Tyrosine Phosphorylation of GABAA Receptor  2-Subunit Regulates Tonic and Phasic Inhibition in the Thalamus

Abstract

GABA-mediated tonic and phasic inhibition of thalamic relay neurons of the dorsal lateral geniculate nucleus (dLGN) was studied after ablating tyrosine (Y) phosphorylation of receptor ␥2-subunits. As phosphorylation of ␥2 Y365 and Y367 reduces receptor internalization, to understand their importance for inhibition we created a knock-in mouse in which these residues are replaced by phenylalanines. On comparing wild-type (WT) and ␥2 Y365/367F ϩ/Ϫ (HT) animals (homozygotes are not viable in utero), the expression levels of GABA A receptor ␣4-subunits were increased in the thalamus of female, but not male mice. Raised ␦-subunit expression levels were also observed in female ␥2 Y365/367F ϩ/Ϫ thalamus. Electrophysiological analyses revealed no difference in the level of inhibition in male WT and HT dLGN, while both the spontaneous inhibitory postsynaptic activity and the tonic current were significantly augmented in female HT relay cells. The sensitivity of tonic currents to the ␦-subunit superagonist THIP, and the blocker Zn 2ϩ , were higher in female HT relay cells. This is consistent with upregulation of extrasynaptic GABA A receptors containing ␣4-and ␦-subunits to enhance tonic inhibition. In contrast, the sensitivity of GABA A receptors mediating inhibition in the female ␥2 Y356/367F ϩ/Ϫ to neurosteroids was markedly reduced compared with WT. We conclude that disrupting tyrosine phosphorylation of the ␥2-subunit activates a sex-specific increase in tonic inhibition, and this most likely reflects a genomic-based compensation mechanism for the reduced neurosteroid sensitivity of inhibition measured in female HT relay neurons.

Monoamine modulation of tonic GABAA inhibition

“…It is now well established that the amplitude of the eGABA A R-mediated tonic current changes in relation to the ambient GABA concentration ( Pavlov et al, 2009 ) is modulated by exogenous agents including neurosteroids, alcohol, and anesthetics ( Belelli et al, 2009 ) and that eGABA A Rs show plasticity in response to changes in sGABA A Rs activity ( Nani et al, 2013 ). As reviewed here, eGABA A Rs are also subject to modulatory actions by the monoamines that can act presynaptically, modulating GABA release, or postsynaptically, directly altering eGABA A R activity (see also the recent findings of postsynaptic GABA B Rs interaction with eGABA A Rs ( Connelly et al, 2013b ;Tao et al, 2013 ).…”

GPCR Modulation of Extrasynapitic GABAA Receptors

“…Moreover, eGABA A Rs are dynamic entities showing plasticity in response to changes in sGABA A Rs activity (Nani et al 2013) and modulation by exogenous agents including neurosteroids, alcohol and anesthestetics (see Chap. 5; (Belelli et al 2009)).…”

Animal models of absence epilepsies: What do they model and do sex and sex hormones matter?

“…Phosphorylation of GABA A R γ2 subunit residues, Y365 and Y367, inhibits GABA A R cell surface endocytosis (Kittler et al, 2008). Mice which heterozygously expressed γ2 subunit in which Y365 and Y367 were mutated to phenylalanines and thus were insensitive to phosphorylation, demonstrated sex-dependent responses (Nani et al, 2013). When γ2 subunit phosphorylation was inhibited, female, but not male mice, increased α4 and δ subunit expression as well as the amplitudes of phasic and tonic GABA A R currents in the lateral geniculate nucleus of the thalamus.…”