Figure 4. Lack of SERT increases the number of functional PFC-to-DRN synapses.
(a) rAAV-CAG-hChR2(H134R)-mCherry was bilaterally injected into the PFC of P4-P5 control or SERT-KO mice. Photograph showing mCherry expression after the PFC AAV injection (upper left). Optogenetic stimulation and electrophysiological patch-clamp recordings were made starting at P28 in coronal sections containing the DRN as shown by the photograph of the immunolabeling of PFC mCherry+ axons innervating to DRN 5-HT neurons, identified by the presence of the enzyme TPH2 (upper right). (b) Amplitude of optogenetically-evoked EPSCs (oEPSCs) at synapses from PFC terminals onto DRN putative 5-HT neurons (left) and non-5-HT neurons (right) at various light stimulation intensities. In Control (SERTCre/+) (5-HT: n=10 cells/5 animals; non-5-HT: n=7 cells/4 animals); in SERT-KO (SERTCre/Cre) (5-HT: n=10 cells/3 animals; non-5-HT: n=6 cells/3 animals). Top: Example traces at 9.8 mW (black/gray) and at 2 mW (red) stimulation); Bottom: Input/Output curves. Two-ways ANOVA on 9.8 mW intensity: Genotype x Cell-type interaction (F1,29 = 0.003, p=0.95); Genotype main effect (F1,29 = 9.32, *p<0.01); Cell-type main effect (F1,29 = 0.51, p=0.48). (c) AMPAR/NMDAR ratios at synapses from PFC-to-DRN 5-HT neurons (left) and non-5-HT neurons (right) in Control (5-HT: n=10 cells/4 animals; non-5-HT: n=7 cells/3 animals), and SERT-KO (5-HT: n=11 cells/3 animals; non-5-HT: n=6 cells; 3 animals). The AMPAR responses were calculated at the peak of −50 mV, whereas NMDAR responses were determined at +40 mV, 50 ms after stimulation. Top: example traces; bottom: bar graphs. Two-ways ANOVA: Genotype x Cell-type interaction (F1,30 = 0.007, p=0.94); Genotype main effect (F1,30 = 0.16, p=0.69); Cell-type main effect (F1,30 = 4.51, p<0.05). Blue bars indicate blue light stimulation. Error bars represent S.E.M.