Ethanol (EtOH) promotes GABAergic synaptic transmission in the central nervous system. We have shown that EtOH enhances the frequency of GABAA receptor-mediated spontaneous IPSCs less powerfully in hippocampal CA1 pyramidal neurons from adolescent animals, compared to those from adults. However, we have also shown that EtOH promotes the firing of hippocampal interneurons, located in stratum lacunosum moleculare (SLM), from adolescent animals more potently than those from adults. Thus the latter finding would appear to be inconsistent with the former. In order to understand this apparent inconsistency, we have now assessed the effects of EtOH on a different subpopulation of hippocampal interneurons; those with somata located in stratum oriens (SO). We found that EtOH-induced enhancement of the frequency of spontaneous action potentials (sAPs) was less in interneurons from adolescent rats, compared to those from adults. In addition, EtOH-induced reduction of the afterhyperpolarization (AHP) decay time constant (τslow) was less pronounced in interneurons from adolescent rats, as was the EtOH-induced increase in the amplitude of the hyperpolarization-activated cation current, Ih. The effect of EtOH on sAP firing frequency was blocked by application of the Ih antagonist, ZD7288. These results indicate that while EtOH promotes the firing of hippocampal interneurons, through promotion of Ih, the developmental expression of this effect differs between interneurons with somata located in SO and SLM.
- The American Society for Pharmacology and Experimental Therapeutics