Introduction to Gene Therapy and Clinical Applications

AbstractTo date, more than 100 clinical trials have used sequence-based therapies to address diseases of the pediatric central nervous system. The first targeted pathologies share common features: the diseases are severe; they are due (mostly) to single variants; the variants are well characterized within the genome; and the interventions are technically feasible. Interventions range from intramuscular and intravenous injection to intrathecal and intraparenchymal infusions. Whether the therapeutic sequence consists of RNA or DNA, and whether the sequence is delivered via simple oligonucleotide, nanoparticle, or viral vector depends on the disease and the involved cell type(s) of the nervous system. While only one active trial targets an epilepsy disorder—Dravet syndrome—experiences with aromatic L-amino acid decarboxylase deficiency, spinal muscular atrophy, and others have taught us several lessons that will undoubtedly apply to the future of gene therapy for epilepsies. Epilepsies, with their diverse underlying mechanisms, will have unique aspects that may influence gene therapy strategies, such as targeting the epileptic zone or nodes in affected circuits, or alternatively finding ways to target nearly every neuron in the brain. This article focuses on the current state of gene therapy and includes its history and premise, the strategy and delivery vehicles most commonly used, and details viral vectors, current trials, and considerations for the future of pediatric intracranial gene therapy.

Relaxin/insulin-like family peptide receptor 4 (Rxfp4) expressing hypothalamic neurons modulate food intake and preference in mice

ObjectiveInsulin-like peptide 5 (INSL5) signalling, through its cognate receptor relaxin/insulin-like family peptide receptor 4 (RXFP4), has been reported to be orexigenic, and the high fat diet (HFD) preference observed in wildtype mice is altered in Rxfp4 knock-out mice. In this study, we used a new Rxfp4-Cre mouse model to investigate the mechanisms underlying these observations. MethodsWe generated transgenic Rxfp4-Cre mice and investigated central expression of Rxfp4 by RT-qPCR, RNAscope and intraparenchymal infusion of INSL5. Rxfp4-expressing cells were chemogenetically manipulated in global Cre-reporter mice using designer receptors exclusively activated by designer drugs (DREADDs) or after stereotactic injection of a Cre-dependent AAV-DIO-Dq-DREADD targeting a population located in the ventromedial hypothalamus (RXFP4VMH). Food intake and feeding motivation were assessed in the presence and absence of a DREADD agonist. Rxfp4-expressing cells in the hypothalamus were characterised by single-cell RNA-sequencing (scRNAseq) and the connectivity of RXFP4VMH cells was investigated using viral tracing. ResultsRxfp4-Cre mice displayed Cre-reporter expression in the hypothalamus. Active expression of Rxfp4 in the adult mouse brain was confirmed by RT-qPCR and RNAscope. Functional receptor expression was supported by cyclic AMP-responses to INSL5 application in ex vivo brain slices and increased HFD and highly palatable liquid meal (HPM), but not chow, intake after intra-VMH INSL5 infusion. scRNAseq of hypothalamic RXFP4 neurons defined a cluster expressing VMH markers, alongside known appetite-modulating neuropeptide receptors (Mc4r, Cckar and Nmur2). Viral tracing demonstrated RXFP4VMH neural projections to nuclei implicated in hedonic feeding behaviour. Whole body chemogenetic inhibition (Di-DREADD) of Rxfp4-expressing cells, mimicking physiological INSL5-RXFP4 Gi-signalling, increased intake of the HFD and HPM, but not chow, whilst activation (Dq-DREADD), either at whole body level or specifically within the VMH, reduced HFD and HPM intake and motivation to work for the HPM. ConclusionThese findings identify RXFP4VMH neurons as regulators of food intake and preference, and hypothalamic RXFP4 signalling as a target for feeding behaviour manipulation.

In-vitro and in-vivo performance studies of a porous infusion catheter designed for intraparenchymal delivery of therapeutic agents of varying size

BackgroundLimitations have previously existed for the use of brain infusion catheters with extended delivery port designs to achieve larger distribution volumes using convection-enhanced delivery (CED), due to poor transmittance of materials and uncontrolled backflow. The goal of this study was to evaluate a novel brain catheter that has been designed to allow for extended delivery and larger distribution volumes with limited backflow of fluid. It was characterized using a broad range of therapeutic pore sizes both for transmittance across the membranes to address possible occlusion and for distribution in short term infusion studies, both in-vitro in gels and in-vivo in canines. MethodsBrain catheters with pore sizes of 10, 12, 15, 20 and 30 µm were evaluated using three infusates prepared in 0.9% sterile saline with diameters approximating 2, 5, and 30 nm, respectively. Magnevist™ was chosen as the small molecule infusate to mimic low-molecular weight therapeutics. Galbumin™ served as a surrogate for an assortment of proteins used for brain cancer and Parkinson’s disease. Gadoluminate™ was used to assess the distribution of large therapeutics, such as adeno-associated viral particles and synthetic nanoparticles. The transmittance of the medium and large tracer particles through catheters of different pore size (15, 20 and 30 µm) was measured by MRI and compared with the measured concentration of the control. Infusions into 0.2% agarose gels were performed in order to evaluate differences in transmittance and distribution of the small, medium, and large tracer particles through catheters with different pore sizes (10, 12, 15, 20 and 30 µm). In-vivo infusions were performed in the canine in order to evaluate the ability of the catheter to infuse the small, medium, and large tracer particles into brain parenchyma at high flow rates through catheters with different pore sizes (10, 15, and 20 µm). Two catheters were stereotactically inserted into the brain for infusion, one per hemisphere, in each animal (N = 6). ResultsThe transmittance of Galbumin and Gadoluminate across the catheter membrane surface was 100% to within the accuracy of the measurements. There was no evidence of any blockage or retardation of any of the infusates. Catheter pore size did not appear to significantly affect transmittance or distribution in gels of any of the molecule sizes in the range of catheter pore sizes tested. There were differences in the distributions between the different tracer molecules: Magnevist produced relatively large distributions, followed by Gadoluminate and Galbumin. We observed no instances of uncontrolled backflow in a total of 12 in-vivo infusions. In addition, several of the infusions resulted in substantial amounts remaining in tissue. We expect the in-tissue distributions to be substantially improved in the larger human brain. Comparison with existing methodsThe new porous brain catheter performed well in terms of both backflow and intraparenchymal infusion of molecules of varying size in the canine brain under CED flow conditions. ConclusionsOverall, the data presented in this report support that the novel porous brain catheter can deliver therapeutics of varying sizes at high infusion rates in the brain parenchyma, and resist backflow that can compromise the efficacy of CED therapy. Additional work is needed to further characterize the brain catheter, including animal toxicity studies of chronically implanted brain catheters to lay the foundation for its use in the clinic.

Levetiracetam and N-Cadherin Antibody Alleviate Brain Pathology Without Reducing Early Epilepsy Development After Focal Non-convulsive Status Epilepticus in Rats.

Focal non-convulsive status epilepticus (fNCSE) is a neurological condition characterized by a prolonged seizure that may lead to the development of epilepsy. Emerging experimental evidence implicates neuronal death, microglial activation and alterations in the excitatory and inhibitory synaptic balance as key features in the pathophysiology following fNCSE. We have previously reported alterations in the excitatory adhesion molecule N-cadherin in rats with fNCSE originating from the hippocampus that subsequently also develop spontaneous seizures. In this study, fNCSE rats were treated intraperitoneally with the conventional anti-epileptic drug levetiracetam in combination with intraparenchymal infusion of N-cadherin antibodies (Ab) for 4 weeks post-fNCSE. The N-cadherin Ab was infused into the fornix and immunohistochemically N-cadherin Ab-stained neurons were detected within the dorsal hippocampal structures as well as in superjacent somatosensory cortex. Continuous levetiracetam treatment for 4 weeks post-fNCSE reduced microglia activation, including cell numbers and morphological changes, partly decreased neuronal cell loss, and excitatory post-synaptic scaffold protein PSD-95 expression in selective hippocampal structures. The additional treatment with N-cadherin Ab did not reverse neuronal loss, but moderately reduced microglial activation, and further reduced PSD-95 levels in the dentate hilus of the hippocampus. Despite the effects on brain pathology within the epileptic focus, neither monotherapy with systemic levetiracetam nor levetiracetam in combination with local N-cadherin Ab administration, reduced the amount of focal or focal evolving into bilateral convulsive seizures, seizure duration, or interictal epileptiform activity during 1 month of continuous electroenephalogram recordings within the hippocampus after fNCSE. Behavioral tests for spatial memory, anxiety, social interaction and anhedonia did not detect gross behavioral differences between fNCSE rats with or without treatment. The results reveal the refractory features of the present rodent model of temporal lobe epilepsy following fNCSE, which supports its clinical value for further therapeutic studies. We identify the persistent development of epilepsy following fNCSE, in spite of partly reduced brain pathology within the epileptic focus.

DDEL-08. CONVECTION-ENHANCED DELIVERY OF NIMUSTINE HYDROCHLORIDE (ACNU) AGAINST PEDIATRIC DIFFUSE INTRINSIC PONTINE GLIOMAS

Diffuse intrinsic pontine gliomas (DIPGs) are amongst the most challenging tumors to treat. Surgery is not an option, the effects of radiation therapy are temporary, and no chemotherapeutic agent has demonstrated significant efficacy. Intracerebral infusion technique of convection-enhanced delivery (CED) for patients with brain tumors could offer a novel approach for effective chemotherapy. We have been working to develop an effective chemotherapy using nimustine hydrochloride (ACNU) with this drug delivery method. After several studies targeting supratentorial recurrent malignant gliomas and recurrent gliomas affecting brainstem, we conducted phase 1 study to evaluate the safety of combination of convection-enhanced delivery of nimustine hydrochloride and systemic temozolomide against recurrent gliomas affecting brainstem. In this study, we demonstrated the safety and feasibility of CED of ACNU as well as real time monitoring of drug distribution by mixing ACNU with contrast agent; Gd-DOTA. We also defined the maximum tolerable concentration in this study and proceeded to phase 2 trial against recurrent gliomas affecting brain stem. However, these trials revealed the difficulty of treating pediatric DIPG at the time of recurrence. Therefore, we decided to treat pediatric DIPG cases at their initial diagnosis in the subsequent study. Aiming at obtaining Shonin approval both for intraparenchymal infusion catheter and drug to infuse into brain parenchyma, we are now conducting Phase II physician-led trial against initially diagnosed pediatric DIPG cases.

Determinants of Intraparenchymal Infusion Distributions: Modeling and Analyses of Human Glioblastoma Trials.

Intra-parenchymal injection and delivery of therapeutic agents have been used in clinical trials for brain cancer and other neurodegenerative diseases. The complexity of transport pathways in tissue makes it difficult to envision therapeutic agent distribution from clinical MR images. Computer-assisted planning has been proposed to mitigate risk for inadequate delivery through quantitative understanding of infusion characteristics. We present results from human studies and simulations of intratumoral infusions of immunotoxins in glioblastoma patients. Gd-DTPA and 124I-labeled human serum albumin (124I-HSA) were co-infused with the therapeutic, and their distributions measured in MRI and PET. Simulations were created by modeling tissue fluid mechanics and physiology and suggested that reduced distribution of tracer molecules within tumor is primarily related to elevated loss rates computed from DCE. PET-tracer on the other hand shows that the larger albumin molecule had longer but heterogeneous residence times within the tumor. We found over two orders of magnitude variation in distribution volumes for the same infusion volumes, with relative error ~20%, allowing understanding of even anomalous infusions. Modeling and measurement revealed that key determinants of flow include infusion-induced expansion and loss through compromised BBB. Opportunities are described to improve computer-assisted CED through iterative feedback between simulations and imaging.

Effects of an Intraparenchymal Injection of Lidocaine in the Rat Cervical Spinal Cord.

Lidocaine effects in the spinal cord have been extensively investigated over the years. Although the intrathecal route is usually used to treat insults occurring in the spinal cord, the local delivery drug via intraparenchymal infusions has gained increasing favor for the treatment of some neurodegenerative disorders. The aim of the present study was to evaluate the behavioral and tissue effects of the intraparenchymal injection of different concentrations of lidocaine into the rat cervical spinal cord. Young male Sprague-Dawley rats were intraparenchymally injected with 0.5%, 1% or 2% lidocaine at the C5 segment of the spinal cord. Other rats were injected with saline solution (sham group). Hot plate test was determined at 0, 1, 2, 3, 7 and 14 post-injection (pi) days. Rats of each experimental group were euthanized either at 1, 2, 3, 7 or 14 pi days. Intact animals were used as controls. Sections of the C5 segment were used for histological, immunohistochemical or immunofluorescence analysis. Injection of 0.5% lidocaine did not affect neuronal counting, did not evoke an inflammatory reaction, nor induce astrocyte activation. Therefore, a concentration of 0.5% lidocaine is suggested to promote anti-inflammatory effects after injury.

DIPG-65. PRELIMINARY EXPERIENCE OF CHRONIC INTERMITTENT CONVECTION ENHANCED DELIVERY OF CARBOPLATIN AND VALPROIC ACID FOR THE TREATMENT OF DIFFUSE INTRINSIC PONTINE GLIOMA FOLLOWING RADIATION THERAPY

Diffuse intrinsic pontine glioma (DIPG) is a lethal disease of middle childhood with few treatment options. The failure of chemotherapy is in part due to poor blood-brain barrier penetration. Convection enhanced delivery (CED) uses direct intraparenchymal infusion to distribute drug through target brain volumes. Valproic acid and carboplatin are readily compatible with CED and kill DIPG cells as monotherapies and with synergy when combined. These drugs were combined and translated into a two-day CED treatment schedule for treatment of DIPG on compassionate grounds using a long-term, implantable, drug delivery system (undergoing approval, Renishaw Plc). This device utilises a bone-anchored transcutaneous port for intermittent drug administration without the need for repeated surgery. 9 patients who had previously received radiotherapy were selected for treatment. Surgical implantation of the device was well-tolerated. A total of 27 cycles (54 infusions) of sodium valproate and carboplatin were delivered achieving infusion volumes between 3.6–5.6 mL per infusion. The most common acute infusion-related side-effects included headache and mild limb weakness and all patients were discharged within 24 hours of finishing treatment. We describe our preliminary experience as a prelude to a forthcoming clinical trial.

Dysfunction in Brain-Derived Neurotrophic Factor Signaling Pathway and Susceptibility to Schizophrenia, Parkinson's and Alzheimer's Diseases.

Brain-Derived Neurotrophic Factor (BDNF) is a dominant neurotrophic factor in the brain which plays a crucial role in differentiation, regeneration and plasticity mechanisms. Binding of the BDNF to its high-affinity Tropomyosin-related kinase B (TrkB) receptor leads to phosphorylation of TrkB, thus activating the three important downstream intracellular signaling cascades within the neural cells including phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT), Phospholipase C-γ (PLCγ), and mitogen-activated protein kinase/extracellular signal-related kinase (MAPK/ERK) pathways. Transcription of these pathways is regulated by cAMP Response Element-Binding protein (CREB) transcription factor, which can upregulate gene expression. In this review, we attempted to explore the role of BDNF and its associated pathways in susceptibility to Schizophrenia (Scz), Alzheimer's (AD), and Parkinson's (PD) diseases. Furthermore, we discuss dysfunction in BDNF signaling pathway and the therapeutic potential of BDNF in the treatment of these disorders. The review covers various therapeutic strategies including BDNF gene therapy, transplantation of BDNFexpressing cell grafts, epigenetic manipulation, and intraparenchymal BDNF protein infusion as well. This review seeks to achieve these goals by reviewing recent studies on BDNF and examining the details of BDNF pathway in any of the above-mentioned diseases.

Theory of porous catheters and their applications in intraparenchymal infusions

Multiport catheters and catheters with a porous surface have been proposed for intraparenchymal infusions of therapeutics in fluid suspensions. Target diseases include brain cancer and serious neurodegenerative diseases, as well as peripheral tumors, for example in the prostate and the liver. We set up the theory for infusions from such devices, in particular the fluid flow equations which demand a coupling between the flow within the catheter and that in tissue. (Such a coupling is not necessary in the theory of infusion from single port catheters.) The new feature of such catheters, treated by our model, is revealed by infusions into inhomogeneous media. Multiport designs have the potential to overcome the limitation of single port catheters, for which the path of the fluid leaving the port is dominated by the inhomogeneities. We solve these equations for some simple cases to illustrate the key design features of porous catheters that show such advantages. The mathematics required for numerical solution with more realistic assumptions is also developed. We confirm the robustness of such catheters, when the ports are sufficiently resistive, against leakage paths that would compromise the infusions from catheters with one or a few large ports. The methods of this paper can be incorporated into a larger planning system for intraparenchymal infusions involving such devices.

Protease-activated receptor 1 and 4 signal inhibition reduces preterm neonatal hemorrhagic brain injury.

This study examines the role of thrombin's protease-activated receptor (PAR)-1, PAR-4 in mediating cyclooxygenase-2 and mammalian target of rapamycin after germinal matrix hemorrhage. Germinal matrix hemorrhage was induced by intraparenchymal infusion of bacterial collagenase into the right ganglionic eminence of P7 rat pups. Animals were treated with PAR-1, PAR-4, cyclooxygenase-2, or mammalian target of rapamycin inhibitors by 1 hour, and ≤5 days. We found increased thrombin activity 6 to 24 hours after germinal matrix hemorrhage, and PAR-1, PAR-4, inhibition normalized cyclooxygenase-2, and mammalian target of rapamycin by 72 hours. Early treatment with NS398 or rapamycin substantially improved long-term outcomes in juvenile animals. Suppressing early PAR signal transduction, and postnatal NS398 or rapamycin treatment, may help reduce germinal matrix hemorrhage severity in susceptible preterm infants.

The Relation between Catheter Occlusion and Backflow during Intraparenchymal Cerebral Infusions

Background/Aims: The distribution of infusate into the brain by convection-enhanced delivery can be affected by backflow along the catheter shaft. This work assesses the following: (1) whether tissue coring and occlusion of the catheter lumen occurs when an open end-port catheter is inserted, (2) whether there is a relationship between intracatheter pressure and backflow, and (3) whether catheter occlusion increases backflow. Methods: Freshly excised monkey brains were used to assess tissue coring and its correlation with the behavior of the line pressure. In vivo infusions of gadolinium solution into monkey putamen at 1 μl/min were conducted with and without a stylet during insertion. The effect of flow during insertion was evaluated in vivo in the pig thalamus. MRI and line pressure were continuously monitored during in vivo infusions. Results: Ex vivo testing showed that open end-port insertions always cored tissue (which temporarily plugs the catheter tip) and increased pressure followed by a rapid fall after its expulsion. Catheter insertion with a stylet in place prevented coring but not flow insertion; neither affected backflow. Conclusion: Open end-port catheters occlude during insertion, which can be prevented by temporarily closing the port with a stylet but not by infusing while inserting. Backflow was not completely prevented by any insertion method.

Does Dabigatran Increase the Risk of Delayed Hematoma Expansion in a Rat Model of Collagenase-induced Intracerebral Hemorrhage?

Delayed hematoma expansion is common in intracerebral hemorrhage (ICH) patients using warfarin. Dabigatran induces fewer hemorrhagic complications compared with warfarin. However, the natural history of dabigatran-related ICH remains unclear. This study aims to clarify whether dabigatran increases the risk of delayed hematoma expansion in a rat ICH model. Male Wistar rats were treated with 2 dosages of dabigatran etexilate (DE: 10 mg/kg, n = 4; 20 mg/kg, n = 3) 30 minutes before ICH induction using intraparenchymal collagenase infusion. Five rats that received saline were used as controls. Magnetic resonance imaging was performed 24 and 48 hours after ICH induction, and serial hematoma volume measurements were obtained using T2-weighted images. Expanded hematoma volumes were calculated by subtracting hematoma volumes at 48 hours from those at 24 hours; the hematoma expansion rate was defined as the ratio of the expanded hematoma volume to that at 24 hours. The mean hematoma volumes (mm(3)) at 24 hours were 13.3 ± 3.3 in the control group, 14.9 ± 2.0 in the 10 mg/kg DE group, and 18.9 ± 7.6 in the 20 mg/kg DE group with no significant intergroup differences (P = .26). The mean hematoma volumes at 48 hours (mm(3)) were 21.7 ± 4.9 in the control group, 22.1 ± 5.0 in the 10 mg/kg DE group, and 23.4 ± 5.8 in the 20 mg/kg DE group with no significant intergroup differences (P = .90). Consequently, there were no significant intergroup differences in the hematoma expansion rates (P = .33). This experimental study of a rat ICH model indicates that dabigatran-related ICH may not increase the risk of delayed hematoma expansion.

Implementation of a chronic unilateral intraparenchymal drug delivery system in a swine model

Systemic delivery of pharmacologic agents has led to many significant advances in the treatment of neurologic and psychiatric conditions. However, this approach has several limitations, including difficulty penetrating the blood-brain barrier and enzymatic degradation prior to reaching its intended target. Here, we describe the testing of a system allowing intraparenchymal (IPa) infusion of therapeutic agents directly to the appropriate anatomical targets, in a swine model. Five male pigs underwent 3.0T magnetic resonance (MR) guided placement of an IPa catheter into the dorso-medial putamen, using a combined system of the Leksell stereotactic arc, a Mayo-developed MRI-compatible pig head frame, and a custom-designed Fred Haer Company (FHC) delivery system. Our results show hemi-lateral coverage of the pig putamen is achievable from a single infusion point and that the volume of the bolus detected in each animal is uniform (1544±420mm(3)). The IPa infusion system is designed to isolate the intracranial catheter from bodily-induced forces while delivering drugs and molecules into the brain tissue by convection-enhanced delivery, with minimal-to-no catheter track backflow. This study presents an innovative IPa drug delivery system, which includes a sophisticated catheter and implantable pump designed to deliver drugs and various molecules in a precise and controlled manner with limited backflow. It also demonstrates the efficacy of the delivery system, which has the potential to radically impact the treatment of a wide range of neurologic conditions. Lastly, the swine model used here has certain advantages for translation into clinical applications.

Isoflurane Post-Treatment Ameliorates GMH-Induced Brain Injury in Neonatal Rats

This study investigated whether isoflurane ameliorates neurological sequelae after germinal matrix hemorrhage (GMH) through activation of the cytoprotective sphingosine kinase/sphingosine-1-phosphate receptor/Akt pathway. GMH was induced in P7 rat pups by intraparenchymal infusion of bacterial collagenase (0.3 U) into the right hemispheric germinal matrix. GMH animals received 2% isoflurane either once 1 hour after surgery or every 12 hours for 3 days. Isoflurane treatment was then combined with sphingosine-1-phosphate receptor-1/2 antagonist VPC23019 or sphingosine kinase 1/2 antagonist N,N-dimethylsphingosine. Brain protein expression of sphingosine kinase-1 and phosphorylated Akt were significantly increased after isoflurane post-treatment, and cleaved caspase-3 was decreased at 24 hours after surgery, which was reversed by the antagonists. Isoflurane significantly reduced posthemorrhagic ventricular dilation and improved motor, but not cognitive, functions in GMH animals 3 weeks after surgery; no improvements were observed after VPC23019 administration. Isoflurane post-treatment improved the neurological sequelae after GMH possibly by activation of the sphingosine kinase/Akt pathway.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Intra-parenchymal ferrous iron infusion causes neuronal atrophy, cell death and progressive tissue loss: Implications for intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating stroke causing considerable tissue destruction from mechanical trauma and secondary degeneration. Free iron, released over days from degrading erythrocytes, causes free radicals that likely contribute to delayed injury. Indeed, an intracerebral injection of iron rapidly kills cells and causes cerebral edema. We expanded upon these observations by: determining a dose–response relationship of iron infusion, examining the structural appearance of surviving striatal neurons, and evaluating injury over months. First, we measured 24-h edema in rats given 3.8, 19.0 or 38.0μg infusions of FeCl2 (i.e., 30μL of a 1, 5 or 10mmol/L solution). Second, rats were given these infusions (vs. saline controls) followed by behavioral assessment and histology at 7days. Third, dendritic structure was measured in Golgi–Cox stained neurons at 7days after a 0.95-μg dose (30μL of a 0.25mmol/L solution). Last, rats survived 7 or 60days post-injection (19.0μg) for histological assessment. Larger doses of iron caused greater injury, but this was generally not reflected in behavior that indicated similar deficits among the 3.8–38.0μg groups. Similarly, edema occurred but was not linearly related to dose. Even after a low iron dose the surviving neurons in the peri-injury zone were considerably atrophied (vs. contralateral side and controls). Finally, continuing tissue loss occurred over weeks with prominent neuronal death and iron-positive cells (e.g., macrophages) at 60days. Iron alone may account for the chronic degeneration found after ICH in rodent models.

Polymer-coated cannulas for the reduction of backflow during intraparenchymal infusions

Infusate backflow or leak-back along the cannula track can occur during intraparenchymal infusions resulting in non-specific targeting of therapeutic agents. The occurrence of backflow depends on several variables including cannula radius, infusate flow rate, and tip location. In this study, polymer coatings that swell in situ were developed and tested with in vitro hydrogel experiments for backflow reduction. Coatings were applied to the external cannula surface in a dual layer arrangement with a poly(vinyl alcohol) outer layer atop an inner poly(ethylene oxide) and alginate layer. Once these coated cannulas were inserted and allotted an 8-10 min waiting period for hydration, backflow during infusions of 4.0 μl of a macromolecular tracer (Evans Blue labeled albumin) was reduced significantly under flow rates of 0.3-0.6 μl/min, allowing for more effective distribution within targeted regions. Polymer coating thicknesses before and after hydrations were 0.035 and 0.370 mm, respectively. Also, backflow data was fit to a model to estimate the effective local compressive stress caused by the hydrated polymers. After withdrawal of the cannula from the insertion site, the hydrated polymer coatings remained within the cavity left in the hydrogel tissue phantom and formed a seal at the infusion site that prevented further backflow during needle withdrawal. Ex vivo infusions in excised porcine brain tissues also showed significant backflow reduction while also demonstrating the ability to leave a polymer seal in the tissue cavity after cannula removal. Thus, application of these polymers as needle or cannula coatings offers a potentially simple method to improve targeting for local drug delivery.

Microglia Modulate Hippocampal Neural Precursor Activity in Response to Exercise and Aging

Exercise has been shown to positively augment adult hippocampal neurogenesis; however, the cellular and molecular pathways mediating this effect remain largely unknown. Previous studies have suggested that microglia may have the ability to differentially instruct neurogenesis in the adult brain. Here, we used transgenic Csf1r-GFP mice to investigate whether hippocampal microglia directly influence the activation of neural precursor cells. Our results revealed that an exercise-induced increase in neural precursor cell activity was mediated via endogenous microglia and abolished when these cells were selectively removed from hippocampal cultures. Conversely, microglia from the hippocampi of animals that had exercised were able to activate latent neural precursor cells when added to neurosphere preparations from sedentary mice. We also investigated the role of CX(3)CL1, a chemokine that is known to provide a more neuroprotective microglial phenotype. Intraparenchymal infusion of a blocking antibody against the CX(3)CL1 receptor, CX(3)CR1, but not control IgG, dramatically reduced the neurosphere formation frequency in mice that had exercised. While an increase in soluble CX(3)CL1 was observed following running, reduced levels of this chemokine were found in the aged brain. Lower levels of CX(3)CL1 with advancing age correlated with the natural decline in neural precursor cell activity, a state that could be partially alleviated through removal of microglia. These findings provide the first direct evidence that endogenous microglia can exert a dual and opposing influence on neural precursor cell activity within the hippocampus, and that signaling through the CX(3)CL1-CX(3)CR1 axis critically contributes toward this process.

Stereotactic Placement of Ventricular Catheters: Does It Affect Proximal Malfunction Rates?

Background: The majority of ventriculoperitoneal (VP) shunt malfunctions are due to proximal catheter failure. Ideal placement of Ommaya reservoirs is desired to avoid toxicity from intraparenchymal chemotherapy infusion. Objective: To determine whether stereotactic placement of ventricular catheters decreases the rate of Ommaya reservoir complications and the rate of proximal VP shunt failure. Methods: Under institutional review board approval, areview of a prospectively collected database was doneidentifying all patients who underwent stereotactic-guided placement of VP shunts and Ommaya reservoirs performed by a single surgeon between November 2007 and November 2009. Neuronavigation was used to preset a surgical plan consisting of an ideal entry point (usually frontal) and target point (ipsilateral foramen of Monro). The navigation probe was passed along this trajectory. After removal of the navigation probe, pre-sized ventricular catheters were passed without a stylet along the created path. Post-operative CT scans and clinical follow-up were assessed. Results: 70 patients (mean age 44.6 years) underwent 52 VP shunt and 18 Ommaya reservoir placement procedures. Rigid cranial fixation was used in all cases. All catheters were placed in a single pass. Mean operative time was 62 min. Mean follow-up was 16.3 months. No proximal malfunctions or Ommaya complications have been seen thus far. One patient required repositioning of an Ommaya reservoir as post-operative CT showed poor placement (1.4%). One patient with hydrocephalus due to cryptococcal meningitis developed an abdominal abscess and required removal of his entire shunt with subsequent replacement. One patient was noted to have a small amount of intraventricular hemorrhage; this did not result in any clinical change and did not require any further intervention. No other surgical complications were noted. Conclusion: In terms of results corroborating decreased proximal malfunction rates, we present the largest series of stereotactic-guided ventricular catheter placements to date. Though time in the operating room is increased due to navigation registration, actual operative time is comparable to procedures without navigation. A longer-term follow-up is needed to assess the longevity of our positive short-term results.