Fig. 4
NAc D1R neurons preferentially send inhibitory inputs to TH-negative neurons in the midbrain. a Schematic of experiment. AAV-ChR2 was injected into the NAc of D1R-Cre mice, and the response was recorded in the midbrain (VTA/SNc). b Representative image of terminals in the midbrain from NAc D1R neurons. Scale bars: 500 μm. ac anterior commissure, ml medial lemniscus. c Electrophysiological properties of Type 1 neurons in the midbrain. d Non-type 1 neurons consist of both Ih-positive and Ih-negative neurons. e Comparison of action potential duration (left) and resting membrane potential (RMP, right) from type 1 and non-type 1 neurons (n = 26 type 1 neurons, n = 28 non-type 1 neurons, from 17 mice, unpaired t test; action potential duration: t52 = 8.7, P = 1 × 10−11; RMP: t52 = 5.6, P = 9 × 10−7). f Proportion of connected and unconnected neurons that were identified as type 1 (n = 26 type 1 neurons, n = 28 non-type 1 neurons, from 17 mice, Chi-square test; χ2 = 30.1, P = 2 × 10−8). g–i Representative images of a non-connected biocytin-filled neuron that was TH-positive. Scale bar: 20 μm. TH tyrosine hydroxylase. j–l Typical example of a connected biocytin-labeled neuron that was TH negative and responsive to light stimulation. Scale bar: 20 μm. m Representative results from a single-cell RT-PCR reaction confirming the Vgat phenotype of a connected cell. n Latency (left axis) and amplitude (right axis) of light-evoked IPSCs in midbrain non-TH neurons. o Summary of TH immunocytochemistry for connected and unconnected neurons (n = 18 TH (+) neurons, n = 21 TH (–) neurons, from 17 mice, Chi-square test; χ2 = 24.9, P = 4 × 10−7). p Electron microscopy image of an mCherry-immunoreactive terminal (mt) that formed a symmetric synapse (arrow) with an unlabeled dendrite (ud). Scale bar: 0.5 μm. q A representative image of a TH-positive dendrite (Td) that established a symmetric synapse (arrow) with unlabeled terminals (ut). Scale bar: 0.5 μm. r A TH-positive dendrite (Td) that established an asymmetric synapse (arrowhead) with unlabeled terminals (ut). Scale bar: 0.5 μm. **P < 0.01
