Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA259

Poster Communications

Excitatory and inhibitory neurotransmission is imbalanced in an animal disease model of episodic ataxia type 6

Y. Kolobkova1, J. Cremer2, S. Buller2, C. Fahlke1, P. Kovermann1

1. ICS-4, Forschungszentrum Jülich, Jülich, Germany. 2. INM-1, Forschungszentrum Jülich, Jülich, Germany.

Episodic ataxias (EAs) are rare neurological syndromes characterized by paroxysmal cerebellar incoordination combined with episodes of migraine, epilepsy, or dystonia. A missense point mutation in the gene coding for SLC1A3 (EAAT1) has been identified in a patient suffering from the severe form EA type 6, with seizures and long lasting episodes of movement disorders (Jen et al., 2005). The mutation predicts the substitution of the conserved proline 290 by an arginine (P290R). EAAT1 functions not only as glutamate transporter, but also as anion channel, and earlier work in heterologous expression systems demonstrated that P290R impairs transport rates and enhances channel activity (Winter et al., 2012; Hotzy et al., 2013). Since genetic ablation of EAAT1 in mice (GLAST-/-) did not result in seizures, and promoted only slight ataxias (Watase et al., 1998), we hypothesized that the increase in glial anion fluxes in P290R EAAT1 might be the trigger for the disease rather than reduced glutamate clearance. To study the consequences of an augmented glial Cl− conductance on hippocampal neurotransmission, we studied excitatory and inhibitory synaptic transmission by whole-cell patch clamping in acute slices of a knock-in mouse model (Slc1a3P290R/+). Quantitative receptor autoradiography demonstrated increased AMPA receptor densities in the hippocampus of Slc1a3P290R/+mice (+31%). We therefore tested AMPA receptor-mediated neurotransmission using whole-cell patch clamping and analysed miniature excitatory postsynaptic currents (mEPSCs) in acute hippocampal slices. Both, the mEPSC amplitudes (WT, 7 ± 0.1 pA; Slc1a3 P290R/+, 9 ± 0.1 pA, ANOVA: p < 0.05) and the mEPSC frequencies (WT, 2.4 ± 0.1 Hz; Slc1a3P290R/+, 3.0 ± 0.1 Hz, ANOVA: p < 0.05) were significantly increased in dentate gyrus (DG) granule cells from mutant samples. Glial EAATs have been recently shown to be involved in glial Cl− homeostasis (Untiet et al., 2015) and an increased anion efflux from glial cells might thus alter [GABA]ext by enhancing the electrochemical driving forces acting on glial Na+/Cl−-dependent GABA transporters (GATs). Using whole-cell patch clamping we measured tonic GABA-mediated Cl− currents in DG granule cells, and demonstrated a decrease in tonic inhibitory Cl− currents in the samples from Slc1a3P290R/+mice (WT, 29 ± 6 pA; Slc1a3P290R/+, 14 ± 3 pA, ANOVA: p < 0.05). These changes in inhibitory and excitatory neurotransmission in the DG could explain the observed seizures by a hyperexcitability of the DG granule cells.

Where applicable, experiments conform with Society ethical requirements