(a,c) Mouse hippocampal cultured neurons were pre-treated for 2 h with either vehicle (Veh: H2O) or ethanol (ETOH: 30 mM). Line graphs represent the average fluorescent calcium signal in dendrites over time from (a) wild type (WT) and (b) Fmr1 KO mice. Baseline was established for 1 min before the addition of GABABR agonist baclofen (Bac: 50 μM) in vehicle- or ethanol-exposed neurons. Baclofen was allowed to equilibrate as indicated by the break between dotted lines. (c) Summary graph shows significant increase in dendritic calcium signal (ΔF/F) with the addition of baclofen in WT neurons pre-treated with ethanol, which was not observed in Fmr1 KO neurons. WT: Veh+Bac= −11.82±3.55, n=8; ETOH+Bac=9.10±1.65, n=14. Fmr1 KO: Veh+Bac=2.81±1.48, n=12; ETOH+Bac=3.74±1.30, n=12. (d) Dendritic calcium imaging was performed as before in hippocampal cultured neurons infected with either vector (rAAV:mSYN-tdTomato) or FMRP overexpression (rAAV:mSYN-FMRP and rAAV:mSYN-tdTomato). Ethanol-induced increase in dendritic calcium is prevented by FMRP overexpression. Vector: Veh+Bac: −6±1.6, n=17 dendrites; ETOH+Bac: 2.5±2.5, n=17 dendrites. FMRP overexpression: Veh+Bac: −4±2, n=11 dendrites; ETOH+Bac: −4.7±1.4, n=27 dendrites. Significance determined by two-way analysis of variance, followed by Tukey’s multiple comparison. Values represent mean±s.e.m.