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  • Title: Mice deficient for the extracellular matrix glycoprotein tenascin-r show physiological and structural hallmarks of increased hippocampal excitability, but no increased susceptibility to seizures in the pilocarpine model of epilepsy.
    Author: Brenneke F, Bukalo O, Dityatev A, Lie AA.
    Journal: Neuroscience; 2004; 124(4):841-55. PubMed ID: 15026125.
    Abstract:
    Recognition molecules provide important cues for neuronal survival, axonal fasciculation, axonal pathfinding, synaptogenesis, synaptic plasticity, and regeneration. Our previous studies revealed a link between perisomatic inhibition and the extracellular matrix glycoprotein tenascin-R (TN-R). Therefore, we here studied neuronal excitability and epileptic susceptibility in mice constitutively deficient in TN-R. In vitro analysis of populational spikes in hippocampal slices of TN-R-deficient mice revealed a significant increase in multiple spikes in the CA1 region, as compared with wild-type mice. This difference between genotypes was only partially reduced after blockade of GABA(A) receptors with picrotoxin, indicating a deficit in GABAergic inhibition and an increase in intrinsic excitability of CA1 pyramidal cells in TN-R-deficient mice. Using a battery of immunohistochemical markers and histological stainings, we were able to identify two abnormalities in the hippocampus of TN-R-deficient mice possibly related to increased excitability: the high number of glial fibrillary acidic protein-positive astrocytes and low number of calretinin-positive interneurons in the CA1 and CA3 regions. In order to test whether the revealed abnormalities give rise to increased susceptibility to seizures in TN-R-deficient mice, we used the pilocarpine model of epilepsy. No genotype-specific differences were found with regard to the time-course of pilocarpine-induced and spontaneous seizures, neuronal cell loss, aberrant sprouting and distribution of synaptic and inhibitory interneuron markers. However, pilocarpine-induced astrogliosis and reduction in calretinin-positive interneurons were less pronounced in TN-R mutants, thereby resulting in an occlusion of effects induced by TN-R deficiency and pilocarpine. Thus, TN-R-deficient mutants show several electrophysiological and morphological hallmarks of increased neuronal excitability, which, however, do not give rise to more accelerated or severe epileptogenesis in the pilocarpine model of epilepsy.
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