Na+/K+-ATPase Inhibition Partially Mimics the Ethanol-Induced Increase of the Golgi Cell-Dependent Component of the Tonic GABAergic Current in Rat Cerebellar Granule Cells

Abstract

Cerebellar granule cells (CGNs) are one of many neurons that express phasic and tonic GABAergic conductances. Although it is well established that Golgi cells (GoCs) mediate phasic GABAergic currents in CGNs, their role in mediating tonic currents in CGNs (CGN-Itonic) is controversial. Earlier studies suggested that GoCs mediate a component of CGN-Itonic that is present only in preparations from immature rodents. However, more recent studies have detected a GoC-dependent component of CGN-Itonic in preparations of mature rodents. In addition, acute exposure to ethanol was shown to potentiate the GoC component of CGN-Itonic and to induce a parallel increase in spontaneous inhibitory postsynaptic current frequency at CGNs. Here, we tested the hypothesis that these effects of ethanol on GABAergic transmission in CGNs are mediated by inhibition of the Na+/K+-ATPase. We used whole-cell patch-clamp electrophysiology techniques in cerebellar slices of male rats (postnatal day 23–30). Under these conditions, we reliably detected a GoC-dependent component of CGN-Itonic that could be blocked with tetrodotoxin. Further analysis revealed a positive correlation between basal sIPSC frequency and the magnitude of the GoC-dependent component of CGN-Itonic. Inhibition of the Na+/K+-ATPase with a submaximal concentration of ouabain partially mimicked the ethanol-induced potentiation of both phasic and tonic GABAergic currents in CGNs. Modeling studies suggest that selective inhibition of the Na+/K+-ATPase in GoCs can, in part, explain these effects of ethanol. These findings establish a novel mechanism of action of ethanol on GABAergic transmission in the central nervous system.

Repeated intermittent alcohol exposure during the third trimester-equivalent increases expression of the GABAA receptor δ subunit in cerebellar granule neurons and delays motor development in rats

“…Several studies have reported that the release of GABA from GoCs is driven by spontaneous firing of these neurons and this GABA contributes to the pool of transmitter that generates the CGN-I tonic (Botta et al, 2010; Carta et al, 2004; Diaz et al, 2011; Diaz et al, 2013; Hamann et al, 2002; Rossi et al, 2003; Wall and Usowicz, 1997). Therefore, we examined the impact of PAE on the amplitude of the GoC-dependent component of CGN-I tonic , which is sensitive to TTX.…”

Sensitivity of GABAergic Tonic Currents to Acute Ethanol in Cerebellar Granule Neurons is Not Age‐ or δ Subunit‐Dependent in Developing Rats

“…Tonic inhibition is mediated via activation of extrasynaptic GABA A Rs primarily by ambient GABA in the extracellular space (Farrant and Nusser, ). While the source of ambient GABA remains unclear (Diaz et al., ; Lee et al., ; Yoon et al., ), we and others have demonstrated that GABA release from Golgi cells significantly contributes to tonic inhibition of CGNs (Bright et al., ; Diaz et al., ; Rossi et al., ). Since their discovery, the majority of extrasynaptic GABA A Rs throughout the central nervous system have been found to express the δ subunit which significantly contributes to their functional activity (reviewed by Farrant and Nusser, ).…”

“…Acute EtOH has been shown to potentiate phasic and tonic GABA transmission in CGNs of adolescent and adult animals (Bright et al., ; Carta et al., ; Diaz et al., ; Hanchar et al., ), but the sensitivity of the GABA system to acute EtOH in immature CGNs is unknown. We found a significant effect of acute EtOH (80 mM) on tonic currents regardless of age (Fig.…”

“…We have previously demonstrated that tetrodotoxin (TTX), an action potential blocker, decreases sIPSC frequency and blocks the component of the tonic current that is dependent on spillover of GABA release in a spontaneous action potential‐dependent manner (Carta et al., ; Diaz et al., ). In addition, TTX also completely blocks the acute effect of EtOH in mature CGNs, suggesting that the actions of EtOH are action potential dependent in older rats (Carta et al., ; Diaz et al., ). Here, we tested whether this is also the case in preweanlings.…”

“…In older animals, deletion of the δ subunit has been shown to abolish tonic currents in mature CGNs (Stell et al., ), consistent with the notion that the δ subunit is essential for expression of a tonic current later in development. In the mature cerebellum, we and others have shown that acute EtOH can increase Golgi cell firing in vivo (Huang et al., ) and in vitro (Botta et al., , ; Kaplan et al., ) via various mechanisms, ultimately resulting in potentiation of tonic currents in CGNs (Carta et al., ; Diaz et al., ).…”