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.

Left Habenular Activity Attenuates Fear Responses in Larval Zebrafish

“…The natural log fold change in fluorescence was fit to a normal distribution and the mean and standard deviation determined. Neurons were deemed responsive if the change in fluorescence intensity post-shock was greater than 1 standard deviation of the mean [52, 53], and responsive neurons on average had a greater than 2-fold increase in neural activity [54]. The initial time point at which neuronal activity increased, for a given neuron, was determined using the MATLAB function ‘ findpeaks ’.…”

Transient Cognitive Impairment in Epilepsy

“…In intact animals, focal IEDs have been generated by electrical stimulation (Collins and Caston, 1979; Gelinas et al, 2016) or after systemic or focal administration of inhibitors of GABA activity (Meldrum and Horton, 1971; Schroeder et al, 1990; Schwartz and Bonhoeffer, 2001; Hirase et al, 2004; Ma et al, 2004; Hernan et al, 2014a, b), kainic acid (Berdyyeva et al, 2016) and pilocarpine (Kleen et al, 2011). Finally, a focal model of epileptic activity has been obtained by the localized microinjection of tetanus toxin (TeNT; Brener et al, 1991; Nilsen et al, 2005; Vannini et al, 2016) that causes an increase of the E/I ratio because of a strong blockade of inhibitory synapses (Ferecskó et al, 2014).…”

MIN1PIPE: A Miniscope 1-Photon-Based Calcium Imaging Signal Extraction Pipeline

“…Recent advances in single-photon-based miniscope technology have further enabled imaging of neural ensemble activities in freely moving animals (Cai et al, 2016; Flusberg et al, 2008; Ghosh et al, 2011), thereby allowing circuits involved in a rich repertoire of animal behaviors to be examined. For example, this technology has been successfully used in probing dynamics of neural circuits involved in innate behaviors (Betley et al, 2015; Douglass et al, 2017; Jennings et al, 2015), decision making (Pinto and Dan, 2015; Carvalho Poyraz et al, 2016), motor control (Klaus et al, 2017), learning and memory (Grewe et al, 2017; Kamigaki and Dan, 2017; Kitamura et al, 2017; Roberts et al, 2017; Roy et al, 2017; Xu et al, 2016), social memory (Okuyama et al, 2016), hippocampal place coding (Ziv et al, 2013), sleep (Cox et al, 2016; Weber and Dan, 2016), bird song (Markowitz et al, 2015), and pathological processes (Berdyyeva et al, 2016). …”