title: Direct Imaging of Hippocampal Epileptiform Calcium Motifs Following Kainic Acid Administration in Freely Behaving Mice.
abstract: Prolonged exposure to abnormally high calcium concentrations is thought to be a core mechanism underlying hippocampal damage in epileptic patients; however, no prior study has characterized calcium activity during seizures in the live, intact hippocampus. We have directly investigated this possibility by combining whole-brain electroencephalographic (EEG) measurements with microendoscopic calcium imaging of pyramidal cells in the CA1 hippocampal region of freely behaving mice treated with the pro-convulsant kainic acid (KA). We observed that KA administration led to systematic patterns of epileptiform calcium activity: a series of large-scale, intensifying flashes of increased calcium fluorescence concurrent with a cluster of low-amplitude EEG waveforms. This was accompanied by a steady increase in cellular calcium levels (>5 fold increase relative to the baseline), followed by an intense spreading calcium wave characterized by a 218% increase in global mean intensity of calcium fluorescence (n = 8, range [114-349%], p < 10(-4); t-test). The wave had no consistent EEG phenotype and occurred before the onset of motor convulsions. Similar changes in calcium activity were also observed in animals treated with 2 different proconvulsant agents, N-methyl-D-aspartate (NMDA) and pentylenetetrazol (PTZ), suggesting the measured changes in calcium dynamics are a signature of seizure activity rather than a KA-specific pathology. Additionally, despite reducing the behavioral severity of KA-induced seizures, the anticonvulsant drug valproate (VA, 300 mg/kg) did not modify the observed abnormalities in calcium dynamics. These results confirm the presence of pathological calcium activity preceding convulsive motor seizures and support calcium as a candidate signaling molecule in a pathway connecting seizures to subsequent cellular damage. Integrating in vivo calcium imaging with traditional assessment of seizures could potentially increase translatability of pharmacological intervention, leading to novel drug screening paradigms and therapeutics designed to target and abolish abnormal patterns of both electrical and calcium excitation.
authors.affiliation: Janssen Research & Development, LLC San Diego, CA, USA.
authors.forename: Tamara K
authors.initials: TK
authors.lastname: Berdyyeva
authors.affiliation: InscopixPalo Alto, CA, USA; Redwood Center for Theoretical Neuroscience, University of California, BerkeleyBerkeley, CA, USA.
authors.forename: E Paxon
authors.initials: EP
authors.lastname: Frady
authors.affiliation: Inscopix Palo Alto, CA, USA.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Nassi
authors.affiliation: Janssen Research & Development, LLC San Diego, CA, USA.
authors.forename: Leah
authors.initials: L
authors.lastname: Aluisio
authors.affiliation: Janssen Research & Development, LLC San Diego, CA, USA.
authors.forename: Yauheniya
authors.initials: Y
authors.lastname: Cherkas
authors.affiliation: Inscopix Palo Alto, CA, USA.
authors.forename: Stephani
authors.initials: S
authors.lastname: Otte
authors.affiliation: Janssen Research & Development, LLC San Diego, CA, USA.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Wyatt
authors.affiliation: Janssen Research & Development, LLC San Diego, CA, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Dugovic
authors.affiliation: Inscopix Palo Alto, CA, USA.
authors.forename: Kunal K
authors.initials: KK
authors.lastname: Ghosh
authors.affiliation: Inscopix Palo Alto, CA, USA.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Schnitzer
authors.affiliation: Janssen Research & Development, LLC San Diego, CA, USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Lovenberg
authors.affiliation: Janssen Research & Development, LLC San Diego, CA, USA.
authors.forename: Pascal
authors.initials: P
authors.lastname: Bonaventure
keywords: calcium imaging; electroencephalography; freely behaving mice; kainic acid; seizure