Figure 2. Oxytocin dampens excitatory synaptic transmission by presynaptic mechanisms.
(A) Traces from VTA DA neurons showing pairs of EPSCs (50 ms ISI) during baseline (top) and following oxytocin application (bottom). From left to right, example traces reflect: the control condition with no additional compounds, the OxtR antagonist L368,899, the PLC blocker U73122, and the V1aR antagonist SR49059. Traces for each neuron are normalized to the amplitude of the first evoked response in the baseline condition. (B) Summary results show paired-pulse ratio during baseline and following oxytocin application in control condition, in the presence of OxtR antagonist L368,899, PLC blocker U73122, and V1aR antagonist SR49059 separately. **p<0.01, Wilcoxon matched-pairs signed rank test. For each condition respectively, n = 8 neurons from six mice, 6 neurons from five mice, 6 neurons from four mice, and 8 neurons from five mice. (C) Summary results show PPR change of the evoked EPSC of VTA DA neurons in response to light stimulation (marked in blue). n = 9 neurons from six mice. Insets show example pairs of EPSCs (50 ms ISI) from one VTA DA neuron at 0 s (before light stimulation) and 120 s (after light stimulation). (D) Summary data for light stimulation-induced EPSC PPR changes with and without OxtR antagonist (L368,899). **p<0.01, Wilcoxon matched-pairs signed rank test, n = 9 neurons from six mice for control condition, n = 6 neurons from four mice in the presence of OxtR antagonist. (E) Example traces show spontaneous EPSCs (sEPSCs, marked with green stars) during baseline (top) and following oxytocin application (bottom). (F) Left: distributions of sEPSC inter-event intervals (IEI) during baseline and following oxytocin application, with summary data for sEPSC frequency. Right: distributions of sEPSC amplitudes and summary data for sEPSC amplitude during baseline and oxytocin application. *p<0.05, Wilcoxon matched-pairs signed rank test, n = 6 neurons from five mice. (G) Left: projection of a z-stack from a VTA DA neuron filled with Alexa Fluor 488 acquired on a two-photon laser-scanning microscope. Right: higher magnification image of the dendrite. Green circle marks the uncaging spot. (H) Example traces of paired uncaging-evoked EPSCs (uEPSCs) at 50 ms ISI, from one dendritic spine during baseline condition (top) and oxytocin application (bottom). Red triangles mark uncaging time-points. (I) Left: summary data for uEPSC amplitudes in a group of dendritic spines from VTA DA neurons during baseline and following oxytocin application. p=0.813, Wilcoxon matched-pairs signed rank test, n = 5 dendritic spines from 4 neurons in three mice. Right: summary data for all uEPSC amplitudes across conditions. p=0.191, Mann-Whitney test, n = 17 dendritic spines for each condition from 16 neurons in four mice. (J) Same as (I), but for paired-pulse ratio. Error bars reflect SEM.
Figure 2—figure supplement 1. Oxytocinergic modulation of paired-pulse ratio in VTA DA neurons.
Figure 2—figure supplement 2. Optical stimulation of oxytocinergic fibers in VTA modulates paired-pulse ratio of evoked EPSCs in DA neurons.
