The PLC/IP3R/PKC pathway is required for ethanol-enhanced GABA release

Abstract

Summary Research on the actions of ethanol at the GABAergic synapse has traditionally focused on postsynaptic mechanisms, but recent data demonstrate that ethanol also increases both evoked and spontaneous GABA release in many brain regions. Using whole-cell voltage-clamp recordings, we previously showed that ethanol increases spontaneous GABA release at the rat interneuron-Purkinje cell synapse. This presynaptic ethanol effect is dependent on calcium release from internal stores, possibly through activation of inositol 1,4,5-trisphosphate receptors (IP3Rs). After confirming that ethanol targets vesicular GABA release, in the present study we used electron microscopic immunohistochemistry to demonstrate that IP3Rs are located in presynaptic terminals of cerebellar interneurons. Activation of IP3Rs requires binding of IP3, generated through activation of phospholipase C (PLC). We find that the PLC antagonist edelfosine prevents ethanol from increasing spontaneous GABA release. Diacylglycerol generated by PLC and calcium released by activation of the IP3R activate protein kinase C (PKC). Ethanol-enhanced GABA release was blocked by two PKC antagonists, chelerythrine and calphostin C. When a membrane impermeable PKC antagonist, PKC (19-36), was delivered intracellularly to the postsynaptic neuron, ethanol continued to increase spontaneous GABA release. Overall, these results suggest that activation of the PLC/IP3R/PKC pathway is necessary for ethanol to increase spontaneous GABA release from presynaptic terminals onto Purkinje cells.

Central Amygdala Neuroplasticity in Alcohol Dependence

“…Rp-cAMP prevents an alcohol-induced increase in mIPSC frequency (Herman et al, unpublished data). Overall, our results in the CeA are similar to those in the cerebellar Purkinje neurons in which the potentiation of GABA release is eliminated in the presence of AC and PKA inhibitors (Kelm et al, 2008) and is also affected by compounds targeting phospholipase C and PKC (Kelm, Weinberg, Criswell, & Breese, 2010). We speculate that the AC/cAMP and PKCε cascades interact to regulate GABA release, and we speculate that the final target for both pathways is downstream of these cascades.…”

Ultrastructure of Synapses in the Mammalian Brain

“…Interestingly, the endocytosis-related proteins clathrin, AP-2, dynamin ( Fig. 9E -G) Lu et al 2007), and an isoform of the exocytosis-related protein Kelm et al 2010. ) syntaxin (Kennedy et al 2010) are all localized to a putative endocytic zone lateral to the PSD.…”

Ethanol modulation of synaptic plasticity

“…The precise signaling cascades responsible for this ethanol modulation are not understood in every case. However, the mobilization of intra-terminal calcium stores (Kelm et al, 2007), perhaps via ethanol-dependent increases in G protein-coupled receptor signaling (Theile et al, 2009), the activation of phospholipase C, and ethanol-sensitive presynaptic protein kinases (Kelm et al, 2008; Kelm et al, 2010b) appear to all be good candidates. Activation of these presynaptic signaling cascades may be the result of specific interactions between ethanol and presynaptic proteins or may be related to ethanol-dependent release of additional neuromodulators.…”

“…This process requires a number of presynaptic signaling pathways, including cAMP, Ca 2+ , and PKC (Kuromi and Kidokoro, 2000; Smith, 1999), cytoskeletal rearrangements (Wang et al, 1996), and phosphorylation of a number of vesicle-associated proteins including synapsins (reviewed in (Turner et al, 1999)). Many of these pathways and proteins have already been identified as acute ethanol targets in other systems (Gordon and Diamond, 1993; Kelm et al, 2010b; Popp and Dertien, 2008). It is worth noting that PTP is frequently expressed as a robust synaptic facilitation occurring just prior to the onset of long-term potentiation (LTP) at many synapses.…”