Decreases in HCN mRNA expression in the hippocampus after kindling and status epilepticus in adult rats

Abstract

SUMMARYPurpose: Studies in animal models and patients have implicated changes in hyperpolarizationactivated cyclic nucleotide-gated cation channel (HCN) expression in the pathogenesis of temporal lobe epilepsy (TLE). However, the nature of HCN changes during the epileptogenic process and their commonality across different TLE models is unknown. Here HCN1 and HCN2 mRNA expression was quantitatively measured at different time points during epileptogenesis in two distinct animal models of TLE; the kainic acid (KA)-induced status epilepticus (SE) and amygdala kindling models. Methods: Hippocampal subregions (CA1, CA3, and dentate gyrus [DG]) and entorhinal cortex were dissected at different time-points. For KA-induced SE animals this was 24 h, 7 days (preepileptic), and 6 weeks (epileptic) post status. For amygdala kindling animals this was 2 weeks after reaching either ''partially kindled'' (one class II/III seizure) or ''fully kindled'' (five class V seizures) states. Quantification of regional hippocampal neuronal loss in the KA-treated animals was done using NeuN immunofluorescence and confocal microscopy. Results: HCN mRNA levels decreased in an isoform and region specific manner at all time points after KA-induced SE. The decrease in neuronal number could not account for all reductions in HCN mRNA levels post-KA insult, implicating transcriptional changes. A reduction in HCN2 mRNA levels was also observed in fully kindled animals in the CA3 region. Conclusions: A reduction in HCN mRNA levels is present in two different models of TLE. This supports the case that a reduction in HCN channel expression is an accompaniment of epileptogenesis in different adult models of TLE.

Effect of low frequency repetitive transcranial magnetic stimulation on kindling-induced changes in electrophysiological properties of rat CA1 pyramidal neurons

“…However, the role of HCN disorders in epilepsy is complex. Studies in experimental models indicate that both up-regulation (Dyhrfjeld-Johnsen et al, 2008;Gill et al, 2006) and down-regulation (Powell et al, 2008;Richichi et al, 2008;Santoro et al, 2010;Shah et al, 2004;Strauss et al, 2004) of HCN channels can be associated with seizures. Our Q5 data were clearly inconsistent with an increase in I h current during the neuronal hyperexcitability in CA1 region of the hippocampus.…”

Decreased hyperpolarization-activated currents in layer 5 pyramidal neurons enhances excitability in focal cortical dysplasia

“…Depending on the cell type and brain region, the inwardly rectifying hyperpolarization-activated current I h contributes to generation of rhythmic activity (McCormick and Pape 1990), determination of the resting membrane potential (Robinson and Siegelbaum 2003), and synaptic integration (Magee 2000;Berger et al 2001). Alterations in I h and HCN expression occur in a variety of seizure models including kainic acid-and pilocarpine-induced epilepsy (Jung et al 2007;Shin et al 2008), early-life hyperthermia (Chen et al 2001), temporal lobe kindling (Powell et al 2008), and absence seizures (Kole et al 2007;Schridde et al 2006;Strauss et al 2004). HCN1 subunitspecific knockout mice have a reduced seizure threshold (Huang et al 2009), whereas HCN2 knockout mice exhibit an absence epilepsy phenotype (Ludwig et al 2003).…”

Inhibition of microglial activation with minocycline at the intrathecal level attenuates sympathoexcitatory and proarrhythmogenic changes in rats with chronic temporal lobe epilepsy

“…injection of the glutamate receptor agonist, KA, to induce a period of continuous seizure activity (status epilepticus) in non-epileptic rats as described previously (Hellier et al, 1998;Powell et al, 2008;Jupp et al, 2012;Powell et al, 2014b;Vivash et al, 2014).…”

“…One week after recovery from the surgery, a continuous 24 h video-EEG-ECG recording was acquired for one week using Compumedics EEG acquisition software (Profusion EEG 4 v4.3, Australia) digitised at 2048Hz as previously described (Powell et al, 2008;Powell et al, 2014b). Each recording was reviewed for seizure activity, and the start and end of a seizure was manually marked on the EEG to allow quantification of the number of seizures and seizure duration.…”

“…To achieve these aims we used a model of acquired epilepsy in rats that manifest spontaneous seizures and many features of acquired epilepsy in humans-the KA-induced post-status epilepticus (post-SE) model (Morimoto et al, 2004;Powell et al, 2008;Jupp et al, 2012). The effect of intrathecal (IT) infusion of the PACAP antagonist, PACAP(6-38), and the microglial antagonist, minocycline, on sympathetic activity, cardiovascular reflex responses, and the electrocardiogram (ECG) were analysed in chronically epileptic and control rats.…”