Apparatus for long-term ventricular access in the awake canine

An apparatus is described that permits lateral ventricular cerebrospinal fluid (CSF) to be sampled or an infusion to be performed into the ventricular system in the awake canine. The device has been used in 25 dogs. CSF was sampled, and experiments involving infusions into the lateral ventricle were performed over a 6- to 24-mo period. The maximum frequency of ventricular cannulation using the apparatus was once per week. Complications occurred in 10 dogs, all of which were successfully treated, permitting experiments to continue. Three fatal complications included meningitis in one animal at 24 mo and seizures in two animals, causing death at 12 and 18 mo. Administration of peptides, bombesin, and somatostatin into the ventricular system was followed by prompt rises in bombesin and somatostatin radioimmunoactivity in the CSF. There were no parallel increases of these peptides in the peripheral blood levels up to 2 h after infusion. Peptides of this molecular weight infused with this apparatus do not seem to leak into peripheral blood. The apparatus permits repeated ventricular cannulation in the awake canine for sampling of CSF and administration of biological substances to determine specific central nervous system action.     

Pharmacokinetics of an intracerebroventricularly administered antibody in rats

The pharmacokinetics (PK) of an antibody in the brain and the spinal cord is insufficiently understood, which is an obstacle to the discovery of antibody drugs that target diseases in the central nervous system. In this study, we focused on the elimination of IgG from cerebrospinal fluid (CSF) circulating in the brain and the spinal cord in rats, and, to evaluate the influence of CSF bulk flow on the clearance of IgG, also examined the PK of inulin in CSF. To monitor their concentrations in CSF, IgG and inulin were co-administered into the lateral ventricle via a catheter, and CSF was collected from the cisterna magna via another catheter time-sequentially. Blood was also obtained from the same individuals, and the concentrations of IgG and inulin in CSF and plasma were measured. The results revealed that PK parameters of IgG were similar to those of inulin; half-life and clearance of IgG were 47.0 ± 6.49 min and 29.0 ± 15.2 mL/day/kg, and those of inulin were 52.8 ± 25.4 min and 29.0 ± 13.3 mL/day/kg. Moreover, deconvolution analysis indicated that all of the IgG administered in the lateral ventricle was transferred to plasma from CSF within 24 hours. This study demonstrated that IgG in CSF was eliminated by bulk flow and transferred totally to blood circulation.     

Development of a Cerebrospinal Fluid Lateral Reservoir Model in Rhesus Monkeys (Macaca mulatta)

Rapid, serial, and humane collection of cerebrospinal fluid (CSF) in nonhuman primates (NHP) is an essential element of numerous research studies and is currently accomplished via two different models. The CSF reservoir model (FR) combines a catheter in the 4th ventricle with a flexible silastic reservoir to permit circulating CSF flow. The CSF lateral port model (LP) consists of a lateral ventricular catheter and an IV port that provides static access to CSF and volume restrictions on sample collection. The FR model is associated with an intensive, prolonged recovery and frequent postsurgical hydrocephalus and nonpatency, whereas the LP model is associated with an easier recovery. To maximize the advantages of both systems, we developed the CSF lateral reservoir model (LR), which combines the beneficial features of the 2 previous models but avoids their limitations by using a reservoir for circulating CSF flow combined with catheter placement in the lateral ventricle. Nine adult male rhesus monkeys were utilized in this study. Pre-surgical MRI was performed to determine the coordinates of the lateral ventricle and location of choroid plexus (CP). The coordinates were determined to avoid the CP and major blood vessels. The predetermined coordinates were 100% accurate, according to MRI validation. The LR system functioned successfully in 67% of cases for 221 d, and 44% remain functional at 426 to 510 d postoperatively. Compared with established models, our LR model markedly reduced postoperative complications and recovery time. Development of the LR model was successful in rhesus macaques and is a useful alternative to the FR and LP methods of CSF collection from nonhuman primates.Abbreviations: CP, choroid plexus; FR, CSF 4th ventricular reservoir model; LP, CSF lateral port model; LR, CSF lateral reservoir model; SER, successful establishment rateSerial ventricular CSF sampling in NHP is a frequent and critical requirement for a wide variety of studies and is predominantly accomplished by using either of 2 models. The 4th ventricle (FR) model, previously referred to as an Ommaya reservoir,⁶ and lateral port (LP) models² are closed, indwelling, subcutaneous systems that allow for serial, rapid, and humane collection of CSF, as well as intraventricular drug administration, in unanesthetized and restrained NHP.The FR model (Figure 1 A) consists of a catheter that is placed in the 4th ventricle and attached to a silastic reservoir that is implanted subcutaneously over the occipital bone. The silastic reservoir is depressed repetitively prior to and after sampling to circulate the CSF throughout the ventricles and catheter system to provide an unbiased sample without volume loss to dead space. The reservoir is accessed percutaneously to obtain a CSF sample via aspiration or to administer drug. The FR model initially was developed in 1977⁶ and continues to be used for pharmacokinetic studies. This system continues to demonstrate a low rate of successful establishment, but once established, the FR model remains patent for prolonged periods without evidence of neurologic sequelae or bleeding from the choroid plexus (CP) in rhesus macaques. The decreased establishment rate of this model is attributed, at least in part, to postsurgical development of hydrocephalus, given that the catheter, which is routed through the aqueduct of Magendie to the 4th ventricle, can obstruct the flow of CSF. In addition, maintaining catheter patency is problematic due to CP bleeding during the recovery period. Postsurgical care and recovery after creating the FR are extensive, frequently requiring prolonged analgesics and steroid administration, with many days needed for complete recovery.Open in a separate windowFigure 1.Evolution of CSF ventricular models, with flow dynamics. (A) Sagittal diagram of original FR (Ommaya) model, with placement in the 4th ventricle. Developed in 1977. Arrows indicate the circulating flow of CSF. (B) Original LP model, with catheter placement in the lateral ventricle and attachment to an IV access port. Developed in 1990. Arrows indicate the static, unidirectional flow of CSF. (C) The LR model, a composite of the 2 earlier CSF models. Arrows indicate the circulating flow of CSF.The LP model (Figure 1 B) consists of a catheter that is implanted in the lateral ventricle and attached to a subcutaneous intravenous access port. The port is accessed percutaneously to obtain the CSF sample or to administer a drug. The LP is a static model, because the CSF is not circulated or mixed through the ventricles, and CSF is obtained via unidirectional flow. The LP model was developed in 1990 for intrathecal drug administration³ and has been used subsequently for CSF collection⁴ by several investigators. CSF sampling with the LP model is restrictive: the volume of the system (that is, the dead space) must be removed at each collection to obtain an unbiased sample, collection is accomplished via gravitational flow and not aspiration, and the collection frequency is dependent on the rate of CSF replacement. In addition, the potential for sample contamination from blood due to CP bleeding remains problematic for the duration of LP implantation. However, the use of the lateral ventricle avoids the postsurgical complication of hydrocephalus. This system demonstrated a high rate of successful establishment with a reduction in the necessary analgesic and steroid administration as well as days to complete recovery, as compared with the FR model. Analysis of our clinical records from 2003 to 2013 revealed a successful establishment rate (SER) of 39% for the FR model; 33% of these systems remained functional for 3 to 7.5 y (

Feeding in satiated sheep elicited by intraventricular injections of CSF from fasted sheep

Cerebrospinal fluid (CSF) was collected from the lateral ventricles of either 24-hr fasted or “satiated” sheep (donors) and injected into the lateral or third ventricle of either 24-hr fasted or “satiated” sheep (recipients). Recipient “satiated” sheep ate more following injections of CSF from fasted donors, as compared to when the same animals were injected with CSF from equally “satiated” donors (e.g., 73±10 vs 16±6g respectively, 15 min post-injection, P <0.01). Feed intake of fasted recipient sheep was slightly depressed following intraventricular injections of CSF from “satiated” donors. Apparently, the composition of cerebrospinal fluid of the donor sheep was affected by the surfeit-deficit state of their energy stores.     

Central action of insulin regulates pulsatile luteinizing hormone secretion in the diabetic sheep model

This study tested the hypothesis that central mechanisms regulating luteinizing hormone (LH) secretion are responsive to insulin. Our approach was to infuse insulin into the lateral ventricle of six streptozotocin-induced diabetic sheep in an amount that is normally present in the CSF when LH secretion is maintained by peripheral insulin administration. In the first experiment, we monitored cerebrospinal fluid (CSF) insulin concentrations every 3-5 h in four diabetic sheep given insulin by peripheral injection (30 IU). The insulin concentration in the CSF was increased after insulin injection, and there was a positive relationship between CSF and plasma concentrations of insulin (r = 0.80, P < 0.01). In the second experiment, peripheral insulin administration was discontinued, and the sheep received either an intracerebroventricular (i.c.v.) infusion of insulin (12 mU/day in 2.4 ml saline) or saline (2.4 ml/day) for 5 days (n = 6) in a crossover design. The dose of insulin (i.c.v.) was calculated to approximate the increase in CSF insulin concentration found after peripheral insulin treatment. To monitor LH secretory patterns, blood samples were collected by jugular venipuncture at 10-min intervals for 4 h on the day before and 5 days after the start of i.c.v. insulin infusion. To monitor the increase in CSF insulin concentrations, a single CSF sample was collected one and four days after the start of the central infusion. The i.c.v. insulin infusion increased CSF insulin concentrations above those in saline-treated animals (P < 0.05) and maintained them at or above the peak levels achieved after peripheral insulin treatment. Central insulin infusion did not affect peripheral (plasma) insulin or glucose concentrations. LH pulse frequency in insulin-treated animals was greater than that in saline-treated animals (3.5 +/- 0.2 vs. 2.3 +/- 0.3 pulses/4 h, P < 0.01), but it was less than that during peripheral insulin treatment (4.8 +/- 0.2 pulses/4 h, P < 0.01). Our findings suggest that physiologic levels of central insulin supplementation are able to increase pulsatile LH secretion in diabetic sheep with low peripheral insulin. These results are consistent with the notion that central insulin plays a role in regulating pulsatile GnRH secretion.     

Relationship of intracerebral pituitary grafts to central neuropeptide systems

Variable amounts of pituitary tissue from neonatal or 30-day-old donor rats were implanted in the recessus triangularis or third ventricle of hypophysectomized male host rats. The pituitary tissue was implanted either immediately or 30 days after hypophysectomy of the host rat. Grafts from donors of either age were capable of maintaining a significant degree of testicular weight in one-third of the implanted animals. Neonatal grafts were not capable of restoring testicular weight when implanted 30 days after hypophysectomy. Final body weights of all graft-bearing animals were greater than those of hypophysectomized controls. The pars distalis of all grafts contained large numbers of cells immunore-active for LH, GH, and ACTH; TSH-immunoreactive cells were sparse. Prolactin-positive cells were extensive in grafts of animals in which the testes were maintained, and virtually absent in grafts of animals with atrophic testes. The fiber systems of three central neuropeptides, LRF, SRIF, and ACTH, were stained and found not to enter the graft. The results suggest that pituitary grafts in the third ventricle may receive their hypophysiotropic neuropeptides from the CSF.     

Role of natriuretic factor in central nervous system (CNS)-induced natriuresis

The presence of a natriuretic factor in the plasma of rats in which a 350 mM Na (high Na) artificial cerebrospinal fluid (CSF) was infused into the lateral ventricle was tested. Blood was obtained from control rats and rats which received an infusion of high Na CSF intraventricular (IVT) for 15 min. The plasma was incubated for 30 min at room temperature, acidified, placed in a boiling-water bath, and then centrifuged. The plasma supernate was assayed for natriuretic activity in pentobarbital anesthetized bioassay rats. Sodium excretion increased 6.5 +/- 1.1 mueq/kg X min in rats which received an infusion of a control saline solution, 13.3 +/- 3.2 mueq/kg X min in rats which received infusion of control plasma supernates, and 32.1 +/- 8.3 mueq/kg X min in those rats which received plasma supernates from rats infused with high Na CSF IVT. Blood pressure was unchanged in all groups. The increment in sodium excretion elicited by plasma supernate from the high Na IVT group was significantly greater than that elicited by either control saline solution or control plasma extracts. Therefore, it is concluded that a heat-stable and nonpressor natriuretic factor is present in the plasma of rats infused IVT with high Na CSF.     

食蟹猴经股静脉导管长期给药方法的建立

目的建立一种可靠的食蟹猴经股静脉导管长期给药的方法.方法选取20只雄性食蟹猴,麻醉后经股静脉造口,插入静脉导管,将植入式通道与导管连接并将其埋植于背部皮下,通过与植入式通道相连的输液泵进行给药.分别于术前1周、术后1周及术后2周测定血常规、血凝、生化等值.结果全部动物都能完成为期3个月的给药,手术感染率、导管堵塞率较低,分别为10%和5%.术后两周89.5%的生理指标与术前相比,差异无统计学意义(P>0.05).结论该实验采用的食蟹猴经股静脉插管并通过输液泵进行长期给药是一种安全、有效的方法,可广泛用于药理学及毒理学实验.     

Muscular Subaortic Stenosis: The Initial Left Ventricular Inflow Tract Pressure as Evidence of Outflow Tract Obstruction

Two types of intraventricular pressure differences within the left ventricle of man are described. The first is encountered in cases of muscular (or fibrous) subaortic stenosis, in which the outflow tract pressure distal to the stenosis (and proximal to the aortic valve) is low, whereas all pressures recorded in the left ventricle proximal to the stenosis, including that just inside the mitral valve (the initial inflow tract pressure) are high.The second type of intraventricular pressure difference may be recorded in patients without muscular subaortic stenosis when a heart catheter is advanced to the left ventricular wall in such a manner that it becomes imbedded or entrapped by cardiac muscle in systole. Such an entrapped catheter records a high intraventricular pressure that is believed to reflect intramyocardial tissue pressure, which normally exceeds intracavitary pressure. In such cases the initial inflow tract pressure is not high and is precisely equal to the outflow tract systolic pressure, i.e. both are recording intracavity pressure. This type of intramyocardial to intracavitary pressure difference may also be encountered in the left ventricle of dogs.The recent suggestion that intraventricular pressure differences in the left ventricle of cases of muscular subaortic stenosis are due to catheter entrapment by cardiac muscle is refuted by using the initial inflow tract pressure as the means of differentiation between the two types of intraventricular pressure differences outlined.     

Modified procedure for implantation of subcutaneous central venous access devices in macaques (Macaca mulatta)

A nonhuman primate model comprising adult male rhesus monkeys (Macaca mulatta) with chronically indwelling subcutaneous central venous access devices provides a unique opportunity to determine plasma pharmacokinetics of new drugs such as anticancer and anti- retroviral agents. The central venous access we use is a low-profile, single-septum, titanium port that is attached to a radiopaque, indwelling catheter; the catheter is implanted in an internal jugular vein. A common complication following placement of the venous access device was migration of the catheter tip. We therefore modified the standard procedure by cutting the silicone catheter and introducing the rigid connector to secure the catheter to the vessel at the insertion site (approximately 9 to 13 cm from the distal end of the catheter). Prior to the use of the connector, three of five catheters migrated within 4 weeks after placement. In contrast, all 13 internal jugular catheters with connectors have remained patent without migration of the catheter tip. Therefore, incorporation of the catheter connector appears to have eliminated the problem of catheter migration.     

3D Modeling of the Lateral Ventricles and Histological Characterization of Periventricular Tissue in Humans and Mouse

The ventricular system carries and circulates cerebral spinal fluid (CSF) and facilitates clearance of solutes and toxins from the brain. The functional units of the ventricles are ciliated epithelial cells termed ependymal cells, which line the ventricles and through ciliary action are capable of generating laminar flow of CSF at the ventricle surface. This monolayer of ependymal cells also provides barrier and filtration functions that promote exchange between brain interstitial fluids (ISF) and circulating CSF. Biochemical changes in the brain are thereby reflected in the composition of the CSF and destruction of the ependyma can disrupt the delicate balance of CSF and ISF exchange. In humans there is a strong correlation between lateral ventricle expansion and aging. Age-associated ventriculomegaly can occur even in the absence of dementia or obstruction of CSF flow. The exact cause and progression of ventriculomegaly is often unknown; however, enlarged ventricles can show regional and, often, extensive loss of ependymal cell coverage with ventricle surface astrogliosis and associated periventricular edema replacing the functional ependymal cell monolayer. Using MRI scans together with postmortem human brain tissue, we describe how to prepare, image and compile 3D renderings of lateral ventricle volumes, calculate lateral ventricle volumes, and characterize periventricular tissue through immunohistochemical analysis of en face lateral ventricle wall tissue preparations. Corresponding analyses of mouse brain tissue are also presented supporting the use of mouse models as a means to evaluate changes to the lateral ventricles and periventricular tissue found in human aging and disease. Together, these protocols allow investigations into the cause and effect of ventriculomegaly and highlight techniques to study ventricular system health and its important barrier and filtration functions within the brain.     

Continuous subcutaneous insulin infusion: an approach to achieving normoglycaemia.

A study was performed to examine the feasibility of achieving long periods of near-normoglycaemia in patients with diabetes mellitus by giving a continuous subcutaneous infusion of insulin solution from a miniature, battery-driven, syringe pump. Twelve insulin-dependent diabetics had their insulin pumped through a subcutaneously implanted, fine nylon cannula; the basal infusion rate was electronically stepped up eightfold before meals. The blood glucose profile of these patients was closely monitored during the 24 hours of the subcutaneous infusion and compared with the profile on a control day, when the patients were managed with their usual subcutaneous insulin. Diet and exercise were standardised on both days. In five out of 14 studies the subcutaneous insulin infusion significantly lowered the mean blood glucose concentration without producing hypoglycaemic symptoms; in another six patients the mean blood glucose concentration was maintained. As assessed by the M value the level of control was statistically improved in six out of 14 studies by the infusion method and maintained in six other patients. To assess the effects of blood glucose control on diabetic microvascular disease it will be necessary to achieve long-term normoglycaemia in selected diabetics. The results of this preliminary study suggest that a continuous subcutaneous insulin infusion may be a means of maining physiological glucose concentrations in diabetics. Though several problems remain--for example, in determining the rate of infusion--longer-term studies with the miniature infusion pumps are now needed.     

Intraventricular insulin potentiates the anorexic effect of corticotropin releasing hormone in rats

Intraventricular corticotropin releasing hormone (CRH) suppresses food intake and body weight as a stress response. Insulin, acting within the brain, also suppresses food intake and body weight, and this suppression is related to caloric homeostasis. We determined if increased insulin within the brain potentiates the anorexic effects of intraventricular CRH. Rats were food deprived for 17 h each day and then given 30-min access to Ensure. One-half received continuous third ventricular infusion of synthetic cerebrospinal fluid via osmotic minipumps, and one-half received insulin (0.6 mU/day). During the infusion, rats also received 0, 0.1, 1.0, or 5.0 microg of CRH into the lateral ventricle just before access to Ensure. Insulin alone had no effect on Ensure intake or body weight. CRH dose dependently reduced Ensure intake in both groups, and the reduction was greater in the insulin group. Hence, central insulin potentiated the ability of centrally administered CRH to suppress food intake. These findings suggest that stress-related influences over food intake, particularly those mediated via CRH, interact with relative adiposity as signaled to the brain by central insulin.     

Impaired lymphatic cerebrospinal fluid absorption in a rat model of kaolin-induced communicating hydrocephalus

It has been assumed that the pathogenesis of hydrocephalus includes a cerebrospinal fluid (CSF) absorption deficit. Because a significant portion of CSF absorption occurs into extracranial lymphatics located in the olfactory turbinates, the purpose of this study was to determine whether CSF transport was compromised at this location in a kaolin-induced communicating (extraventricular) hydrocephalus model in rats. Under 1-3% halothane anesthesia, kaolin (n = 10) or saline (n = 9) was introduced into the basal cisterns of Sprague-Dawley rats, and the development of hydrocephalus was assessed 1 wk later using MRI. After injection of human serum albumin ((125)I-HSA) into a lateral ventricle, the tracer enrichment in the olfactory turbinates 30 min postinjection provided an estimate of CSF transport through the cribriform plate into nasal lymphatics. Lateral ventricular volumes in the kaolin group (0.073 +/- 0.014 ml) were significantly greater than those in the saline-injected animals (0.016 +/- 0.001 ml; P = 0.0014). The CSF tracer enrichment in the olfactory turbinates (expressed as percent injected/g tissue) in the kaolin rats averaged 0.99 +/- 0.39 and was significantly lower than that measured in the saline controls (5.86 +/- 0.32; P < 0.00001). The largest degree of ventriculomegaly was associated with the lowest levels of lymphatic CSF uptake with lateral ventricular expansion occurring only when almost all of the lymphatic CSF transport capacity had been compromised. We conclude that lymphatic CSF absorption is impaired in a kaolin-communicating hydrocephalus model and that the degree of this impediment may contribute to the severity of the induced disease.     

Stem cell‐mediated natural tissue engineering

Recently, we demonstrated that a fully differentiated tissue developed on a ventricular septal occluder that had been implanted due to infarct‐related septum rupture. We suggested that this tissue originated from circulating stem cells. The aim of the present study was to evaluate this hypothesis and to investigate the physiological differentiation and transdifferentiation potential of circulating stem cells. We developed an animal model in which a freely floating membrane was inserted into each the left ventricle and the descending aorta. Membranes were removed after pre‐specified intervals of 3 days, and 2, 6 and 12 weeks; the newly developed tissue was evaluated using quantitative RT‐PCR, immunohistochemistry and in situ hybridization. The contribution of stem cells was directly evaluated in another group of animals that were by treated with granulocyte macrophage colony‐stimulating factor (GM‐CSF) early after implantation. We demonstrated the time‐dependent generation of a fully differentiated tissue composed of fibroblasts, myofibroblasts, smooth muscle cells, endothelial cells and new blood vessels. Cells differentiated into early cardiomyocytes on membranes implanted in the left ventricles but not on those implanted in the aortas. Stem cell mobilization with GM‐CSF led to more rapid tissue growth and differentiation. The GM‐CSF effect on cell proliferation outlasted the treat ment period by several weeks. Circulating stem cells contributed to the development of a fully differentiated tissue on membranes placed within the left ventricle or descending aorta under physiological conditions. Early cardiomyocyte generation was identified only on membranes positioned within the left ventricle.     

Dissimilar Aluminum and Gallium Permeation of the Blood-Brain Barrier Demonstrated by In Vivo Microdialysis

Aluminum (Al) and gallium (Ga) permeations of the blood-brain barrier (BBB) were assessed in rats. Unbound extracellular Al and Ga concentrations were ascertained at the two potential sites of BBB permeation, cerebral capillaries and choroid plexuses, by implantation of microdialysis probes in the frontal cortex and lateral ventricle, respectively. A microdialysis probe implanted in the jugular vein revealed unbound blood Al or Ga concentrations. Al or 67Ga citrate was administered via the femoral vein. Peak Al and Ga concentrations were seen within the first 10 min at all three sites. Area under the curve (concentration vs. time to final sample) values were calculated using RSTRIP. Within-rat overall frontal cortical/blood and lateral ventricular/blood ratios [brain/blood ratios (oBBRs)] were calculated from area under the curve values. Aluminum frontal cortical oBBRs were significantly higher than those for the lateral ventricle. Ga oBBRs were not significantly different between the two sites. Al and Ga oBBRs were significantly different in the lateral ventricle. These results suggest that the primary site of A1 permeation across the BBB is at cerebral capillaries, whereas Ga permeation across the BBB does not significantly differ between cerebral capillaries and choroid plexuses. The use of Ga as a model to study Al pharmacokinetics may not be appropriate in the elucidation of the site or mechanism of Al entry into the brain.     

A METHOD FOR THE STUDY OF CHOLESTEROL BIOSYNTHESIS IN THE CENTRAL NERVOUS SYSTEM

Abstract—

• 1 After intraperitoneal injection, there is negligible incorporation of [2-¹⁴C]-mevalonic lactone into the CNS of the adult rat.
• 2 Mevalonic lactone injected into the CSF is quickly transferred to blood.
• 3 Mevalonic lactone injected in the cistema magna or the lateral ventricle of the brain does not diffuse readily into the whole CSF. Spinal cord cholesterol is most heavily labelled after intracisternal injection, as is brain cholesterol after intraventricular administration.
• 4 After intraventricular perfusion, the diffusion of mevalonic lactone into the ventricle opposite the side of the injection is increased when the rate of perfusion is doubled from 5 to 10 μ1/hr. After injection, optimal homogeneity is obtained if a large volume (70μl) is administered.
• 5 An increase in the volume of injection from 70 μl to 130μl does not alter the distribution of activity between the left and right ventricles, nor does it increase the diffusion of mevalonic lactone from ventricle to spinal cord CSF.
• 6 The mean yield of mevalonic lactone incorporation into brain cholesterol is much higher after injection than after perfusion of precursor into the lateral cerebral ventricle.

     

Vascularizing the tissue surrounding a model biosensor: how localized is the effect of a subcutaneous infusion of vascular endothelial growth factor (VEGF)?

Implantable continuous biosensors would improve disease management but long term function of such devices have been limited by a hypovascular foreign body capsule that inhibits influx of analytes. To assess whether capsule vascularity could be increased, we studied the histologic effects of a 28-day continuous infusion of vascular endothelial growth factor (VEGF) (0.45 microg/day) vs. saline from the surface of a model disk biosensor that was implanted subcutaneously in rats. At day 40, tissue was obtained at varying distances from the infusion port and capsular microvessels were counted using two histologic techniques. VEGF treatment led to a marked increase in capillary density. In tissue located 1 mm away from the infusion site, capillary density in VEGF-treated animals was 200-300% higher than in saline controls. Tissue located 13 mm away, but not 25 mm away, also demonstrated neovascularization. Serum obtained from a distant vein during the infusion did not show an elevated concentration of VEGF. These data demonstrate that a subcutaneous infusion of VEGF creates localized neovascularization of the foreign body capsule and suggest that systemic effects of VEGF are avoidable. Vascularization of a foreign body capsule surrounding a subcutaneous biosensor might well extend its useful life.     

Ventricular motion during the ejection phase: a computational analysis.

In the present paper, the study of the ventricular motion during systole was addressed by means of a computational model of ventricular ejection. In particular, the implications of ventricular motion on blood acceleration and velocity measurements at the valvular plane (VP) were evaluated. An algorithm was developed to assess the force exchange between the ventricle and the surrounding tissue, i.e., the inflow and outflow vessels of the heart. The algorithm, based on the momentum equation for a transitory flowing system, was used in a fluid-structure model of the ventricle that includes the contractile behavior of the fibers and the viscous and inertial forces of the intraventricular fluid. The model calculates the ventricular center of mass motion, the VP motion, and intraventricular pressure gradients. Results indicate that the motion of the ventricle affects the noninvasive estimation of the transvalvular pressure gradient using Doppler ultrasound. The VP motion can lead to an underestimation equal to 12.4 +/- 6.6%.     

Non-surgical alternatives to invasive procedures in mice

We have developed and validated catheterization protocols in mice that allow for simultaneous infusion and sampling. A sampling catheter was inserted in the lateral vein of the tail, while the animals were infused either intravenously or intragastrically through a second catheter placed in the contralateral lateral vein or via an intragastric catheter, respectively. The applicability of these methods of infusion and blood sampling were validated by conducting urea kinetics utilizing stable isotopes. These non-surgical procedures are non-invasive, inexpensive, fast to perform and animals do not require a recovery period before their use.