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. Author manuscript; available in PMC: 2015 Feb 19.
Published in final edited form as: Science. 2014 Apr 18;344(6181):313–319. doi: 10.1126/science.1249240

Fig. 2.

Fig. 2

DA neuron-specific overexpression of HCN2 channel induces an antidepressant behavioral effect and triggers a homeostatic response via an increase in compensatory K+ currents. (A) Cre-inducible HSV-LS1L-HCN2-eYFP injection into the VTA of TH-Cre mice. (B) Confocal image showing colocalization (merge) of Cre-induced HCN2 (eYFP) expression in VTA DA neurons (TH) of TH-Cre mice. Quantification shows that HCN2-expressing TH+ cells were 47±4% of total TH+ neurons in the VTA and there was no expression of HCN2 in TH- neurons (2–3 sections per mouse; n = 4). Scale bar 100 μm; green, eYFP; red, TH. (C) Virally expressed HCN2 significantly increases Ih (t13 = 2.73, P < 0.05; n = 7–8cells/group, 3 mice/group) and (D) firing rate (t25 = 6.86, P < 0.0001; n = 13–14 cells/4 mice/group) in VTA DA neurons as compared to control (eYFP) 24 hours post injection. (E and F) Experimental timeline and schematic. Behavioral effects of susceptible mice expressing HSV-LS1L-HCN2-eYFP or control HSV-LS1L-eYFP in DA neurons of the VTA on (G) social interaction test (t22 = 3.72, P < 0.01; n = 12), (H) sucrose preference test (t18 = 3.40, P < 0.01; n = 10) and (I) immobility time during forced swim test (t18 = 2.87, P < 0.05; n = 10). (J to L) Neuronal effects of 6 days of expression of HSV-LS1L-HCN2-eYFP (■) compared to HSV-LS1L-eYFP (□) in DA neurons of the VTA in susceptible mice on (J) firing rate (t19 = 5.48, P < 0.0001; n = 10–11), (K) Ih measurements (at −130 mV: t22 = 4.51, P < 0.001; at −120 mV: t18 = 3.25, P < 0.005) and (L) K+ currents (−70 mV to +20 mV/10 mV step): Peak (at +20 mV: t16 = 5.70, P < 0.001; at +10 mV: t16 = 5.28, P < 0.001), sustained (at +20 mV: t16 = 2.480, P < 0.05). (M) Sample traces at 100 pA current injection and statistic data of decreased excitability in susceptible mice expressing HCN2 compared to eYFP control (at 100 pA: t12 = 3.21, P < 0.01; at 150 pA: t12 = 2.73, P < 0.05; at 200 pA: t12 = 2.54, P < 0.05; n = 7 cells/6–7 mice per group). Error bars, ± s.e.m. * P < 0.05, ** P < 0.01, *** P < 0.001.