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Introduction: Surgical interventions in mice require appropriate pain relief to ensure animal welfare and to avoid influence of pain on research findings. Carprofen is a non-steroidal anti-inflammatory drug commonly used as an analgesic for interventions inducingmild tomoderate pain in laboratory rodents. Despite its frequent use, species-specific data on pharmacokinetics (PK), side effects, and potential impact on behavioral pain indicators are limited. Methods: We determined PK and tolerability profiles of carprofen in healthy male and female C57BL/6Jmice (n = 42), administered at highest recommended doses via single subcutaneous (s.c.) injection (20 mg/kg) and oral self-administration (25 mg/kg/24 h) per drinking water (d.w.) for 5 days. Plasma concentrations were measured at various time points after the start of the treatment (n = 6 per time point), and side effects were evaluated using amodified Irwin test battery, hematology, and histopathology. Additionally, potential interference with cage-side behaviors commonly used for pain assessment, such as the mouse grimace scale, wheel running, burrowing, nesting, and grooming activity, was investigated. Results: Maximum plasma concentrations of 133.4 ± 11.3µg/ml were reached 1 h after single s.c. injection with an elimination half-life of 8.52 h. Intake from d.w. resulted in a steady state within 24 h after the start of the treatment with plasma levels of around 60µg/ml over 5 days in both sexes. The medicated water was well-accepted, and increased d.w. intake was observed in the first 24 h after exposure (p < 0.0001). The Irwin test revealed only minor influence on tested behavior and physiological functions. However, during treatment via d.w., an increase in body temperature (p < 0.0001) was observed, as well as a reduction in voluntary wheel running activity by 49-70% inmalemice. Moreover, grooming behavior was slightly affected. Hematology and histopathology were without pathological findings that could be attributed to carprofen treatment. High-dose carprofen can be considered safe and of favorable PK for both administration routes assessed in healthy C57BL/6J mice of both sexes. Further efficacy evaluation of carprofen as monoanalgesic or component of multimodal post-surgical regimens is clearly encouraged; however, the impact on behavioral markers used for pain assessment should be considered in this context. [ABSTRACT FROM AUTHOR]

Unmet needs in the treatment of chronic otitis media and Eustachian tube dysfunction (ETD) triggered the development of stents for the Eustachian tube (ET). In this study, for the first time, stents were placed in an artificially blocked ET to evaluate stent function. Eight adult female sheep were injected with stabilized hyaluronic acid (HA) on both sides to induce ETD. Subsequently, a tapered nitinol ET stent was inserted on one side, and animals were examined bilaterally by endoscopy, tympanometry, cone beam computed tomography, and final histology. Seven of the stents were placed in the desired cartilaginous portion of the ET. At the end of the study, one stented side appeared slightly open; all other ET orifices were closed. Tympanometry revealed re-ventilation of the middle ear in four out of seven correctly stented animals within 3 to 6 weeks after stent insertion. The major amount of HA was found at the pharyngeal orifice of the ET anterior to the stent. Thus, the stent position did not completely align with the HA position. While a functional analysis will require refinement of the experimental setup, this study provides first promising results for stent insertion in a sheep model of ETD. [ABSTRACT FROM AUTHOR]

The Eustachian tube (ET) is a bottleneck when it comes to middle ear (ME) health. If its function is impaired, this can lead to serious consequences for the patient, such as hearing problems or deafness. Therefore, this study investigated a tapered nitinol stent (3–5 mm × 14 mm) for the human ET as a potential new permanent treatment for chronic Eustachian tube dysfunction (ETD) and thus ME ventilation disorders. The self-expanding stent was inserted unilaterally into the ET of 24 sheep with observation periods of 3, 6, and 12 months. Local tissue effects and the safety of the stent insertion were analyzed based on regular endoscopic checks, weekly tympanometry measurements, final imaging, and histological examinations. The animals showed no stent-related health restrictions. However, the individual anatomy and stenting procedure had an influence on the results. The tissue reaction in the endoscopic examinations was mild even though no concomitant antibiotics were administered. After all three monitoring periods, stented ETs had a significantly larger ET lumen than the non-stented contralateral ETs. However, tissue growth was detected in the stent. Overall, the first long-term study on an ET stent showed that the tapered ET stent could be a promising treatment option for ETD. [ABSTRACT FROM AUTHOR]

Experimental craniotomies are a common surgical procedure in neuroscience. Because inadequate analgesia appears to be a problem in animal-based research, we conducted this review and collected information on management of craniotomy-associated pain in laboratory mice and rats. A comprehensive search and screening resulted in the identification of 2235 studies, published in 2009 and 2019, describing craniotomy in mice and/or rats. While key features were extracted from all studies, detailed information was extracted from a random subset of 100 studies/year. Reporting of perioperative analgesia increased from 2009 to 2019. However, the majority of studies from both years did not report pharmacologic pain management. Moreover, reporting of multimodal treatments remained at a low level, and monotherapeutic approaches were more common. Among drug groups, reporting of pre- and postoperative administration of non-steroidal anti-inflammatory drugs, opioids, and local anesthetics in 2019 exceeded that of 2009. In summary, these results suggest that inadequate analgesia and oligoanalgesia are persistent issues associated with experimental intracranial surgery. This underscores the need for intensified training of those working with laboratory rodents subjected to craniotomies. [ABSTRACT FROM AUTHOR]

Introduction: Sheep are frequently used in translational surgical orthopedic studies. Naturally, a good pain management is mandatory for animal welfare, although it is also important with regard to data quality. However, methods for adequate severity assessment, especially considering pain, are rather rare regarding large animal models. Therefore, in the present study, accompanying a surgical pilot study, telemetry and the Sheep Grimace Scale (SGS) were used in addition to clinical scoring for severity assessment after surgical interventions in sheep. Methods: Telemetric devices were implanted in a first surgery subcutaneously into four German black-headed mutton ewes (4–5 years, 77–115 kg). After 3–4 weeks of recovery, sheep underwent tendon ablation of the left M. infraspinatus. Clinical scoring and video recordings for SGS analysis were performed after both surgeries, and the heart rate (HR) and general activity were monitored by telemetry. Results: Immediately after surgery, clinical score and HR were slightly increased, and activity was decreased in individual sheep after both surgeries. The SGS mildly elevated directly after transmitter implantation but increased to higher levels after tendon ablation immediately after surgery and on the following day. Conclusion: In summary, SGS- and telemetry-derived data were suitable to detect postoperative pain in sheep with the potential to improve individual pain recognition and postoperative management, which consequently contributes to refinement. [ABSTRACT FROM AUTHOR]

Status epilepticus (SE) is a clinical emergency with high mortality. SE can trigger neuronal death or injury and alteration of neuronal networks resulting in long-term cognitive decline or epilepsy. Among the multiple factors contributing to this damage, imbalance between oxygen and glucose requirements and brain perfusion during SE has been proposed. Herein, we aimed to quantify by neuroimaging the spatiotemporal course of brain perfusion during and after lithium-pilocarpine-induced SE in rats. To this purpose, animals underwent 99mTc-HMPAO SPECT imaging at different time points during and after SE using a small animal SPECT/CT system. 99mTc-HMPAO regional uptake was normalized to the injected dose. In addition, voxel-based statistical parametric mapping was performed. SPECT imaging showed an increase of cortical perfusion before clinical seizure activity onset followed by regional hypo-perfusion starting with the first convulsive seizure and during SE. Twenty-four hours after SE, brain 99mTc-HMPAO uptake was widely decreased. Finally, chronic epileptic animals showed regionally decreased perfusion affecting hippocampus and cortical sub-regions. Despite elevated energy and oxygen requirements, brain hypo-perfusion is present during SE. Our results suggest that insufficient compensation of required blood flow might contribute to neuronal damage and neuroinflammation, and ultimately to chronic epilepsy generated by SE. [ABSTRACT FROM AUTHOR]

Purpose: Alterations in brain glucose metabolism detected by 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) positron emission tomography (PET) may serve as an early predictive biomarker and treatment target for epileptogenesis. Here, we aimed to investigate changes in cerebral glucose metabolism before induction of epileptogenesis, during epileptogenesis as well as during chronic epilepsy. As anesthesia is usually unavoidable for preclinical PET imaging and influences the distribution of the radiotracer, four different protocols were compared. Procedures: We investigated 18F-FDG uptake phase in conscious rats followed by a static scan as well as dynamic scans under continuous isoflurane, medetomidine-midazolam-fentanyl (MMF), or propofol anesthesia. Furthermore, we applied different analysis approaches: atlas-based regional analysis, statistical parametric mapping, and kinetic analysis. Results: At baseline and compared to uptake in conscious rats, isoflurane and propofol anesthesia resulted in decreased cortical 18F-FDG uptake while MMF anesthesia led to a globally decreased tracer uptake. During epileptogenesis, MMF anesthesia was clearly best distinctive for visualization of prominently increased glucometabolism in epilepsy-related brain areas. Kinetic modeling further increased sensitivity, particularly for continuous isoflurane anesthesia. During chronic epilepsy, hypometabolism affecting more or less the whole brain was detectable with all protocols. Conclusion: This study reveals evaluation of anesthesia protocols for preclinical 18F-FDG PET imaging as a critical step in the study design. Together with an appropriate data analysis workflow, the chosen anesthesia protocol may uncover otherwise concealed disease-associated regional glucometabolic changes. [ABSTRACT FROM AUTHOR]

Objective: Identification of patients at risk of developing epilepsy before the first spontaneous seizure may promote the development of preventive treatment providing opportunity to stop or slow down the disease. Methods: As development of novel radiotracers and on‐site setup of existing radiotracers is highly time‐consuming and expensive, we used dual‐centre in vitro autoradiography as an approach to characterize the potential of innovative radiotracers in the context of epilepsy development. Using brain slices from the same group of rats, we aimed to characterise the evolution of neuroinflammation and expression of inhibitory and excitatory neuroreceptors during epileptogenesis using translational positron emission tomography (PET) tracers; 18F‐flumazenil (18F‐FMZ; GABAA receptor), 18F‐FPEB (metabotropic glutamate receptor 5; mGluR5), 18F‐flutriciclamide (translocator protein; TSPO, microglia activation) and 18F‐deprenyl (monoamine oxidase B, astroglia activation). Autoradiography images from selected time points after pilocarpine‐induced status epilepticus (SE; baseline, 24 and 48 hours, 5, 10 and 15 days and 6 and 12‐14 weeks after SE) were normalized to a calibration curve, co‐registered to an MRI‐based 2D region‐of‐interest atlas, and activity concentration (Bq/mm2) was calculated. Results: In epileptogenesis‐associated brain regions, 18F‐FMZ and 18F‐FPEB showed an early decrease after SE. 18F‐FMZ decrease was maintained in the latent phase and further reduced in the chronic epileptic animals, while 18F‐FPEB signal recovered from day 10, reaching baseline levels in chronic epilepsy. 18F‐flutriciclamide showed an increase of activated microglia at 24 hours after SE, peaking at 5‐15 days and decreasing during the chronic phase. On the other hand, 18F‐deprenyl autoradiography showed late astrogliosis, peaking in the chronic phase. Significance: Autoradiography revealed different evolution of the selected targets during epileptogenesis. Our results suggest an advantage of combined imaging of inter‐related targets like glutamate and GABAA receptors, or microglia and astrocyte activation, in order to identify important interactions, especially when using PET imaging for the evaluation of novel treatments. [ABSTRACT FROM AUTHOR]

Background: Neuroinvasive larvae of the worldwide occurring zoonotic roundworms Toxocara canis and T. cati may induce neurotoxocarosis (NT) in humans, provoking a variety of symptoms including cognitive deficits as well as neurological dysfunctions. An association with neuropsychological disorders has been discussed. Similar symptoms have been described in T. canis-infected mice, whereas data on T. cati-induced NT are rare. Therefore, it was aimed to obtain insights into the impact on neurobehaviour as well as progression of neurological symptoms and behavioural alterations during the course of NT directly comparing T. canis- and T. cati-infected mice as models for human NT. Methodology/Principal findings: C57BL/6 mice were orally infected with 2000 embryonated T. canis or T. cati eggs, respectively, the control group received tap water. Mice were screened weekly for neurobehavioural alterations and memory function starting one day prior infection until 97 days post infection (pi; T. canis-infection) and day 118 pi (T. cati-infection, uninfected control). Mostly motoric and neurological parameters were affected in T. canis-infected mice starting day 20 pi with severe progression accompanied by stereotypical circling. In contrast, T. cati-infected mice mostly showed reduced response to sudden sound stimulus (indicator for excitability) and flight behaviour starting day 6 pi. Interestingly, enhanced grooming behaviour was observed exclusively in T. cati-infected mice, indicating a possible role of neurotransmitter dysregulation. Reduced exploratory behaviour and memory impairment was observed in both infection groups with delayed onset and less severe progression in T. cati- compared to T. canis-infected mice. Conclusions/Significance: Results highlight the need to consider T. cati beside T. canis as causative agent of human NT. Findings provide valuable hints towards differences in key regulatory mechanisms during T. canis- and T. cati-induced NT, contributing to a comprehensive picture and consequently a broader understanding of NT, which will aid in developing strategies towards prevention in addition to novel diagnostic and therapeutic approaches. [ABSTRACT FROM AUTHOR]

Objective: Acquired epilepsy is a devastating long-term risk of various brain insults, including trauma, stroke, infections, and status epilepticus (SE). There is no preventive treatment for patients at risk. Attributable to the complex alterations involved in epileptogenesis, it is likely that multitargeted approaches are required for epilepsy prevention. We report novel preclinical findings with isoflurane, which exerts various nonanesthetic effects that may be relevant for antiepileptogenesis.Methods: The effects of isoflurane were investigated in two rat models of SE-induced epilepsy: intrahippocampal kainate and systemic administration of paraoxon. Isoflurane was either administered during (kainate) or after (paraoxon) induction of SE. Magnetic resonance imaging was used to assess blood-brain barrier (BBB) dysfunction. Positron emission tomography was used to visualize neuroinflammation. Long-term electrocorticographic recordings were used to monitor spontaneous recurrent seizures. Neuronal damage was assessed histologically.Results: In the absence of isoflurane, spontaneous recurrent seizures were common in the majority of rats in both models. When isoflurane was administered during kainate injection, duration and severity of SE were not affected, but only few rats developed spontaneous recurrent seizures. A similar antiepileptogenic effect was found when paraoxon-treated rats were exposed to isoflurane after SE. Moreover, in the latter model, isoflurane prevented BBB dysfunction and neurodegeneration, whereas isoflurane reduced neuroinflammation in the kainate model.Interpretation: Given that isoflurane is a widely used volatile anesthetic, and is used for inhalational long-term sedation in critically ill patients at risk to develop epilepsy, our findings hold a promising potential to be successfully translated into the clinic. Ann Neurol 2016;80:896-908. [ABSTRACT FROM AUTHOR]

Pharmacoresistance to antiepileptic drugs (AEDs) is a major challenge in epilepsy therapy, affecting at least 30% of patients. Thus, there is considerable interest in the mechanisms responsible for such pharmacoresistance, with particular attention on the specific cellular and molecular factors that lead to reduced drug sensitivity. Current hypotheses of refractory epilepsy include the multidrug transporter hypothesis, which posits that increased expression or function of drug efflux transporters, such as P-glycoprotein (Pgp), in brain capillaries reduces the local concentration of AEDs in epileptic brain regions to subtherapeutic levels. In the present study, this hypothesis was addressed by evaluating the efficacy of six AEDs in wildtype and Pgp deficient Mdr1a/b −/− mice in the intrahippocampal kainate model of mesial temporal lobe epilepsy. In this model, frequent focal electrographic seizures develop after an initial kainate-induced status epilepticus. These seizures are resistant to major AEDs, but the mechanisms of this resistance are unknown. In the present experiments, the focal nonconvulsive seizures were resistant to carbamazepine and phenytoin, whereas high doses of valproate and levetiracetam exerted moderate and phenobarbital and diazepam marked anti-seizure effects. All AEDs suppressed generalized convulsive seizures. No significant differences between wildtype and Pgp-deficient mice were observed in anti-seizure drug efficacies. Also, the individual responder and nonresponder rates in each experiment did not differ between mouse genotypes. This does not argue against the multidrug transporter hypothesis in general, but indicates that Pgp is not involved in the mechanisms explaining that focal electrographic seizures are resistant to some AEDs in the intrahippocampal mouse model of partial epilepsy. This was substantiated by the finding that epileptic wildtype mice do not exhibit increased Pgp expression in this model. [ABSTRACT FROM AUTHOR]

Rat strains such as Sprague–Dawley (SD) or Wistar are widely used in epilepsy research, including popular models of temporal lobe epilepsy in which spontaneous recurrent seizures (SRS), hippocampal damage, and behavioral alterations develop after status epilepticus (SE). Such rats are randomly outbred, and outbred strains are known to be genetically heterogeneous populations with a high intrastrain variation. Intrastrain differences may be an important reason for discrepancies between studies from different laboratories, but the extent to which such differences affect the development of seizures, neurodegeneration, and psychopathology in post-SE models of epilepsy has received relatively little attention. In the present study, we induced SE by systemic administration of pilocarpine (following pretreatment with lithium) in SD rats from different breeders (Harlan, Charles River [CRL], Taconic) as well as different breeding locations of the same breeder (Harlan–Winkelmann [HW] in Germany vs. Harlan Laboratories [HL] in the Netherlands). Some experiments were also performed in Wistar rats. Pilocarpine was administered by a ramp-up dosing protocol that allows determining interindividual differences in susceptibility to the convulsant. Marked intrastrain differences in induction of SE and its long-term consequences were found. Sprague–Dawley rats from HW were significantly more sensitive to SE induction than all other SD substrains. The majority of SD rats from different vendors developed SRS after SE except SD rats from HL. The CRL-SD rats markedly differed in basal behavior and SE-induced behavioral alterations from other SD substrains. Susceptibility to pilocarpine was hardly affected by the estrous cycle. The marked intrastrain differences provide an interesting tool to study the impact of genetic and environmental factors on seizure susceptibility, epileptogenesis, and relationship between behavior and epilepsy and vice versa. [ABSTRACT FROM AUTHOR]

Background In human medicine, adverse outcomes associated with switching between bioequivalent brand name and generic antiepileptic drug products is a subject of concern among clinicians. In veterinary medicine, epilepsy in dogs is usually treated with phenobarbital, either with the standard brand name formulation Luminal® or the veterinary products Luminal® vet and the generic formulation Phenoleptil®. Luminal® and Luminal® vet are identical 100 mg tablet formulations, while Phenoleptil® is available in the form of 12.5 and 50 mg tablets. Following approval of Phenoleptil® for treatment of canine epilepsy, it was repeatedly reported by clinicians and dog owners that switching from Luminal® (human tablets) to Phenoleptil® in epileptic dogs, which were controlled by treatment with Luminal®, induced recurrence of seizures. In the present study, we compared bioavailability of phenobarbital after single dose administration of Luminal® vet vs. Phenoleptil® with a crossover design in 8 healthy Beagle dogs. Both drugs were administered at a dose of 100 mg/dog, resulting in 8 mg/kg phenobarbital on average. Results Peak plasma concentrations (Cmax) following Luminal® vet vs. Phenoleptil® were about the same in most dogs (10.9 ± 0.92 vs. 10.5 ± 0.77 μg/ml), and only one dog showed noticeable lower concentrations after Phenoleptil® vs. Luminal® vet. Elimination half-life was about 50 h (50.3 ± 3.1 vs. 52.9 ± 2.8 h) without differences between the formulations. The relative bioavailability of the two products (Phenoleptil® vs. Luminal® vet.) was 0.98 ± 0.031, indicating that both formulations resulted in about the same bioavailability. Conclusions Overall, the two formulations did not differ significantly with respect to pharmacokinetic parameters when mean group parameters were compared. Thus, the reasons for the anecdotal reports, if true, that switching from the brand to the generic formulation of phenobarbital may lead to recurrence of seizures are obviously not related to a generally lower bioavailability of the generic formulation, although single dogs may exhibit lower plasma levels after the generic formulation that could be clinically meaningful. [ABSTRACT FROM AUTHOR]

Purpose: One important mechanism for chemoresistance of tumours is overexpression of the adenosine triphosphate-binding cassette transporter P-glycoprotein (Pgp). Pgp reduces intracellular concentrations of chemotherapeutic drugs. The aim of this study was to compare the suitability of the radiolabelled Pgp inhibitors [C]tariquidar and [C]elacridar with the Pgp substrate radiotracer ( R)-[C]verapamil for discriminating tumours expressing low and high levels of Pgp using small-animal PET imaging in a murine breast cancer model. Methods: Murine mammary carcinoma cells (EMT6) were continuously exposed to doxorubicin to generate a Pgp-overexpressing, doxorubicin-resistant cell line (EMT6AR1.0 cells). Both cell lines were subcutaneously injected into female athymic nude mice. One week after implantation, animals underwent PET scans with [C]tariquidar ( n = 7), [C]elacridar ( n = 6) and ( R)-[C]verapamil ( n = 7), before and after administration of unlabelled tariquidar (15 mg/kg). Pgp expression in tumour grafts was evaluated by Western blotting. Results: [C]Tariquidar showed significantly higher retention in Pgp-overexpressing EMT6AR1.0 compared with EMT6 tumours: the mean ± SD areas under the time-activity curves in scan 1 from time 0 to 60 min (AUC) were 38.8 ± 2.2 min and 25.0 ± 5.3 min ( p = 0.016, Wilcoxon matched pairs test). [C]Elacridar and ( R)-[C]verapamil were not able to discriminate Pgp expression in tumour models. Following administration of unlabelled tariquidar, both EMT6Ar1.0 and EMT6 tumours showed increases in uptake of [C]tariquidar, [C]elacridar and ( R)-[C]verapamil. Conclusion: Among the tested radiotracers, [C]tariquidar performed best in discriminating tumours expressing high and low levels of Pgp. Therefore [C]tariquidar merits further investigation as a PET tracer to assess Pgp expression levels in solid tumours. [ABSTRACT FROM AUTHOR]

Approximately one-third of epilepsy patients are pharmacoresistant. Overexpression of P-glycoprotein and other multidrug transporters at the blood-brain barrier is thought to play an important role in drug-refractory epilepsy. Thus, quantification of regionally different P-glycoprotein activity in the brain in vivo is essential to identify P-glycoprotein overactivity as the relevant mechanism for drug resistance in an individual patient. Using the radiolabeled P-glycoprotein substrate (R)-[11C]verapamil and different doses of coadministered tariquidar, which is an inhibitor of P-glycoprotein, we evaluated whether small-animal positron emission tomography can quantify regional changes in transporter function in the ratbrain at baseline and 48 h after apilocarpine-induced status epilepticus. P-glycoprotein expression was additionally quantified by immunohistochemistry. To reveal putative seizure-induced changes in blood-brain barrier integrity, we performed gadolinium-enhanced magneticresonance scansona 7.0 tesla small-animal scanner. Before P-glycoprotein modulation, brainuptakeof (R)-[11C]verapamilwaslowin all regions investigated in controlandpost-status epilepticus rats. After administration of 3mg/kg tariquidar, which inhibits P-glycoproteinonly partially,we observed increased regional differentiation in brain activity uptake in post-status epilepticus versus control rats, which diminished after maximal P-glycoprotein inhibition. Regional increases in the efflux rate constant k2 , but not in distribution volume VT or influx rate constant K1 , correlated significantly with increases in P-glycoprotein expression measured by immunohistochemistry. This imaging protocol proves to be suitable to detect seizure-induced regional changes in P-glycoprotein activity and is readily applicable to humans, with the aim to detect relevant mechanisms of pharmacoresistance in epilepsy in vivo. [ABSTRACT FROM AUTHOR]

Overactivity of the multidrug efflux transporter P-glycoprotein (P-gp) at the blood-brain barrier (BBB) is believed to play an important role in resistance to central nervous system drug treatment. ( R)-[11C]verapamil (VPM) PET can be used to measure the function of P-gp at the BBB, but low brain uptake of VPM hampers the mapping of regional differences in cerebral P-gp function and expression. The aim of this study was to evaluate the dose-response relationship of two potent P-gp inhibitors and to investigate if increased brain uptake of VPM mediated by P-gp inhibition can be used to assess regional differences in P-gp activity. Two groups of Sprague-Dawley rats ( n = 12) underwent single VPM PET scans at 120 min after administration of different doses of the P-gp inhibitors tariquidar and elacridar. In an additional six rats, paired VPM PET scans were performed before and after administration of 3 mg/kg tariquidar. Inhibitor administration resulted in an up to 11-fold increase in VPM brain distribution volumes (DV) with half-maximum effective dose (ED50) values of 3.0 ± 0.2 and 1.2 ± 0.1 mg/kg for tariquidar and elacridar, respectively. In paired PET scans, 3 mg/kg tariquidar resulted in regionally different enhancement of brain activity distribution, with lowest DV in cerebellum and highest DV in thalamus. Our data show that tariquidar and elacridar are able to increase VPM brain distribution in rat brain up to 11-fold over baseline at maximum effective doses, with elacridar being about three times more potent than tariquidar. Regional differences in tariquidar-induced modulation of VPM brain uptake point to regional differences in cerebral P-gp function and expression in rat brain. [ABSTRACT FROM AUTHOR]

Abstract: Over-expression of blood–brain barrier P-glycoprotein is considered as a major hurdle in the treatment of various CNS disorders. A down-regulation strategy is considered as one means to counteract disease- or therapy-associated induction of P-glycoprotein. Here, we evaluated whether a targeting of P-glycoprotein can be achieved in mouse brain capillary endothelial cells using siRNA. A 4-day treatment paradigm with once daily hydrodynamic intravenous injections of siRNA resulted in a significant reduction of the P-glycoprotein-labeled area in the hippocampal hilus and parietal cortex. P-glycoprotein expression proved to be down-regulated in these brain regions by 31 and 16%, respectively. An impact of siRNA administration on density of brain capillaries was excluded by quantification of the endothelial cell marker GLUT-1. In conclusion, the study provides first preliminary evidence that a down-regulation of P-glycoprotein can be achieved in brain capillary endothelial cells by administration of siRNA in vivo. [Copyright &y& Elsevier]