Figure 4.

GDNF increases the firing of the NAc-projecting DA neurons in the VTA. The retrograde tracer Neuro-DiI was injected bilaterally into the NAc. A, Representative coronal section confirming the injection sites within the NAc. Arrows indicate tracer deposit. The double arrows indicate the anterior commissure. Scale bar, 1 mm. B, Representative images showing that numerous Neuro-DiI-labeled VTA neurons are also TH positive. Shown are dual-channel fluorescent images for DiI (red), TH (green), and overlay (yellow). The arrowheads indicate cells labeled with DiI and stained for TH (right). Scale bars: left, 500 μm; right, 50 μm. C, Representative images showing a DiI-labeled VTA neuron that was selected for electrophysiology. Top, Red fluorescent image. Bottom, DIC image. Scale bar, 20 μm. D, Bar graph summarizing the mean increase by GDNF (200 ng/ml) in the firing rate of Neuro-DiI-labeled VTA neurons. *p < 0.05. n = 8 cells.