Abstracts

Rapid loss of dendritic HCN channel expression following status epilepticus

Abstract number : 1.031
Submission category : 1. Translational Research
Year : 2010
Submission ID : 12972
Source : www.aesnet.org
Presentation date : 12/3/2010 12:00:00 AM
Published date : Dec 2, 2010, 06:00 AM

Authors :
S. Jung, L. Warner, J. Pitsch, A. Becker and Nicholas Poolos

Rationale: Hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels are voltage-gated ion channels expressed in hippocampal and neocortical pyramidal neuron dendrites that diminish excitability. We and others have demonstrated the loss of expression and downregulation of gating of HCN channels during the development of epilepsy following status epilepticus (SE): the density of Ih, the current mediated by HCN channels, declined to 40-50% of control levels by 1 wk after pilocarpine-induced SE, along with an ~50% loss of HCN1 protein expression (Jung et al., 2007; 2010). Both remained decreased at 3-5 wk in chronically epileptic animals, while loss of HCN1 mRNA expression began at 3 d post-SE and persisted at 30 d (Marcelin et al., 2009). In the present study, we sought to characterize the acute timecourse of the post-SE decrease in Ih, and its molecular correlates. Methods: Dendritic cell-attached patch clamp recordings in CA1 hippocampal neurons were obtained in brain slices from rats after pilocarpine-induced SE, along with Western blotting for HCN1 protein, and real-time RT-PCR for HCN1 mRNA. Results: At 1 h post-SE, Ih was significantly decreased compared to control levels (all values reported as % of control), with Ih at maximal activation reduced to 50 2.0 %, p<.01 vs. control), while HCN1 protein (95 3.0 %) and mRNA levels (98 11 %) were unchanged. At 1 d post-SE, Ih declined further (27 1.0 %, p<.05 vs. 1 hr levels), and HCN1 protein levels had also declined to 54 10 % (p<.01), while HCN1 mRNA levels remained unchanged (110 22%). We then replicated the rapid loss of Ih with an in vitro model of SE. Hippocampal slices from na ve rats were perfused with solution containing 0 Mg2 , 50 ?M bicuculline, and stimulation (5 stimuli at 50 Hz) of the perforant path to CA1 every two minutes for 1 hr, which produced electrographic seizure-like events recorded extracellularly in str. pyramidale. After 1 hr of this in vitro SE, dendritic Ih declined to 56 13% of control (p<.05) , similar to that seen with in vivo SE. Conclusions: These results demonstrate rapid loss of dendritic Ih, occurring within 1 hr post-SE, elicited by SE both in vivo and in vitro, and persisting during chronic epilepsy. Following in vivo SE, there is a delayed loss of HCN1 protein expression beginning at 1 day, while loss of HCN1 transcription is not seen until 3 days post-SE. This shows that dendritic HCN channelopathy begins at the earliest timepoints following SE, and that the early loss of Ih and HCN1 protein expression precedes the downregulation of HCN1 gene transcription, thus may be due to post-translational mechanisms.
Translational Research