Aberrant Synaptic Activation ofN-Methyl-d-aspartate Receptors Underlies Ethanol Withdrawal Hyperexcitability

Abstract

Chronic ethanol exposure may induce neuroadaptive responses in N-methyl-D-aspartate (NMDA) receptors, which are thought to underlie a variety of alcohol-related brain disorders. Here, we demonstrate that hyperexcitability triggered by withdrawal from chronic ethanol exposure is associated with increases in both synaptic NMDA receptor expression and activation. Withdrawal from chronic ethanol exposure (75 mM ethanol, 5-9 days) elicited robust and prolonged epileptiform activity in CA1 pyramidal neurons from hippocampal explants, which was absolutely dependent upon NMDA receptor activation but independent of chronic inhibition of protein kinase A (PKA). Analysis of Sr 2ϩ -supported asynchronous NMDA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs) was employed to assess changes in NMDA neurotransmission. After chronic exposure, ethanol withdrawal was associated with an increase in mEPSC amplitude 3.38-fold over that after withdrawal from acute ethanol exposure. Analysis of paired evoked ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid EPSCs and spontaneous mEPSCs indicated that withdrawal after chronic exposure was also associated with a selective increase in action potential evoked but not spontaneous transmitter release probability. Immunoblot analysis revealed significant increases in total NR1, NR2A, and NR2B subunit expression after chronic exposure and unaffected by PKA-inhibition manner. Confocal imaging studies indicate that increased NR1 subunit expression was associated with increased density of NR1 expression on dendrites in parallel with a selective increase in the size of NR1 puncta on dendritic spines. Therefore, neuroadaptation to chronic ethanol exposure in NMDA synaptic transmission is responsible for aberrant network excitability after withdrawal and results from changes in both postsynaptic function as well as presynaptic release.

Phosphorylation Regulates Removal of Synaptic N-Methyl-d-Aspartate Receptors after Withdrawal from Chronic Ethanol Exposure

“…In some experiments, 10 M H89 (SigmaAldrich) was added to the neuronal cultures during the final 2 days of chronic ethanol treatment. [This time period was chosen because of the tendency of long-term exposure to protein kinase A (PKA) inhibitors to promote apoptosis in some systems, as noted in Hendricson et al (2007).] To determine the effects of kinase inhibitors during ethanol withdrawal, 10 M 4,5,6,7-tetrabromobenzotriazole (TBB; Sigma-Aldrich) or 10 M H89 was added to the ethanol-free replacement media used during the ethanol withdrawal time course, as noted above.…”

Homers regulate drug-induced neuroplasticity: Implications for addiction

“…Repeated alcohol administration alters basal glutamate content in the NAC [e.g., 38, [246][247][248] and sensitizes the capacity of alcohol to elevate extracellular glutamate levels, at least within the NAC [38,39,[249][250][251]. Moreover, repeated alcohol administration produces an enduring up-regulation in both iGluR and mGluR expression, function, as well as increased glutamate receptor trafficking to, and clustering within, the plasma membrane [39,123,[213][214][215][216][252][253][254]. As these neuroadaptations are implicated in the development of alcohol dependence, tolerance, and addiction [123,127,148,153,[214][215][216], recent immunoblotting studies examined the consequences of repeated alcohol exposure upon the protein expression of Homer isoforms within the NAC.…”

Accumbens Homer2 Overexpression Facilitates Alcohol-Induced Neuroplasticity in C57BL/6J Mice

“…Moreover, the hyperexcitable state observed during early withdrawal from alcohol is attributed to a rebound upregulation in glutamate receptor expression and their trafficking to the postsynaptic density Carpenter-Hyland et al, 2004;Chandler, 2003;Chandler et al, 1999Chandler et al, , 2006Hendricson et al, 2007;Trevisan et al, 1994). Our data are consistent with other reports for alcohol demonstrating an upregulation in the expression of Group1 mGluRs and NMDA receptors during either shortor long-term withdrawal from various alcohol treatment regimens (eg Carpenter-Hyland and Carpenter-Hyland et al, 2004;Chandler et al, 1999;Hendricson et al, 2007;Qiang and Ticku, 2005;Sheela Rani and Ticku, 2006;Simonyi et al, 1996Simonyi et al, , 2004Sircar and Sircar, 2006;Trevisan et al, 1994). Moreover, our present data are consistent with the preliminary results of other immunoblotting studies in our laboratory demonstrating an upregulation in NAC Homer2a/b/NR2 expression following repeated bouts of binge alcohol drinking (Szumlinski et al, 2006b) and an injection number-dependent increase in NAC Homer2a/b/Group1 mGluR/NR2 expression at 24 h following i.p.…”