Regionally specific expression of high-voltage-activated calcium channels in thalamic nuclei of epileptic and non-epileptic rats

Mol Cell Neurosci. 2014 Jul;61:110-22. doi: 10.1016/j.mcn.2014.06.005. Epub 2014 Jun 7.

Abstract

The polygenic origin of generalized absence epilepsy results in dysfunction of ion channels that allows the switch from physiological asynchronous to pathophysiological highly synchronous network activity. Evidence from rat and mouse models of absence epilepsy indicates that altered Ca(2+) channel activity contributes to cellular and network alterations that lead to seizure activity. Under physiological circumstances, high voltage-activated (HVA) Ca(2+) channels are important in determining the thalamic firing profile. Here, we investigated a possible contribution of HVA channels to the epileptic phenotype using a rodent genetic model of absence epilepsy. In this study, HVA Ca(2+) currents were recorded from neurons of three different thalamic nuclei that are involved in both sensory signal transmission and rhythmic-synchronized activity during epileptic spike-and-wave discharges (SWD), namely the dorsal part of the lateral geniculate nucleus (dLGN), the ventrobasal thalamic complex (VB) and the reticular thalamic nucleus (NRT) of epileptic Wistar Albino Glaxo rats from Rijswijk (WAG/Rij) and non-epileptic August Copenhagen Irish (ACI) rats. HVA Ca(2+) current densities in dLGN neurons were significantly increased in epileptic rats compared with non-epileptic controls while other thalamic regions revealed no differences between the strains. Application of specific channel blockers revealed that the increased current was carried by L-type Ca(2+) channels. Electrophysiological evidence of increased L-type current correlated with up-regulated mRNA and protein expression of a particular L-type channel, namely Cav1.3, in dLGN of epileptic rats. No significant changes were found for other HVA Ca(2+) channels. Moreover, pharmacological inactivation of L-type Ca(2+) channels results in altered firing profiles of thalamocortical relay (TC) neurons from non-epileptic rather than from epileptic rats. While HVA Ca(2+) channels influence tonic and burst firing in ACI and WAG/Rij differently, it is discussed that increased Cav1.3 expression may indirectly contribute to increased robustness of burst firing and thereby the epileptic phenotype of absence epilepsy.

Keywords: Genetic rat model of absence epilepsy; HVA Ca(2+) channels; L-type Ca(2+) channels; Thalamus; Tonic firing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic beta-2 Receptor Agonists / pharmacology
  • Albuterol / analogs & derivatives
  • Albuterol / pharmacology
  • Animals
  • Animals, Newborn
  • Biophysical Phenomena / drug effects
  • Biophysical Phenomena / genetics
  • Biophysical Phenomena / physiology
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / genetics
  • Calcium Channels / metabolism*
  • Disease Models, Animal
  • Electric Stimulation
  • Epilepsy / genetics
  • Epilepsy / pathology*
  • Epilepsy / physiopathology
  • Immunosuppressive Agents / pharmacology
  • Membrane Potentials / drug effects
  • Membrane Potentials / genetics
  • Membrane Potentials / physiology*
  • Mutation Rate
  • Nerve Tissue Proteins / metabolism
  • Neurons / drug effects
  • Neurons / physiology
  • Rats
  • Rats, Wistar
  • Salmeterol Xinafoate
  • Tacrolimus / analogs & derivatives
  • Tacrolimus / pharmacology
  • Thalamic Nuclei / metabolism*
  • Thalamic Nuclei / pathology
  • Up-Regulation / genetics
  • Up-Regulation / physiology*

Substances

  • Adrenergic beta-2 Receptor Agonists
  • Calcium Channel Blockers
  • Calcium Channels
  • Immunosuppressive Agents
  • Nerve Tissue Proteins
  • Salmeterol Xinafoate
  • immunomycin
  • Albuterol
  • Tacrolimus