AMPA receptors on developing medial septum/diagonal band neurons are sensitive to early postnatal binge-like ethanol exposure

Abstract

The impact of binge-like, early postnatal ethanol treatment on AMPA or kainate whole cell currents was examined in acutely isolated medial septum/diagonal band (MS/DB) neurons. AMPA (10 or 100 μM) current was inhibited by GYKI 52466, a selective AMPA receptor (AMPAR) antagonist, in all neurons isolated on postnatal day (PD) 5–8, PD 12–15 or PD 32–35. Cyclothiazide, a selective inhibitor of AMPAR desensitization, also effectively potentiated AMPA currents. This suggests that non-NMDA, ionotropic glutamate receptors on immature MS/DB neuron are predominantly AMPARs. Concentration-dependent kainate (10–1000 μM) application evoked nondesensitizing currents that exhibited an increase in the maximum response by the end of first postnatal month, consistent with developmental regulation of AMPAR function. Acute 3 s ethanol application (100 mM) consistently blunted AMPA- and kainate currents ∼20–30% across age groups. Inhibition was sustained during continuous ethanol superfusion lasting 10–12 min without evidence of acute tolerance. Repeated oral intubation of rat pups with ethanol (5.25 g/kg/day on PD 4–9), which models third trimester human binge drinking, resulted in peak blood ethanol levels of ∼350 mg/dl (measured 90 min after PD 6 dosing). AMPA or kainate currents were upregulated in neurons isolated on PD 32–35 by earlier ethanol intubation suggesting that binge-like intoxication augments developing AMPAR function. Despite this augmentation of AMPAR function, no significant changes were found in the sensitivity of AMPA currents to GYKI 52466, cyclothiazide or acute ethanol (100 mM) sensitivity or in the levels of GluR1/GluR2 subunit proteins from MS/DB tissue. These results indicate that non-NMDA ionotrophic glutamate receptors on immature MS/DB neurons, which are largely of the AMPAR subtype, are moderately sensitive to immediate inhibition by ethanol. Repeating this inhibition during early postnatal binge-like intoxication can augment normal development of AMPAR function.