Genetic and pharmacological manipulations that alter metabolism suppress seizure-like activity in Drosophila

Glial expression of Drosophila UBE3A causes spontaneous seizures modulated by 5-HT signaling

Misexpression of the E3 ubiquitin ligase UBE3A is thought to contribute to a range of neurological disorders. In the context of Dup15q syndrome, excess genomic copies of UBE3A is thought to contribute to the autism, muscle tone and spontaneous seizures characteristic of the disorder. In a Drosophila model of Dup 15q syndrome, it was recently shown glial-driven expression of the UBE3A ortholog dube3a led to a "bang-sensitive" phenotype, where mechanical shock triggers convulsions, suggesting glial dube3a expression contributes to hyperexcitability in flies. Here we directly compare the consequences of glial- and neuronal-driven dube3a expression on motor coordination and neuronal excitability in Drosophila. We utilized IowaFLI tracker and developed a hidden Markov Model to classify seizure-related immobilization. Both glial and neuronal driven dube3a expression led to clear motor phenotypes. However, only glial-driven dube3a expression displayed spontaneous immobilization events, that were exacerbated at high-temperature (38 °C). Using a tethered fly preparation we monitored flight muscle activity, we found glial-driven dube3a flies display spontaneous spike discharges which were bilaterally synchronized indicative of seizure activity. Neither control flies, nor neuronal- dube3a overexpressing flies display such firing patterns. Prior drug screen indicated bang-sensitivity in glial-driven dube3a expressing flies could be suppressed by certain 5-HT modulators. Consistent with this report, we found glial-driven dube3a flies fed the serotonin reuptake inhibitor vortioxetine and the 5HT 2A antagonist ketanserin displayed reduced immobilization and spike bursting. Together these findings highlight the potential for glial pathophysiology to drive Dup15q syndrome-related seizure activity.

Effects of valproate on seizure-like activity in Drosophila melanogaster with a knockdown of Ube3a in different neuronal populations as a model of Angelman Syndrome

Angelman Syndrome is a rare, genetically induced neurodevelopmental disorder. This disorder stems from a mutation or deletion of the maternal UBE3A gene. Characteristics of this disease include developmental delay, recurring seizures, and severe intellectual disabilities. We studied seizure activity in male Drosophila melanogaster with a knockdown of Ube3a in different neuronal populations (GABAergic, glutamatergic, mushroom body, and all neurons) and investigated the effects of the antiseizure medication (ASM) on seizure-like activity. Epileptiform activity was monitored in individual fruit flies using imaging chambers and mechanically induced seizures using a vortex assay. A positive control was also used: eas (easily shocked seizure phenotype). Seizure activity was analyzed for sums of seizure durations, number of seizures, and total time to return to normal activity. Ube3a knockdowns in GABAergic neurons elicited more seizure-like episodes than knockdowns in glutamatergic neurons and were on par with the positive control group and those with knockdowns in the mushroom bodies. We have established a method whereby valproate could be administered through food rather than through injections to effectively treat epileptiform activity. We demonstrated that if Ube3a is not knocked down pan-neuronally, Angelman Syndrome seizure-like activity can be studied using Drosophila melanogaster and therefore allows for high-throughput drug discovery.

Characterization of Seizure Induction Methods in Drosophila

Epilepsy is one of the most common neurologic disorders. Around one third of patients do not respond to current medications. This lack of treatment indicates a need for better understanding of the underlying mechanisms and, importantly, the identification of novel targets for drug manipulation. The fruit fly Drosophila melanogaster has a fast reproduction time, powerful genetics, and facilitates large sample sizes, making it a strong model of seizure mechanisms. To better understand behavioral and physiological phenotypes across major fly seizure genotypes we systematically measured seizure severity and secondary behavioral phenotypes at both the larval and adult stage. Comparison of several seizure-induction methods; specifically electrical, mechanical and heat induction, show that larval electroshock is the most effective at inducing seizures across a wide range of seizure-prone mutants tested. Locomotion in adults and larvae was found to be non-predictive of seizure susceptibility. Recording activity in identified larval motor neurons revealed variations in action potential (AP) patterns, across different genotypes, but these patterns did not correlate with seizure susceptibility. To conclude, while there is wide variation in mechanical induction, heat induction, and secondary phenotypes, electroshock is the most consistent method of seizure induction across known major seizure genotypes in Drosophila.

The addition of a lipid-rich dietary supplement eliminates seizure-like activity and paralysis in the drosophila bang sensitive mutants

OBJECTIVE

To investigate the effect that a diet supplemented with KetoCal 4:1, a commercially available dietary formula consisting of a 4:1 ratio of fats to carbohydrates plus proteins, had on the seizure-like activity (SLA) and paralysis normally exhibited by the Drosophila Bang-sensitive (BS) paralytic mutants following mechanical shock.

METHODS

Given that dietary changes are known to reduce seizures in humans and animal models, three BS mutants, easily-shocked (eas), bang-senseless (para^bss), and technical knockout (tko), were fed a standard cornmeal/yeast/sugar diet supplemented with 10% KetoCal 4:1 (KetoCal-sup diet). Newly eclosed BS flies were fed this diet for 3-7 days and the effect this had on SLA, paralysis, locomotor activity, triglyceride levels, and glucose levels was examined.

RESULTS

All three genotypes displayed significant reductions in SLA and BS sensitivity following mechanical shock. After only 3 days on the diet, 95% of tko flies no longer exhibited SLA or paralysis, and near complete suppression of the BS phenotype was seen by day 7. In the case of eas, there was a 78% reduction of SLA after 3 days on the diet and SLA was completely suppressed by day 7. The para^bss flies showed a similar but less robust reduction of SLA on the diet as there was only a 68% reduction of SLA and paralysis following 7 days on the diet. The diet did not suppress activity globally as tko flies had increased basal locomotor activity on the diet while the para^bss and eas flies showed no significant change in basal activity. The KetoCal-sup diet did not significantly alter the triglyceride levels or the total glucose levels in the BS mutants. In addition, the SLA and BS suppression was maintained even when the BS mutants were transitioned back to a standard fly diet.

CONCLUSIONS

The SLA and paralysis associated with the Drosophila BS phenotype can be effectively suppressed by transient exposure to a KetoCal-sup diet. This suppression was not dependent upon long term maintenance of the diet and it was not associated with alterations in total glucose or triglyceride levels in these flies.

A Systematic Review on Non-mammalian Models in Epilepsy Research

Epilepsy is a common neurological disorder characterized by seizures which result in distinctive neurobiological and behavioral impairments. Not much is known about the causes of epilepsy, making it difficult to devise an effective cure for epilepsy. Moreover, clinical studies involving epileptogenesis and ictogenesis cannot be conducted in humans due to ethical reasons. As a result, animal models play a crucial role in the replication of epileptic seizures. In recent years, non-mammalian models have been given a primary focus in epilepsy research due to their advantages. This systematic review aims to summarize the importance of non-mammalian models in epilepsy research, such as in the screening of anti-convulsive compounds. The reason for this review is to integrate currently available information on the use and importance of non-mammalian models in epilepsy testing to aid in the planning of future studies as well as to provide an overview of the current state of this field. A PRISMA model was utilized and PubMed, Springer, ScienceDirect and SCOPUS were searched for articles published between January 2007 and November 2017. Fifty-one articles were finalized based on the inclusion/exclusion criteria and were discussed in this review. The results of this review demonstrated the current use of non-mammalian models in epilepsy research and reaffirmed their potential to supplement the typical rodent models of epilepsy in future research into both epileptogenesis and the treatment of epilepsy. This review also revealed a preference for zebrafish and fruit flies in lieu of other non-mammalian models, which is a shortcoming that should be corrected in future studies due to the great potential of these underutilized animal models.

Metabolic rate and hypoxia tolerance are affected by group interactions and sex in the fruit fly (Drosophila melanogaster): new data and a literature survey

Population density and associated behavioral adjustments are potentially important in regulating physiological performance in many animals. In r-selected species like the fruit fly (Drosophila), where population density rapidly shifts in unpredictable and unstable environments, density-dependent physiological adjustments may aid survival of individuals living in a social environment. Yet, how population density (and associated social behaviors) affects physiological functions like metabolism is poorly understood in insects. Additionally, insects often show marked sexual dimorphism (larger females). Thus, in this study on D. melanogaster, we characterized the effects of fly density and sex on both mass-specific routine oxygen consumption (V̇O₂) and hypoxia tolerance (P_Crit). Females had significantly lower routine V̇O₂ (∼4 µl O₂ mg⁻¹ h⁻¹) than males (∼6 µl O₂ mg⁻¹ h⁻¹) at an average fly density of 28 flies·respirometer chamber⁻¹. However, V̇O₂ was inversely related to fly density in males, with V̇O₂ ranging from 4 to 11 µl O₂ mg⁻¹ h⁻¹ at a density of 10 and 40 flies·chamber⁻¹, respectively (r²=0.58, P<0.001). Female flies showed a similar but less pronounced effect, with a V̇O₂ of 4 and 7 µl O₂ mg⁻¹ h⁻¹ at a density of 10 and 40 flies·chamber⁻¹, respectively (r²=0.43, P<0.001). P_Crit (∼5.5 to 7.5 kPa) varied significantly with density in male (r²=0.50, P<0.01) but not female (r²=0.02, P>0.5) flies, with higher fly densities having a lower P_Crit. An extensive survey of the literature on metabolism in fruit flies indicates that not all studies control for, or even report on, fly density and gender, both of which may affect metabolic measurements.

Summary: Technical advances allowing oxygen consumption measurement in individual fruit flies actually take them out of their normal highly social context, resulting in higher oxygen consumption rates than in natural groups.

The ATP-sensitive K channel is seizure protective and required for effective dietary therapy in a model of mitochondrial encephalomyopathy

Effective therapies are lacking for mitochondrial encephalomyopathies (MEs). MEs are devastating diseases that predominantly affect the energy-demanding tissues of the nervous system and muscle, causing symptoms such as seizures, cardiomyopathy, and neuro- and muscular degeneration. Even common anti-epileptic drugs which are frequently successful in ameliorating seizures in other diseases tend to have a lower success rate in ME, highlighting the need for novel drug targets, especially those that may couple metabolic sensitivity to neuronal excitability. Furthermore, alternative epilepsy therapies such as dietary modification are gaining in clinical popularity but have not been thoroughly studied in ME. Using the Drosophila ATP6¹ model of ME, we have studied dietary therapy throughout disease progression and found that it is highly effective against the seizures of ME, especially a high fat/ketogenic diet, and that the benefits are dependent upon a functional K_ATP channel complex. Further experiments with K_ATP show that it is seizure-protective in this model, and that pharmacological promotion of its open state also ameliorates seizures. These studies represent important steps forward in the development of novel therapies for a class of diseases that is notoriously difficult to treat, and lay the foundation for mechanistic studies of currently existing therapies in the context of metabolic disease.

Inappropriate Neural Activity during a Sensitive Period in Embryogenesis Results in Persistent Seizure-like Behavior

Maturation of neural circuits requires activity-dependent processes that underpin the emergence of appropriate behavior in the adult. It has been proposed that disruption of these events, during specific critical periods when they exert maximal influence, may lead to neurodevelopmental diseases, including epilepsy [1, 2, 3]. However, complexity of neurocircuitry, coupled with the lack of information on network formation in mammals, makes it difficult to directly investigate this hypothesis. Alternative models, including the fruit fly Drosophila melanogaster, show remarkable similarities between experimental seizure-like activity and clinical phenotypes [4, 5, 6]. In particular, a group of flies, termed bang-sensitive (bs) mutants have been extensively used to investigate the pathophysiological mechanisms underlying seizure [7, 8, 9, 10, 11, 12]. Seizure phenotype can be measured in larval stages using an electroshock assay, and this behavior in bs mutants is dramatically reduced following ingestion of typical anti-epileptic drugs (AEDs; [13]). In this study we describe a critical period of embryonic development in Drosophila during which manipulation of neural activity is sufficient to significantly influence seizure behavior at postembryonic stages. We show that inhibition of elevated activity, characteristic of bs seizure models, during the critical period is sufficient to suppress seizure. By contrast, increasing neuronal excitation during the same period in wild-type (WT) is sufficient to permanently induce a seizure behavior. Further, we show that induction of seizure in WT correlates with functional alteration of motoneuron inputs that is a characteristic of bs mutants. Induction of seizure is rescued by prior administration of AEDs, opening a new perspective for early drug intervention in the treatment of genetic epilepsy.

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Activity manipulation defines a critical period for circuit functionality

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Abnormal activity during the critical period induces seizure

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Early drug intervention prevents seizure occurrence at postembryonic stages

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Seizure behavior correlates with aberrant synaptic excitation of motoneurons

The kdr-bearing haplotype and susceptibility to Plasmodium falciparum in Anopheles gambiae: genetic correlation and functional testing

Background

Members of the Anophelesgambiae species complex are primary vectors of human malaria in Africa. It is known that a large haplotype shared between An. gambiae and Anophelescoluzzii by introgression carries point mutations of the voltage-gated sodium channel gene para, including the L1014F kdr mutation associated with insensitivity to pyrethroid insecticides. Carriage of L1014F kdr is also correlated with higher susceptibility to infection with Plasmodium falciparum. However, the genetic mechanism and causative gene(s) underlying the parasite susceptibility phenotype are not known.

Methods

Mosquitoes from the wild Burkina Faso population were challenged by feeding on natural P. falciparum gametocytes. Oocyst infection phenotypes were determined and were tested for association with SNP genotypes. Candidate genes in the detected locus were prioritized and RNAi-mediated gene silencing was used to functionally test for gene effects on P. falciparum susceptibility.

Results

A genetic locus, Pfin6, was identified that influences infection levels of P. falciparum in mosquitoes. The locus segregates as a ~3 Mb haplotype carrying 65 predicted genes including the para gene. The haplotype carrying the kdr allele of para is linked to increased parasite infection prevalence, but many single nucleotide polymorphisms on the haplotype are also equally linked to the infection phenotype. Candidate genes in the haplotype were prioritized and functionally tested. Silencing of para did not influence P. falciparum infection, while silencing of a predicted immune gene, serine protease ClipC9, allowed development of significantly increased parasite numbers.

Conclusions

Genetic variation influencing Plasmodium infection in wild Anopheles is linked to a natural ~3 megabase haplotype on chromosome 2L that carries the kdr allele of the para gene. Evidence suggests that para gene function does not directly influence parasite susceptibility, and the association of kdr with infection may be due to tight linkage of kdr with other gene(s) on the haplotype. Further work will be required to determine if ClipC9 influences the outcome of P. falciparum infection in nature, as well as to confirm the absence of a direct influence by para.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0924-8) contains supplementary material, which is available to authorized users.

A low-cost method for analyzing seizure-like activity and movement in Drosophila

Video tracking systems have been used widely to analyze Drosophila melanogaster movement and detect various abnormalities in locomotive behavior. While these systems can provide a wealth of behavioral information, the cost and complexity of these systems can be prohibitive for many labs. We have developed a low-cost assay for measuring locomotive behavior and seizure movement in D. melanogaster. The system uses a web-cam to capture images that can be processed using a combination of inexpensive and free software to track the distance moved, the average velocity of movement and the duration of movement during a specified time-span. To demonstrate the utility of this system, we examined a group of D. melanogaster mutants, the Bang-sensitive (BS) paralytics, which are 3-10 times more susceptible to seizure-like activity (SLA) than wild type flies. Using this novel system, we were able to detect that the BS mutant bang senseless (bss) exhibits lower levels of exploratory locomotion in a novel environment than wild type flies. In addition, the system was used to identify that the drug metformin, which is commonly used to treat type II diabetes, reduces the intensity of SLA in the BS mutants.