Calcium Release from Presynaptic Internal Stores Is Required for Ethanol to Increase Spontaneous γ-Aminobutyric Acid Release onto Cerebellum Purkinje Neurons

Abstract

Recent data have demonstrated that ethanol increases ␥-aminobutyric acid (GABA) release in many brain regions, but little is known about the mechanism responsible for this action. Consistent with previous results, ethanol increased miniature inhibitory postsynaptic current (mIPSC) frequency at the interneuron-Purkinje cell synapse in the slice and in mechanically dissociated neurons. These data suggest that ethanol is increasing spontaneous GABA release at this synapse. It is generally accepted that ethanol increases levels of intracellular calcium and that changes in intracellular calcium can alter neurotransmitter release. Therefore, we examined the contribution of calcium-dependent pathways to the effect of ethanol on spontaneous GABA release at the interneuron-Purkinje cell synapse. Ethanol continued to increase mIPSC frequency in a nominally calcium-free extracellular solution and in the presence of a voltage-dependent calcium channel inhibitor, cadmium chloride. These data suggest that influx of extracellular calcium does not play a critical role in the mechanism of ethanol-enhanced spontaneous GABA release. However, a sarco/ endoplasmic-reticulum calcium ATPase pump inhibitor (thapsigargin), an inositol 1,4,5-trisphosphate receptor antagonist (2-aminoethoxydiphenylborate) and a ryanodine receptor antagonist (ryanodine) significantly reduced the ability of ethanol to increase mIPSC frequency. In addition, ethanol was still able to increase mIPSC frequency in the presence of intracellular 1,2-bis(2-aminophenoxy)ethane-N,N,NЈ,NЈ-tetraacetic acid (BAPTA) and a cannabinoid receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM-251); thus, retrograde messengers are not involved in ethanol-enhanced spontaneous GABA release. Overall, these data suggest that calcium release from presynaptic internal stores plays a vital role in the mechanism of ethanol-enhanced spontaneous GABA release at the interneuronPurkinje cell synapse.

Effects of Ethanol on GABAA Receptors in GABAergic and Glutamatergic Presynaptic Nerve Terminals

“…In addition to having direct effects on postsynaptic receptors, EtOH has been shown to modulate GABA and glutamate release from their nerve terminals (Hendricson et al, 2004;Kelm et al, 2007;Jia et al, 2008). EtOH can enhance GABA release in hippocampal slices via a number of mechanisms: increasing spontaneous action potential firing in GABAergic interneurons, decreasing the kainate-driven firing of these neurons, and enhancing presynaptic voltagedependent Ca 2ϩ channels (VDCCs) by inhibiting the voltagedependent K ϩ channels.…”

Synaptic Effects Induced by Alcohol

“…Examination of spontaneous and miniature GABAergic IPSCs allows investigators to determine whether the frequency of synaptic events is altered (a likely presynaptic change), or whether the amplitude is affected (likely a postsynaptic change). Such analyses have consistently shown that sISPC and mIPSC frequencies are increased at EtOH concentrations associated with intoxication, at least in the amygdala, cerebellum, hippocampus and VTA Zhu and Lovinger 2006;Theile et al 2008;Roberto et al 2003;Kelm et al 2007). These effects are rapid at onset and rapidly reversible following EtOH removal from tissue.…”

“…1). Increases in fast GABAergic synaptic transmission during EtOH treatment have been observed in cerebellum, hippocampus, ventral tegmental area (VTA), hypoglossal nucleus, and amygdala, both basolateral and central nuclei Ming et al 2006;Kelm et al 2007;Theile et al 2008;Zhu and Lovinger 2006;Roberto et al 2003;Sebe et al 2003;Ziskind-Conhaim et al 2003). These studies have been carried out mostly in brain slices and isolated brain neurons.…”

Mechanisms of Action and Persistent Neuroplasticity by Drugs of Abuse

“…Ethanol enhances GABA release from presynaptic terminals, which contributes to synaptic inhibition (for reviews, see Siggins et al, 2005;Lovinger and Roberto, 2013). These data are obtained mostly from brain slices and isolated neurons from the cerebellum, HC, VTA, and amygdala (Ariwodola et al, 2003;Roberto et al, 2003;Kelm et al, 2007;Theile et al, 2008). The mechanism of ethanol enhancement of GABA release is not well established, but ethanol may interact with mechanisms involved in intracellular calcium release, increasing presynaptic calcium concentrations (Kelm et al, 2007).…”

“…These data are obtained mostly from brain slices and isolated neurons from the cerebellum, HC, VTA, and amygdala (Ariwodola et al, 2003;Roberto et al, 2003;Kelm et al, 2007;Theile et al, 2008). The mechanism of ethanol enhancement of GABA release is not well established, but ethanol may interact with mechanisms involved in intracellular calcium release, increasing presynaptic calcium concentrations (Kelm et al, 2007). The possible role of intracellular signaling pathways in this ethanol effect is suggested by findings that GABA release is diminished in cerebellar Purkinje neurons by PKA inhibitors and in the CeA in mice lacking PKC« (Bajo et al, 2008;Kelm et al, 2008).…”