Spontaneous and optogenetically induced cortical spreading depolarization in familial hemiplegic migraine type 1 mutant mice.

Mechanisms underlying the migraine aura are incompletely understood, which to large extent is related to a lack of models in which cortical spreading depolarization (CSD), the correlate of the aura, occurs spontaneously. Here, we investigated electrophysiological and behavioural CSD features in freely behaving mice expressing mutant CaV2.1 Ca2+ channels, either with the milder R192Q or the severer S218L missense mutation in the α1 subunit, known to cause familial hemiplegic migraine type 1 (FHM1) in patients. Very rarely, spontaneous CSDs were observed in mutant but never in wildtype mice. In homozygous Cacna1aR192Q mice exclusively single-wave CSDs were observed whereas heterozygous Cacna1aS218L mice displayed multiple-wave events, seemingly in line with the more severe clinical phenotype associated with the S218L mutation. Spontaneous CSDs were associated with body stretching, one-directional slow head turning, and rotating movement of the body. Spontaneous CSD events were compared with those induced in a controlled manner using minimally invasive optogenetics. Also in the optogenetic experiments single-wave CSDs were observed in Cacna1aR192Q and Cacna1aS218L mice (whereas the latter also showed multiple-wave events) with movements similar to those observed with spontaneous events. Compared to wildtype mice, FHM1 mutant mice exhibited a reduced threshold and an increased propagation speed for optogenetically induced CSD with a more profound CSD-associated dysfunction, as indicated by a prolonged suppression of transcallosal evoked potentials and a reduction of unilateral forepaw grip performance. When induced during sleep, the optogenetic CSD threshold was particularly lowered, which may explain why spontaneous CSD events predominantly occurred during sleep. In conclusion, our data show that key neurophysiological and behavioural features of optogenetically induced CSDs mimic those of rare spontaneous events in FHM1 R192Q and S218L mutant mice with differences in severity in line with FHM1 clinical phenotypes seen with these mutations.

Impaired θ-γ Coupling Indicates Inhibitory Dysfunction and Seizure Risk in a Dravet Syndrome Mouse Model.

Dravet syndrome (DS) is an epileptic encephalopathy that still lacks biomarkers for epileptogenesis and its treatment. Dysfunction of NaV1.1 sodium channels, which are chiefly expressed in inhibitory interneurons, explains the epileptic phenotype. Understanding the network effects of these cellular deficits may help predict epileptogenesis. Here, we studied θ-γ coupling as a potential marker for altered inhibitory functioning and epileptogenesis in a DS mouse model. We found that cortical θ-γ coupling was reduced in both male and female juvenile DS mice and persisted only if spontaneous seizures occurred. θ-γ Coupling was partly restored by cannabidiol (CBD). Locally disrupting NaV1.1 expression in the hippocampus or cortex yielded early attenuation of θ-γ coupling, which in the hippocampus associated with fast ripples, and which was replicated in a computational model when voltage-gated sodium currents were impaired in basket cells (BCs). Our results indicate attenuated θ-γ coupling as a promising early indicator of inhibitory dysfunction and seizure risk in DS.

Apnea Associated with Brainstem Seizures in Cacna1aS218L Mice Is Caused by Medullary Spreading Depolarization.

Seizure-related apnea is common and can be lethal. Its mechanisms however remain unclear and preventive strategies are lacking. We postulate that brainstem spreading depolarization (SD), previously associated with lethal seizures in animal models, initiates apnea upon invasion of brainstem respiratory centers. To study this, we assessed effects of brainstem seizures on brainstem function and respiration in male and female mice carrying a homozygous S218L missense mutation that leads to gain-of-function of voltage-gated CaV2.1 Ca2+ channels and high risk for fatal seizures. Recordings of brainstem DC potential and neuronal activity, cardiorespiratory activity and local tissue oxygen were performed in freely behaving animals. Brainstem SD occurred during all spontaneous fatal seizures and, unexpectedly, during a subset of nonfatal seizures. Seizure-related SDs in the ventrolateral medulla correlated with respiratory suppression. Seizures induced by stimulation of the inferior colliculus could evoke SD that spread in a rostrocaudal direction, preceding local tissue hypoxia and apnea, indicating that invasion of SD into medullary respiratory centers initiated apnea and hypoxia rather than vice versa Fatal outcome was prevented by timely resuscitation. Moreover, NMDA receptor antagonists MK-801 and memantine prevented seizure-related SD and apnea, which supports brainstem SD as a prerequisite for brainstem seizure-related apnea in this animal model and has translational value for developing strategies that prevent fatal ictal apnea.SIGNIFICANCE STATEMENT Apnea during and following seizures is common, but also likely implicated in sudden unexpected death in epilepsy (SUDEP). This underlines the need to understand mechanisms for potentially lethal seizure-related apnea. In the present work we show, in freely behaving SUDEP-prone transgenic mice, that apnea is induced when spontaneous brainstem seizure-related spreading depolarization (SD) reaches respiratory nuclei in the ventrolateral medulla. We show that brainstem seizure-related medullary SD is followed by local hypoxia and recovers during nonfatal seizures, but not during fatal events. NMDA receptor antagonists prevented medullary SD and apnea, which may be of translational value.

Brainstem spreading depolarization and cortical dynamics during fatal seizures in Cacna1a S218L mice.

Sudden unexpected death in epilepsy (SUDEP) is a fatal complication of epilepsy in which brainstem spreading depolarization may play a pivotal role, as suggested by animal studies. However, patiotemporal details of spreading depolarization occurring in relation to fatal seizures have not been investigated. In addition, little is known about behavioural and neurophysiological features that may discriminate spontaneous fatal from non-fatal seizures. Transgenic mice carrying the missense mutation S218L in the α1A subunit of Cav2.1 (P/Q-type) Ca2+ channels exhibit enhanced excitatory neurotransmission and increased susceptibility to spreading depolarization. Homozygous Cacna1aS218L mice show spontaneous non-fatal and fatal seizures, occurring throughout life, resulting in reduced life expectancy. To identify characteristics of fatal and non-fatal spontaneous seizures, we compared behavioural and electrophysiological seizure dynamics in freely-behaving homozygous Cacna1aS218L mice. To gain insight on the role of brainstem spreading depolarization in SUDEP, we studied the spatiotemporal distribution of spreading depolarization in the context of seizure-related death. Spontaneous and electrically-induced seizures were investigated by video monitoring and electrophysiological recordings in freely-behaving Cacna1aS218L and wild-type mice. Homozygous Cacna1aS218L mice showed multiple spontaneous tonic-clonic seizures and died from SUDEP in adulthood. Death was preceded by a tonic-clonic seizure terminating with hindlimb clonus, with suppression of cortical neuronal activity during and after the seizure. Induced seizures in freely-behaving homozygous Cacna1aS218L mice were followed by multiple spreading depolarizations and death. In wild-type or heterozygous Cacna1aS218L mice, induced seizures and spreading depolarization were never followed by death. To identify temporal and regional features of seizure-induced spreading depolarization related to fatal outcome, diffusion-weighted MRI was performed in anaesthetized homozygous Cacna1aS218L and wild-type mice. In homozygous Cacna1aS218L mice, appearance of seizure-related spreading depolarization in the brainstem correlated with respiratory arrest that was followed by cardiac arrest and death. Recordings in freely-behaving homozygous Cacna1aS218L mice confirmed brainstem spreading depolarization during spontaneous fatal seizures. These data underscore the value of the homozygous Cacna1aS218L mouse model for identifying discriminative features of fatal compared to non-fatal seizures, and support a key role for cortical neuronal suppression and brainstem spreading depolarization in SUDEP pathophysiology.

Kainate-induced epileptogenesis alters circular hole board learning strategy but not the performance of C57BL/6J mice.

Patients with mesial temporal lobe epilepsy (mTLE) frequently show cognitive deficits. However, the relation between mTLE and cognitive impairment is poorly understood. To gain more insight into epilepsy-associated alterations in cognitive performance, we studied the spatial learning of C57BL/6J mice five weeks after kainate-induced status epilepticus (SE). Typically, structural hippocampal rearrangements take place within five weeks after SE. Mice were monitored by exposing them to four tasks with a focus on spatial memory and anxiety: the circular hole board, modified hole board, novel object-placement task, and elevated plus maze. On the circular hole board, animals showed a higher preference for hippocampus-independent strategies after SE. In contrast, no change in strategy was seen on the modified hole board, but animals with SE were able to finish the task more often. Animals did not have an increased preference for a relocated object in the novel object-placement task but showed an increased locomotion after SE. No indications for altered anxiety were found when tested on the elevated plus maze following SE. These data suggest that the circular hole board is a well-suited paradigm to detect subtle SE-induced hippocampal deficits.

Simultaneous in vivo measurements of receptor density and affinity using [11C]flumazenil and positron emission tomography: comparison of full saturation and steady state methods.

The binding of PET radiotracer [(11)C]flumazenil to the GABA(A) receptors is described by the receptor density (B(max)) and binding affinity (K(D)). The estimation of B(max) and K(D) is usually based on Scatchard analysis including at least two PET scans at steady state of various specific activities. Recently, a novel full saturation method to estimate both B(max) and K(D) was proposed, in which a saturating dose of flumazenil is given to cover a wide range of different receptor occupancies within a single scan. The aim of the present study was a direct comparison of steady state and full saturation methods for determining B(max) and K(D) of [(11)C]flumazenil in the same group of male Sprague-Dawley rats. Fourteen rats underwent 3 consecutive [(11)C]flumazenil scans of 30 min duration each. A tracer dose was injected at the start of the first scan. Prior to the second scan the tracer was mixed with 5, 20, 100 or 500 µg unlabelled (cold) flumazenil to cover a wide range of receptor occupancies during the scan. The third scan was performed during a constant intravenous infusion of unlabelled flumazenil, resulting in ~50% GABA(A) receptor occupancy. The first and third scans were part of the steady state method, whilst the second scan was performed according to the full saturation method. For both methods, B(max) and K(D) were then derived by compartmental modelling. Both methods yielded similar B(max) and K(D) estimates. The full saturation method yielded B(max) values of 37 ± 5.8 ng · mL(-1) and K(D) values of 7.6 ± 2.0 ng · mL(-1), whilst the steady state method yielded B(max) values of 33 ± 5.4 ng · mL(-1) and K(D) values of 7.1 ± 0.8 ng · mL(-1). The main advantage of the full saturation method is that B(max) and K(D) can be obtained from a single PET scan.

(R)-[11C]verapamil PET studies to assess changes in P-glycoprotein expression and functionality in rat blood-brain barrier after exposure to kainate-induced status epilepticus.

BACKGROUND: Increased functionality of efflux transporters at the blood-brain barrier may contribute to decreased drug concentrations at the target site in CNS diseases like epilepsy. In the rat, pharmacoresistant epilepsy can be mimicked by inducing status epilepticus by intraperitoneal injection of kainate, which leads to development of spontaneous seizures after 3 weeks to 3 months. The aim of this study was to investigate potential changes in P-glycoprotein (P-gp) expression and functionality at an early stage after induction of status epilepticus by kainate. METHODS: (R)-[11C]verapamil, which is currently the most frequently used positron emission tomography (PET) ligand for determining P-gp functionality at the blood-brain barrier, was used in kainate and saline (control) treated rats, at 7 days after treatment. To investigate the effect of P-gp on (R)-[11C]verapamil brain distribution, both groups were studied without or with co-administration of the P-gp inhibitor tariquidar. P-gp expression was determined using immunohistochemistry in post mortem brains. (R)-[11C]verapamil kinetics were analyzed with approaches common in PET research (Logan analysis, and compartmental modelling of individual profiles) as well as by population mixed effects modelling (NONMEM). RESULTS: All data analysis approaches indicated only modest differences in brain distribution of (R)-[11C]verapamil between saline and kainate treated rats, while tariquidar treatment in both groups resulted in a more than 10-fold increase. NONMEM provided most precise parameter estimates. P-gp expression was found to be similar for kainate and saline treated rats. CONCLUSIONS: P-gp expression and functionality does not seem to change at early stage after induction of anticipated pharmacoresistant epilepsy by kainate.

Pharmacokinetics of clindamycin in pregnant women in the peripartum period.

The study presented here was performed to determine the pharmacokinetics of intravenously administered clindamycin in pregnant women. Seven pregnant women treated with clindamycin were recruited. Maternal blood and arterial and venous umbilical cord blood samples were obtained. Maternal clindamycin concentrations were analyzed by nonlinear mixed-effects modeling with the NONMEM program. The data were best described by a linear three-compartment model. The clearance and the volume of distribution at steady state were 10.0 liters/h and 6.32 x 10(3) liters, respectively. Monte Carlo simulations were performed to determine the area under the concentration curve (AUC) for the free (unbound) drug (f) in maternal serum for 24 h divided by the MIC (fAUC(0-24)/MIC). At a MIC of 0.5 mg/liter, which is the EUCAST breakpoint, the attainment at the lower 95% confidence interval (CI) was 24.6 if the level of protein binding was 65%, and this value concurred well with the target value of 27. However, for higher degrees of protein binding, as has been described in the literature, the attainment was lower, down to 10.2 for a protein binding level of 85% (lower 95% CI). The concentrations in umbilical cord blood were lower than those in maternal blood. The concentration-time profiles in maternal serum indicate that the level of exposure to clindamycin may be too low in these patients. Together with the lower concentrations in umbilical cord blood, this finding suggests that the current dosing regimen may not be adequate to protect all neonates from group B streptococcal disease.

Mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) modeling in translational drug research.

The use of pharmacokinetic-pharmacodynamic (PK-PD) modeling in translational drug research is a promising approach that provides better understanding of drug efficacy and safety. It is applied to predict efficacy and safety in humans using in vitro bioassay and/or in vivo animal data. Current research in PK-PD modeling focuses on the development of mechanism-based models with improved extrapolation and prediction properties. A key element in mechanism-based PK-PD modeling is the explicit distinction between parameters for describing (i) drug-specific properties and (ii) biological system-specific properties. Mechanism-based PK-PD models contain specific expressions for the characterization of processes on the causal path between drug exposure and drug response. The different terms represent: target-site distribution, target binding and activation and transduction. Ultimately, mechanism-based PK-PD models will also characterize the interaction of the drug effect with disease processes and disease progression. In this review, the principles of mechanism-based PK-PD modeling are described and illustrated by recent applications.

Pharmacokinetics of amoxicillin in maternal, umbilical cord, and neonatal sera.

The pharmacokinetics of amoxicillin were studied in umbilical cord and neonatal sera relative to maternal concentrations in prevention of neonatal group B streptococcus infection. The subjects were 44 pregnant women receiving amoxicillin as 1 or 2 g as an intravenous infusion. To measure the concentrations, blood samples were obtained from the mother, the arterial and venous umbilical cord, and the neonate. The pharmacokinetics were characterized by a five-compartment model by using nonlinear mixed-effects (population) modeling. The population estimates for the clearance, central volume of distribution, and the two peripheral maternal volumes of distribution were 19.7 +/- 0.99 liters/h, 6.40 +/- 0.61 liters, and 5.88 +/- 0.83 liters (mean +/- standard error), respectively. The volume of distribution of the venous umbilical cord and the neonatal volume of distribution were 3.40 liters and 11.9 liters, respectively. The pharmacokinetic parameter estimates were used to simulate the concentration-time profiles in maternal, venous umbilical cord, and neonatal sera. The peak concentration in the venous umbilical cord serum was 18% of the maternal peak concentration. It was reached 3.3 min after the maternal peak concentration. The concentration-time profile in neonatal serum was determined by the profile in venous umbilical cord serum, which in turn depended on the profile in maternal serum. Furthermore, the simulated concentrations in maternal, venous umbilical cord, and neonatal sera exceeded the MIC for group B streptococcus for more than 90% of the 4-h dosing interval. In a first approximation, the 2-g infusion to the mother appears to be adequate for the prevention of group B streptococcal disease. However, to investigate the efficacy of the prophylaxis, further studies of the interindividual variability in pharmacokinetics are indicated.

Changes in GABAA receptor properties in amygdala kindled animals: in vivo studies using [11C]flumazenil and positron emission tomography.

PURPOSE: The purpose of the present investigation was to quantify alterations in GABA(A) receptor density in vivo in rats subjected to amygdala kindling. METHODS: The GABA(A) receptor density was quantified by conducting a [(11)C]flumazenil (FMZ) positron emission tomography (PET) study according to the full saturation method, in which each animal received a single injection of FMZ to fully saturate the GABA(A) receptors. Subsequently, the concentration-time curves of FMZ in blood [using high-pressure liquid chromatography with UV detector (HPLC-UV) or high-performance liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS)] and brain (with PET-scanning) were analyzed by population modeling using a pharmacokinetic model, containing expressions to describe the time course of FMZ in blood and brain. RESULTS: The GABA(A) receptor density (B(max)) in kindled rats was decreased by 36% compared with controls. This is consistent with a reduction of 28% in electroencephalography (EEG) effect of midazolam in the same animal model, suggesting that a reduced number of GABA(A) receptors underlies the decreased efficacy of midazolam. Furthermore, receptor affinity (K(D)) was not changed, but the total volume of distribution in the brain (V(Br)), is increased to 178% of control after kindling, which might indicate an alteration in the transport of FMZ across the blood-brain barrier. CONCLUSIONS: Both the GABA(A) receptor density (B(max)), and possibly also the blood-brain barrier transport of FMZ (V(Br)) are altered after kindling. Furthermore, this study indicates the feasibility of conducting PET studies for quantifying moderate changes in GABA(A) receptor density in a rat model of epilepsy in vivo.

Amoxicillin pharmacokinetics in pregnant women with preterm premature rupture of the membranes.

OBJECTIVE: This study was undertaken to study the pharmacokinetics of intravenously administered amoxicillin in pregnant women with preterm premature rupture of the membranes (PPROM). STUDY DESIGN: Healthy women with PPROM were recruited and treated with amoxicillin (2 g initially and 1 g subsequently). Blood samples were obtained from the opposite arm and concentrations determined with the use of high-pressure liquid chromatography. Nonlinear mixed-effects modeling was performed in nonlinear mixed effect (population) modeling. RESULTS: The pharmacokinetics of 17 patients was described by a 3-compartment model. Clearance and volume of distribution at steady state were 22.8 L/h and 21.4 L/h, respectively, similar to values in nonpregnant individuals. There was little variability between patients. No relationship was observed between values of individual pharmacokinetic parameters and various covariates. CONCLUSION: The pharmacokinetics of amoxicillin in pregnant patients with PPROM similar to nonpregnant individuals. Given the small interindividual variability in pharmacokinetics, no dose adjustments are required to account for differences between subjects under normal circumstances.

The influence of labour on the pharmacokinetics of intravenously administered amoxicillin in pregnant women.

AIMS: Many physiological changes take place during pregnancy and labour. These might change the pharmacokinetics of amoxicillin, necessitating adjustment of the dose for prevention of neonatal infections. We investigated the influence of labour on the pharmacokinetics of amoxicillin. METHODS: Pregnant women before and during labour were recruited and treated with amoxicillin intravenously. A postpartum dose was offered. Blood samples were obtained and amoxicillin concentrations were determined using high-pressure liquid chromatography. The pharmacokinetics were characterized by nonlinear mixed-effects modelling using NONMEM. RESULTS: The pharmacokinetics of amoxicillin in 34 patients was best described by a three-compartment model. Moderate interindividual variability was identified in CL, central and peripheral volumes of distribution. The volume of distribution (V) increased with an increasing amount of oedema. Labour influenced the parameter estimate of peripheral volume of distribution (V(2)). V(2) was decreased during labour, and even more in the immediate postpartum period. For all patients the population estimates (mean +/- SE) for CL and V were 21.1 +/- 4.1 l h(-1) (CL), 8.7 +/- 6.6 l (V(1)), 11.8 +/- 7.7 l (V(2)) and 20.5 +/- 15.4 l (V(3)) respectively. CONCLUSIONS: The peripheral distribution volume of amoxicillin in pregnant women during labour and immediately postpartum is decreased. However, these changes are not clinically relevant and do not warrant deviations from the recommended dosing regimen for amoxicillin during labour in healthy pregnant patients.

Synthesis and preliminary preclinical evaluation of fluorine-18 labelled isatin-4-(4-methoxyphenyl)-3-thiosemicarbazone ([18F]4FIMPTC) as a novel PET tracer of P-glycoprotein expression.

BACKGROUND: Several P-glycoprotein (P-gp) substrate tracers are available to assess P-gp function in vivo, but attempts to develop a tracer for measuring expression levels of P-gp have not been successful. Recently, (Z)-2-(5-fluoro-2-oxoindolin-3-ylidene)-N-(4-methoxyphenyl)hydrazine-carbothioamide was described as a potential selective P-gp inhibitor that is not transported by P-gp. Therefore, the purpose of this study was to radiolabel two of its analogues and to assess their potential for imaging P-gp expression using PET. RESULTS: [18F]2-(4-fluoro-2-oxoindolin-3-ylidene)-N-(4-methoxyphenyl)hydrazine-carbothioamide ([18F]5) and [18F]2-(6-fluoro-2-oxoindolin-3-ylidene)-N-(4-methoxyphenyl)hydrazine-carbothioamide ([18F]6) were synthesized and both their biodistribution and metabolism were evaluated in rats. In addition, PET scans were acquired in rats before and after tariquidar (P-gp inhibitor) administration as well as in P-gp knockout (KO) mice.Both [18F]5 and [18F]6 were synthesized in 2-3% overall yield, and showed high brain uptake in ex vivo biodistribution studies. [18F]6 appeared to be metabolically unstable in vivo, while [18F]5 showed moderate stability with limited uptake of radiolabelled metabolites in the brain. PET studies showed that transport of [18F]5 across the blood-brain barrier was not altered by pre-treatment with the P-gp inhibitor tariquidar, and uptake was significantly lower in P-gp KO than in wild-type animals and indeed transported across the BBB or bound to P-gp in endothelial cells. CONCLUSION: In conclusion, [18F]5 and [18F]6 were successfully and reproducibly synthesized, albeit with low radiochemical yields. [18F]5 appears to be a radiotracer that binds to P-gp, as showed in P-gp knock-out animals, but is not a substrate for P-gp.

Biomarkers in epilepsy-A modelling perspective.

Biomarkers can be categorised from type 0 (genotype or phenotype), through 6 (clinical scales), each level representing a part of the processes involved in the biological system and drug treatment. This classification facilitates the identification and connection of information required to fully (mathematically) model a disease and its treatment using integrated information from biomarkers. Two recent reviews thoroughly discussed the current status and development of biomarkers for epilepsy, but a path towards the integration of such biomarkers for the personalisation of anti-epileptic drug treatment is lacking. Here we aim to 1) briefly categorise the available epilepsy biomarkers and identify gaps, and 2) provide a modelling perspective on approaches to fill such gaps. There is mainly a lack of biomarker types 2 (target occupancy) and 3 (target activation). Current literature typically focuses on qualitative biomarkers for diagnosis and prediction of treatment response or failure, leaving a need for biomarkers that help to quantitatively understand the overall system to explain and predict differences in disease and treatment outcome. Due to the complexity of epilepsy, filling the biomarker gaps will require collaboration and expertise from the fields of systems biology and systems pharmacology.

Optogenetic induction of cortical spreading depression in anesthetized and freely behaving mice.

Cortical spreading depression, which plays an important role in multiple neurological disorders, has been studied primarily with experimental models that use highly invasive methods. We developed a relatively non-invasive optogenetic model to induce cortical spreading depression by transcranial stimulation of channelrhodopsin-2 ion channels expressed in cortical layer 5 neurons. Light-evoked cortical spreading depression in anesthetized and freely behaving mice was studied with intracortical DC-potentials, multi-unit activity and/or non-invasive laser Doppler flowmetry, and optical intrinsic signal imaging. In anesthetized mice, cortical spreading depression induction thresholds and propagation rates were similar for invasive (DC-potential) and non-invasive (laser Doppler flowmetry) recording paradigms. Cortical spreading depression-related vascular and parenchymal optical intrinsic signal changes were similar to those evoked with KCl. In freely behaving mice, DC-potential and multi-unit activity recordings combined with laser Doppler flowmetry revealed cortical spreading depression characteristics comparable to those under anesthesia, except for a shorter cortical spreading depression duration. Cortical spreading depression resulted in a short increase followed by prolonged reduction of spontaneous active behavior. Motor function, as assessed by wire grip tests, was transiently and unilaterally suppressed following a cortical spreading depression. Optogenetic cortical spreading depression induction has significant advantages over current models in that multiple cortical spreading depression events can be elicited in a non-invasive and cell type-selective fashion.

Parametric Methods for Dynamic 11C-Phenytoin PET Studies.

In this study, the performance of various methods for generating quantitative parametric images of dynamic 11C-phenytoin PET studies was evaluated. Methods: Double-baseline 60-min dynamic 11C-phenytoin PET studies, including online arterial sampling, were acquired for 6 healthy subjects. Parametric images were generated using Logan plot analysis, a basis function method, and spectral analysis. Parametric distribution volume (VT) and influx rate (K1) were compared with those obtained from nonlinear regression analysis of time-activity curves. In addition, global and regional test-retest (TRT) variability was determined for parametric K1 and VT values. Results: Biases in VT observed with all parametric methods were less than 5%. For K1, spectral analysis showed a negative bias of 16%. The mean TRT variabilities of VT and K1 were less than 10% for all methods. Shortening the scan duration to 45 min provided similar VT and K1 with comparable TRT performance compared with 60-min data. Conclusion: Among the various parametric methods tested, the basis function method provided parametric VT and K1 values with the least bias compared with nonlinear regression data and showed TRT variabilities lower than 5%, also for smaller volume-of-interest sizes (i.e., higher noise levels) and shorter scan duration.

Altered GABAA receptor density and unaltered blood-brain barrier [11C]flumazenil transport in drug-resistant epilepsy patients with mesial temporal sclerosis.

Studies in rodents suggest that flumazenil is a P-glycoprotein substrate at the blood-brain barrier. This study aimed to assess whether [11C]flumazenil is a P-glycoprotein substrate in humans and to what extent increased P-glycoprotein function in epilepsy may confound interpretation of clinical [11C]flumazenil studies used to assess gamma-aminobutyric acid A receptors. Nine drug-resistant patients with epilepsy and mesial temporal sclerosis were scanned twice using [11C]flumazenil before and after partial P-glycoprotein blockade with tariquidar. Volume of distribution, nondisplaceable binding potential, and the ratio of rate constants of [11C]flumazenil transport across the blood-brain barrier (K1/k2) were derived for whole brain and several regions. All parameters were compared between pre- and post-tariquidar scans. Regional results were compared between mesial temporal sclerosis and contralateral sides. Tariquidar significantly increased global K1/k2 (+23%) and volume of distribution (+10%), but not nondisplaceable binding potential. At the mesial temporal sclerosis side volume of distribution and nondisplaceable binding potential were lower in hippocampus (both ∼-19%) and amygdala (both ∼-16%), but K1/k2 did not differ, suggesting that only regional gamma-aminobutyric acid A receptor density is altered in epilepsy. In conclusion, although [11C]flumazenil appears to be a (weak) P-glycoprotein substrate in humans, this does not seem to affect its role as a tracer for assessing gamma-aminobutyric acid A receptor density.

Towards a mechanism-based analysis of pharmacodynamic drug-drug interactions in vivo.

The combination of drugs is a common practice for enhancing the efficiency of drug treatment, but selection of the optimal combination and the optimal doses remains a matter of trial and error. Prediction of synergistic, additive and antagonistic responses to drug combinations in vivo is therefore of considerable interest. The present review discusses the application of mathematical and statistical models to assess combined drug action by response surface modelling. The most commonly applied models are designed to distinguish between synergistic and additive responses on the basis of a single parameter to indicate whether a drug combination acts synergistic or not. It is, however, recognized that these relatively simple models often do not adequately describe complex drug interactions. This has led to the application of increasingly complex models with multiple drug interaction parameters that can describe a wide range of synergistic and antagonistic responses in a single-response surface. The capability to describe response surfaces with high resolution offers the opportunity to develop an understanding of the mechanisms that underlie the observed combined drug response. Operational models for drug interaction constitute a highly versatile framework for mechanism-based modelling by taking the signal transduction properties of the drug combination into account. On this basis, it is predicted that the occurrence of synergism is favoured by convergence of drug signals late in the signal transduction pathway as opposed to proximal convergence. Furthermore, a high efficiency of signal transduction poses in general a barrier to the occurrence of synergism. The in vivo application of operational models with advanced response surface modelling techniques will facilitate the rational development of synergistic drug combinations.

Multi-omics profile of the mouse dentate gyrus after kainic acid-induced status epilepticus.

Temporal lobe epilepsy (TLE) can develop from alterations in hippocampal structure and circuit characteristics, and can be modeled in mice by administration of kainic acid (KA). Adult neurogenesis in the dentate gyrus (DG) contributes to hippocampal functions and has been reported to contribute to the development of TLE. Some of the phenotypical changes include neural stem and precursor cells (NPSC) apoptosis, shortly after their birth, before they produce hippocampal neurons. Here we explored these early phenotypical changes in the DG 3 days after a systemic injection of KA inducing status epilepticus (KA-SE), in mice. We performed a multi-omics experimental setup and analyzed DG tissue samples using proteomics, transcriptomics and microRNA profiling techniques, detecting the expression of 2327 proteins, 13401 mRNAs and 311 microRNAs. We here present a description of how these data were obtained and make them available for further analysis and validation. Our data may help to further identify and characterize molecular mechanisms involved in the alterations induced shortly after KA-SE in the mouse DG.