Biology subjects

Metcalf, C. S.

Publications and source records attributed to Metcalf, C. S..

3 recordsLinked to original sources

bioRxiv2021

Evaluation of spontaneous seizure activity, sex-dependent differences, behavioral comorbidities, and alterations in CA1 neuron firing properties in a mouse model of Dravet Syndrome

Dravet syndrome (DS) is a rare childhood epilepsy disorder resulting in spontaneous, recurrent seizures (SRS) and behavioral co-morbidities. To facilitate the discovery and development of anti-seizure drugs for DS, the contract site of the NINDS Epilepsy Therapy Screening Program (ETSP) has continued to evaluate a mouse model of DS. Scn1aA1783V/WT mice exhibited increased hyperactivity, thigmotaxis, and deficits in nest-building behavior. Ex-vivo brain slice electrophysiology experiments revealed increased excitability of hippocampal CA1 neurons specifically due to increased action potential firing frequency in response to brief depolarizations and decreased frequency of spontaneous GABAergic synaptic events. A video-EEG study revealed mice had on average, 1 seizure per day, with males seizing significantly more frequently than females. Increased proportion of seizure activity occurred during the dark phase of the light/dark cycle in both sexes. While clobazam, a drug commonly prescribed to patients with DS, had no effect on SRS activity at the tested doses, the seizure history and frequency observed in this study aids in determining the sample sizes and experimental timeline needed for adequately powered preclinical drug studies. Overall, this study provides a broad description of the Scn1aA1783V/WT mouse and highlights the utility of this model in therapy discovery.

pharmacology and toxicology↗

bioRxiv2020

Spontaneous recurrent seizures in an intra-amygdala kainate microinjection model of temporal lobe epilepsy are differentially sensitive to antiseizure drugs

The discovery and development of novel antiseizure drugs (ASDs) that are effective in controlling pharmacoresistant spontaneous recurrent seizures (SRSs) continues to represent a significant unmet clinical need. The Epilepsy Therapy Screening Program (ETSP) has undertaken efforts to address this need by adopting animal models that represent the salient features of human pharmacoresistant epilepsy and employing these models for preclinical testing of investigational ASDs. One such model that has garnered increased interest in recent years is the mouse variant of the Intra-Amygdala Kainate (IAK) microinjection model of mesial temporal lobe epilepsy (MTLE). In establishing a version of this model, several methodological variables were evaluated for their effect(s) on pertinent quantitative endpoints. Although administration of a benzodiazepine 40 minutes after kainate (KA) induced status epilepticus (SE) is commonly used to improve survival, data presented here demonstrates similar outcomes (mortality, hippocampal damage, latency periods, and 90-day SRS natural history) between mice given midazolam and those that were not. Using a version of this model that did not interrupt SE with a benzodiazepine, a 90-day natural history study was performed and survival, latency periods, SRS frequencies and durations, and SRS clustering data were quantified. Finally, an important step towards model adoption is to assess the sensitivities or resistances of SRSs to a panel of approved and clinically used ASDs. Accordingly, the following ASDs were evaluated for their effects on SRSs in these mice: phenytoin (20 mg/kg, b.i.d.), carbamazepine (30 mg/kg, t.i.d.), valproate (240 mg/kg, t.i.d.), diazepam (4 mg/kg, b.i.d.), and phenobarbital (25 and 50 mg/kg, b.i.d.). Valproate, diazepam, and phenobarbital significantly attenuated SRS frequency relative to vehicle controls at doses devoid of observable adverse behavioral effects. Only diazepam significantly increased seizure freedom. Neither phenytoin nor carbamazepine significantly altered SRS frequency or freedom under these experimental conditions. These data demonstrate that SRSs in this IAK model of MTLE are pharmacoresistant to two representative sodium channel-inhibiting ASDs (phenytoin and carbamazepine) but not to GABA receptor modulating ASDs (diazepam and phenobarbital) or a mixed-mechanism ASD (valproate). Accordingly, this model is being incorporated into the NINDS-funded ETSP testing platform for treatment resistant epilepsy. HighlightsO_LIAn intra-amygdala kainate model of TLE was evaluated for pharmacoresistant seizures C_LIO_LIAdministration of midazolam during status epilepticus did not affect mortality C_LIO_LIModel characteristics were evaluated over a 90-day natural history study C_LIO_LISpontaneous seizures were resistant to phenytoin and carbamazepine C_LIO_LISpontaneous seizures were sensitive to valproic acid, diazepam, and phenobarbital C_LI

neuroscience↗

bioRxiv2020

Development of an Antiseizure Drug Screening Platform for Dravet Syndrome at the NINDS contract site for the Epilepsy Therapy Screening Program

ObjectiveDravet syndrome (DS) is a rare, but catastrophic genetic epilepsy, with 80% of patients with carrying a mutation in the SCN1A gene. Currently, no anti-seizure drug (ASD) exists that adequately controls seizures. Patients with DS often present clinically with a febrile seizure and generalized tonic-clonic seizures that continue throughout life. To facilitate the development of ASDs for DS, the contract site of the NINDS Epilepsy Therapy Screening Program (ETSP) has evaluated a mouse model of DS using the conditional knock-in Scn1aA1783V/WT mouse. MethodsSurvival rates and temperature thresholds for Scn1aA1783V/WT were determined. Prototype ASDs were administered via intraperitoneal injections at the time-to-peak effect, which was previously determined, prior to the induction of hyperthermia-induced seizures. Protection was determined if ASDs significantly increased the temperature at which Scn1aA1783V/WT mice seized. ResultsApproximately 50% of Scn1aA1783V/WT survive to adulthood and all have hyperthermia-induce seizures. The results suggest that hyperthermia-induced seizures in this model of DS are highly refractory to a battery of ASDs. Exceptions were clobazam, tiagabine, and the combination of clobazam and valproic acid with add-on stiripentol, which elevated seizure thresholds SignificanceOverall, the data demonstrate the proposed model for DS is suitable for screening novel compounds for the ability to block hyperthermia-induced seizures and heterozygous mice can be evaluated repeatedly over the course of several weeks, allowing for higher throughput screening. Key Points O_LIScn1aA1783V/WT mice have a 50% survival rate and all have hyperthermia-induced seizures. C_LIO_LICommon DS treatments such as CLB and combinatorial therapy of CLB, VPA, and STP increase temperature thresholds in Scn1aA1783V/WT mice. C_LIO_LISodium channel blockers, such as CBZ and LTG, decrease temperature thresholds of Scn1aA1783V/WT mice as predicted. C_LIO_LIScn1aA1783V/WT mice are highly pharmacoresitant to common ASDs C_LIO_LIThe Scn1aA1783V/WT may be a useful preclinical drug screening platform for the treatment of DS. C_LI

pharmacology and toxicology↗