Effects of acid-sensing ion channel-1A (ASIC1A) on cocaine-induced synaptic adaptations

Chronic drug abuse is thought to induce synaptic changes in nucleus accumbens medium spiny neurons (MSNs) that promote subsequent craving and drug-seeking behavior. Accumulating data suggest acid-sensing ion channels (ASICs) may play a critical role. In drug naive mice, disrupting the ASIC1A subunit produced a variety of synaptic changes reminiscent of wild-type mice following cocaine withdrawal, including increased AMPAR/NMDAR ratio, increased AMPAR rectification, and increased dendrite spine density. Importantly, these changes in Asic1a(-/- ) mice were normalized by a single dose of cocaine. Here we sought to understand the temporal effects of cocaine exposure in Asic1a(-/- ) mice and the cellular site of ASIC1A action. Six hours after cocaine exposure, there was no effect. However, 15 h, 24 h and 4 days after cocaine exposure there was a significant reduction in AMPAR/NMDAR ratio in Asic1a(-/- ) mice. Within 7 days the AMPAR/NMDAR ratio had returned to baseline levels. Cocaine-evoked changes in AMPAR rectification and dendritic spine density followed a similar time course with significant reductions in rectification and dendritic spines 24 h after cocaine exposure in Asic1a(-/- ) mice. To test the cellular site of ASIC1A action on these responses, we disrupted ASIC1A specifically in a subpopulation of MSNs. We found that effects of ASIC1A disruption were cell autonomous and restricted to neurons in which the channels are disrupted. We further tested whether ASIC1A disruption differentially affects MSNs subtypes and found AMPAR/NMDAR ratio was elevated in dopamine receptor 1-expressing MSNs, suggesting a preferential effect for these cells. Finally, we tested if protein synthesis was involved in synaptic adaptations that occurred after ASIC1A disruption, and found the protein synthesis inhibitor anisomycin normalized AMPAR-rectification and AMPAR/NMDAR ratio in drug-naive Asic1a(-/- ) mice to control levels, observed in wild-type mice. Together, these results provide valuable mechanistic insight into the effects of ASICs on synaptic plasticity and drug-induced effects and raise the possibility that ASIC1A might be therapeutically manipulated to oppose drug-induced synaptic changes and behavior.

Automated summary

Chronic drug abuse induces synaptic changes in nucleus accumbens medium spiny neurons that promote craving and drug-seeking behavior. Acid-sensing ion channels (ASICs) may play a critical role in these changes. Disrupting the ASIC1A subunit in drug-naive mice produced synaptic changes similar to those seen during cocaine withdrawal, and these changes were normalized by cocaine. The effects of ASIC1A disruption in mice after cocaine exposure were observed to occur 15 hours, 24 hours, and 4 days later, and returned to baseline levels after 7 days. ASIC1A disruption was found to be cell autonomous and restricted to neurons where the channels are disrupted. Testing also showed that dopamine receptor 1-expressing medium spiny neurons were preferentially affected. Protein synthesis was found to be involved in the synaptic adaptations after ASIC1A disruption.