Effects of ethanol on glycinergic synaptic currents in mouse spinal cord neurons

Abstract

Ethanol increased the frequency of miniature glycinergic currents [miniature inhibitory postsynaptic currents (mIPSCs)] in cultured spinal neurons. This effect was dependent on intracellular calcium augmentation, since preincubation with BAPTA (an intracellular calcium chelator) or thapsigargin [a sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pump inhibitor] significantly attenuated this effect. Similarly, U73122 (a phospholipase C inhibitor) or 2-aminoethoxydiphenyl borate [2-APB, an inositol 1,4,5-trisphosphate (IP₃) receptor (IP3R) inhibitor] reduced this effect. Block of ethanol action was also achieved after preincubation with Rp-cAMPS, inhibitor of the adenylate cyclase (AC)/PKA signaling pathway. These data suggest that there is a convergence at the level of IP₃R that accounts for presynaptic ethanol effects. At the postsynaptic level, ethanol increased the decay time constant of mIPSCs in a group of neurons (30 ± 10% above control, n = 13/26 cells). On the other hand, the currents activated by exogenously applied glycine were consistently potentiated (55 ± 10% above control, n = 11/12 cells), which suggests that ethanol modulates synaptic and nonsynaptic glycine receptors (GlyRs) in a different fashion. Supporting the role of G protein modulation on ethanol responses, we found that a nonhydrolyzable GTP analog [guanosine 5'-O-(3-thiotriphosphate) (GTPγS)] increased the decay time constant in ∼50% of the neurons (28 ± 12%, n = 11/19 cells) but potentiated the glycine-activated Cl(-) current in most of the neurons examined (83 ± 29%, n = 7/9 cells). In addition, confocal microscopy showed that α1-containing GlyRs colocalized with Gβ and Piccolo (a presynaptic cytomatrix protein) in ∼40% of synaptic receptor clusters, suggesting that colocalization of Gβγ and GlyRs might account for the difference in ethanol sensitivity at the postsynaptic level.

Structure and Pharmacologic Modulation of Inhibitory Glycine Receptors

“…Additional analysis found that low ethanol concentrations (#50 mM) potentiate glycinergic currents by increasing the apparent affinity of GlyR with no change in efficacy (Aguayo et al, 1996;Crawford et al, 2007;Perkins et al, 2008), and showed that alcohol effects on glycinergic currents were developmentally regulated in cultured spinal neurons (Tapia et al, 1997;Tapia and Aguayo, 1998). Other studies have demonstrated that ethanol affects GlyR expressed in hypoglossal motoneurons (Eggers and Berger, 2004;Aguayo et al, 2014), the spinal cord (Celentano et al, 1988;Mariqueo et al, 2014), and ventral tegmental area neurons (Ye et al, 2001).…”

Drunken Membranes: Short-Chain Alcohols Alter Fusion of Liposomes to Planar Lipid Bilayers

“…Currently, there is little direct evidence of enhanced or reduced transmitter release from affected regions of the brain or whether excitatory or inhibitory neurons are involved. Multiple studies have measured changes in synaptic transmission between neurons following addition of alcohol, but most propose a postsynaptic target (17,(32)(33)(34). Additionally, the vast majority of studies are done in whole animal or tissue slice preparations where observation of an ethanol effect depends on a sequence of both pre-and postsynaptic events involving many proteins.…”

The Level of NMDA Receptor in the Membrane Modulates Amyloid-β Association and Perforation

“…Interestingly, this effect was specific for NMDARs since overexpression of GlyRs did not affect A␤ association to the membrane. This differential effect might be relevant for the disease because GlyRs, unlike NMDARs, are inhibitory proteins that are mainly expressed in spinal cord neurons [45,46], which are believed to be largely unaffected by the disease.…”