Spontaneous Seizures and Altered Gene Expression in GABA Signaling Pathways in amind bombMutant Zebrafish

Abstract

Disruption of E3 ubiquitin ligase activity in immature zebrafish mind bomb mutants leads to a failure in Notch signaling, excessive numbers of neurons, and depletion of neural progenitor cells. This neurogenic phenotype is associated with defects in neural patterning and brain development. Because developmental brain abnormalities are recognized as an important feature of childhood neurological disorders such as epilepsy and autism, we determined whether zebrafish mutants with grossly abnormal brain structure exhibit spontaneous electrical activity that resembles the long-duration, high-amplitude multispike discharges reported in immature zebrafish exposed to convulsant drugs. Electrophysiological recordings from agar immobilized mind bomb mutants at 3 d postfertilization confirmed the occurrence of electrographic seizure activity; seizure-like behaviors were also noted during locomotion video tracking of freely behaving mutants. To identify genes differentially expressed in the mind bomb mutant and provide insight into molecular pathways that may mediate these epileptic phenotypes, a transcriptome analysis was performed using microarray. Interesting candidate genes were further analyzed using conventional reverse transcriptase-PCR and real-time quantitative PCR, as well as whole-mount in situ hybridization. Approximately 150 genes, some implicated in development, transcription, cell metabolism, and signal transduction, are differentially regulated, including downregulation of several genes necessary for GABA-mediated signaling. These findings identify a collection of gene transcripts that may be responsible for the abnormal electrical discharge and epileptic activities observed in a mind bomb zebrafish mutant. This work may have important implications for neurological and neurodevelopmental disorders associated with mutations in ubiquitin ligase activity.

Cross-species pharmacological characterization of the allylglycine seizure model in mice and larval zebrafish

“…Moreover, spiking activities in controls were observed occasionally, but the patterns were considerably different from those observed for AG-treated larvae. These were characterized by single spikes of very short duration and have been described previously by Baraban and colleagues as bursts of synchronized activity [62].…”

Validation of the Zebra-fish Pentylene Tetrazol Seizure Model: Behaviour Assay for Assessing Anti-Epileptic Drug Efficacy

“…Zebra-fish larvae exhibited signs of agitation within seconds after exposed to PTZ. The larvae swam along the periphery of the multi-well plate, thus displaying stage I seizure-like behaviour as described previously [15]. This was succeeded by rapid 'whirlpool-like' movement, and then followed by a short pause before swimming in a rapid, jerky manner with occasional body-stiffening and loss of posture (larva turning onto its side or back).…”

“…Numerous studies have showed that adult or zebra-fish larvae exposed to PTZ exhibit increased locomotor activity, seizure-like behavior, and epileptiform electrographic activity [15,19] [ [22][23][24], which have a good correlation between zebra-fish and rodent data [15,17,21,25]. Also, many researchers have used zebra-fish seizure model for anti- convulsions in zebra-fish larvae was assessed through quantification of the high-speed moved distance.…”

“…epileptic compound discovery, and proved that zebra-fish can be a very useful model for anticonvulsant drug screening and early efficacy in vivo assessment [15,19,26,27]. These models are currently in existence that subserves particular roles in achieving these aims, but all have their limitations [26].…”

“…Because of the genetic similarity between zebra-fish and humans, zebra-fish larvae offer significant advantages for high-throughput drug screening [8,[11][12][13]. Following on work first described by Baraban et al in 2005 [14], several groups have confirmed the abnormal seizurelike behaviors, ictal and interictal like electrical activity and c-fos expression in brain regions when zebra-fish larvae exposed to pentylene tetrazole (PTZ) [15]. With regard to anticonvulsant screens, mediumto high-throughput screening is possible in 96-well format using an automated locomotor tracking system for the sensitivity to common antiepileptic drugs in this model [16].…”